Wheat (Triticum aestivum), mustard (Brassica juncea), gram (Cicer arietinum) and barley (Hordeum vulgare) seedlings were raised in soils of different tilth created in microplots during 1981 and 1982. Amplitude in diurnal seed-zone temperature and soil moisture content increased with tilth coarseness. At low soil moisture levels, seedling emergence of wheat and mustard decreased with increasing clod size while that of gram and barley increased. These effects were not significant at high soil moisture levels. Shoot growth of all the crops was higher under coarse tilth than under fine tilth at both moisture levels. Root growth of wheat and mustard decreased with increasing clod size while that of gram and barley increased, at both moisture levels. Mustard had the highest seedling emergence at the low moisture level. Seedling emergence and shoot growth were higher under high moisture than under low moisture for all crops. Root growth varied depending upon the type of crop.

The influence of air temperature (T), vapour pressure deficit (vpd), irradiance (Q) and leaf water potential (ψ) on diurnal stomatal movement of coffee plants was examined under field and controlled environmental conditions. Leaves of plants grown under shade had larger stomatal conductance (g) values than plants grown in open sun. Stomatal responses to vpd under constant temperature conditions were very strong, indicating that ambient humidity could play a major role in controlling stomatal aperture. Changes in g as vpd increased probably contributed to observed reductions in the rate of net photosynthesis (Pn), though the effect of vpd on Pn was smaller.

The information collected from an experiment on tea, in which two plucking intervals and three plucking standards were imposed, allowed analysis of the effects on the total value of output (Cloughley et al., 1983; Cloughley, 1983). The analysis can be extended and its practical relevance improved by incorporating harvesting and manufacturing costs. Using information collected in another experiment and readily available economic information the effects of incorporating these costs are presented. A method of simultaneously determining optimal plucking interval and standard is described.

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.

Obtaining yield–density relationships for perennials is difficult. Apart from the long time span involved, problems are also posed by the different types of uncertainty associated with field experimentation. Consequently researchers have explored alternative means. This study uses survey data as an alternative. The data show sufficient variability around the density which is regarded as optimal for Typica variety of coconut (158 palms ha−1) to be of value for estimating its yield–density function. A quadratic function gives a good fit to the data. Results suggest that the yield maximizing density of variety Typica form typica is relatively insensitive to the influence of fertilizer practices adopted by farmers and to variations by agroclimatic sub-regions.

Dry matter production and partitioning in old clonal tea bushes pruned and maintained at different heights were investigated. New tissues (leaves, new branches and small roots) consti- tuted a small fraction of the total dry matter in all bushes pruned and initially maintained at 70, 40, 25 and 10 cm high, 36 months after pruning. Leaf/frame dry matter ratio was larger and the shoot/root and frame/root ratios were smaller in the bushes initially maintained at 10 cm than in the bushes maintained at other heights. Yields per unit area of the plucking surface were greatest in the smallest bushes initially maintained at 10 cm in 42 months of recording but on the basis of the available space they were greatest in the large bushes initially maintained at 70 cm.

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.

Two extensions to the Land Equivalent Ratio (LER) concept, the Effective LER and the Staple LER, are evaluated for an intercrop of two species. The use of different standardizing sole-crop yields in the Effective LER equation is emphasized for the formation of different comparisons between intercrop and sole-crop yields. The Staple LER for different standardizing sole-crop yields is introduced. The equivalence of the Staple and Effective LERs under certain conditions is shown and illustrated.

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 vertical distribution of water potentials within the leaf canopy, along the stem and within the soil profile of a winter wheat crop was analysed and it is concluded the failure by previous workers to recognize the significance of petiolar resistance has probably resulted in over-estimates of the resistance of the soil to water uptake by root systems of field crops.

From an analysis of the water relations of several winter wheat crops an equation is developed to describe the extraction of soil water reserves by crop root systems, based upon values of soil water potential, root xylem potential and ‘effective’ resistance to water uptake which can be obtained from field experiments. The equation provides an empirical basis to specify the minimum desirable root system for efficient capture of soil water reserves, to analyse the effects of differing root distributions and thus to help identify situations where it would be profitable to modify rooting either by tillage or by plant breeding.

