Effectiveness of Straw Mulch for Alleviating Drought Stress of Grain Sorghum

Abstract

This study was carried out to evaluate the effectiveness of straw mulch to reduce drought stress and to stabilize the productivity of grain sorghum. F1 hybrid variety, E59, was planted on April 20 in four treatments: irrigation-straw mulch, irrigation-no mulch, no irrigation-straw mulch, and no irrigation-no mulch treatments with three replications. Severe water stress occured only during the late grain filling stage because of the unusual delayed end of rainy season this year. Leaf water potentials of grain sorghum measured by pressure chamber during drought stress period were slightly high in mulch treatments, irrespective of soil water conditions by irrigation. Leaf diffusive resistances measured by porometer were high in no mulch treatment of which leaf water potential was lower than in mulch treatment. The amount of evapotranspiration of mulch treatment was lower than no mulch treatment under unirrigated conditions from July 19 to July 30, but there were no differences of evapotranspiration between mulch and no mulch treatments under irrigated conditions. The amount and rate of water consumption to the depth of 40 cm in soil for the same period as above mentioned were less in mulch treatment under unirrigated conditions because of the reduction of evaporation from soil surface. The growth of grain sorghum was not accelerated by mulch under irrigated conditions. However, the growth in mulch treatment was more vigorous under unirrigated conditions. Grain yields harvested on August 20 were high in mulch treat-ment, even if only slightly high under irrigated conditions. From these results, it was concluded that mulch is effective to reduce the adverse effect of water stress by the depression of evapotranspiration and the maintenance of relative high leaf water potential in limited water conditions.