Sudan - Gezira study mission (Vol. 3 of 15) : Annex II : agriculture in the Gezira

RESTRICTa UNN39 Vol. 3 := c; rm G EZ IR A S T UDY M I^S3SI O N g ANNEX II - AGRICULTURE IN ThE GEZIRA _-, == Un-~ == Rr~~~~~~~~~~  ANNEX II AGRICULTURE IN THE GEZIRA TABLE OF CONTENTS CHAPTER PAGE 1. AGRICULTURE IN THE GEZIRA ..................... 1 Introduction ....... ..... ......... *** 1 The broad agricultural problems ...... 3 Arrangement of the annex............. 4 2. SOILS AND FERTILITY IN THE GEZIRA ............. 5 Chemical Properties of Gezira Soils........ 5 Normal soils: salts and exchangeable. sodium.....* .... so.w. 5 : pH of soil............. 6 : plant nutrients..o..... 7 : maintenance of chemical properties0......... 7 : secondary salinization. 8 Saline sois.....il... s.*... 8 Physical Properties of Gezira Soils ........ 9 Swelling and shrinking.*k... 9 Permeabilitym.............. ..... 10 Maintenance of physical properties... 11 Maintenance of Soil Fertility ......... ...... 11 Fallowse............................. 11 3. PRESENT AND FUTURE AREA OF GEZIRA ............. 14 Future Expansion .............. a 14 Agricultural ZonGs in the Gezira ........... 17 4. FLUCTUATION AND VARIATION IN COTTON YIELDS.... 19 Cotton Production and Yields .............. 19 Average yields ..................... . 20 Factors Causing Annual Fluctuation in Cotton Yield . ........... . 20 Soils .6.00000.90... O0-.0.. ................. 20 Rainfall: ..o. .... .... .......- 20 :pre-sowing rainfall ........ 21 :planting dates.......o...... 21 Pests and diseases:,, ............& 21 :diseases. ....... o .. .o ...o.. .. 22 :soil bacteriophages.he..... 22 :spryn pes tserval.......6 23 ; spraying intervl val... 23  - iii - CHAPTER PAGE : aerial spraying ............ 24 : local spraying ............. 24 Factors Causing Local Variation in Cotton Yield .......... 0.0.0.0..... .... ............ 25 Soils ..0.0 ............ .9-0 ......... . ... .. 25 Rainfall ................ . ... ............. 25 Surface drainage .... a .... . ......... . 25 5. INCREASING YIELDS .............................. ...... . 27 Potential yields ...................... 27 The importance of yield increases..... 30 Techniques for Increasing Crop Yields ....... 32 Varietal improvement and seed distributions ............ 32 : seed multiplication ........0 32 : cotton breeding ............ 33 Efficient use of fertilizer: .......... 33 : uneven distribution of fertilizer ......... ...... 35 : time of application to cotton......... ... 35 Quality of cultivations:.............. 36 : split ridging.............. 37 Perennial weed control*................ 37 6. CREATING CONDITIONS FOR INCREASED PRODUCTION... 39 Extension Services.. ............. 39 Holdings and Rotations.... . ......... 40 Identifiable holdings 40 Rotations: ................. o...................... 40 : Gezira Main .............. 41 : ManagilO .................. , 41 : choice of rotation. 41 Position of holdings in numrbers 43 Alternative Crops o ....... . 43 Annual crops..r. o ps..o..o...... &..... 43 Perennial croo p.....0... 44 Substitution Crops. . 44 Groundnuts and Dura.....u 44 Upland cotton ...... 44 Fodder and pasture speciesi........... 45 Livespecialized.livestockoenterprises. 45 Communal hers......... 46 Specialized livestock enterprises... 46 Foder........ 47  - iv - CHAPTER PAGE Mechanization ............................ 48 Mechanical operations: ................ 0 48 : stalk pulling ......... ... 0 48 : cotton harvesting.,......... 49 : other operationsv............. 49 : canal clearing.....o...... o 50 Organization of Mechanization.....,.... 50 Machinery cooperatives..o...,.....a... 52 Cost of cultivation....o..*oo...o....o 52 7. -IRRIGATION AND DRANAGE........ 53 Use of the Additional Water Available under the 1959 Nile Waters Agreement...,.. ...f. 53 The dead season:..... o .. . ... ....... 53 : maintenance of the irrigation network ....... 54 : water requirement in April- June, ... ...o.o ...... 55 Estimates of irrigation requirement: 55 :over- and under-watering..... 55 : peak demand,..........O...*. 56 Increasing network capac.ity,.*..&*..., 56 Maintenance of the Irrigation Network ...... 57 Measurement of water flows........o... 57 Escape channels0 n.. .* . ... . . .O .... 58 Drainageoo ... .... o.oo... *.oo.... 58 Maintenance of the drainage network.e... 59 Field drainage.. ....... ........ .e. 60 Watering the Fields . ..... ............... . . . 60 Graded waterings ........ ... ...... 61 Watering techniques.oo ..............s.. 62 8. RESEARCH . ... .............. 64 Agricultural Research. 64 The Ministry of Agriculture. . 64 The Ministry of Animal Resources. 65 Other Ministries . . 65 The University of Khartoum.o 66 The Advisory Council ................ 66 The roles of research organization..... 66 Dissemination of research.............. 66 Agricultural Research Programs.om... ... 67 : medium-term... .............. 67 : long-term research.......... 68 Collection of data, .. . ... ..... . 70  APPENDICES TO ANNEX II 1. SOILS IN THE GEZIRA 2. IRRIGATION AND AGRONOMY 3. MECHANIZATION 4. LIVESTOCK 5. AGRICULTURAL EXTENSION IN THE GEZIRA  ANNEX II C H A P T E R 1 AGRICULTURE IN THE GEZIRA Introduction The rainfall in the vast triangle of land between the Blue and Wfhite Niles is not sufficient to support a thriving, settled agriculture without irrigation. Traditionally the area was peopled by nomadic and semi-nomadic pastoralists, growing precarious crops of duraly/ and dukhn2/ during the short rainy season and moving their herds in search of water and grazing during the long, hot, dry season. The beginning of irrigation in the area dates back to 1907, when Garstin proposed the construction of a dam at Sennar. To test the suitability of the area for cotton - the only obvious cash crop for which a market demand then existed - a pumping station was erected at Tayiba, a few miles north of Wad Medani. Other pump stations followed and the area growing irrigated cotton increased from 250 feddans 3! in 1911 to 22,000 feddans in 1925, when the Sennar Dam, postponed because of World War I, was completed. The availability of water for gravity irrigation spurred expansion and the cotton area increased to 200,000 feddans by 1933/4. The building of the Sennar Dam had necessitated international negotiations on the division of the Nile Waters between the Sudan and Egypt. The 1929 Agreement effectually dictated the pattern of 1/ Dura = Sorghum vulgare, sorghum, Guinea corn. 2/ Dukhn = Pennisetum typhoideum, millet. An explanation of other technical terms and Sudanese words used in the text will be found in the Glossary. 3/ 1 feddan = 1.038 acres = 0.42 hectares. The equivalents of other Sudanese measures used in the text will be found in the Glossary.  -2 - ANNEX II expansion and land use in the Gezira until a new Agreement, allocating more water to the Sudan and allowing much greater latitude in the seasonal pattern of irrigation, was reabhed in 1959.1/ The signing of the 1959 Agreement, which took account of the proposed dams at Sudd el Ali (the "Aswan High Dam") Khashm el Girba and Roseires, had been anticipated and arrangements made to allow an increase in area of the Gezira Scheme. The development of the Managil Extension started a new phase of rapid expansion, the first land being cropped in 1960. By 1964/5 the area controlled by the Sudan Gezira Board reached 1.81 million feddans of which 1.76 million were regularly irrigated: cotton was grown on 508,000 feddans. Land is still being brought into cultivation along the fringes of Gezira Main and Managil 2/ but, with the Scheme hemmed in by the Blue and VJhite Ni)les and by the Managil ridge to the south, the limits of expansion are in sight. Over the 40 years since the start of gravity irrigation, the production of cotton from the Gezira has increased at an average annual growth rate of 3.5 percent but this had been achieved almost wholly by increasing the area. Leaving aside the crisis years of the early 1930's (caused by devastation by pests and diseases), there had been little improvement in the yield of cotton crops, in spite of the introduction of modern pesticides and fertilizers. Little information is available about the yield of other crops, but there is no indication that there has been any improvement: the standard of animal husbandry may well be worse than it was in the area before the creation of the irrigation scheme. A feature of the Gezira Scheme, not usually associated with irrigation schemes, has been the remarkable year-to-year variations in cotton yield. Some fluctuation would be understandable in periods of rapid expansion b-ut there was no improvement during 1935-58, years of consolidation. These fluctuations - aggravated by WIde rzovements in the world price of the sole cashl crop, co> ton - havTe had an unsettling effect on the income and lives of the farmers and on the economy of the country. 