Influence of biofertilizers and organic amendments on nitrogenase activity and phototrophic biomass of soil under wheat

The role of blue green algal (BGA) biofertilizers has been limited to its relevance and utilization in rice crops, and scanty information is available on their use in conjunction with organic amendments and their influence on wheat (Triticum aestivum) . An experiment was conducted from November 2003 to April 2004 in the fields of the Indian Agricultural Research Institute (IARI), New Delhi, India to evaluate the effect of vermicompost, farmyard manure and biofertilizers (BGA and Azotobacter ) in different combinations with chemical fertilizers (N 40 P 30 K 30 ) in wheat (var. HD 2687). Selected soil biological parameters (cyanobacterial diversity/abundance, nitrogenase activity and the phototrophic biomass of soil cores) were measured. The application of vermicompost in combination with BGA biofertilizer (B+V+N 40 P 30 K 30 ) brought about a significant increase in nitrogenase activity (from 0.1 in N 80 P 30 K 30 to 2.0 nmoles mg chl −1 h −1 ), while Azotobacter + BGA (+N 40 P 30 K 30 ) treatment gave the highest values of chlorophyll (1.19 μg g −1 soil). The addition of vermicompost and farmyard manure (+N 40 P 30 K 30 ) enhanced cyanobacterial abundance, and cyanobacterial genera such as Nostoc, Anabaena, Calothrix, Oscillatoria and Phormidium were the dominant forms observed under the wheat crop. The synergistic effect of organic amendments, biofertilizers and chemical fertilizers, especially BGA inoculants, advocates their utilization in wheat crops to improve soil fertility.