The genus Vigna includes seven species of pulse, two African and five Asian. While the Asian species are within the subgenus Ceratotropis, the two African species are in different sections of the subgenus Vigna, namely Catjang (V. unguiculata) and Vigna (V. subterranea). Limited gene flow is possible within subgenus Ceratotropis, but none has as yet been demonstrated between subgenera nor between sections within subgenus Vigna. Parallel evolutionary trends are apparent in all species, with considerable increase in seed and pod size. Erect bush forms have evolved in all cultigens except V. aconitifolia and V. subterranea. The former has not apparently changed much in vegetative form under domestication, while the geocarpy of the latter precludes erect growth. Future prospects for the Asiatic grams would be better if yield levels could be improved. The cowpea is likely to remain an important crop at present levels of performance although there is room for improvement. There seems little immediate prospect of expanded ground bean production under existing conditions.

A serious problem in long-term field experiments is that soil is moved from plot to plot as a result of cultivations. The problem is often overlooked and very few attempts have been made to quantify this movement under varying conditions.

A simple, mathematical model for approximating the movement of soil in one horizontal dimension by repeated tillage with one or more tillage implements is presented. The model describes the development with time of a concentration gradient of substance, by means of the solution of a diffusion equation. The model is in agreement with ‘the central limit theorem’, when it is used for the situation where the same cultivations are repeated many times in alternating directions.

The model fitted well to data taken from the literature.

A previously presented model for one-dimensional soil movement by repeated tillage is extended for use under the more complex conditions of long-term field experiments, for (i) following the two-dimensional movement (along and across the plots) of accumulating substances (nutrients, disease organisms, etc.) caused by tillage; (ii) determining the smallest acceptable plot size from given conditions, when planning new long-term field experiments and (iii) determining the size of the discard relative to the size of the treated plot.

Diagrams are given from which rough estimations can be made of both the movement of accumulating substances in long-term field experiments and the smallest acceptable plot size, when a computer with the necessary facilities is not available.

It is proposed that two distinct objectives should be recognized in the evaluation of intercropping advantages: (i) a biological objective to determine the increased biological efficiency of intercropping and (ii) a practical objective to determine the advantages that are likely to be obtained by a farmer. The sole crop systems with which intercropping must be compared to satisfy these objectives are defined. Evaluation in relative, absolute, monetary and nutritional units is discussed and some aspects of presenting intercropping data in graphical form are illustrated.

The effects of intercropping, mulching and staking on growth and yield of three tomato varieties were evaluated in four field trials in 1982 and 1983. Fruit yields of the improved varieties were significantly reduced by intercropping with okra but the yield of a local variety was unaffected. Though the yield of okra when grown with tomato varieties was less than that of a sole crop, the combined yield of the two crops in mixtures was more than the means of the species in monoculture. Relative Yield Totals (RYT) increased to maxima of about 1.42 and 1.39 when the local variety was grown with okra in 1982 and 1983 trials, respectively. Mulching and staking significantly increased vegetative growth, yield and yield components of the tomato plants. Mulched plants grew taller and had more branches and a greater number and weight of fruits than staked plants. Improved varieties responded better to mulching and staking than the local variety. Growing improved varieties of tomato in sole stands with proper mulching and staking is therefore recommended.

Three maize cultivars, BACOA, SAW and COCA, were evaluated when intercropped with cocoyams at a density of 50 000 maize plants and 10 000 cocoyam stands ha−1. BACOA which matures in 120 days, and SAW (130 days) transmitted significantly more light to the lower canopy than COCA, which has spreading leaves and matures in 150 days. Relative yields for BACOA, SAW and COCA in pure stands were 72, 100 and 85%, respectively, while those for cocoyams in BACOA/cocoyam, SAW/cocoyam and COCA/cocoyam mixtures were 82, 58 and 54%, respectively, showing that COCA significantly suppressed the yield of cocoyam when intercropped.

Yields of a COCA type with erect leaves increased as plant density increased from 20 000 to 50 000 plants ha−1 in pure stands, while yields of COCA with spreading leaves increased as plant density increased from 20 000 to 40 000 plants ha−1 but decreased when plant population increased to 50 000 plants ha−1. When COCA with erect leaves was intercropped with cocoyams, cocoyam tuber yields were fairly stable and maize yields continued to increase significantly as plant density increased from 20 000 to 50 000 plants ha−1, whereas the yields of COCA with spreading leaves and cocoyams were greatly reduced when intercropped and when the plant population increased from 20 000 to 50 000 plants ha−1.

Intercropping Brussels sprouts with cabbage was studied in two experiments comparing four different intercropping systems with sole crop production. Intercropping presented no agronomic or management problems because both crops had compatible cultural and crop protection requirements. Analysis of Land Equivalent Ratios and Relative Value Totals showed that the four intercropping systems gave consistently larger yields than the sole crops. In one experiment profitability, measured by the gross margin, was higher from all of the intercropping systems and costs per unit of produce were reduced. Similar results were obtained with one intercropping system in the other experiment. Alternative methods of evaluating the results in economic terms are discussed, together with the implications of intercropping in high-input systems of vegetable production.

Data from mulched tea show that an earlier defined ratio of temperature fluctuations in thermally homogeneous soil can be successfully used in rating the thermal efficiency of artificial grass mulches. The efficiency of a natural mulch of growing grass is also determined for comparison. It is demonstrated that the use of the ratio is more precise than using average temperatures in assessing the effects of the mulches.

The results of field experiments conducted with millet cultivars inoculated with different nitrogen-fixing bacteria at the ICRISAT Centre, Hyderabad, India are described. Significant interactions were observed between host cultivars and bacterial strains, but some cultivars showed consistently increased grain and dry matter yields, suggesting the possibility of exploiting suitable plant and nitrogen-fixing bacterial associations for increasing grain yield. Inoculation also resulted in increased nitrogen uptake up to 14.9 kg ha−1, and larger grain nitrogen contents.

Experiments on harvesting sweet potato as a green vegetable and as a root crop are described. Whole shoots yielded 62% more than shoot tips. Similar total shoot yields were harvested whether tip removal was at two, three or four week intervals. Root yield was decreased by 31 to 48% by removing shoot tips, while removing whole shoots led to root yield decreases of 48 to 62%. Harvesting shoots at two week intervals gave 72% reduction in root yield, compared with 50% with four week intervals. There were fewer and smaller tubers as the frequency of shoot harvests increased. There were varietal differences in response to shoot removal For reasonable yields of both shoot tips and tuberous roots harvesting shoot tips at four week intervals is recommended.