1/ For details of both Agreements and their effects, see Appendix 2, Irrigation and Agronomy. 2/ The word "Gezira" means island in Arabic. The word is still used to describe the irrigation scheme as a whole, but is also applied to the original land area. In this Annex "Gezira" connotes the whole irrigated area: the new extensions are called "Managil" and the original land, "Gezira Main".  - 3 - ANNEX II Ancient and modern history relates notable examples of catastrophes which are now known to have been due to the increase of salts, especially sodium salts, in irrigated soils. These salts affect the crops in two ways: directly, by toxic action: and indirectly by spoiling the physical properties of the soil that are most necessary for irrigated agriculture. Areas with naturally saline soils were excluded as the Gezira Main expanded in 1925-34: this was not done, however, in the Managil extensions. Salinization also occurs as a secondary process, by the accumulation in the soil of salts brought in by irrigation water. The possibility of such secondary salinization has caused much concern since the earliest days of irrigation in the Gezira, and the lack of yield response to fertilizers and other modern technique has led to much discussion of the possibility of a decline of fertility. The Broad Agricultural Problems in the Gezira The basic agricultural problems facing the Gezira may be simplified into five broad questions:- 1. Is the fertility of Gezira soils declining, through exhaustion of plant nutrients, through secondary salinization or any other cause? What are the factors maintaining fertility: are any practices incompatible with these factors? Is there a serious threat of secondary salinization? 2. How long can increased production through expansion of area be maintained? What is the limit, imposed by topography, soils or water, on expansion? 3. What are the factors which cause violent annual fluctuations in yield? How can Lhey be nminimized? 4. What measures can be taken to increase yield levels of all crops (and of animal production)? What are the agricultural incentives and discentives in the adoption of measures? What new crops can be introduced to diversify farmers' incomes? 5. What are the best ways of utilizing the additional water available under the 1959 Nile Wdaters Agreement and especially the storage water to be available from Roseires Dam? Should the "dead season" be abolished? Is the irrigation network adequate?  - 4 ANNEX II Arrangement of Annex on Agriculture The mission's findings on these broad questions are set out in this Annex. Supporting evidence and more comprehensive discussion together with recommendations on other agricultural matters, are included in five appendices: (1) Soils; (2) Irrigation and Agronomy; (3) Mechanization; (4) Livestock; and (5) Extension Services. A Glossary and list of abbreviations are attached to the Report. Cotton. The agriculturalist is concerned with the growing of a crop of seed-cotton and its delivery to the Board for processing. Apart from ensuring that the varieties he grows have good qualities and a favorable lint/seed ratio, he has no direct control over the conver'sion of his crop into the commercial product "cotton" and seed. In this agricultural Annex, therefore (unless otherwise stated) cotton implies seed-cotton as grown by the farmer: cotton yields mean yields of seed-cotton: and cotton production means the amount of crop delivered by farmers to the ginneries.  ANNEX II C H A P T E R 2 SOILS AND FERTILITY IN THE GEZIRA The soils of the Gezira area are largely sediments, brought down by the Blue Mile, derived from the basic rocks of the Ethiopian Highlands. They are deep, without any bedding, and the water table is commonly 10-20 rm below the surface. The top soil is a heavy, alkaline clay, containing 50-70 per cent clay, 15-30 per cent silt, 10-25 per cent fine sand and little or no coarso sand. The clays are montmorillonitic (or possibly illitic): the sand is mainly quartz, together with some potassium feldspar, augite and epidote (tIe last two supplying magnesium and calcium respectively). Although devoid of beds of other materials, there is a differentiation down the soil profile. The surface is loose and granular, dark brown or dark grey brown in color, with many cracks. Below this, a transitional layer of brown clay overlies a grey layer at a depth of 30-75 cm. Many of the factors which are known, or believed, to influence yield tend to undergo changes near this grey layer: total salts, sodium, nitrates and bulk density all increase, while pore space decreases. The grey layer is nearer the surface in soils giving poor yields, and in Managil generally, than in high yielding areas in Gezira Main. The influence of the grey layer is due partly to physical impedance to plant roots but mechanical rupturing of the layer would be prohibitive&v expensive: research is needed to see whether special cropping or watering techniques could alleviate conditions at The grey layer. I. CHEIWICAL PROPERTIES OF GEZIRA SOILS 1/ A. Normal Soils Salts and Exchangeable Sodium Calcium is the dominant cation on the exchange complex, which 1/ Abnormal conditions, e.g. excessive salinity, secondary salinization, etc. are considered later.  -6 ANNEX II has an exchange capacity of about 1 milli-equivalent per gram (m.ee/g), but sodium is always present and increases with depth, being found as carbonate in the upper layers and as sulphate at greater depths0 The amount of sodium in the top 30-45 cm of soil varies, being higher (exchan- geable sodium percentage (Sos.p.) 20) in north Gezira Main than in the south (e.s.p. 9): the few analyses from Managil are inconclusive. j Most plants likely to be grown in Gezira will tolerate these "normal" con- centrations of sodium: only citrus is likely to be adversely affected below e.s.p. 20: in pot experiments where the effect of sodium on soil structure were eliminated cotton was not affected below e.s.p0 30. Early research deonstrated a relationship (at Dueim Pump Scheme) between sodium levels and yield but attempts to apply the findings to Gezira were not markedly successful. The "Sodium Value" developed from this work remains of use in separating the best from the worst soiDs but does not place intermediate soils in any sequence related to yield. The total salts, and thus conductivity, increase with depth: there is an indication that poor yields are associated with rapid increases. There are no indications of serious concentratiohs of toxic ions, e.g. boron content of cotton reached 30-85 percent of toxic levels in Managil but only 20 percent in samples from G.A.R.S. Iron deficiency in groundnuts has been treated, but no increase in yield resulted. Trials at the GOA.R.S. in which cotton was grown in soils with a low sodium content imported from Gash (e.s.p. 2 as compared with 8 in the Gezira soil used) suggest that the levels of exchangeable sodium in normal Gezira soils may be a limiting factor in obtaining the maximum feasible yields. However, the mission found no evidence that normal levGl3 of either sodium or total salts were actually depressing yields in the field with present standards of cultivation. Nevertheless, the total salt and oxohangeable sodium content of normal soils are two of the factors affecting yield. A better under- standing of their role is important in attempts to develop better land use capability criteria for use in Gezira and in new areas. Their influence at normal levels must be a factor in the study of secondary salinization and saline soils. The mission recommends: a. laboratory examinations of soils should include chemical 1/ In nearby Rahad, 70 percent of thousand of samples show e.s.p. of 1O-15 in the tn)p 45 cm but values exceeding e.s.p. 15 in the 45 to 95 cm layer of the proficle.  