The efficiency of many intercropping research programmes could be improved if research workers made fuller use of modern statistical knowledge about experimental design. Important statistical considerations for experimental design and plot sampling are reviewed and their relevance to intercropping research assessed. The general philosophy of factorial structure and blocking, and specific ideas on the use of systematic designs and monocrop plots, are discussed.

Effectively nodulated plants of 3 cultivars of chickpea, classified as early, mid-late and late-maturing, were grown to reproductive maturity in 12 factorial combinations of simulated tropical environments in growth cabinets. Cultivars varied in sensitivity but all responded as quantitative long-day plants and flowered earlier in longer photoperiods. Differences in temperature had important consequences, especially on the duration of the reproductive phase and overall crop longevity; they also induced plants to flower at the same time in different photo-periods. Early flowering plants did not necessarily mature early; others taking twice as long to come into flower had short reproductive periods and came to maturity at the same time. Relations between phenology, morphology and seed yield are described and compared with similar data for field-grown plants. Screening for ‘adaptation to environment’ in chickpeas is discussed.

Trials carried out at a range of locations in northern Nigeria showed that gross cash returns from mixtures were never less than those from sole groundnuts, confirming results from the main research station at Samaru. In many cases they were considerably higher and in the Northern Guinea Savanna, where the system is most widely practised, showed a high probability of returns greater than the sole crop median. Increasing attention is being paid to haulm yield and the possibility that sole groundnut may be more profitable near large towns because of haulm value.

Experiments were carried out to examine the effects of agri-silviculture in three different ecological zones of Southern Nigeria. The four treatments considered were Gmelina arborea (forest tree crop) alone, Gmelina + maize, Gmelina + yam, and Gmelina + cassava, each treatment being replicated 8 times in each location. Composite soil samples, collected from two surface layers of each treatment plot, were analysed. Inter-planting young forest plantations with food crops usually increased soil N and P, at the slight expense of soil organic carbon. However, exchangeable Ca, Mg and K contents, pH, and soil N and P contents, were not statistically different among the treatment plots.

Growth and interception of Photosynthetically Active Radiation (PAR) in a maize/pigeonpea intercrop and sole maize and sole pigeonpea crops grown in large plots in an operational research watershed at ICRISAT research centre were compared. Growth and yield of the maize crop, in pure stands and in intercrop, were not significantly different. Efficiency of dry matter production, calculated from the relations between dry matter production and cumulative intercepted PAR, was highest for the maize/pigeonpea intercrop, followed by sole maize and sole pigeon-pea, proving the utility of such intercrops in making better use of resources in the Semi-Arid Tropics (SAT).

Regression analysis, stability variance method, and the genotype-grouping technique were used to investigate the relative yield stability of 20 soyabean genotypes, grown in 12 diverse environments in Malaysia in 1978. With the regression analysis, four genotypes were observed to be unstable for grain yield; however, for the remaining 16 genotypes with non-significant regression coefficients, a substantial proportion of the g × e interaction was non-linearly related to the environmental indices. With the second and third methods less than half of the genotypes turned out to be stable for grain yield. Generally, for some genotypes, the stability classification was the same for all three methods.

The yields of four potato varieties (two old and two new) in trials and in agriculture were compared. The six possible paired comparisons of means and of variety-on-variety regressions showed genotype–environment interactions. Trials and agricultural data agreed rather poorly as to both means and regressions, suggesting that further studies are desirable, in diverse crops, of the ability of trials to predict agricultural yields.

Variation in the growth of young vegetatively-propagated tea in the nursery was studied. Erect shoots grew more vigorously, furnishing cuttings which rooted better and produced stronger plants than those from the weaker, inclined shoots. When erect shoots were artificially inclined they showed reduced terminal bud activity and shoot growth, while inclined shoots artificially erected commenced bud activity and made growth like naturally inclined and erect shoots respectively. Pruning adequately fertilized mature tea bushes at 40 cm above ground level produced vigorous shoots and at 6–8 months furnished more acceptable cuttings that produced better plants, while non-pruned bushes produced less suitable shoots and cuttings. Young unpruned plants produced weak shoots with fewer and poorer cuttings. The practical implications of these findings are discussed.

High plant populations caused a reduction in pod set and consequently in seed yield. Removal of axillary branches reduced the average weight of seed and percentage seed oil on primary racemes, indicating transport of photosynthate from branch leaves to storage sites in pods on primary racemes. Debranching at low densities was also associated with premature senescence of leaves and desiccation of immature pods, suggesting that branch removal need not have an exclusively simple nutritional basis. High canopy density reduced oil content, and seeds borne on primary racemes had lower oil levels than those on axillary branches.

Seasonal fertilizer response of napier grass (Pennisetum purpureum) was measured on various soils in Brunei. Climate was moderately humid over the three-year experimental period, with the longest dry spell about 4 months. Optimal fertilizer N levels (balanced with other nutrients) ranged from about 240 to 900 kg/ha/yr on the different soil types and under different moisture conditions. Dry forage yields at the optimum fertilizer levels ranged from 5 t/ha/yr on sandy soil under dry conditions, to 55 t/ha/yr on a sandy clay loam with adequate water. Moderate production of about 20 t/ha/yr was obtained on acid sulphate soil with fertilizer and lime. Digestible nutrient and protein levels of 60-day forage were about 55 and 10% respectively.

An investigation was made at the Mwea Irrigation Settlement, Kenya, to discover the reason why rice units which were transplanted earlier gave higher yields. Yields over an 11-year period were examined in relation to meteorological data and cultivation activities. It was found that the period during which the units were flooded prior to transplanting correlated with the date of transplanting, with longer preflooding periods causing higher yields and not the transplanting date. A yield/temperature relationship was also established.

Trials were made of the performance of batches of forage sorghum and maize, sown at different times of year. The optimum sowing periods of sorghum variety Abu Sabeen and maize variety 113 were found to be February to October and November to January respectively. Of the various climatic factors considered in this study, mean daily temperature was of greatest importance in affecting yield. The overall performance of sorghum was superior to that of maize, probably because of its relatively higher salt tolerance.