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.

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.

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 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.

Water depth at or shortly after planting is critical for the establishment and subsequent tolerance of excess water in rice. A crop transplanted early in the season produced twice as much grain as a later planted crop. A semi-dwarf variety (CR 1018) and a taller variety (CR 1030) performed similarly after early transplanting, but the tall variety performed better when planted late under excess water. Seedling age did not greatly alter the yields when crops were transplanted early, but after late planting 45-day-old seedlings were best.

Cotton leaf reddening was studied in irrigated vertisols at the Gezira Research Farm over three seasons. The percentage leaf reddening was negatively correlated with seed cotton yield. Plants showing symptoms of reddening produced smaller and fewer leaves which did not persist long enough to sustain the reproductive parts. Deficiencies of nitrogen and phosphorus were found to be responsible for the reddening symptoms. Nitrogen application, late August sowing and frequent control of insect pests all significantly reduced the incidence of reddening. Other possible remedies are discussed.

The presence of free water on both surfaces of the leaves of shaded and unshaded coffee trees was evaluated at Cenicafé, Colombia. Rainfall was the main source of humidity and dew was not registered during the experiment. Five mm of rain caused canopy saturation and water began to reach the underside of the leaves. The period of wetness lasted 9.7 hours on average and no significant moisture differences were found between leaves on east or west facing branches, at different levels within the tree, or externally or internally positioned on the branches, either for exposed or shaded trees. Between 1700 and 0500 h (local time), a close relation was found between the time of rain initiation and the duration of the period of wetness. Leaves dried out at approximately 1000 h.

The performance of a cassava clone susceptible to cassava mosaic disease (CMD) was tested over two successive years for CMD development, plant vigour and yield of fresh tuberous roots. Cuttings from plants with different CMD infection levels were used. There was a significant increase in mosaic incidence, severity and proportion of leaves showing symptoms of the disease in the subsequent crop as the levels of CMD primary infection in planting material increased. Plant height and stem diameter were also adversely affected and the yield of plants from severely affected cuttings was reduced by 60–70%.