The mineral N (NH4 + NO8) in soils at a savanna site was low at the time of crop planting except after groundnuts and when dung had been used. Nitrification occurred whatever the previous crop, but the numbers of nitrifying bacteria were small and varied with the level of substrate ammonium.

The growth of two varieties of white yam was analysed from planting in December to harvest in September. Four stages were recognized, viz.: dormancy, rapid growth of vine and root, rapid tuber development accompanied by leaf senescence and tuber maturity followed by reduction in tuber weight. The period of rapid growth coincident with maximum demand for nutrients was early June, suggesting that fertilizer should be applied in mid-May so that it is available in June.

Variation in the percentage of nitrogen, phosphorus and potassium content of a variety of white yam, grown without fertilizer, and the nutrients removed per acre by various portions of the plant, were determined. The time to apply fertilizers, and the most suitable portion of the plant for foliar analysis, were deduced from the changes in nutrients with age. The effect of nitrogen fertilizer on yield, and the nutrient content of the harvested tuber, were studied. The influence of a yam crop in a rotation is discussed.

Comparison of an overhead boom sprayer (Monica Mist) with a conventional air-assisted sprayer (Conomist) showed that the former gave relatively poor cover, but control of coffee berry disease (CBD) was equally good with both machines. It is suggested that the success of overhead spraying is dependent upon effective redistribution of fungicide within the tree canopy during rain.

Hand-pollinated pods of the Crin Elite establishment cocoa progeny C77 X C23 showed that pod maturity, based on pod age, significantly affected bean viability as well as leaf area, leaf number, plant height and plant girth of the seedlings produced. Beans extracted from immature unripe cocoa pods only 15 weeks from hand-pollination were more than 50 per cent viable and produced seedlings vigorous enough for transplanting to the field after 20 weeks in the nursery compared with beans from 25-week-old normal, mature-ripe cocoa pods. Loss by black pod disease (Phytopthora palmivora Butl) could therefore be avoided and time of waiting for pods to attain normal maturity and ripening saved, by early harvesting.

The persistence of residues of gamma BHC and malathion on bhindi fruits was estimated by bioassay using 1-day-old male Drosophila flies. Although the initial deposits were heavy, they dissipated quickly, with half-lives of approximately 4 and 2 days for gamma BHC and malathion respectively.

Aflatoxin was found in forty-one out of seventy-four samples of various pulses, whereas Aspergillus flavus occurred in all samples, and there was an apparent correlation between the occurrence of the fungus and the level of the toxin in haricot beans. There was evidence that the toxin was produced in haricot beans after harvest, and drying the pods immediately after harvest is therefore suggested as a method of controlling mould growth and the formation of aflatoxin.

At Samaru (11° 10′N, 7° 39′E) the growing season for rain-fed annual crops is 180 to 200days. Sole cropping, relay cropping and intercropping of long season sorghum, early millet or maize and late planted cowpeas were evaluated for most effective use of this period, all crops being cultivated mechanically. Relay cropping and intercropping gave 59 and 80 per cent more return per acre respectively than a sole crop of sorghum, the increases coming mainly from higher cereal yields. Some criteria applicable to intercropping are recognized.

Mechanized crop production schemes continue to be the main source of grain sorghum in the Sudan, where fertilizer experiments have shown that applications of NP and NPK significantly increase the grain yield of continuous sorghum, though economic increases could be obtained by the application of nitrogen.

The total N uptake, crude protein content, and recovery of N in rice grains varied with varieties. Increased levels of N application gave increases in total N uptake and crude protein content in the grains, though recovery of N in the grains decreased with increased levels of nitrogen application. Irrespective of varieties and levels of application, three split dressings of nitrogenous fertilizer gave greater total N uptake, crude protein content, and recovery of N in the rice grains than where all the N was applied at the time of transplanting of seedlings.

Oil palms with white stripe have greatly reduced yields. In the chlorotic areas of the leaflets, columnar palisade cells fail to develop and there is a reduction in air-space volume of the spongy mesophyll. Leaf area and photosynthetic activity are also reduced. Recovery of palms showing symptoms was spasmodic. The condition is discussed in relation to boron, to N/K ratio, polyphenols and availability of photosynthate.

A comparison has been made of drip and conventional check basin methods of irrigation, using onions and ladies finger as test crops. Significant increases in yield and water use efficiency in drip irrigated over conventionally irrigated plots resulted from increased availability of soil moisture at low tensions and reduced surface evaporation losses. Reduced soil strength in drip irrigated plots was also a factor resulting in increased yield of onions.