The questions and design of pasture research in tropical Australia and the resulting technologies address problems encountered in the prevailing extensive beef-production systems. In African pastoral systems, forage resource use is more intensive and complex, and production aims are manifold. An example of applied research in central Nigeria illustrates the usefulness of certain components of Australian pasture technology but the need to adapt them, particularly with respect to pasture utilization and management, within trials deliberately designed to address the differing problems in the local pastoral system.

This paper concludes the series with comments on regression, covariance analysis, and correlation. The importance of choosing a regression function, whether linear or non-linear, appropriate to problem and data is emphasized and the nature of parameter estimation is outlined. The merits of transformation of variates and the importance of introducing a proper number of parameters are briefly discussed. Common misunderstandings of the meaning of ‘the regression of y on x’ for experimental data are related to the analysis of covariance.

Regression with two or more regressors increases the computations but does not alter principles. Adjustment of means by use of covariance analysis is a much under-exploited technique in its direct sense; it also offers a computationally convenient way of handling missing observations and related problems. An attempt is made to overcome the confusions of interpretation between the regression equations of y on x and of x on y. A final section warns against misuses of correlation coefficients; the opportunities for misuse are too many for brief summary, yet such coefficients can be helpful when interpreted with care.

Trees are important sources of food in both the humid and semi-arid tropics. Some species have been exploited for centuries and are widely distributed around the world, others have been cultivated only in limited areas, while most are still essentially wild. The potential for rapid genetic improvement by clonal selection is enormous and well-proven by the recent history of some species. Trees can yield as much food per hectare as most C3 annual crops – although special problems may have to be overcome to ensure regular bearing of fruit and nut trees. Trees also offer great ecological and social benefits.

Nodulated plants of three USA cultivars of lentil (Lens culinaris) were grown in controlled environment cabinets. They were given either 20 or 80 ppm inorganic nitrogen and experienced a mean temperature of 12.3° C during the vegetative period, i.e. until 73–77 days after sowing. Factorial combinations of above- (29°/11° C) and below-average (23°/8° C) day/night temperatures were then imposed, to give four mean temperatures within the range of 16.6° to 21.1° C until reproductive maturity. Post-flowering vegetative dry-matter production and seed yields were dominated by treatment effects on the initiation and growth of branches. Warmer temperatures accelerated progress towards maturity, limited branching and restricted dry-matter production; at a mean temperature of 20° C plants were almost barren. The implications of these and previous data to lentil crop production and to the use of controlled environments in lentil breeding programmes are discussed.

Pre-flowering insect infestation of cowpea, Vigna unguiculata, was monitored in weedy and weed-free plots in 1986 and 1987 in Akure, Nigeria. Weediness generally reduced infestations of both the leafhopper, Empoasca dolichi, and the flea beatle, Ootheca mutabilis. However, seed yield was reduced in the weedy plots despite heavier pre-flowering insect populations in the plots kept weed-free.

The response of chickpea to irrigation and phosphorus was studied at Kharagpur in Eastern India. Irrigation scheduling was based on the ratio between irrigation water applied and cumulative pan evaporation (ID/CPE), and had little effect on dry matter accumulation. Increasing the frequency and amount of irrigation reduced the number and dry weight of nodules per plant, which increased to a maximum 70 days after sowing and then declined. Irrigation significantly reduced grain yield as a result of excessive vegetative growth at the expense of pod formation. Application of phosphorus promoted nodulation and increased both nodule dry weight and the concentration of N, P and K in grain and stover. Uptake of N, P and K by the crop was also increased.

Yields of maize were determined in six years, on two soils, at up to four nitrogen levels following early and late planting. Without fertilizer nitrogen, high rainfall at the beginning of the growing season reduced yield on one soil but not on the other, while high rainfall at late silking and high total rainfall in the growing season reduced yields on both soils. As the level of fertilizer nitrogen increased, the negative effects of rainfall on yield tended to disappear. A three week delay in planting sometimes increased and sometimes decreased yield. The probable reasons for the observed effects of rainfall on yield are discussed.