7 ANNEX II measurements, especially of e.s.p., soluble salts and gypsum. b. yields should be correlated with these measurements and other factors. c. field trials should be made to endeavor to leach down salts in soils where the concentration is normally high in the top 30-45 cm. The pH of the soil / enerally 8,5 to 9.5 in 1:5 water suspension (1/10)7 is generally somewhat higher in the upper layers where socium carbonate is present but there is no close correlation between pH and e.s.p. High total salts - rather than high sodium - tend to depress pH. Plant nutrients. Gezira soils are very low in organic matter (the general level being under one percent), and in total nitrogen but nitrate nitrogen is fairly high. There has been no demonstrable change in total nitrogen in soils cultivated for 20 years without fertilizer at G.A.R.SO, although, as would be expected, nitrate levels have fallen over the years. Because of the high demand of cotton for nitrate, much research has been done on soil nitrates and the SOG.BO introduced the use of nitrogenous fertilizers as soon as they became economic. In spite of the high cost of nitrogenous fertilizers, the mission considers that special techniques to increase or conserve soil nitrates should only be adopted if their cost is very low and they do not conflict with other requirements. The mission is, of course, concerned with the efficient use of fertilizer and with the elimination of weeds, which can reduce soil nitrate levels by 80 per cent. Some nitrogen -- equivalent to a few kg of urea per feddan - is "fixed" by micro-organisms and more by lubia and other leguminous crops0 Care must be taken to see that introduced legume foddors are accompanied by the appropriabe Rhizobium: a microbiologist should assist with field studies of new pasture and fodder production methods. The mission does not consider, however, that the role of legume in cotton yields should now be allowed to dictate their relative positions in the crop rotation where there are conflicting considerations. Analyses of soils from Gezira Main indicate levels of 0.26 per- cent K and 0.05 percent P. While not high in comparison to other heavy soils (many of which contain 1.0 and 0.1 percent respectively), supplies of potassium and phosphorus appear to have been adequate for past cropping patterns. The recent introduction of groudnuts may deplete soil reserves but well planned fertilizer trials will quickly detect deficiencies. Maintenance of Chemical Properties. The mission found no evidence that the soil's chemical resources were being seriously depleted by present  -8 - AINEX II cropping patterns and were unlikely to be by those proposed. Nitrate levels have decreased, and potassium and phosphate levels may do so, but reserves in normal Gezira and Managil soils can be restored with standard N, P or K fertilizers. There is no evidence that increasing salt and/or sodium levels is leading to a decline in fertility in normal soils. Secondary Salinization. It is most unlikely that irrigation will cause a rise in the ground water table in the Gezira or Managil: in such impermeable soils little, if any, rain or irrigation water will reach the water table 10-20 m below ground level. Fortunately, the quality of the Blue Nile water is good, with a favorable calcium/sodium ratio (average 2.88:1) and a low bicarbonate content l/o 1000 m3 of irrigation water contain about 8.3 kg of sodium so thatTeven very heavy irrigations (6000 m3 per feddan per year) will contain only 50 kg sodium. Even under the most pessimistic assumption that all this sodium goes into the exchange complex it will take 12-15 irrigation seasons to raise the sodium level by one milli-equivalent, Because of the high exchange capacity of the soils, it will take 93-120 years to raise the eschange sodium per- centage from 10 to 20 under the 4-course rotation proposed for the Gezira Main; with the 3-course proposed for Managil, it will take 105-135 years. The mission is convinced that the majority of Gezira soils have a useful life of at least a century and is confident that advancing technology will find answers to the problem of secondary salinization long before it becomes of more than local importance. B. Saline Soils Secondary salinization will be more damaging in those saline areas which have been included, mainly in the north and west of the Scheme. In these soils, already high in salts and sodium, the grey layer is close to the surface: cracking (and thus'ileaching") does not proceed to any depth, the amount of water entering the soil is reduced, and the salts are concentrated in a shallow surface zone. The resulting high osmotic pressure will aggravate the already marginal soil moisture supply. The improvement of these soils will include any measure which will increase the depth of cracking and thus of water penetration. Saline areas in Managil should be kept under a three course rotation: they should never be used for pasture pilot schemes nor for fodder irrigated for 11 months of the year; excess water from canals should never be released onto fallows in saline areas: particular care should 1/ Where bicarbonate is high both calcium and magnesium are precipitated as the insoluble carbonate, giving a relative increase in sodium in the solution.  - 9 - ANNEX II be taken to ensure that mechanical blading to control perennial weeds is done to the full 30 cm depth, or deeper if possible. Great care will be needed in watering these areas: the aim is to get the maximum amount of water as deep as possible in the soil but overwatering must be avoided since excess water will evaporate, depositing salt on the surface. There may be an advantage in growing deep-rooted crops, e.g. berseem, wnich will dry out lower horizons, causing cracking. The practice of withdrawing areas where soil salinity is very high from the normal tenancy system must continue. Some areas may be suitable for forestry plots, others should be farmed directly by the Board, growing deep-rooted crops with long fallow periods to encourage cracking and "leaching" by rainwater. In the worst cases, crops of Atriplex could be grown and removed for burning: trials have shown that one crop will remove 250 kg sodium per feddan, II. PHYSICAL PROPERTIES OF GEZIRA SOILS Irrigated agriculture in the Gezira is dominated by two physical properties of the clay soils: their swelling and shrinking during wetting/ drying cycles and their impermeability. These factors are profoundly affected by the chemical properties of the exchange complex. A. Swelling and Shrinking The soils swell markedly on wetting: upward surface movements of 12.5 cm have been measured -- a serious matter in an irrigation system where the designed command from the Minor Canals is normally 20-40 cm. 2 Swelling occurs at all depths to which water penetrates: movements have been detected at 150 cm. The resulting pressures in the soil are relieved by the squeezing up of gilgai, which interferes with water control in the fields, Equal shrinkage occurs on drying: since the pressure has been relieved by gilgai formation, and the dry soil will not flow back to its original position, extensive cracking occurs. Cracking has been studied for many years: the average crack width varies from year to year: the depth depends on penetration of water. In nature, the annual cracking pattern is usually unique, only coinciding with the previous years pattern after particularly dry seasons: thus cracking is no more extensive and the cracks no wider or deeper if the land is left fallow without irrigation for more than one year. Under irrigation, however, cracks follow the same pattern as in the preceding cycle. Many unmeasured parameters affect the actual volume 1/ Agriculture in the Sudan, Ed. J. Tothill. Oxford Univ. Press, London 1952.  - 10 - ANNEX IT of the cracks but extrapolation from simple tests suggests that in a typical soil, drying from field capacity to wilting point, cracks develop that would reach 49o m3 er feddan if the wetting/drying cycle extended to a depth of 60 cm. 17 Cracks only start to close up after they are completely filled with water, and thus the volume of water applied in a normal irrigation (400 m3 per feddan) may be able to enter the soil through the cracks. Shrinking continues as drying procedes beyond wilting point: at the end of a prolonged spell of dessication the volume of cracks may be twice that calculated above. At the same time, large quantities of air are drawn into the soil and are trapped on rewetting. The absence of layering in the Gezira soils has been ascribed to cracking: during the dry season particles fall down the cracks, leading to thorough and intimate mixing. Pieces of salty surface crusts may be mixed into the profile in this way or, with other debris, washed down cracks by the first flow of rain or irrigation water: thus cracking replaces in part the leaching action which occurs on more permeable soils under higher rainfall or irrigation. The cracking phenomenum is not confined to the very large and noticeable cracks. It occurs on a smaller scale inside individual clods as they dry: on gentle rewetting, the swelling pushes the clod apart into smaller pieces, giving an attractive loamy texture which has led to the use of the name self-mulching to describe these soils. This agriculturally- desirable texture can be preserved, e.g. on the top of large ridges, but under normal cultivation the particles break down into an increasing clayey consistency as wetting proceeds. Permeability. Measurement of permeability is rendered difficult by the almost inevitable presence of cracks in the sample. Capillary rise is more easily measured: it is much lower in samples from Managil, suggesting that permeability there is lower than on Gezira Main. This is to be expected, since sodium has a marked effect on permeability: the capillary rise of a Gezira Main sample was decreased to 20 per cent by saturating with sodium solutions. There are few observations on the rate of water intake into the soil in the absence of cracks. A figure of 10 cm per day has been quoted for Rahad soils, but a lower figure for a Gezira soil, 5.8 cm, seems 1/ The volume of the cracks is only 240 m3 if the wetting/drying cycle extends to 30 cm.  - 11 - ANNEX II more realistic: such low figures would make Gezira soils virtually unmanageable under irrigation were it not for the cracks. Movement of water in the soil is very slow: 24 hours after irrigation only the top 30 cm contain any appreciable available water. Again, cracks save the situation: where soils crack freely to good depths, water will penetrate and be followed by roots. Where the grey layer is near the surface, cracks will not be deep so that water and roots will be confined to a shallow zone. Saturating Gezira clays with calcium increases the permeability fivefold and in practical field trials quite small dressings of gypsum (e.g. 1-4 mt per feddan) markedly increased water penetration0 This early test should be followed up, but the mission found no evidence that general dressings with gypsum were necessary nor economic at present. In the special case of the establishment of small-seeded pasture species on pilot schemes, the application of moderate amounts (in irrigation water) to improve seed-bed texture may be justified. A consequence of the low permeability of the Gezira soils is that internal soil drainage, which m-ght help in removing salts and sodium accumulating from irrigation water, is almost impossible. Field tests confirm calculations that drains would have to be one meter apart to be effective. Gypsum dressings allowed a two meter spacing but even if this could be increased fivefold to ten meters the mission considers that the cost of gypsum and drainage would be absolutely prohibitive. The problem of internal drainage, which has worried authorities since the inception of the Scheme, must await advances in technology but experimentation should continue.: Maintenance of Physical Properties. The mission found no evidence that the physical properties of Gezira Main soils had deteriorated over the 4O years of cropping, when the soil has, for the most part, been fallow for about four years out of every eight. The evidence on Managil soils, which have been fallow about two years in six, is scanty: the land has not been cropped lohg enough for any effects to become apparent. III. MAINTENANCE OF SOIL FERTILITY From its consideration of the soils and yields the mission found no evidence that the fertility of normal Gezira soils had been declining under the rotations used in the past. Rotation trials (dominated by cotton) have been a feature of research in Gezira since the earliest days but there is little evidence on more intensive rotations, with efficient modern fertilizer applications and pest control. The mission recommends that this weakness should be remedied in future research programs. Fallows. The soil factors necessary for good growth include ample  - 12 - ANNEX If nutrients, soil moisture and soil aeration: these combined with optimum biological conditions (choice of varieties, absence of pests and diseases) and proper management ensure good yields but a superabundance of any one factor cannot compensate for deficiencies in another. Ample nutrients can be supplied to Gezira soils "from the bag" as fertilizer. In planning future rotations, the mission was therefore most concerned with the two other factors, soil moisture and aeration. In the impermeable Gezira soils, these factors depend on cracking dur-ing the wetting/drying cycles. The mission thus has grave doubts as to the feasibility of growing perennial crops. Trials with pastures should be confined to a maximum of six 360 feddan pilot schemes, although in view of the potential value of pasture these should be given priority. The introduction of any future perennial crop (e.g. sugar cane, kenaf) should be preceded by careful soil management trials. There would be less doubt about the feasibility of growing an occasional annual crop through the dry period, In particular, the benefits of growing leguminous fodder crops with eleven months of irrigation are such that the mission recommends that it should be adopted on up to ten per cent of the fodder area: obviously, a watch must be kept for adverse effects on the soil. It is the longer periods of dessication which promote good cracking and restore soil structure. In the past, this function has been discussed in terms of "fallow years" but the rainless period between crops allows considerable drying out of the soil: in particular, aeration occurs. On present evidence, the mission considers this drying period between crops an essential part of the farming system which should be taken into account in calculations of cropping intensity. The traditional notation in which the intensity is expressed as the percentage of land cropped during the cycle (e.g. F - C - D - L is called 75 per cent) is not adequate for these soils. Intensity should be expressed on a "cropped month" basis (when,e,g. F - C - D - L becomes 39.6 per cent) and rotation sequences designed to ensure that there is an adequate drying period between crops to restore soil structure. The full year of fallow is needed for a variety of reasons. Pest and disease control, and the build up of soil nitrates, are no longer overriding considerations but there is at present no alternative to the mechanical method of controlling pernnial weeds, which can only be accomplished on a wide scale in a full fallow year. A full year's fallow will allow the development of deep, wide cracks, favoring deep burying of surface salt accumulations. From its consideration of the various functions, the mission concluded that, in the immediate future, there should be at least one full yearts fallow in every four years. New techniques (especially  - 13 - ANJNEX Fr herbicides) may change the situation in future and trials should be laid down immediately on rotation units to study any changes in soil properties under crop rotations with different frequencies of fallows: e.g. one fallow every six, eight, nine or twelve years. The fertilizer applications, cultivation, spraying, etc. of these trials should be the same as those currently adopted on the rest of the Scheme: the rotations proposed for Rahad could be included0 The present system of preparing the first ridges during the dry period encourages rapid drying and aeration of the top soil and should be continued. There is no record of the effect on soil structure of pre- sowing irrigations in March, which the mission recommends for agronomic reasons. The extra wetting/drying cycle may be expected to produce a better surface texture: if it is alsn found in practice to hinder the development of deep cracks, it may be necessary to reconsider the desirability of routine pre-sowing irrigations on saline soils or where the grey layer is very near the surface.  