The effects of annual precipitation and its distribution on grain yield of dryland cereals

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Abstract
SUMMARY: Data collected from 1968 to 1981 were used to study the effects of annual precipitation and its distribution on grain yield of three barley and six wheat varieties from 19–47 environments.The percentage of the variation in grain yield explained by annual precipitation varied with variety and species (5–31% in barley and 31–79% in wheat). The distribution of precipitation was the major factor affecting grain yield, although it varied with variety, and explained 72–92% of the variation in barley and from 75 to 98% in wheat.Only 33 of the 144 simple correlation coefficients between grain yield and precipitation during each of the 16 fortnightly periods were significant. The expected average effect on yield due to additional precipitation above the mean showed positive effects in barley during the presowing and heading to flowering periods; no consistent trend was found in the wheat.Improved agronomic practices could alleviate the adverse effects of the low and unevenly distributed precipitation by reducing losses and increasing storage of water in the soil. Breeding could contribute greatly towards high and stable yields in drylands.