Fairfield Smith's variance law is extended to study simultaneously the effect of plot size and its rectangularity (which quantifies shape) on variance. This model is fitted to two seasons' data on sorghum grain yield generated from uniformity trials under rainfed conditions. Some implications of the fitted model are discussed.

In symbiotically-dependent chickpea, nodule mass and rates of nitrogenase activity increased when vegetative growth increased rapidly, but declined during fruiting. The specific activity of nodules declined as their mass rapidly increased. Nodule mass and rates of nitrogenase activity varied between genotypes, as did the point of maximum activity, which in some genotypes occurred before fruit growth dominated shoot growth. Current N2-fixation supplied most of the nitrogen for pod and seed growth, but in some genotypes mobilization of nitrogen from vegetative parts was evident. Seed attracted up to 50% of assimilated nitrogen; residual nitrogen was contained mainly in leaf and pod tissue, though in one genotype stem nitrogen was plentiful.

A small farmer in the tropics often grows a range of crops to protect himself against failure in a bad season. It is suggested that guidance on the choice of species, and the proportions between them, can be gained by studying past cropping figures, such as those collected for FAO purposes. Two cases are distinguished for systems using two species, (a) when the crops serve much the same purpose and are interchangeable in use, and (b) when they serve different purposes and a certain minimum is required of each. Special attention is given to intercropping, in which the two species are grown in close association.

A number of upland rice varieties were grown in the highlands of northern Thailand at altitudes of 800, 1200, and 1450 m in 1978 and 1979. Growth rate declined and growth duration was extended as altitude increased. At the 1200 and 1450 m sites yield was severely restricted by spikelet sterility, probably induced by cool temperatures. Some varieties were completely sterile at the highest altitude, where yields ranged up to 2.6 t ha−1. At 800 m several varieties yielded more than 5 t ha−1 in 1978, but yields at this lower site were reduced by about 20% in 1979. Translocation to the grain of assimilates stored in the vegetative parts appeared to have been restricted. Lodging was a problem at all sites.

Gas exchange measurements were carried out on four cassava cultivars, M. COL22, M. MEX59, M. COL638, and M. VEN218, under a range of light intensities, to investigate possible differences in photosynthesis and transpiration. Over the range of photon flux density 100–1500 μE m−2 s−1 leaves showed a light saturation response typical of C-3 plants with little increase in photosynthetic rate above 1000–1500 μE m−2 s−1 (200–300 Wm−2 PAR). At light saturation there were significant differences in photosynthetic rates between cultivars, with the highest 10% greater than the lowest. Part of the response could be attributed to increased stomatal aperture, and a greater part to a direct effect of light intensity on the photosynthetic apparatus. Transpiration increased with light intensity levels, but no significant differences were observed between cultivars.

Fourteen smallholder coconut plantations, subdivided into 27 uniform sub-units, were surveyed in an area around Dala, in Western Malaita, Solomon Islands. Most units (17 out of 27) had densities of 160–200 palms ha−1 with a median light transmission of 50–55%. Palm growth was poor due to low soil K, and copra yields averaged only 540 kg ha−1 year−1 Batiki (Ischaemum aristatum) was the most important sown grass, and its productivity was significantly related to stocking rate and weed control, but not directly with light transmission. Farmers should thin dense palm stands, adjust stocking rates in relation to actual areas of pasture available, and institute careful and adequate weed control.

A field experiment was conducted for two consecutive years commencing in 1979–80 on the Indo-Gangetic alluvial soil of Pura to investigate the requirements for zinc of wheat, chickpea, mustard and Egyptian clover. Chickpea and Egyptian clover were more sensitive to zinc deficiency than wheat and mustard, respectively. Average total dry matter production by Egyptian clover and wheat was larger than mustard and chickpea. Egyptian clover and wheat required more zinc to achieve maximum dry matter production but they also recovered from the soil a larger proportion of applied zinc than chickpea and mustard. Mustard produced the most dry matter per unit of zinc absorbed.

The relation between source potentials and sink capacities of four cassava (Manihot esculenta Crantz) varieties with different characteristics was investigated by means of reciprocal grafts. There were marked differences in the sink capacities (average stock effects) and source potentials (average scion effects) of the varieties.

The effects of soil fertilization and plant age on the nutrient composition of various parts of five Nigerian cassava varieties were studied to identify suitable index plant tissue(s), sensitive growth stage(s) and optimum nutrient concentrations, to develop better fertilizer practices for the crop. The third month from planting was the most sensitive stage for diagnostic sampling, when N status was best reflected in leaf blades and K in petioles. N and P were most concentrated in leaf blades and least in root tubers. The largest root tuber yields after 12 months were associated with leaf blade analyses of 5% N, 0.4% P and 2% K at 3 months after planting.