Relationships between topsoil depth and yields of rain-fed sorghum, pearl millet, and castor bean
1990
Vittal, K. P. R. | VIJAYALAKSHMI, K. | RAO, U. M. B.
We evaluated the effect of topsoil depth on yields of rain-fed sorghum, pearl millet, and castor bean over 4, 4, and 5 years, respectively, on an in situ prepared continuous topsoil gradient in a typic Haplustalf. This systematic gradient emulated the natural topsoil variations of a watershed. The positive relationships obtained by regression analysis between topsoil depth and crop yield factors under the widely varying rainfall conditions were highly significant (r > 0.72). The response (slope) and rainfall during critical periods of crops were related curvilinearly in sorghum and pearl millet and linearly in castor bean. These differences were due to the sorghum and pearl millet being able to complete growth during the monsoon season, whereas castor bean depended upon the stored moisture for completing its cycle. A rainfall greater than 30 and 41 mm/week during critical periods had an adverse effect on yield for sorghum and pearl millet because of temporary stagnation, leaching losses, and beating action of rain droplets on the flowers. For deep-rooted castor bean, increase in stored moisture with rainfall helped to increase the yields due to spike bearing under receding moisture conditions. The weighted mean grain responses over long periods were 105, 77, and 109 kg/ha/cm of topsoil for sorghum, pearl millet, and castor bean, respectively. Thus, a reduction in topsoil depth with time due to intense rainfall on the complex slopes of watersheds in semiarid tropics affects yields adversely under dryland farming conditions.
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