Optimizing non-symbiotic nitrogen fixation in an acid Vertisol

Abstract

The Bejucal area, a region in Central Trinidad has food crops as its main agricultural activity. As part of a programme to enhance nitrogen availability to plants in this region, observations were made on various aspects of asymbiotic N fixation. Laboratory experiments conducted on air-dried, sieved soil taken from a 0–30 cm depth in the Bejucal region, indicated that the Bejucal clay (Chromic dystraquerts, very fine, mixed acid) has the potential to provide biologically fixed N utilizing the inherent soil micro-organisms. Using the acetylene reduction assay method, it was found that nitrogenase activity was higher under anaerobic than aerobic conditions. The assessment of the effect of various factors on nitrogenase activity indicated that, under anaerobic conditions, 75% water holding capacity (WHC), 2% glucose and 0.5% urea resulted in the highest nitrogenase activity in this soil whereas under aerobic conditions, 100% WHC, 3% glucose and 0.5% urea resulted in the highest activity. Greater understanding of the inherent asymbiotic nitrogen microbial population may increase their potential use in providing nitrogen for crop production and possibly reduce the use of applied fertilizer nitrogen in acid Vertisols.