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.

The objectives and management policy of an experimental farm for studies on the sugar beet crop are described. Farm yields of sugar beet and cereals are discussed in relation to yields in experiments and on a national scale. Some aspects of experimental accuracy and design are considered.

Simple methods are described for the analysis of daily rainfall measurements. The distinctive feature is that each year provides one number for any event or characteristic of interest. The resulting observations are then analysed, assuming that they are a simple random sample from a single distribution. An estimate of the probability of an event can be made directly from its relative frequency of occurrence, or alternatively a distribution (such as the normal) can be fitted. The methods are applied to agronomic questions on dry spells, the start, end and length of the growing season, and the distribution of amounts of rainfall through the year. Examples are given from Nigeria and India.

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.

The use in analysis of variance of six different ways of calculating the Land Equivalent Ratio (LER) was assessed. Criteria used are (1) normality of the residuals of LER values after fitting block and treatment effects, (2) precision of comparisons arising from the analysis of variance, and (3) possible bias in the means. These were examined in detail for data from one experiment and consistency of the results was investigated for seven other sets of data. Separate standardization in each block had no advantages over using the same standardization in all blocks. The use of many different divisors can lead to problems in the statistical analysis of LERs.

The strategy and associated practical details are described of a research programme which seeks to make effective use of controlled environment facilities in providing information and screening techniques useful to lentil breeders. Two principal objectives were (a) that genotypes grown in artificial climates should respond to whatever factors are being investigated in a manner which reflects their responses and relative sensitivity to different agroclimates in the field, and (b) to deploy controlled environment facilities for the longest period which is feasible during each calendar year and with maximum benefit:cost ratio.

A probabilistic model of daily rainfall can be used to derive results of potential value to agriculture. A simple example shows how this model works, but more realistic models are also fitted, using standard statistical computer packages, and examples of the results are presented graphically. The modelling approach is compared and contrasted with direct methods of analysing daily rainfall.

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.

The integration of a microcomputer-based data-capture and data-processing system into an existing mainframe computing environment in a crop research institute is described. The system includes hand-held data terminals and electronic balances. Some computing terms are explained in an appendix.

Growth and developmental stages of Alaska peas, from planting to dry seed maturity, were examined and described. Node counts were determined by designating the cotyledonary node as 0 and counting successive nodes up the plant to the highest visible one with unexpanded stipules. Five additional nodes are already determined in the shoot apex beyond the highest one with unexpanded stipules, indicating that damage to the shoot apex would result in losses of flowers and fruits that would have developed later if damage had not occurred.

Barley (Hordeum sativum) and field beans (Vicia faba) were grown in pure stands, alternate-row mixtures and within-row mixtures in two field experiments. In both experiments the Land Equivalent Ratio (LER), based on seed yield, was consistently greater than 1.0 only when the crops were grown in alternate rows. The LER was greatest (1.8) when the mixture included more barley than beans. Reasons for the yield advantage of alternate row planting are discussed. Barley was more competitive than beans in mixtures, but this was not significantly affected by planting pattern.

Experiments in Tanzania have shown that green gram planted one week before bulrush millet produced a complimentary protein energy balance optimal for a cereal–legume diet. Grain yields were increased due to additive intercropping (by 13%) and replacement intercropping (27%). Green gram plants were more competitive than bulrush millet plants at the seedling stage but were overpowered in later growth stages.

We describe the insertion and reinstatement of a simple lined access pit that allows for the permanent installation of tensiometers, piezometers, etc. in soil that is cultivated annually. The presence of the access pit did not affect the hydrology of the soil in its vicinity. We give an example of the application of results from tensiometers permanently installed in this way.

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.

The auxin-transport-inhibiting morphactin chlorflurenolmethylester (CFM; Methyl 2-chloro-9-hydroxyfluorene-9-carboxylate) breaks the dormancy of axillary buds in young coffee plants and produces orthotropic shoots. A concentration of CFM as low as 50 mg/litre induced an average of 24 orthotropic shoots per 6-month-old seedling. This approach could provide a fast and inexpensive method of vegetative propagation for raising disease-resistant cultivars if adult clones respond similarly to the seedlings used here and the treatment does not adversely affect the propagation of induced shoots.

The performance of three tropical grasses and three legumes (buffel grass, rhodes grass, green panic, butterfly pea, phillipesara and alfalfa), grown in pure stand and in legume–grass mixtures, was evaluated over two seasons when cut monthly at 0, 7 or 14 cm high. Harvesting at 7 cm favoured total dry matter and crude protein production in all cases, with highest yields from butterfly pea grown alone. Buffel grass was the best dry matter producer among grasses in pure stand, while rhodes grass–butterfly pea mixture was the best legume–grass mixture. Forage of these low-protein tropical grasses could be significantly improved by growing them in mixture with legumes.

The nitrate–N profile of soil was studied in sole and parallel multiple-cropping systems of pigeonpea and maize and of sugarcane and blackgram. In sole cropping there was more nitrate–N in the deeper horizons because of leaching from the inter-row spaces of row crops, whereas the nitrate content was drastically reduced in parallel cropping at more than 30 cm deep as N in the inter-row spaces was better utilized by the crops. The yield of two crops, when combined, was more in parallel cropping than the sum of crops grown separately, and the Land Equivalent Ratio was higher in parallel-cropping systems than in sole cropping.

A series of experiments was designed to evaluate a wide range of possible cropping systems for deep Vertisols of the Indian semi-arid tropics. The introduction of a rainy season maize crop, compared with traditional fallowing, had little effect on the yields of post-rainy season crops of sorghum, chickpea and pigeonpea. Introducing a rainy season sorghum crop caused severe yield reductions of post-rainy season crops in one year but only slight reductions in two subsequent years. Intercrop systems of maize/pigeonpea or sorghum/pigeonpea, and a three-crop system of maize/pigeonpea/chickpea, appeared very promising. Gross returns were usually much higher for the improved systems that utilized both the rainy and post-rainy seasons, though differences in net returns were not quite so great because of the extra costs of growing the additional rainy season crops.

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.