Four fertilizer placement methods (ring, sideband, broadcast and furrow) applied ten weeks after planting were compared in nine experiments to determine the best method for fertiliza- tion of white yam (Dioscorea rotundata). Significant yield differences due to the treatments were observed at Mbato, Umudike and Igbariam in 1980 and at Nsukka and Igbariam in 1981. Best yields overall were obtained with the sideband method, followed by broadcast, ring and furrow in that order. However, man-days taken to fertilize one hectare by ring, sideband, furrow and broadcast methods were 11.2, 10.9, 2.8 and 1.5, respectively, so that in this regard, broadcast is preferable to the other placement methods.

A three-year experiment examined the possibility of increasing the cropping intensity of a medium-deep Alfisol (red soil) by using sequential, relay, ratoon or intercropping systems. It was found that a short-season mungbean (Vigna radiata) crop could be taken before the commonly-grown castor crop but that castor yields were reduced by the delayed sowing. If the castor was sown after the harvest of mungbean in a sequential system the profits were less than from a sole castor system. Relay-sowing the castor 20 days before the harvest of mungbean gave 9 $US ha−1 greater profit than sole castor, but this is probably not enough to justify the more intensive double crop system. On the other hand a reasonable yield of horsegram (Macrotyloma uniflorum) could be produced after an early pearl millet crop, giving a worthwhile extra profit of 21 $US ha−1 compared with sole pearl millet. Ratooning the sorghum gave ratoon yields that averaged only 14% of the first crop, so this system was not considered suitable for these lighter Alfisols.

Intercropping systems of pearl millet/groundnut, sorghum/pigeonpea and groundnut/pigeonpea gave average yield increases of 24, 47 and 46%, respectively, compared with both component crops grown separately. Compared with growing only the higher value sole crop, increases in profits were 16, 82 and 120 $US ha−1 for the same three systems, respectively. It is concluded that intercropping systems provide the best opportunity for increasing cropping intensity on medium-deep Alfisols.

In a study of the optimum population for melon when intercropped with maize, melon at 5000, 10 000, 15 000 and 20 000 plants ha−1 was intercropped with maize at 40 000 plants ha−1. Melon biomass and seed yield increased linearly with population density in mixed and pure stands while maize yield components were virtually unaffected. Intercropping reduced melon seed yields, mainly because of a reduction in number of fruits per plant, but did not affect seed size. For good weed and erosion control and increased total yields, maize can be intercropped with up to 20 000 plants ha−1 of melon.

Field trials designed to investigate the effects of nitrogen, phosphorus and potassium on the yield, starch and dry matter content of white guinea yam were conducted over a four year period in south western Nigeria. The optimum level of nitrogen for successful production of white guinea yam was 35 kg ha−1 in a forest Alfisol that had been under cultivation for at least two years. Nitrogen, phosphorus and potassium had no significant effect on starch content, but large applications of phosphorus and potassium significantly decreased dry matter accumulation.

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.

Under rainfed conditions in north west India, intercropping with soyabean, peanut, greengram and clusterbean reduced sunflower yields by 25–50%. The number of pods per plant and grain yield of the leguminous intercrops were also reduced. The maximum LER (1.05) was obtained from the sunflower–greengram mixture. Intercropping increased the protein percentage of the sunflower but decreased that of the companion legumes. It had no effect on percentage oil content of sunflower.

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.

A two year field study designed to investigate the effect of spacing on yield of two cowpea cultivars in the savanna and forest zones of Nigeria showed that cowpea yields were larger in the savanna than in the forest zone at all spacings employed. Inter-row spacing wider than 60 cm and intra-row spacing closer than 10 cm could be used for improved seed yield in the savanna zone, while 60 × 20 cm (83 333 plants ha−1) would be optimum for cowpea production in the forest zone.