Influence of Herbicide and Soil Amendments on Soil Nitrogen Dynamics, Microbial Biomass, and Crop Yield in Tropical Dryland Agroecosystems

Nitrogen (N) dynamics is the key factor for designing management strategies to achieve sustained crop productivity. A 2‐yr field experiment was performed to examine the influence of herbicide (butachlor [2‐chloro 2′6′ diethyl‐n‐butoxy‐methylacetanilide]; HC) alone or in combination with soil amendments on N dynamics involving N mineralization rate (N min ), inorganic N pool, N uptake (N up ) by plants, soil microbial biomass N, and crop yield in tropical dryland agroecosystems. The N min rate showed distinct seasonal patterns which decreased from rice period to summer fallow except herbicide + animal manure (farmyard manure; HC + AM) and herbicide + crop residue (wheat [ Triticum aestivum L.] straw; HC + CR) treatments.The annual rate of N min , inorganic N pool, and crop yield were higher in HC + AM, herbicide + chemical fertilizer (NPK; HC + CF), herbicide + green manure {dhaincha [ Sesbania aculeata (Willd.) Pers.] shoots; HC + GM} while comparable in HC + CR and HC treatments relative to control (CO). Soil moisture content better predicted variation in N min rate compared to soil temperature. Plant N up and crop yield relative to CO was higher in HC + CF, HC + GM, and HC + AM, comparable in HC + CR while lower in the HC treatment. Annual N min rate explained a significant part of variations in annual soil microbial biomass N, inorganic N pool, plant N up , and crop yield. Results indicate that combined application of HC + AM result in relatively sustained availability of inorganic N and higher crop yield throughout the annual cycle.