Herding and farming environments in sub-Saharan Africa are described briefly. The relative importance of crops and livestock is described for each environment. A matrix of crop-livestock interactions is defined for each environment and the reasons for each type of relation are noted. Farming systems are defined as segregated or completely integrated, according to the degree of crop-livestock integration on the farm. Points at which farming systems research (FSR) might be undertaken to improve interactions between crops and livestock are noted for both systems.

Artificial defoliation of okra 4, 6 and 8 weeks after sowing generally delayed flowering, decreased plant height and stem girth at flowering and reduced the harvest duration. Pod length, pod diameter, mean pod weight and number of pods plant−1 were also decreased by defoliation but pod yield ha−1 was not.

The removal of leaves from the upper half of the stem only had a similar effect to complete defoliation whereas the removal of leaves from the lower half only had no significant effect, indicating that the leaves on the upper stem contributed more to growth and yield than those lower down. Significant time × degree of defoliation interactions occurred for most growth and yield parameters.

Procedures for better decision making in agricultural research are considered. Fanning Systems Adaptive Research (FSAR) has evolved to complement the more traditional research approach, allowing better decisions to be made on recommendations to fanners and on priorities for technical research. This is done through the identification of research results most relevant to the development of specific farming systems; the testing of these results by experiments in farmers' fields; and the identification of factors limiting productivity in local farming systems.

FSAR involves interdisciplinary cooperation between production agronomists, farm economists and, where appropriate, animal production scientists, in close cooperation with other production specialists and with farmers.

Farming systems in west Asia and north Africa have evolved to cope with the problems of highly variable and, frequently, chronically deficient rainfall. Cereals (mainly wheat and barley) are the dominant arable crops with food legumes (chickpea, lentil and faba bean) occupying only 5 to 10% of the area planted to cereals. Livestock is closely integrated into the farming system and crop production practices often reflect the importance of animals as a major source of income, particularly on the smaller farms. Soils of the region are predominantly calcareous, frequently phosphate deficient, and their depth and texture are important in determining the maximum amount of water that can be stored which, in turn, may determine the effective length of the growing season.

Rain falls mainly during the winter months so that crops must often rely on stored soil moisture when they are growing most rapidly. Analysis of equations relating crop growth and water use shows that there are three ways in which the ‘water use efficiency’ of dry matter production can be increased. First, the amount of dry matter produced per unit of water transpired might be increased; second, if the water supply is limited, the amount of water transpired might be increased relative to evaporation from the soil surface; and third, the total amount of water used might be increased to produce extra growth provided that this results in increased transpiration rather than simply increasing evaporation from the soil surface.

These three possible routes to increased crop growth are reviewed in relation to possible improvements in water management and crop genotypes in the Mediterranean environment. Scope for improving transpiration efficiency is limited although genotypic differences exist and may be useful in the future. More immediately, changes in crop management, such as applications of fertilizer, improved tillage and better weed control, will all increase the amount of water transpired. Application of mulches will also reduce evaporation from the soil surface but crop residues are usually eaten by livestock and are, therefore, often unavailable.

The barley/livestock farming system of west Asia is used as a case study to illustrate how the Fanning Systems Programme of ICARDA has developed on-farm research programmes of direct relevance to current farming systems. Research on experimental sites directed at improving water use efficiency has been developed into on-farm trials and into collaborative trials with the Syrian Soils Directorate.

Four isolates of Azolla pinnata collected from Bangkok, Bangladesh, Vietnam and India grew well when used in paddy fields both before and after transplanting with rice varieties of different heights and times to maturity. Azolla increased plant height, tillering, 1000-grain weight, grain and straw yields, nitrogen concentration and uptake, and soil fertility.

The response of rice to Azolla was similar to that obtained by applying 60 kg N ha−1 as urea in three split applications. The different Azolla isolates differed in their growth, N2-fixation and response to rice crops and soil fertility. All these characteristics were better in the isolates from Bangkok and Vietnam than in those from Bangladesh and India. Azolla growth and N2-fixation were better with short rice varieties (IR-36, Ratna and Kalinga-II) than with Mahsuri, a tall rice variety, but Mahsuri, having a longer growing season, showed a better response to Azolla.

The conservation of genetic resources is discussed in relation to the stages in the evolution of crop plants. Strategies for the collection and conservation of wild species, landraces and advanced cultivars are considered in relation to the pratical needs of plant breeders and other users.

Five diverse sorghum genotypes were sown at sole crop density and at intercrop density without cowpea and with two contrasting cowpea genotypes, in the post-rainy season at Hyderabad, India. The interaction of sorghum genotype with sowing density was significant for sorghum dry fodder and grain yield, but the interaction of sorghum genotype with cowpea was not, because of compensation between yield components. The likely response of sorghum genotypes to intercropping can therefore be assessed initially from the performance of low density sole crops, followed by assessment in the presence of a single standard cowpea variety.

