The response of six cane varieties to nitrogen fertilization (0, 70 and 140 kg. N/ha.) has been studied. Results of three ratoon crops from 23 trials on representative sites throughout Mauritius indicate that optimum fertilization is around 70 kg. N/ha. Three levels for optimum nitrogen in the third leaf blade have been established, namely 1·93, 2·05 and 2·22 per cent corresponding roughly to the sub-humid, humid and super-humid areas of Mauritius.

Sources of variation in the leaf area of rice were examined from 11,356 sample leaves. The three major sources of variability, in decreasing order, were variation among leaves within tillers, variation among tillers within hills, and variation among hills within plots. Within the same tiller upper leaves were larger than the lower ones, except for the flag leaf. Larger leaves were also associated with the taller tillers in a hill. For assessing leaf areas of rice in experimental plots, it is suggested that all leaves from the middle tiller of each sample hill be measured. Furthermore, to avoid border effects, at least two outermost rows on each side of a plot should be excluded from leaf area determinations.

The effects of plant population on the yields of four commercially important Malawian groundnut cultivars have been investigated. Pod number per plant was found to be the most variable component, bearing an inverse relationship to plant density. Kernel weight and shelling percentage were low at reduced populations, and yields and kernel size declined at very high populations. The effect of plant habit upon spacing requirement is discussed and recommendations are made.

Substantial improvement is reported in a quality measure, large seed size, after only one generation of mass selection from a bulk ‘Chalimbana’ population of Zambian land races of the inbred species Arachis hypogaea L. There were large positive correlations between seed size as planted and the subsequent mean size harvested. Large seed also tended to produce an increased proportion of 2- rather than 3-seeded pods, further improving both crop uniformity and quality. Total yield was unaffected, or possibly even slightly enhanced, by planting larger kernels. The circumstantial advantages of mass as opposed to pedigree selection methods are discussed.

Thirteen cultivars of cassava were planted, widely spaced, and harvested after two, three, five and seven months. Differences in root yield after seven months were caused by variations in rate of root bulking, and were not associated with differences in onset of root bulking, which occurred during the second month of growth in all varieties that produced thickened roots.

Boron deficiency in cotton occurs widely in northern Nigeria, where its extent and severity appear to be increasing, particularly under intensive agriculture. The deficiency may be aggravated by fertilizer application, specially nitrogen. Soil boron status varies greatly but is generally very low and often less than is considered necessary elsewhere. Superphosphate containing added boron corrects deficiency safely and satisfactorily.

Cotton varieties differ in their sensitivity to boron deficiency. Breeding for tolerance of deficiency offers some scope for yield increases under the prevailing non-intensive conditions under which most of the crop is grown in northern Nigeria, but cannot be considered a complete solution to the problem.

Intercropping maize with pigeon peas, in a mixed stand or in alternate rows, significantly reduced the grain yield of maize but not of pigeon peas. Maize grown alone produced the maximum grain yield ha.−1 week−1, whereas maize and pigeon peas grown in alternate rows produced maximum proteins ha.−1 week−1 and absorbed the maximum amounts of potassium, calcium and magnesium. Pigeon peas grown in a pure stand produced minimum grain yield and proteins ha.−1 week−1, and absorbed minimum amounts of nutrients. The problem of intercropping maize with pigeon peas under optimum nitrogen fertilization is discussed.