ANNEX II C H A P T E R 3 PRESENT AND FUTURE AREA OF GEZIRA The Gezira irrigation scheme compromises two interdependent irrigation networks, the Gezira Main and the Managil, each commanding almost a million feddans. Water is taken from the Blue Nile at Sennar, 57 km south of the scheme, and distributed through a vast network of channels to over 77,000 holdings. The organizational unit is the Block, which varies in size but is usually 20,000 to 30,000 feddans of irrigable land. There are 91 Blocks, of which 47 are in Gezira and 44 in Managil; administratively, the Blocks are organized into twelve Groups. The rotation unit served by a minor canal is 720 feddans in Gezira Main and 54~O feddans in Managil but the irrigation unit, or number, is 90 feddans throughout the scheme.l/ Every howasha, or field, is ten feddans. Within this vast area, changes are always occurring, e.g. saline patches are removed from cultivation, or allocated to forestry; at the present time, new land is being brought into cultivation along the southern borders of the scheme. New intensified rotations are being put into use, but at the same time not every farmer makes use of his full allocation of lubia land. All these changes are reported in due course but it is usually quite some time after the end of the cropping year before final agricultural statistics are available and a further twelve months before the related accounts are issued. The mission therefore adopted as its "baset" the most recent year for which agricultural and cost data was available, i.e. 1964/5. FUTURE EXPANSION The mission received several estimates of the additional area of potentially useful land in and around the Gezira Scheme that could be commanded by pump or gravity schemes from the main canals. There is a clear danger of over-enthusiastic expansion. The economics of pumping water from the Gezira canals on to high sites, rather than 1/ For a brief description of the irrigation system, see Appendix 2.  - 15 - ANNEX II using it in some other scheme where gravity flow is available, should be carefully evaluated. The development of marginally saline soils will create problems in the futture and will absorb canal capacity which might more usefully be employed in raising the productivity of good areas. In the absence of comprehensive data, the mission concluded that a variety of factors would limit future expansion to an area of about 160,000 feddans of irrigable land more than in 1964/5, bringing the total area of the Scheme to just over 2 million feddans, including Abdel Magid../ Table 1 compares the area of crops as it was in the base year with the mission's expectations for the final total area. Provided equipment was not diverted to other schemes, the additional land could be cropped by 1968/9. The S.G.B. should therefore give immediate consideration to the problems of providing land for the mission's various proposals (e.g. demonstration centers, permanent pastures) so that land in new developments can be reserved for any farmers who must be moved before land becomes available in new schemes on the opposite bank of the Blue Nile. 1/ Abdel Magid is a 36,000 feddan scheme to the north-west of Gezira Main. Until recently it was administered by the White Nile Schemes Board but it was taken over by the S.G.B. on July 1, 1966. It must, in any case, be included in agricultural planning, since it draws its water from the Gezira irrigation network.  - 16 - ANNEX DI Table 1: GEZIRA SCHEME AREAS Area in thousands of feddans 1964/5 1968/9 a/ Cotton 508 557 Dura 255 275 Lubia 71 215 Groundnuts 60 210 Wheat 75 1140 Fallow 775 510 Laborers' dura (1 fallow) 6 8 Gardens 25 414 Forestry, resting, etc. 36 140 Pilot schemes, demonstration, dairies, etc. - 11 1811 2010 or or more than 1.8 mi'llion 2 million a/ Includes Abdel Magid.  - 17 - ANNEX I The mission's estimate of potential expansion is 28,000 feddans greater than that envisaged by the consultants for the Roseires Project.l/ As will be seen later, however, the two estimates of total water usage are similar, the mission believing that more efficient irrigation practices can be introduced. AGRICULTURAL ZONES IN THE GEZIRA While the climatological data for Managil does not cover a sufficiently long period to permit strict statistical analysis, the mission concluded that Managil could safely be treated as a single agricultural zone since the rainfall increases from south-east to north-west (i.e. across the shorter axis of the area). From a detailed analysis of 15 years' weather records from Gezira Main, however, the mission concluded that it should be treated agriculturally as two zones; the drier north, comprising Abdel Magid, North, North-West and rmost of Mesellemiya Groups; and the wetter south, comprising South and Center Group. The transition zone, Wad Shair and part of Mesellemiya Groups, is most conzveniently considered as part of the north zone. 'The new areas along the southern fringes have a four- course rotation and are more conveniently included in the south zone, even though some may draw water from the Managil system. An estimate of approximate distribution of crops by zones in the 1970's is shown in Table 2. It should be stressed, however, that one of the main themes of the mission's agricultural policy is local flexibility within a general pattern. The areas shown are not rigid targets but guide-lines suggesting an appropriate pattern. The rotations on which Table 2 is based, and the irrigation requirements, are discussed in a later chapter. 1/ Memorandum on the Utilization of Water from Roseires Reservoir. Sir A. Gibb and Partners, Sir M. MacDonald and Partners, unpublished.  - 18 - ANNEX 1'X Table 2: GEZIRA SCHEME ESTIMATED DISTRIBUTION OF CROPS BY ZONES IN THE 1970's area in thousands of feddans GEZIRA MANAGIL Errors TOTAL a/ due to North Zone South Zone RoundingY Cotton (excluding experiments etc.) 175 125 257 557 Dura (including laborers' plots) 87 61 127 275 Lubia,fodder,etc. 89 62 64 215 / Groundnuts 23 125 64 -2 210 Wheat 141 - - -1 140 Garden 22 11 11 44 Fallow 151 122 240 ) 510 Laborers' dura plots ) and fallow 2 2 4) -3 8 Demonstrations etc. 3 3 5 ) 11 693 511 772 -6 1970 Forestry,resting etc. 40 2010 Phillipesara grown on fallow 66 66 122 a/ As Table 1. b/ Full details of farmers' crops are given in Appendix 2,Agronomy, Table 5, where demonstrations etc. are included in fallow,as this is the general allocation of the land on which they would be sited. c/ Includes about 22,000 feddans irrigated for eleven months each year.  ANNEX II C H A P T E R 4 FLUCTUATIONS AND VARIATIONS IN COTTON YIELDS The Gezira Scheme was conceived because of cotton, and its construction and operation has been financed almost entirely from the proceeds of the sale of cotton. It is not surprising, therefore, that statistics and data on every cotton crop have been carefully preserved. There is much less information on the tenantst own traditional crops - dura and lubia -- while groundnuts, wheat and phillipesara are new intro- ductions for which data is available for a very short period. Even had a wealth of data been available for every crop, however, the overwhelming importance of cotton, both to the farmer and the country, would have warranted special attention to cotton yields. COTTON PRODUCTION AND YIELDS The history of the Gezira since the opening of the Sennar Dam is divided into three phases: 1925-35, a period of rapid expansion of the gravity-irrigated area followed by devastating attacks by pests and diseases. 1936-58, a period of consolidation, with no significant expansion. The benefits of the new resistant cotton varieties and rotations became apparent and nitrog3norzs fertilizers and modern pesticides were introduced during the last few years of this phase. 1958-66, a period of rapid expansion in Managil. Aerial spraying and fertilizers became routine practice over the whole area. Privately-owned tractors entirely replaced bull ploughs for split ridging and torading in the last few years of this phase. Production During the 40-year period, the total production of cotton has increased at an average rate of 3.48 per cent per annum (see Fig.l), although there have been marked fluctuations in production from year to year.  - 20 - ANNEX II An examination of yields shows that this increased production is almost entirely due to greater area. An inverse relationship between yield and area is to be expected in periods of expansion, but Fig. 2 shows that the improvement in yields was very small even during the years of consolidation, 1936-1958. Average Yields Fig. 2 graphica'lly illustrates the violent annual fluctuations in yield. These fluctuations entail a practical difficulty - the choice of a meaningful average yield for planning purposes. Fig. 2 shows that the statistical average increased from 4.17 k.p.f. to 4.42 k0p.f. in the 24 crop years from 1935-58 but over the past 20 seasons, the overall average has fallen again to 4.18 k.pof. The short-term, 5-year moving average yields for the whole scheme were 3.692 k.p.f. up to 1964/5 and 3.880 k.p.f. up to 1965/6. FACTORS CAUSING ANNUAL FLUCTUATIONS IN COTTON YIELD During the 20 seasons 1945-65 (when the overall average' was 4.18 k.p.f.) the annual yields fluctuated from under 3 k.p.f, (3 seasons) to over 6 k.p.f. (3 seasons), i.e. from yields that would be thought poor on undeveloped rainlands in some countries to those associated with large- scale irrigation in many parts of the world. The cause of this fluctua- tion has been studied almost continually since the inception of the Scheme. Soils The soils were exonerated from blame since crops grown at G.A.R.S. in soil imported from Gash were subject to the same yield fluctuations0 The very high yields obtained in some years (e.g. 6e782 k0po,f in 1950/') confirm that Gezira soils are a good medium for growing cotton. The mission made a detailed analysis of the yields in 40 Blocks in Gezira Main (for which records over 16 years were available) and found that inherent soil fertility per se was not a major factor in accounting for yield fluctuations. There was no evidence of decline in yield, yet equally none that the introduction of fertilizers (and/or insecticides) had let to increases or reductions of fluctuations. Rainfall Before the general introduction of fertilizers and insecticides, Crowther had developed a formula relating yields to the total rainfall in the preceding year and to the immediate pre-sowing rainfall. These factors were concerned in the carry over of insect pests and, particularly, with the natural build-up of soil nitrates, and it is not surprising  SUDAN: GEZIRA FARM PRODUCTION OF SEED COTTON (MILLIONS OF KANTARS) 2.5 2.5 2.0 2.0 1.5 1.5 Log Ye 2.61171+ 0.0148423x 1.0 1.0 .5 .5 0 J l l O 1925/26 1930/31 1935/36 1940/41 1945/46 1950/51 1955/56 1960/61 1965/66 CROP YEARS > Growth 3.48 percent per annum I B RD -3185  ANNEX I FIGURE 2 SUDAN: GEZIRA SEED COTTON AREAS AND YIELDS 800,000 _ -AREAS-_ _ -(FEDIDANS)- _ 0_0 100,000 _ ___ __ ___ 10,000 _ _ _____ 1,0 0 0_ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ --SEMI-LOGtARITHMIC SCALE 100 1III LII LW) 1I I hUI fLI J 1911/12 1915/16 1920/21 1925/26 1930/31 1935/36 1940/41 1945/46 1950/51 1955/56 1960/61 1965/66 CROP YEARS YIELDS 8 -(KANTARS'PER FEDDAN) 7 _ _ _ _ _ _ _ _ 5A V~~~ A A ~~417 - .42 3 A VI/\/ ____ 2 . ~~~~~~~~~~~~~~~~~Regression for 24 years 2 l 1934/35 to 1957/58 y = 4.157 + 0 008xO 1911/12 1915/16 1920/21 1925/26 1930/31 1935/36 1940/41 1945/46 1950/51 1955/56 1960/61 1965/66 CROP YEARS IBRD-3186  21- ANNEX II that estimates prepared from Crowther's formula have become less reliable in recent years. Whilst economic policy making requires advanced fore- casts of cotton yield, very little emphasis should be given to estimates made before the crop has reached an advanced stage of growth. The cotton crop in the Gezira is planted during the wettest months of the year and even though the correlation between the Crowther's formula and yields is no longer close, it is hardly reasonable to suppose that the introduction of fertilizers, etc., has entirely eliminated the effect of rainfall. The mission therefore made an analysis, details of which are given in Appendix 2, of the effect of rainfall on planting dates, etc. Pre-sowing Rainfall. The requirements for the best germination and early growth of cotton in the Gezira have not been specifically evaluated but it is clear that "poor" cotton seasons are associated with low rain- fall prior to the middle of July and vice-versa. The beneficial effects of pre-sowing irrigations on yields (and the marked reduction in labor needed for weeding subsequent crops)had been shown in trials in 1947-51, but water could not be used for this purpose under the old Nile Waters Agreement. The S.G.B. has introduced pre-sowing irrigation progressively since 1963/h. No related yield data was available but the mission endorses the practice and recommends its general adoption as a means of reducing annual fluctuations as well, it is hoped, as of raising general yield levels. Planting Dates. A detailed examiaation of rainfall patterns indicate that attempts to plant all the cotton in the Scheme during a specified period are likely to increase fluctuations in yield. The mission recommends that there should be more local control over planting dates: it is shown in Appendix 2 that, for example, Turabi Block should be planted in the 25 days ending 18th August whereas in Hag Abdalla Block it may be delayed until the end of August, when the plants will ga'n the advantage of higher solar radiation during early growth. Pests and Diseases The ravages of pests and diseases of the cotton crop brought near disaster to the Gezira Scheme in the early 1930 s and the fear of further epidemics has strongly influenced the design of cropping patterns, the aims of research and plant breeding and agricultural thinking generally until the present day. The breeding of disease-resistant strains of cotton, and the advent of modern insecticides and the means of applying them rapidly to vast areas, have greatly reduced the chances of new catastrophes but the fact remains that pest and diseases cause a general reduction of yields and play a very significant role in the annual fluctuations in yield. 1/ 1/ Ann. Rep. Res. 1962/3. Jackson et al. Crop.. ehys. Section,  - 22 - ANNEX II Diseases. Apart from the use of resistant strains of cotton, the main defence against the major diseases of cotton, bacterial blight and leaf curl, is the various plant hygiene measures, most of which are enforced by law. The planting dates of alternative host plants to leaf curl, or to the white-fly which spreads it (lubia, bamia, kerkade, etc.) are controlled by the Board and, when necessary, host weeds are eradicated by concerted action. These measures appear to be effective: some relaxation may be possible in the year3 to come but the mission does not recommend any immediate changes. The main plant hygiene measure is the pulling out of cotton plants, the sweeping up of loose debris, and the burning of all cotton crop residues on the howasha where they were grown. This "clean-up'? campaign is expensive, both in terms of money and of labor, but it appears to be conscientiously carried out. The Board has devised and manufactured tens of thousands of stalk-pullers - aids to manual work - but pulling is a long and arduous job carried out in the hottest part of the year. The mechanization of pulling is an obvious and urgent objective. Prototype machines were designed some years age, but a primary aim of the design was to collect the stalks for processing and the machines - apart from being expensive - had a very low rate of work. A more recent design shows great promise and the mission recommends that development should proceed as rapidly as possible: the Board should provide any necessary funds, although the machine, if successful, will be needed for all cotton crops in the Sudan. A word of caution is necessary. Mechanized stalk pulling may prove almost as expensive as hand labor. Further, the extent to which pickers depend on the income from pulling to justify their journey to the Gezira is not known: a serious situation could arise if mechanization of pulling reduced the harvesting labbr beyond a critical point. Finally, mechanisa- tion will only be useful if it results in a speeding-up of the operations actual harm will be done if the "cleaning-up'" is delayed while farmers wait for a machine to arrive. For this reason, both the S.G.B. and Drivate contractors should buy and operate the pullers: easy credit facilities should be made available to contractors as soon as a satisfac- tory commercial version is available. Soil Bacteriophages. Recent research has shown that naturally- occurring bacteriophages in the soil will destroy the bacteria which cause bacterial blight. The debris must be reduced to small pieces and intimately mixed with the soil, which must then be flooded, and further work is needed to establish practical methods of applying this knowledge. Only bacteria are destroyed by this treatment: viruses (notably those causing leaf curl) are not affected and treatment would have to be followed up by a "clean-up" campaign to eliminate every living cotton ratoon 1/ which 1/ Ratoon - new shoots springing up from the stumps or tap-roots of the previous crop.  - 23 - ANNEX TI might carry over virus infections from season to season. Again, a word of caution is necessary. Chopping and burying the debris will probably cost much more than mechanized pulling and poor work will be far less noticeable than would incomplete pulling. One possible outcome of this research, which the mission recommends should be pursued, is that it may prove possible to condone - or even encourage - the practice of sweeping dead leaves and other debris into cracks. Pests. Because of its indeterminate fruiting habit, Barbadense cotton has to be protected for a long period (5 months from early buds to the last developed mature bolls) and the pest complex is not identical with that found on Upland cotton elsewhere. In the early part of the season, persistent systemic insecticides are needed to control sucking insects. Later, at the very first appearance of bollworms, contact poisons are needed but once the bollworms are established inside the bolls they cannot be attacked by either systemic or contact poisons. The development of new insecticidal formulations, and of new means of employing them, is extremely rapid and it is obviously essential that specialists in the Sudan - and in the Gezira in particular - should continuously investigate new'products and techniques. Spraying Intervals. Systematic spraying at regular intervals based upon the life cycles of pests is practiced in some areas where Upland cotton is grown but, because of the long period over which protection is needed, is probably not economic with Barbadense cotton. The Mlinistry of Agriculture bears the ultimate responsibility for identifying and controlling pests in the Sudan. At the present time, both the Ministry and the S.G.B. maintain teams of observers in the Gezira Scheme to count pests and to report when insect populations reach alarm:i.g proportions. The S.G.B. has recently obtained the assistance of four expatriate entomologists, to be based at key points throughout the Scheme, but their arrival coincided with the missionts departure and details of their assignment were not known. This duplication of specialists and trained observers appeared very wasteful to the mission. Only one group is required: the mission recommends that the Ministry should train S.G.B. employees and should make periodic checks on their efficiency but should not continue to duplicate network of observers. The mission also recommends that the recognition, entomology and control of pests should be included in all staff training programs: in the future, extension workers should teach farmers to recognize and report pests and to undertake simple control measures for themselves. The mission also recommends that the observers should be trained  - 24 - ANNEX II to be alert for the first signs of pest build-up and that the authorization of spraying should be decentralized to at least regional level. The number of sprayings has increased steadily over the years: in 1965/6 most of the cotton crop was sprayed at least four times and wheat was also sprayed for the first time. The mission do not consider this adequate for Barbadense cotton and confidentally predict that more sprays will prove economic. There is little research data relevant to the economics of more frequent spraying on a large scale. The present series of trials, started in 1962/3, compares 0, 1 and 2 sprayings only: even if comparisons with "no spray" are valid in close proximity to such a large sprayed area, the results are of little practical value since no responsible authority could now consider the abandonment of spraying. The mission recommends comparisons of 4, 8 and 12 sprays, applied to large areas from the air, using the same techniques that are applied throughout the rest of the Scheme. Aerial Spraying. The mission endorses the S.G.B. policy of using aircraftfor all routine, large scale spraying operations. The direct operating cost of tractor-mounted sprayers are less than the contract rate for aerial spraying but ground equipment is at a disadvantage in the tall irrigated cotton crops: operationally, the messir must be broken down before tractors can enter the howasha and they cannot work for several days after irrigation, making it difficult to devise economic working schedules: technically, they are very much slower than aircraft and (at least with present equipment) do not give such an efficient distribution of insecticide. The contractors appear to carry out operations conscientiously and the contract rates compare reasonably with those in other parts of the world. The mission does not consider that the SOG.B. should purchasa its own fleet of aircraft: the high capital cost and expense of employing pilots and technicians would undoubtedly increase the cost of spraying. The present contract system should continue, bids being called on a regional basis. Local Spraying. A number (about 4 per Group) of the S.G.B.'s tractor-mounted sprayers are still used each year to spray flea beetle infections (against which Land Rover exhaust-sprayers are also used) and to spray areas inaccessible to aircraft, e.g. under power lines. The deployment of these tractors and their crews from the central base, with all the concomittant allowances and privileges, seems wasteful and the mission recommends trials with motorized knapsack sprayers. If these are found successful, they should be issued to Blocks and field staff given discretion to use them, not only against flea beetles but on foci of other insect infestations.  - 25 - ANNEX 17 FACTORS CAUSING LOCAL VARIATIONS IN COTTON YIELDS The natural factors which cause annual fluctuations in yield also cause local variations. Soils, as has been seen, vary from north to south and some Blocks include a proportion of poor soils. It has been shown that "good" numbers always yield well, retaining their position above the Block average regard- less of the season. Many efforts have been made to correlate these better- than-average yields with factors such as sodium value, clay content, etc. correlations have been found, but no simple factor has yet proved capable of classifying soil capabilities in order of merit. Obviously, some patches of soil yield better than others: these natural patches will n't coincide with the man-made Block boundaries nor with the irrigation lay-out and there will be local variations in yield. Rainfall, like soils, varies from north to south: as with the soils, the most favorable areas are in the southern part of the Gezira. It is noc surprising, therefore, that an examination of Block average yields for Gezira Main (Fig. 3) shows a general, but not invariable, decline from soaith to north. The general decline in yield, from 5.25 k.p.f. to 4 k.p.f., shows a close correlation with rainfall (r - +0.9). It is to be hoped that improved water regimes will reduce the part that rainfall plays in this variation, although the part due to soils will always remain. Analysis of Block yields on Gezira Main showed that the standard deviation about the mean increased from 0.7 k.p.f. in 1949/50 to 1.3 k.p.f. in 1963A, indicating that the range of differences between Blocks has increased markedly in the past 15 years. Important differences were apparent from a detailed study of the yields of individual Blocks and of neighboring pairs of Blocks. As will be seen from Fig. 3, some Blocks outyield their immediate geographical neighbors: thus Block 9, Seed Farm, is slightly better than Block 8, Hamad el Nil, which in turn is better than Block 4, Wad el Attaya: Block 16, Tayiba is better than Block 15, Medina. In every instance chosen it was found that there was linear trend showing unmistakably that the relative yield trends in the pairs were changing in a manner that could not possibly be ascribed to changing soil fertility or to natural events. These linear changes were not minor: the overall improvement was nearly 2 k.p.f. in some cases: see samples in Fig. 4. The only feasible explanation of these changes is that differences in crop husbandry, i.e. the annual cultivations, weeding, distribution gf fertilizers, etc. cause major variations in yield, and that standards were improving more rapidly in the better of the pairs of Blocks.  