This paper, concerned with agricultural development planning problems in the Sahelian and Sudanian (semi-desert and savanna) zones in Africa between 10 and 16° North, describes a plan for Darfur, Western Sudan. This aims to modernize a stagnant and primitive technology and out-dated land rights which, in the face of rapid population increase and climatic change, are reducing the long-term carrying capacity of the land. The development plan (H.T.S., 1974) has been based on a 2-year (1972–73) survey by a team of physical and social scientists, financed by the Overseas Development Administration of the United Kingdom and the Ministry of Agriculture in the Sudan.

Two cocoa progenies, T85/799×T17/359 and E1:C43/291×T63/967 (Series IIB hybrid), were compared for degree of infestation by 17 insect species comprising a Coccid, an Aphis, a Mirid and six ants. A significantly greater proportion of trees of the second variety was infested by the mealybugs Planococcus citri Risso and Pseudococcus hargreavesi Laing, by the Lecaniid scale Gascardia sp. nr. zonatus Newst., by the aphis Toxoptera aurantii Boys, by attendant ants Camponotus spp., and Crematogaster spp., and by the ant Polyrhachis laboriosa F. Smith. Because of differences in habitat requirement between the four Hemiptera, it is postulated that it is more likely that the response is due to a physiological difference between the two progenies than to a purely environmental difference.

Hybrids made for the first time on six experimental photosensitive sorghum seed parents (whose breeding is described) were tested with their pollen parents, which included good dwarf varieties, in replicated small plot trials at Samaru in 1972. Grain yields of up to 5000 kg./ha. were recorded from hybrids with acceptable plant types and grain qualities, which was 40 per cent more than from the best varieties. Some hybrids, though giving over 6000 kg./ha., were unacceptable due to excessive plant height or poor grain appearance. Seed parent yields, determined in an adjacent trial, ranged from 1700 to 2900 kg./ha.

Total yield and yield components (tuber numbers and mean tuber weights) of six local sweet potato cultivars were compared in wet and dry season crops. There were significant negative correlations between tuber number and mean tuber weight in five of the six cultivars, and positive correlations between these yield components and total yield, suggesting that cultivars may be grouped into ‘tuber number-tuber weight’ and ‘tuber weight’ types, as well as a ‘random type’ in which yield is related to neither component. Marketable yield tended to be directly related to both components, and cultivars with lower tuber numbers usually produced a higher percentage of marketable yields. The significance of these findings for sweet potato yield improvement is discussed.

Nitrogen fertilizer applied to the surface of the soil in the field did not increase the yield of Bragg soybeans, and at higher levels reduced it, but may or may not significantly reduce soybean nodulation and plant height. In a pot experiment, there was evidence that deeply applied N increased plant height and dry weight of a non-nodulating isoline of Clark soybeans 46 days after planting.

The main axis of a Principal Components Analysis, based on measurements of width and depth of canopy of two cocoa progenies was shown to be an index of canopy size and the second axis an index of shape. Mean scores of the progenies T85/799×T17/359 and E1:C43/291×T63/967 (Series IIB hybrid) on these axes showed that their canopies did not differ significantly in shape, but that the canopy size of Series IIB trees was on average greater than that of T85/799×T17/359. Regression lines of log numbers per tree of Planococcus citri Risso against canopy size of the two progenies were parallel, indicating that for a given canopy size P. citri was 2·3 times more prevalent in trees of Series IIB than in T85/799×T17/359. A similar analysis with the combined numbers per tree of seven mealybug species showed that they were 1·9 times more prevalent in Series IIB than in T85/799×T17/359 trees of the same size.

Variabilities in total yield, marketable yield and components of yield (tuber numbers and mean tuber weights) were studied in six sweet potato cultivars over two seasons, in crops harvested at two dates. Yield variability was high, particularly in marketable tubers, and was related to either or both components of yield. High-yielding cultivars had lower variabilities and the commercial cultivar 049 the lowest. The contribution of yield components to variability in total yield was evaluated and sources of yield variation were attributed to planting material, tuber development and season.

The response of tomatoes to applied N, P and K was determined in six trials in the forest and savannah zones of Nigeria. In the savannah area, N was the most deficient nutrient, with an optimum level of 60 kg. N/ha., while P and K were required at lower rates of between 20–60 kg. P2O5 and K2O/ha. depending on initial soil nutrient status and moisture availability. In forest soils developed from sedimentary rocks, P requirement was high (120 kg. P2O5/ha.) and response to N was small, but K could be important on the well-drained soils in this area because of low K reserves (0·1 per cent total K) compared with soils from igneous rocks in the savannah with more than 0·6 per cent total K. The potential of the savannah for large-scale tomato production is discussed, as well as factors limiting yields in Western State of Nigeria.

