Synchronizing nitrogen availability through application of organic inputs of varying resource quality in a tropical dryland agroecosystem

Abstract

A 2-year field experiment was conducted to evaluate the impact of management practices involving manipulation of quantity and quality of exogenous inputs on soil N-mineralization rate, N availability and microbial biomass in a rice–barley rotation in a tropical dryland agroecosystem. At the beginning of each annual cycle an equivalent amount of N was added through chemical fertilizer and three organic inputs: Sesbania shoot (high quality resource, C/N 16, lignin/N 3.2, polyphenol + lignin/N 4.2), wheat straw (low quality resource, C/N 82, lignin/N 34.8, polyphenol + lignin/N 36.8) and Sesbania + wheat straw (high and low quality resources mixed). The N-mineralization rate was dominated by ammonification in this dryland agroecosystem. N-mineralization exhibited a distinct seasonal pattern, decreasing from the rice period through the summer fallow period, except in Sesbania + wheat straw and wheat straw treatments which showed a slight increase during the early stages of barley period. The rate of N-mineralization showed a significant relationship with soil moisture and microbial biomass N. During the rice period, N-mineralization rate and available-N was highest in the fertilizer treatment followed by Sesbania > Sesbania + wheat straw > wheat straw. During the barley period, highest N-mineralization rate and available-N was observed in Sesbania + wheat straw followed by wheat straw > Sesbania > fertilizer. Adding Sesbania + wheat straw resulted in consistently higher levels of microbial biomass N, N-mineralization rate and available-N through the annual cycle compared to single application of Sesbania and wheat straw, indicating synergy between the two inputs, favoring more efficient utilization of N. It is suggested that mixed application of high and low quality resources can modulate N release, resulting in relatively higher synchronization which can help in minimizing N loss from agroecosystem.