The cowpea genotypes were affected by the presence of sorghum but not by the sorghum genotype. This suggests that the effect on the cowpea can be ignored when selecting a sorghum genotype for intercropping, and that a cowpea genotype for intercropping can be selected in the presence of a single sorghum genotype. However, these conclusions arc unlikely to apply to rainy season sowings, when sorghum dominates the intercrop more completely.

In 1981 and 1982, three crop protection regimes were compared with an unsprayed control for cowpea grown alone and in mixtures with maize, sorghum and cotton. Unsprayed cowpea in mixtures with maize had yields which suggested some pest escape in 1981 but not in 1982. When sprayed, only the maize–cowpea mixture showed much yield advantage over sole crops. For maize–cowpea in 1983, a very dry year, only the alternate row mixtures showed a yield advantage and three spray applications gave cowpea yields as good as those resulting from six applications. The late, photosensitive cowpea variety Acq 1696 had better yields than the medium maturity TVx1948·01 F in the mixed crop but was greatly inferior as a sole crop.

Two slow-release nitrogen fertilizers, isobutylidene diurea (IBDU) and sulphur-coated urea (SCU), and urea plus nitrapyrin were compared with urea alone for their effect on the growth and nitrogen uptake of ryegrass in a greenhouse experiment.

The IBDU and the SCU were applied in one dressing before sowing and the urea in five dressings (one after each cut). Dry matter yield and nitrogen uptake of the six cuts at the optimum levels of 3 and 6 g N pot−1 (equivalent to 1120 and 2240 kg N ha−1 on a weight basis) were similar for the slow-release fertilizers and urea, showing that SCU and IBDU can be effective sources of nitrogen for ryegrass at rates far above those regarded as safe for conventional nitrogen fertilizers when applied in a single dose.

Nitrapyrin at 20 ppm effectively inhibited nitrification for 12 weeks, then its effect rapidly declined, disappearing after 18 weeks. Ryegrass growth was retarded by nitrapyrin treatment, probably as a result of an accumulation of NH4-N in the soil.

Gypsum application and irrigation increased yield in early maturing groundnut genotypes in experiments using line source and conventional irrigation. Response to gypsum varied with genotype; with some gypsum increased yields at all water application rates, in some genotypes there was no response, while with others gypsum increased yield in drought conditions.

In a separate study of the effect of gypsum and drought on pod initiation and development in three groundnut genotypes, gypsum did not greatly influence pod initiation when adequate irrigation was applied, but was beneficial when water was withheld during pod set and again during pod filling. Crops where the combination of gypsum and genotype were most advantageous in the first drought period subsequently grew more slowly so that there were no final differences in response to gypsum. Cultivar EC 76446(292) had a higher requirement for gypsum and was more susceptible to drought than the other two genotypes.

Branches are an important yield attribute of the mustard (Brassica junceo)crop. However, not all the branches are equally productive and some of those arising from the basal portion of the plant may form parasitic sinks for assimilates. The effect of de-branching at the 50% flowering stage in the apical (AHD) and the basal halves (BHD) of two mustard genotypes, Pusa Bold and Varuna, was examined. The BHD treatment increased the seed yield per plant of Pusa Bold by 36% and of Varuna by 75% over the control. The increase in yield due to the BHD treatment was mainly due to an improvement in the total number of pods per plant in both genotypes. In Pusa Bold, an improvement in both 1000-seed weight and number of seeds per pod, mainly on late formed branches, was also observed. The AHD treatment reduced seed yield but not significantly so. The results suggest that improvement in the yield of mustard cultivars by suppressing branching on the basal portion of plants should be possible.

The base temperature and thermal time for different development stages of spring wheat cultivars were calculated using a linear relation between the rate of development and the mean temperature. The results show that germination, emergence, tillering and leaf elongation (the vegetative phase) have a base temperature around 2°C but the elongation of the culm and the reproductive phase (tillering-maturity) have a base temperature over 6°C. A general model to describe the time to maturity of spring wheats, which takes account of these different phases, is proposed.

A range of planting times, with sequential harvests to age 24 months, was used to determine crop growth and yield of cassava at two locations, one having a humid tropical climate and the other humid sub-tropical. Yield was doubled during the second year at the sub-tropical site. At the tropical site yield was very high after one year, but root rots occurred in the second year. The dry matter percentage of storage roots fluctuated seasonally and was highest during the cooler months when canopy vigour was lowest. Known or inferred environmental controls of the yield-determining factors of growth rate, growth duration, and partitioning to harvestable organs were used to interpret the results and thus derive guidelines for timing of planting and harvesting in moist environments.

The seasonal water use patterns and leaf water potential of chillies (Capsicum annum var. annum) grown as a monocrop and as an intercrop between soyabeans (Glycine max) were studied under a weekly and two weekly irrigation regime on a red duplex soil in Northern Victoria, Australia. Irrigation at two weekly intervals resulted in a temporal stratification of water extraction over the growing season, the soyabeans making their maximum demand during the reproductive phase. Senescence of the soyabeans at the R6–R7, growth stage was accompanied by an increase in water uptake by the intercropped chillies. No corresponding increase in water uptake was observed in monocropped chillies irrigated every two weeks or in intercropped or monocropped chillies irrigated weekly. Leaf water potential of the intercropped chillies was, for the most part, greater than that of the corresponding monocrops.

