SUMMARYA series of population density and row spacing trials were carried out with sorghum in conditions of increasingly severe water stress from 1980 to 1984. In conditions of reasonable water availability, increasing density resulted in increased leaf area indices, dry weight production and grain yields. In conditions of severely limiting water availability, increasing density resulted in developmental delays, density-dependent mortality and reduced plant dry weights, with little increase in dry weight production per hectare. In these conditions grain yields were reduced by increasing density. The proportion of dry weight allocated to grain declined with increasing density and decreasing plant size, a consequence of the requirement for a minimum plant size to support grain production. When plant size was reduced below a critical range, disproportionately large reductions in grain yield resulted.Optimum densities for grain production varied from below 10 000 plants ha−1 in dry conditions to over 120 000 plants ha−1 in moist conditions. Medium density treatments produced the largest grain yields on a long term basis, but the low density treatment showed a reduced risk of crop failure and greater yield stability.
SUMMARYPlant growth, development and yield were monitored in sorghum/cowpea intercropping trials in Botswana during the drought seasons of 1982/3 and 1983/4. The cowpea proved to be more competitive than sorghum in these arid conditions, resulting in substantial increases in sorghum mortality and developmental delay, and substantial decreases in sorghum leaf area indices, dry weight production and grain yield. Intercropping in standard rows at medium plant densities resulted in Land Equivalent Ratios considerably less than 1.0, in contrast to earlier trials in Botswana in higher rainfall years which demonstrated intercropping advantages. Low density, wide row intercropping resulted in some small intercropping advantages, suggesting that this treatment may have potential in Botswana's variable climatic conditions.
SUMMARYThe effects of variety and fertilizer on wheat and barley production, and of inoculation with rhizobium on Vicia crop production under rain-fed conditions were observed in farmers' fields in Balochistan from 1985 to 1988. Weeding and application of phosphate fertilizer had little effect on wheat yields, but in the ‘good‘ rainfall year, 1986/87, application of nitrogen fertilizer resulted in increased economic yields. Barley varieties from Syria generally produced better grain yields and, with the exception of Arabi abiad, poorer straw yields than a local variety. Genotype–environment analyses indicated that Arabi abiad could be expected to produce more grain, similar amounts of straw and larger gross benefits than the local variety in all except the most severe environments, when crop failure was inevitable. V. villosa ssp. dasycarpa showed negligible amounts of cold damage, and produced greater herbage and straw yields than the other legume crops. Inoculation with Rhizobium leguminosarum produced large yield increases in 1986/87.The economic returns from crop production were poor and variable, but the results suggest that the productivity of the crop–livestock system could be increased by greater emphasis on barley, and by the introduction of Arabi abiad barley and V. villosa ssp. dasycarpa.D. J. Rees et al.: Cultivos regadospor la lluvia de las tierras altas de Balochistan.
S U M M A R YCatchment basins were prepared within bunded fields from 1986 to 1988, with ratios of catchment area to cropped area of 1:1 or 2:1. Annual rainfall varied from 102 to 282 mm.Run-off from the catchment basins increased water storage in the cropped areas by 55 and 43 % of the rain falling on the catchments in the 1:1 and 2:1 treatments, respectively. Yields increased considerably on a cropped area basis by water harvesting, but not always sufficiently to compensate for the loss of cropped land. Averaged over all trials, yields from the 1:1 treatment were 95 % of the control yields. Yields-in the 2:1 treatments were reduced by waterlogging damage.The cost of catchment set-up was low compared with the reduced seed and ploughing costs in the water-harvesting treatments, resulting in 18 and 31 % reductions in overall costs for the 1:1 and 2:1 treatments, respectively. Net benefits for the 1:1 treatment equalled or exceeded those of the control, but were 32 % lower for the 2:1 treatment. Within-field water harvesting with a 1:1 crop: catchment ratio thus reduced risk by reducing investments in seed and animal draught power, whilst maintaining yields and net benefits, suggesting that it could be of considerable benefit to farmers in an environment with a high risk of crop failure. Catchment preparation on unused land adjacent to cropped land, and further research aimed at reducing waterlogging damage, could both lead to improvements in farmers' circumstances in upland Balochistan.
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