Maize was grown for six years on two soil series in annual rotation with groundnuts, soyabean, lab-lab and sunflowers, and for up to four years after two year crops of pigeonpea. Nitrogen left by the annual legumes was estimated to vary from 0.0 to 52.2 kg ha−1 depending on year, soil and species. Summed over three successive maize crops, nitrogen left by two year crops of pigeonpea varied from 23.5 to 109.6 kg ha−1. Vigorous vegetative growth and low seed yield in the legume were associated with increased residual nitrogen. Groundnuts left more nitrogen on the more fertile soil. High rainfall at the beginning of the maize cropping season was associated on one soil series with the complete disappearance of residual nitrogen from the immediately preceding legume crop.

Seedlings of 48 genotypes of barley were grown in a glasshouse in different rooting media to determine the possible range of variation in root and shoot systems. Plants grown in nutrient solution produced shoots which were larger than those grown in sand and perlite, but in sand and perlite almost twice as much root length was produced per unit of shoot area. There were large differences between genotypes in both root and shoot growth.

The effects of growing medium on rooting were studied in more detail on six of the genotypes. Plants grown in soil and nutrient solution had longer lateral roots than those grown in sand and perlite. Genotypic variation in growth was large but the range of root and shoot growth in a particular medium was similar. Generally, the ranking of the genotypes was similar in both studies and in all media.

Five genotypes of barley (Arabic Abiad, Beecher, Cytris, Rihane ‘S’ and Swanneck) were grown under rainfed conditions at Breda and Ghrerife in northern Syria. During the winter, rates of shoot growth were similar at both sites but by anthesis crops at Breda were almost twice as large as crops at Ghrerife. Overall, Arabic Abiad was heavier and had a greater green area than other genotypes at both stem elongation and anthesis and, by maturity, had the greatest shoot dry mass and grain yield.

Differences in root dry mass between sites were small so that crops at Ghrerife had a higher ratio of root:total plant mass at anthesis and maturity than those at Breda. Rooting depth was shallower at Ghrerife but root length densities in the layers below 15 cm were greater than at Breda. Arabic Abiad had the longest root system below 15 cm at both sites. The genotypes did not differ in total seasonal water use at either site but there were differences in the patterns of water use during the early spring. Arabic Abiad used more water below 15 cm in the period from mid-February to mid-March and less during grain-filling than other genotypes.

The greater yields of Arabic Abiad may be associated with the greater root lengths below 15 cm and the correspondingly faster rates of water use during early spring. Yields of barley were greater when more water was used before anthesis; there appeared to be no advantages in saving water for use during grain-filling in this region.

The effects of spacing and lopping on a mesquite (Prosopis juliflora) and Karnal grass (Leptochloa fusca) agroforestry system on an alkaline soil at Karnal in India was examined over a three year period from planting. There were no significant differences in the height and diameter of the mesquite or in the number of branches at different spacings, but growth was significantly improved by lopping. The oven dried biomass obtained from lopped branches over a 40 month period was greatest at a 2 × 2 m spacing. The green forage yield of Karnal grass was greatest under mesquite spaced 4 × 4 m apart and was markedly improved under lopped mesquite. The inorganic composition of the Karnal grass, including trace elements, made it a valuable fodder in an area with an adverse alkaline soil environment. The calcium and potassium content of the grass increased and the sodium content decreased in successive cuttings. Mesquite and Karnal grass grown together reduced soil pH and EC and improved the organic carbon and available nitrogen content of the soil.

The effects of planting potato tubers on four different sides of two ridge orientations was investigated. Soil temperature was coolest on the northern side, followed by the western, eastern and southern sides. Fifty percent emergence took place in 24, 42 and 49 days for tubers planted on the northern, western and eastern sides, respectively. Only 22% of tubers planted on the southern side emerged. The best yield and quality was obtained by planting on the northern side, followed successively by the eastern, western and southern sides of the ridge.