Criteria for evaluating different intercropping situations are suggested, and the Land Equivalent Ratio (LER) concept is considered for situations where intercropping must be compared with growing each crop sole. The need to use different standardizing sole crop yields in forming LERs is discussed, and a method of calculating an ‘effective LER’ is proposed to evaluate situations where the yield proportions achieved in intercropping are different from those that might be required by a farmer. The possible importance of effective LERs in indicating the proportions of crops likely to give biggest yield advantages is discussed.

A technique has been developed and tested for successfully grafting large, leafy cowpea shoots onto roots, which may be nodulated or not. Grafting per se had no significant effect on either the production or distribution of vegetative or reproductive dry matter compared with control plants left intact throughout growth. Furthermore, numerical components of yield and the concentration (%) and content (mg) of nitrogen in respective plant components were remarkably invariant. Examples are discussed of the variations in nitrogen nutrition which can be achieved and the potentials of the technique in general.

Factorial combinations of three daylengths (11, 12 and 15 h), warm and cool days (30° and 22° C) and warm and cool nights (18° and 10°C) were imposed on nodulated plants of three chickpea cultivars grown in pots in controlled environment growth cabinets. The treatments had large effects on growth, phenology and seed yield and no single environmental regime was optimal for all successive stages of development. Root growth and nodulation were extremely responsive to the environment experienced by the shoot. Conclusions are drawn on the potential contribution of these data to the development of empirical screening techniques suitable for large, segregating populations in field programmes devoted to the production of chickpea cultivars better adapted to their intended environments.

In a three-year field experiment on acid peat (pH 3.47) up to 12 t/ha lime increased peat pH (0–30 cm depth) by 0.061/t. Annual guinea grass dry matter increased in quadratic relation with liming up to pH 4.20 (12 t/ha lime) but there was no difference between the cvs Sigor and Colonoa. Liming decreased the N, P and K, but increased the Ca and Mg contents of the harvested grass. Liming also increased the uptake of all five nutrients investigated, either linearly or curvilinearly.

Twenty soyabean genotypes, grown in 12 environments, showed significant g × e interactions for grain yield and most of the other traits. The g × s interactions were unimportant, but the g × 1 and g × 1 × s were of considerable magnitude for most traits. The experiments provided estimates of genotypic, environmental and genotype-environmental variance. The presence of a high environmental variance for grain yield suggested the possibility of raising yield levels through improved management practices.

The relation between some growth parameters in polybag oil palm nursery seedlings were assessed. ‘Non-destructive’ parameters such as leaf number, seedling height and girth were highly and positively correlated with one another and with the dry weight of seedlings. Amongst the ‘destructive’ parameters only leaf area, height/weight ratio and fresh weight were positively correlated with dry weight. The Leaf Area Index was poorly correlated with other parameters examined. The relevance of these findings to the selection of oil palm seedlings for transplanting into the field is discussed.

Studies of the effects of age on yield components and nutrients status of Celosia argentea cultivars showed the highest crude protein content, total vitamin C and leaf/stem ratio in leaves harvested 5 to 7 weeks after sowing, but the highest total marketable and edible yields, as well as total crude protein, 15 weeks after sowing. The narrow-leaved local cultivar gave higher crude protein per cent and vitamin C than the broad-leaved one, but its yield of edible leaf was lower. Breeding potentials of the cultivars were highlighted.

Five types of mulches (black plastic, stone chippings and three types of grass) and a control were used on young clonal tea plants following transplanting. Soil temperature differences were observed in the first two years but disappeared when the tea canopy had developed to cover over 40% or more of the soil surface. Stem diameter, yield (during the first two years) and total dry matter production were positively correlated with soil temperatures over the range 14–21°C. Beneficial effects of raising soil temperature by black plastic mulch were short-lived, but the detrimental effect of reducing temperature by grass mulches was more severe and long lasting. Grass mulches induced shallow rooting, as a result of which the tea was more susceptible to drought.

Soil moisture content and plant water status of young clonal tea plants were affected differently by five different types of mulches (black plastic, stone chippings and three types of grass) when compared with a control without mulch. During prolonged droughts, soil moisture content was generally highest under Napier grass and black plastic but any type of mulch was better than no mulch in conserving moisture to 90 cm depth. Tensiometer data at the onset of rains after an unusual prolonged dry season suggest that the infiltration was fastest under grass mulches. After four years of continuous application grass mulches had significantly most effect on water holding capacity, but induced shallow rooting systems, which made the mulched tea more susceptible to drought.

The effect of Rhizobium strain and low levels of nitrogen on growth and nitrogen fixation was studied on 5 seedlines of Phaseolus vulgaris. All plants responded to irrigation when low levels of nitrogen were supplied throughout each experiment during vegetative growth, but the final seed yield was not significantly affected. All strains induced less nodule tissue and lower nitrogenase activity per plant when nitrogen was applied; some strains were less sensitive than others. The proportion of the plant's nitrogen estimated to be derived from fixation (based on acetylene reduction) and fertilizer was affected by host genetics. Nodulated plants had nitrogenase activities comparable with other grain legumes and responded to combined nitrogen during vegetative growth, but this was not reflected in grain yield.

Yield of swamp rice on acid sulphur soil was increased by liming and could be related to soil pH but was unaffected by drainage and differences in H2S in the soil. The seedling stage was most sensitive to acid and yield could be dramatically improved by planting mature vigorous seedlings. Survival of seedlings, tillering and panicle formation were the most important yield components affected by liming and acidity. Liming also increased spikelet number and grain size to a lesser degree. The optimal economic lime level for 3-week seedlings was around 4 t/ha but could be lower with 5-week seedlings.

Increasing plant density in maize from 8 to 32 plants/m2, without irrigation, had little effect on the time of ear primordia differentiation but delayed the time of silking (by up to 16 days), reduced the potential grain sites available for pollination and the number of grains pollinated, and increased grain abortion during the grain fill period. In cv LG11 sufficient fertile ears were retained to maintain grain yield throughout the wide range in density, whereas yield fell in Anjou 210 due to barrenness after silking, which was the major factor responsible for the intolerance of this variety to high density. However, in a variety such as Anjou 210, which has a tendency to barrenness under stress, the grain content of the end product would not be affected at the plant densities normally used for maize silage.