In a field experiment, the effects of irrigating crops alternately with sodic water (high in sodium adsorption ratio and ) and good quality canal water were investigated for six years on a well drained sandy loam (Typic Ustochrept). The irrigation treatments included: irrigation with non-sodic canal water (CW), irrigation with sodic water (SW), CW irrigation alternating with one or two SW irrigations, and two CW irrigations alternating with one SW irrigation. The results showed that the use of sodic water increased the sodium saturation of the soil and decreased rice and wheat yields. The build-up of sodium depended on the number of SW irrigations during the season. The increase in sodium saturation and decline in crop yields were progressive over the years. The improvements in yield due to alternating sodic and non-sodic irrigations compared with the use of sodic water alone increased over the years. Alternating sodic and non-sodic irrigations could therefore be considered a practical way to alleviate the problems caused by sodic water. The number of sodic irrigations during a season should, however, be kept to a minimum and the build-up of sodium in the soil over time should be monitored.

Seed inoculation with Bacillus polymyxa markedly increased the yields of rice and chickpea crops, while Pseudomonas striata caused a greater impact on crop production when used with rock phosphate or super-phosphate in a wheat crop. The effect of the phospho-microbe inoculants was greater in phosphorus-deficient soils.

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.

Azolla and blue-green algae (BGA) inoculated in a rice field produced a higher biomass and fixed more nitrogen in transplanted than in direct-seeded rice. Application of Azolla, BGA, composts of Eichhomia and Azolla and green manuring with Sesbania increased tiller numbers, height, grain and straw yields, and nitrogen uptake by rice in both the transplanted and the direct-seeded crop. The growing and incorporating of three Azolla crops with the rice crop produced more grain than the use of other nitrogen sources but the rice crops showed a poor response to inoculation with BGA. The yield of rice following green manuring with Sesbania or the use of two crops of Azolla after transplanting was similar to that of a crop receiving 60 kg N ha−1 as urea, but smaller yields resulted from the use of composts of Azolla and Eichhornia.

The growth of roots and shoots was measured in stands of groundnut grown at a number of populations on stored water in central India. Total weight and length of roots per unit land area increased with population density, but the proportional increases were much less than for shoot weight. Consequently the root:total weight ratio increased from 0.3 in the densest stand to almost 0.5 in the widely spaced crop. The denser stands produced a greater proportion of their roots at depth. In wide rows there was little change in rooting density across the inter-row space.

Total dry matter per unit land area increased with population, although the weight per plant was less in denser stands. Although the crops were harvested prematurely, pod yield per unit land area, unlike total dry matter, was no greater in dense stands than in more widely spaced crops. The greatest number of pods per unit land area was recorded at an intermediate population density.

Continuous cropping of a tropical Ultisol with or without nitrogen fertilizer increased soil acidification and reduced soil organic matter and productivity. Addition of nitrogen fertilizer failed to increase yields. This was apparently due to the decline in soil pH, an increase in the amount of soluble aluminium, and consequent inefficient utilization of added nutrients. Continuous use of ammonium sulphate as a nitrogen source hastened the development of both surface and subsoil exchange acidity.

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.

Effects of simulated and actual grazing at the tillering stage on tiller production and other agronomic characters were studied over a number of seasons at two sites in northern Syria with two local barley landraces. In general, grazing encouraged tiller production but reduced head number per unit area because of a higher tiller mortality or infertility. Seed number per head and seed weight were not affected by grazing except in one season. Grazing delayed heading and maturity and reduced plant height. Simulated and actual grazing produced similar effects on the different characters investigated.

Results of farm-level experiments with pearl millet are reported from four villages in semi-arid Niger in 1982 and 1983. Crop establishment, yield loss factors (insects, diseases, striga) and economics of new practices were studied in a randomized design which included density, fertility, cultivar, and intercropping with cowpea as treatments. Improved cultivars did not establish significantly better than local ones, but fertilizer occasionally improved establishment. Incidence of yield loss factors was low, and only small effects of cultivar and fertilizer were seen. Fertilizer increased grain yields of the local cultivar by as much as 153%. The use of fertilizer and improved cultivars increased grain yields by as much as 171% over an unfertilized local millet. Even without government subsidies, fertilizer use was profitable for 56% of farmers on all cultivars. In general, fertilizers and improved cultivars had a small positive impact on profitability, with little adverse impact on grain yield variability, so that they could be recommended to farmers with some prospect of success. The intercropping treatment failed in both years, and would have to be modified before extension.

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.

The effect of a single grazing at the tillering stage on barley yield and economic returns was studied with two widely grown local landraces over five seasons at Tel Hadya and two seasons at Breda in northern Syria. In general, grazing reduced both grain and straw yield, particularly the latter. The percentage of grain yield reduction was similar at the two sites. Grazing increased net revenue on average, though there were marked seasonal differences. This increase was higher at Breda, the drier site, a finding which contradicts the commonly-held belief that grazing is unprofitable in dry areas.

Stands of groundnut were grown at four densities on water stored in a medium depth alfisol in central India. Evaporation was estimated from changes in soil water content, and partitioned between transpiration and evaporation from the soil surface. Seasonal transpiration was strongly influenced by plant population, and approached a maximum as the population density increased to 23 plants m−2. Evaporation from the soil surface was only a small component of the seasonal water balance in dense stands, and was little affected by planting density. Differences in transpiration rate between spacings were greatest early in the season, but diminished when the denser stands ran out of water. The denser stands extracted more water from deep in the profile. Plants in widely spaced rows preferentially extracted water from near the row; water mid-row was only used later in the season.