Bean yield at two sites in Costa Rica was affected by the interactions of maize and bush bean cultivars with cropping system (relay, row intercropping and sole cropping). The maize culti-vars were grouped according to leaf area index (LAI) and plant height. At a site with a severe weed problem, leafy maize of intermediate height allowed the most bean yield in relay but the least in intercropping. Tall, leafy maize allowed as much yield of intercropped beans as short, less leafy cultivars. In intercrops, tall maize plants shaded the beans less, while in relay crops leafy plants of intermediate height shaded and suppressed weed growth so benefiting the following bean crop. At the other site, all maize groups had the same effect on beans whether grown in relay or intercropped. Leafy maize cultivars of medium height are preferable for sole crops and for relay cropping of beans at physiological maturity when weeds are a problem, but less leafy types are better for bean intercropping or for relay crops where the beans are planted before maize maturity. Plant types selected for sole cropping are not necessarily best for poly-cultures and one crop may affect another even when their periods of active growth do not overlap.

The effects of three shade densities, NPK fertilizers and fertilizer-pest/disease relationship on Amazon cocoa (Theobroma cacao L.) over a 20-year period are reported. Yields equivalent to the mean yield from the unfertilized plots were achieved in about 3, 4 and 6 years in fertilized plots under the no shade (S0), medium shade (S1) and heavy shade (S2) treatments, respectively. There were three growth phases, each characterized by a different yield trend. No appreciable changes in the exchangeable Ca and Mg were observed during the experiments, but K dropped to 68% of its initial value while the available P of the unfertilized and the S0 plots fell by 38%. Fertilizer recommendations for P and K should take account of overhead shade. The effect of N application was often negative. No direct relationship was observed between fertilizer treatment and the incidence of pest/blackpod/swollen shoot virus (SSV) disease of cocoa. SSV infection was greatest under S0. Cocoa farms in Ghana cannot maintain high yields (above 1000 kg dry cocoa ha−1) beyond 15 years of intensive cropping.

The effect of variations in the relative sowing time and density of component crops in a maize/cowpea intercrop were examined in two experiments. In the first experiment, maize and cowpea were sown together, and either 10 or 21 days before or after each other. Maize yield was reduced when sown at the same time or after cowpea; intercrop cowpea yields were less than sole cowpea yields at all sowings. In the second experiment, maize densities of 35, 50 and 70 × 103 plants ha−1 were combined with cowpea densities of 70, 100 and 140 × 103 plants ha−1. Increasing the density of either crop in the mixture resulted in increases in total yield. Maize reduced cowpea yields more than the effect of cowpea on maize yields. In terms of LER and total seed protein yield, there was no advantage of either staggered sowings over simultaneous sowing or of the various intercrop density combinations, except between the lowest and the highest densities of either maize or cowpea. The LERs appeared to follow the trends in cowpea yields and total seed protein yields the trends in maize yields.

Two experiments, one irrigated and one dryland, were conducted at a site having a seasonally-dry, tropical climate. A range of planting times, with sequential harvests to age 24 months, was used to study cassava growth and yield. Very high yields of 35 to 45 tonnes dry matter per hectare were recorded for the irrigated experiment. Water limitation restricted yields to 15 to 26 tonnes in the dryland experiment. Known or inferred environmental controls of the yield-determining factors of growth rate, growth duration, and partitioning of assimilates to harvest-able organs were used to interpret the results and thus derive general guidelines for the timing of planting and harvesting in seasonally-dry environments.

The growth of Amaranthus hybridus under different daylight intensities was assessed in terms of physical, morphological and biochemical parameters. Maximum growth in many respects was achieved at about 70% of full daylight. However, full daylight favoured chlorophyll stability and maximum accumulation of total dry matter, carbohydrate, chlorophyll and ascorbic acid. The leaf area ratio increased uniformly with decrease in light intensity. Ageing was accelerated by full daylight. Reduced light intensity reduced dry matter accumulation in the roots more than in the stems or leaves.

Hypocotyl length in groundnut is a function of sowing depth. In field experiments deep sowing increased the mass of hypocotyl but decreased that of roots, pods and haulm. Few nodules were formed on the hypocotyls of plants from shallow sown seeds (4–5 cm deep). More hypocotyl nodules occurred on Virginia types when deep sown but the number and activity of nodules on the roots decreased. Nodules on the hypocotyl appeared later and fixed less nitrogen than root nodules. Although hypocotyl nodules fixed nitrogen during the later stages of plant growth, this activity could not compensate for the loss in nitrogenase activity due to deeper sowing. Deeper sowing also resulted in decreased pod yields.