Inorganic P fractions in rhizosphere and yield of onion amended with organics and inorganic P in soybean (Glycine max L.): onion (Allium cepa L.) cropping system

Abstract

A field experiment was conducted with soybean-onion cropping sequence in a high P Alfisol to study the response to P levels either alone or in combination with PSB, biochar, humic acid and citric acid to study the direct, residual and cumulative effects of the treatments imposed on inorganic P fractions and yield of onion. Among the inorganic P fractions estimated, saloid-P is the smallest pool and Ca-P is the largest pool. Cumulative application of 30 kg P2O5 ha-1 along with biochar resulted in mean inorganic P fractions viz., saloid-P, Al-P, Fe-P, occluded-P and Ca-P of 3.11, 11.1, 50.5, 16.1 and 397 against 2.68, 9.3, 39.0, 14 and 358 mg kg-1 without organics. Among the organics, biochar application to soybean was found to be benefited more due to the cumulative application of 30 kg P2O5 ha-1 resulting in a mean bulb yield of 24.1 t ha-1 against 20.0 t ha-1 due to the residual effect, the yield response being 20.5 per cent. There was significant positive correlation between Ca-P and onion yield (r = 0.889**) in the high P Alfisol.