EFFECT OF SOIL MOISTURE STRESS ON UPTAKE AND RECOVERY OF TAGGED NITROGEN BY WHEAT

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Abstract
Labelled 15NH4NO3 was used in a growth chamber to study the effect of moisture stress on the utilization of nitrogen by wheat. This made it possible to determine the recovery of nitrogen (N) in the soil-plant system of two Chernozemic soils. Moisture stress effects were less evident in a clay soil than in a loam. Approximately 55% of the N utilized by the growing plants came from organic soil-N mineralized during the growing period. From 59 to 71% of the initial fertilizer plus soil mineral-N was utilized by the plants. Twenty to 36% remained in the soil, and 1 to 17% was lost. Losses were greatest in soils exposed to high moisture stress and were related to the residual NO3-N levels in the soil. They were attributed to denitrification. Immobilization of N was highest at low moisture stress where plant growth was the greatest, but mineralization was unaffected by the moisture stress applied. It was estimated that 5.0 to 6.2 kg N were required to produce 100 kg of wheat, the highest efficiency of N utilization being obtained at low soil moisture stress.

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