SUDAN: GEZIRA FIFTEEN YEAR AVERAGE COTTON YIELD AND RAINFALL BLOCKS I TO 34, 1949/50 TO 1963/64 55 e I I 1 1 X 1 I 1 1 1 1 1 X 1 1 1 1 1 E F I X 650 HAG ABDALLAH SEED-~FARM 600 HAMAD EL NIL ~50 550 z 50 < j / t COTTON YIELD @ LEFT SCALE) '- - 500 cr TAYIBA m W cn ~~~~~~~~~~~~~~~~~~~~~~~~~~~FETEIS G ~45 WAD EL BUR IL KETEIR- 450 m1 I-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~- RADMA S 4F1:'~~~A 40050 w - MEDINA Li %. 1 23 4 56789019112 13413415 16 17 18 19 20 2122 232425 2627 2829 30 3132 33 34 BLOCK NUMBER IR 38 40 D ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~IR 3187  ANNEX U FIGURE 4 SUDAN: GEZIRA COMPARISONS OF COTTON YIELDS OF NEIGHBORING BLOCKS (DIFFERENCES IN YIELD-KANTARS PER FEDDAN) BLOCK 9, SEED FARM, COMPARED WITH BLOCK 8, HAMAD EL NIL +3 +3 +2 +2 REGRESSION COEFFICIENT 0.082| +1 A +1 O ,aBLOCK 8 i/t - ;! a- O 0 -I -X I ^ t A K BLOCK 9 -2 V 0 ll i y | : | 0 |-2 1945/46 1950/51 1955/56 1960/61 1964/65 CROP YEARS BLOCK 8, HAMAD EL NIL, COMPARED WITH BLOCK 7, WAD EL ATTAYA +2 +2 REGRESSION COEFFICIENT 0.070 +1 A A +1 O BLOCK 7 > - O 0 I I I I B~~~~~~BLO CK 8 _-I _-I 1945/46 1950/51 1955/56 1960/61 1964/65 CROP YEARS BLOCK 16, TAYIBA, COMPARED WITH BLOCK 17, MEDINA +2 , , +2 REGRESSION COEFFICIENT 0.095A +1 A+ - I " _-J~ 1945/46 1950/51 1955/56 1960/61 1964/65 CROP YEARS IBRD -3188  - 26 - ANNEX It Standards of crop husbandry -- which, in view of the system for regulating cotton cultivation, means also management -- are thus a very important factor in the local variations in yield. Their effect is probably greater than those due to soils and rainfall: unlike those due to natural causes, the variations due to different standards of crop husbandry can be remedied. The remedies are obviously better training of inspectors, extension work to encourage farmers to adopt better methods of husbandry, etc. Surface Drainage The problem of removing surplus water (from rainstorms, the release of excess water from canals onto irrigated land, or from over-irrigation) recurs every wet season. If this surplus is not removed quickly enough, soils become waterlogged, causing poor aeration, and plants receive a severe check whic46ffects their yielding ability: weeding becomes physically impossible, and yields are reduced by competition: in severe cases, seedlings are washed away or suffer so much that the fields have to be replanted, after the optimum date, wasting labor and reducing yields. similarly, yields are reduced where planting is delayed on fields which are known to be prone to flooding. Flooding -- and delays in anticipation of flooding -- vary from Block to Block: "rainkill" (the phrase used for "flood damage") necessitated replanting about 1 per cent of the cotton area while 3 per cent was left unsown because of flooding in 1964/5 1/. It is thus an obvious cause of variations in Block average yields and has a direct and devastating eTfect on morale and the livelihood of many individual farmers. Surface drainage, and the mission's proposals for improvements, are discuszed in detail in Chapter 7. 1/ Ann. Crop Rep. S.G.B. 1964/5.  ANNEX II C H A P T E R 5 INCREASING YIELDS The mission's consideration of the factors which cause variation in cotton yields indicates a clear possibility of increasing yields generally; if the variation within Blocks is increasing without a general increase in yields, some Blocks have found ways to obtain higher yields; if a Block's average has increased, some farmers in that Block must be growing better crops. The soils, in spite of variations and poor patches, are capable of giving better results with cotton; and there is no reason whatever to suppose that this does not also apply equally to other crops. This point is stressed to emphasize that the mnission's proposals for increasing yields include few new methods or approaches. The main thereof this chapter is the encouragement of the best known methods of crop husbandry. Extension services and other incentives which are discussed in the next chapter, will be needed to encourage farmers to adopt these methods. POTENTIAL YIELDS Research plots have indicated that the Gezira soils are capable of giving very high yields. There is sometimes disappointment when methods which give excellent results in trials fail to live up to expectations when applied to the Scheme as a whole. In some cases (that of fertilizer will be discussed in detail) this is due to the method of application of research findings. In every case, however, experience shows that the actual levels of yields obtained in small- scale trials cannot be expected on a field scale. An analysis by the mission suggested that field scale yields should never be estimated at more than 70 percent of those obtained from small plots, even in the case of variety trials, etc., where application techniques are less important. Research results were not, however, the only criteria in the mission's assessment of potential yields. Results regularly obtained by the good farmers on good Blocks, the probable effect of poor soils and rainfall distribution on the overall Scheme average, etc., were all  - 28 - ANNEX II considered. Table 3 shows the potential yields which the mission believes are technically feasible 1/if their recommendations, especially with regard to crop husbandry, are put into effect by a reasonably high proportion of farmers (i.e. good extension services are assumed). These feasible yields are long-term averages but at the same time annual fluctuations should be reduced. 1/ For obvious reasons, the mission has found it prudent to use slightly lower yields in considering the economics of tenancies in the future.  Table 3: IUR0VEHENT POTENTIAL A.IX II Cron Present Potential Yield Remarks Yield Remarks Cotton L!.2 k.o.f. Long-term average: 5.8 k.p.f. (1700 lb. seed-cotton per feddan).With G.0.T. 35 percent this gives 600 lb. lint,which has been the Seed Farm average over past ten years Groundnuts 0.6 m.t. Accurate data on tenant's crops 1.1 m.t. (2500 lb. per feddan). An average of 1.25 in shell very scanty and for short in shell mi.t. has been obtained over past three years per feddan period of years. per feddan as V.F.E. Wheat 0.3 m.t. Difficulties in early years o.6 m.t. (1300 lb. per feddan). Experimental yields per feddan reduce average. 0.66 m.t. was per feddan have been 0.9 m.t. per feddan. obtained from 5,000 feddans in 1960/1 and from 20,000 feddans in 1963/h. Dura 0.5 m.t. 0.7 m.t. (150) lb. per feddan). Dura gives threefold per feddan per feddan gain with 2N but potential average assumes that it will be difficult to persuade farmers to make major changes in the growing of thls i traditional croo. Fodder: Irrigated Lubia - h m.t. Later planting assumed dry matter per feddan Rainfed Philli- pesara - 2 m.t. dry matter per feddan. uood fodder 1 cow or 8 Throughout year, 30'DO lb. milk per cow. will support: ewes per feddan. h cattle Durin-- limited fattening season or 20 sheep per feddan  30- ANNEX II The Importance of Yield Increases Table 4 emphasizes the potential value of extension work and other efforts to increase yields in efforts to improve production of the Gezira; constant prices 1/ are assumed: Table 4: EFFECT OF EXPANSION, INTENSIFICATION AND BETTER YIELDS ON PRODUCTION (at constant prices) Item Production Index Original Rotations 1. 1962/3, (prior to major efforts at intensification). Average yields except for cotton. Actual area 1.76 million feddans. 100 2. Same rotation as 1. over tot&l pr6jected area of 1.97 million feddans. 112 3. Same as 2. but mission's potential yield. 142 S.G.B. Intensified Rotations 1. 1964/5, (intensified rotations in use). Average yield for cotton averages for other crops. Actual area 1.81 million feddans. 119 2. Same rotation as 1. over total projected area of 1.97 million feddans 130 3. Same as 2. but mission's potential yield. 173 Mission's Proposed Rotation 1. _ 2. Average yields over total projected area of 1.97 million feddans. 146 3. Same as 2. but mission's potential yield. 192 1/ The follouing farm gate values have bf-en vs,-