The fifth leaf of tomato plants sampled at the early flowering stage (seventh to eighth week after sowing) gave good assessments of N, P and K requirements of the tomato crop growing in the field but total N was less useful than nitrate-nitrogen for diagnosing nitrogen needs. The levels of critical N, P and K in the crop were 0·4 per cent NO3-N, 0·4 per cent P and 4 per cent K, with severe deficiencies when levels were less than 0·1, 0·15 and 2 per cent respectively.

Effects of sowing dates, population, fertilizer, weeding and variety inputs on yield were measured, as well as labour required to apply the inputs. Sowing date was the most important, response to others being dependent upon this factor. Population was least important, but increased in value as fertilizer level was raised. Labour requirements were so increased by applying the ‘package’ that subsistence farmers, whose families are fully occupied as the sole source of labour, would be unable to cope without reducing the area under cultivation. Thus yield response to a package must be higher than hitherto considered acceptable, and the risk of not obtaining this increase probably contributes to the rejection of such recommendations by subsistence farmers.

The effect of boron nutrition on the susceptibility of young tenera oil palm seedlings to red spider mite attack was studied. Highest concentrations of mites were recorded in seedlings which had received little or no boron in the growing media. Injuries by mites were greatest when the leaves had the highest number of mites per unit area, the lowest boron concentration and the lowest concentration of cyanidin.

Bulbs of 20 onion cultivars were stored at 30°C and assessed for rotting and sprouting. No evidence of heritable resistance to high-temperature rotting was found, but the suppression of sprouting by high temperatures appeared to be a common character of onion cultivars.

Genotypic correlations and path coefficients were used to determine the importance of various characters as components of yield in castorbean. Number of primary branches per plant and 100-seed weight had high positive correlations with yield per plant and with each other. Oil content was significantly and positively correlated with 100-seed weight. The path analysis revealed that number of clusters per plant, number of branches, height at maturity and yield of the first spike had the highest direct effect on yield per plant. Sixteen selection indices were constructed using these four yield components, the index combining all four being about 54 per cent more efficient than straight selection based on yield alone.

Low and unreliable rainfall, combined with high summer evaporation rates, frequently lead to poor yields and crop failure in Botswana agriculture. Over three test years it has been shown that the soil can store up to 100 mm. of available moisture at planting time, which represents about half the water requirement of a crop of sorghum, and the balance is likely to be met (P = 0.05) during the current growing season. Sorghum grain yields have been doubled (2007 kg./ha.) after fallow compared with 1028 kg./ha. after non-fallowed pre-treatments. The advantages of a farming system based on a bare summer fallow are discussed, and reference is made to the implications of its wider adoption.

The response of groundnut plants to CCC was investigated by applying concentrations of 0, 500, 1000 and 1500 ppm three times as a foliar spray. CCC at 500 ppm gave more kernels, and heavier yields of pods, kernels and oil, than 1000 or 1500 ppm or the control treatment. Application of CCC resulted in a greater percentage of shell and of moisture in the whole pod than in the control.

Optimum transplanting age and relative growth rate in three groups of rice varieties differed with types and maturity periods. Transplanting 52 day old seedlings reduced the shoot number, and the magnitude of reduction was higher in early than in mid-early and medium varieties. Early transplanting reduced the number of days to flowering in all three groups compared with transplanting later. Senescence was much earlier in early types transplated as 52 day old seedlings. Grain production in early types was more sensitive to late transplanting than the mid-early and medium types. Medium varieties outyielded the early and mid-early ones when transplanted at 38 days after seeding.

Equal volumes of irrigation water, applied in different ways to a crop of haricot beans in two seasons, showed that the best practice was 60 mm. irrigation every ten days.

Effects are reported of some factors which may influence emergence and establishment of pigeon pea (Cajanus cajan (L.) Millsp.), including seeding depth, seed dressing, seed grading, seeding rate, variety and temperature. The effect of seeding rate was dependent on mean germination percentage in the field, but circumstantial observations on other factors of possible consequence in determining plant stand are also discussed.

Work was conducted in Alexandria and Sakha districts, Egypt, to study the influence of planting dates and seeding rates on yield of seed cotton, yield components and fibre properties of Egyptian cotton, Menoufi variety, during 1970–1972. Four planting dates were studied, together with four seeding rates. The number of lost plants decreased as planting date was delayed, and the highest yield of seed cotton resulted from the third date of planting (20–23 March) using hand-drilling. Neither planting dates nor seeding rates had significant effects on most of the other characteristics studied.