A consideration of the apparent lack of general success of minor pulse crops can lead to a better appreciation of the factors which have made the major pulses successful. The relevant factors are both biological and economic. High productivity based on an efficient physiology, amenability to local agronomic practices and a satisfactory range of ecological tolerance are prime prerequisites for success. Aspects of quality, palatability, lack of toxic factors (or ease of detoxification), ease of preparation and cooking and the more imponderable questions of consumer preference are equally important. If any of these prerequisites are not adequately met success in cultivation is improbable. At the present time the lack of more extensive success of the winged bean appears to be due to some deficiency in ecological tolerance, and of the horse-gram and jack and sword beans to a lack of palatability; the Hausa groundnut (Kersting's groundnut) suffers from a probably inefficient physiology while limited consumer acceptance has possibly restricted production of pigeonpea and hyacinth bean. The rather limited evolutionary advance achieved by this group of pulses is probably directly related to their somewhat restricted production and the relatively low level of selection pressures to which they have been subjected.

Grain yield of maize (Zea mays L.) was decreased by 30, 38 and 34 kg ha−1 for each day by which sowing was delayed after the first planting in March in 1978, 1980 and 1981, respectively. Yield reduction was associated with reduced plant size (plant and ear heights, tassel weight and branch numbers), ear number, ear weight, grain weight, ear length, ear diameter and kernel weight. High yields can thus be obtained by planting with the first rains of the year, especially if a good rate of emergence and seedling vigour under relatively hot, dry soil conditions can be ensured either culturally or genetically.

Simple linear correlations, stepwise multiple regressions and path-coefficient analyses were used to determine the relation between grain yield of maize (Zea mays L.) and weather factors in a three year study involving several planting dates within each year. Maximum and minimum relative humidity, which demonstrated negative relationships with yield, were the most reliable factors, both directly and indirectly, for predicting yield. Temperature (including accumulated heat units), sunshine hours and total and effective rainfall generally showed negligible direct effects on yield. Potential evaporation, which showed positive correlation, had a negative direct influence on grain yield. We conclude that, whenever possible, path analysis should be used as well as correlation and regression analyses in explaining the complex multiple interactions of yield and weather factors in crop production.

Intercropped corn and soyabean were grown in a randomized block design (RBD) and a systematic design (SD) in 1981 and 1982 to evaluate total yield, yield complementarity, crop competition and land-use efficiency as affected by corn and soyabean densities. In the RBD, three corn density treatments were applied to corn–corn–soyabean–soyabean, corn–corn–soyabean, and corn–soyabean intercrop row patterns and to monocultures. In the SD, 9 or 10 corn densities were factorially combined with up to 13 soyabean densities in a corn–soyabean row pattern (91 cm spacing). In the RBD, total intercrop yields were similar to corn monoculture yields (60.8 to 62.7 t ha−1 in 1981) in the corn–corn–soyabean and corn–soyabean patterns at high corn densities but were less at low density. The corn–corn–soyabean–soyabean pattern yielded 87% of the corn monoculture at high density in 1982. These results were confirmed in the SD, where total intercrop yields were highly responsive to corn density and poorly responsive to soyabean densities. Both experiments indicated that high corn row densities are needed to maintain yields in corn–soyabean intercrops, possibly higher than the levels studied. Land equivalent ratios were above 1.0 for all but the low density corn–corn–soyabean–soyabean pattern in the RBD. The ability of an intercrop with as many as half the corn rows replaced by soyabean to produce yields similar to corn monoculture indicates a biological complementarity for dry matter production in the mixtures.

Twenty improved upland rice cultivars were evaluated in yield trials at three locations for three successive years in south-western Nigeria. Highly significant genotype x environment interactions were observed, indicating that some cultivars yielded better in some locations than others. The use of regression analysis adequately identified the cultivars best suited to each environment. S2d values (measures of stability) for the cultivars ranged from 0.0007 to 0.2196, the cultivars with smaller values being more stable at the respective locations. The more adaptable cultivars have high mean yields and a deviation from regression as small as possible. The cultivar best adapted to good environments was code 3 (an improved selection from the cross Lac 23 x IR 528) with a yield of 3.36 t ha−1, while code 9 (a sister selection from the same cross) was best adapted to poor environments. Code 8 (a selection from the cross IR 154/O.S. 6 and 63–83) showed general adaptability. Once grain quality has been evaluated some of these cultivars might therefore replace code 18, the currently recommended upland rice cultivar, in the rain-forest zone.

Wheat (Triticum aestivum), mustard (Brassica juncea), gram (Cicer arietinum) and barley (Hordeum vulgare) seedlings were raised in soils of different tilth created in microplots during 1981 and 1982. Amplitude in diurnal seed-zone temperature and soil moisture content increased with tilth coarseness. At low soil moisture levels, seedling emergence of wheat and mustard decreased with increasing clod size while that of gram and barley increased. These effects were not significant at high soil moisture levels. Shoot growth of all the crops was higher under coarse tilth than under fine tilth at both moisture levels. Root growth of wheat and mustard decreased with increasing clod size while that of gram and barley increased, at both moisture levels. Mustard had the highest seedling emergence at the low moisture level. Seedling emergence and shoot growth were higher under high moisture than under low moisture for all crops. Root growth varied depending upon the type of crop.

Dry matter production and partitioning in old clonal tea bushes pruned and maintained at different heights were investigated. New tissues (leaves, new branches and small roots) consti- tuted a small fraction of the total dry matter in all bushes pruned and initially maintained at 70, 40, 25 and 10 cm high, 36 months after pruning. Leaf/frame dry matter ratio was larger and the shoot/root and frame/root ratios were smaller in the bushes initially maintained at 10 cm than in the bushes maintained at other heights. Yields per unit area of the plucking surface were greatest in the smallest bushes initially maintained at 10 cm in 42 months of recording but on the basis of the available space they were greatest in the large bushes initially maintained at 70 cm.

Four fertilizer placement methods (ring, sideband, broadcast and furrow) applied ten weeks after planting were compared in nine experiments to determine the best method for fertiliza- tion of white yam (Dioscorea rotundata). Significant yield differences due to the treatments were observed at Mbato, Umudike and Igbariam in 1980 and at Nsukka and Igbariam in 1981. Best yields overall were obtained with the sideband method, followed by broadcast, ring and furrow in that order. However, man-days taken to fertilize one hectare by ring, sideband, furrow and broadcast methods were 11.2, 10.9, 2.8 and 1.5, respectively, so that in this regard, broadcast is preferable to the other placement methods.