Growth and development of the tropical grain legumes are generally highly sensitive to photo-thermal regime, so that seasonal and regional effects on phenology and yield potential can be large. Yet failure adequately to recognize and fully exploit the consequences of genotype × latitude/sowing date × density interactions has frequently constrained both agronomic and genetic advance with these species. Thus there is opportunity for short term productivity improvements through agronomic strategies which accept the implications of phenological plasticity, and seek to optimize management practices such as sowing date and sowing density, to exploit more effectively the yield potential and broaden the adaptation of existing cultivars. The greatest physiological potential for genetic improvement in the productivity of the tropical grain legumes lies not with increasing total biomass, but with increasing the proportion of bio-mass partitioned into seed, i.e. with improved harvest index (HI). There are difficulties in selecting for higher HI, including its association with phenology, although the latter provides the most powerful tool for manipulating HI in the short term. As with the cereals, more productive genotypes are likely to be characterized by reduced sensitivity to photothermal conditions, shorter growth duration, a more synchronous reproductive ontogeny, and greater HI, than is typical of traditional cultivars. Accordingly, optimal sowing densities will be higher, and crops will need more inputs, better management and more effective protection, than afforded to them in subsistence systems of production. Moreover, the increases in productivity will be achieved, at least partially, at the expense of the potential for yield homeostasis in adverse environments, and of non-seed components such as forage, fuel or tubers - attributes that are often highly valued in subsistence agriculture where many of the tropical food legumes are presently grown. Improvement programmes will therefore need to adopt strategies in particular situations which reflect local perceptions of the importance of productivity improvement relative to that of minimizing inputs and risk.

The effects of coffee berry disease (CBD) on yield are usually estimated by counting infected berries on marked branches throughout fruit development. This method is impractical when surveys are required of yield losses over large areas of extensively cultivated peasant coffee. A survey method is described for estimating yield potentials and the loss in yields due to severe CBD infection under such conditions. The method exploits the relation between numbers of flowering nodes and yield per tree, and requires a single subjective estimate of disease incidence on young expanding berries. Yield losses are estimated from the changes in this relation resulting from berry infection. Results are presented for peasant coffee at different stages of rehabilitation in Ethiopia. They indicate that the method is suitable for estimating.production in agronomic improvement projects and for identifying areas where CBD incidence might economically justify fungicide spraying.

At a field site in central India, four populations of groundnut (Arachis hypogaea L.) were grown on stored water to investigate how the production of shoot and root dry matter is related to transpired water and intercepted radiation. Throughout the season, total dry matter was closely related to transpiration (slope = 3.0 mg dry matter g−1 water) and the amount of radiation intercepted by foliage (slope = 0.74 g dry matter MJ−1 radiation intercepted). Accumulated transpiration increased linearly with intercepted radiation at 0.37 kg water MJ−1 in the sparser stands. In the densest spacing, the initial slope of the relation at 0.28 kg MJ−1 decreased later in the season because water deficits curtailed growth without a concomitant reduction in the interception of radiation.

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.

Dry matter production in a bushy and spreading cultivar of sweet potato was studied in two trials comparing dry matter partitioning between plant components. The bushy cultivar, VSP-2, accumulated more tuber dry matter than the spreading cultivar, BNAS-51. The number and yield of tubers of VSP-2, was also greater but its foliage dry weight was less than that of BNAS-51. The vine and root dry weight of BNAS-51 increased with time but that of VSP-2 reached a peak about 10–12 weeks after planting. The tuber dry weight of BNAS-51 at harvest was similar to its foliage dry weight but that of VSP-2 was three times greater. The proportion of total dry matter partitioned to the tubers of VSP-2 was greater than that in BNAS-51 at all stages of growth.

A field study was conducted in 1985 at two locations in Maryland, USA, to test the influence of environment (location), input level (N fertilization), management (component density combinations), and measure of performance on recommendations for a maize/soyabean intercrop. Location affected the degree of intercrop yield depression of each crop; the effect of N on relative competitive abilities; the maximum Land Equivalent Ratio (LER) and maximum modified Staple Land Equivalent Ratio (SLER); the difference between LER and SLER; the optimum density combinations and change in optima in response to N; and the N level at which the greatest land use efficiency was achieved. Given the complexity of the environmental effects, recommendations based on the trials have a very narrow range of applicability.

The objective of this paper is to identify the major factors responsible for the differences in transpiration rate (T) between stands of groundnut grown at three row spacings on stored water in central India. A method of analysis is developed to distinguish between the impact on transpiration of ground cover (which varied threefold between spacings) and of root:shoot ratio, which was substantially greater in the wider row spacings. When the soil was wet, both T and the canopy conductance, gc, were approximately proportional to the fraction (f) of incident radiation intercepted by foliage. But when the soil water content decreased below a threshold value, T/f and gc/f decreased because of an increase in stomatal resistance. Stomatal closure in response to soil water stress occurred sooner in the denser stands, partly because of more rapid depletion of soil water. A second contributory factor was that the sparser stands (which had a relatively large root:shoot ratio) had a greater capacity to keep stomata open as the soil water deficit increased.