Straw retention and inhibitor application reduce the leaching risk of mineral N in no-tillage systems of Northeast China

To clarify the effects of maize straw retention combined with reduced fertilization and urease/nitrification inhibitors on the accumulation and leaching potential of mineral N in the deep soil profile of no-tillage agroecosystem.

A ¹⁵N-tracing micro-plot experiment was conducted with four treatments (NPK, traditional NPK fertilization; NPKS, NPK with maize straw retention; RNPKS, NPKS with 20% fertilizer-N reduction; and RNPKSI, RNPKS with inhibitors application) in the Mollisol of Northeast China. We analyzed fertilizer-N transformation dynamics in different soil N pools, quantified the fertilizer N use efficiency in crops, and evaluated fertilizer-derived nitrate leaching losses throughout the complete maize growing period.

Our analyses revealed that, compared to the NPK treatment, NPKS, RNPKS, and RNPKSI remarkably reduced the accumulation of urea-derived mineral-N during maize seedling stage by enhancing the transformation of urea-N into fixed NH₄⁺-N and organic-N pools, both of which could be quickly released for maize uptake following the extension of crop growth periods. At the maize ripening stage, soil NO₃⁻-N and ¹⁵N-labeled urea-derived NO₃⁻-N, which migrated vertically to a depth of 80–100 cm, were significantly reduced by treatments of RNPKS and RNPKSI without minimizing crop yields when compared with NPK.

Our results suggest that combining maize straw retention with reduced fertilization and the application of urease/nitrification inhibitors can be efficient management practices for lowering urea N leaching risk, improving N use efficiency, and maintaining or even increasing crop yields by enhancing soil N retention and supply in the croplands of Northeast China.