Effect of soil moisture fluctuations on legume nodulation and nitrogen fixation in a black earth soil

Abstract

The field nodulation of cowpea (Vigna sinensis) and four native legumes-Cassia mimosoides, Glycine tomentosa, Psoralea tenax and Vigna lanceolata was examined under fluctuating moisture conditions. An absence of nodules was recorded during excessively wet or dry conditions. Nodule loss with decreasing moisture was attributed partly to mechanical removal of nodules from the roots by the shrinking day. During wet periods, soil aeration was considered to be the limiting factor. Improved aeration of wet soil increased the plant dry weight and nodule numbers in soybeans, resulting in an increase in nitrogen fixation. Nitrogen analysis showed that with improved aeration 61 % of the total plant nitrogen came from fixation, in comparison with 33% under poor aeration.