Controlled-release nitrogen fertilizer and long-term straw return synergistically improve wheat yield and reduced the nitrogen losses by regulating soil microbial communities and soil organic nitrogen components

Abstract

Context and problem

Soil organic nitrogen (SON), the primary form of total soil nitrogen, regulates nitrogen retention, transformation, and supply. Controlled-release nitrogen fertilizers (CRNF) and straw return enhance soil fertility and reduce nitrogen losses, yet the synergistic effects of their long-term combination on SON dynamics, gaseous nitrogen emissions, and microbial-mediated nitrogen cycling remain poorly understood—limiting their optimized use in cropping systems.

Objective

The objective of this study was to investigate the changes in different soil organic nitrogen components and the soil microbial regulatory mechanisms under various straw and nitrogen fertilizer management practices.

Methods

This study, based on a wheat field experiment involving long-term straw return (started in 2015), included the following treatments: straw removal with common urea (N-CU), straw removal with CRNF (N-CRNF), straw return with common urea (R-CU), and straw return with CRNF (R-CRNF). We studied gaseous N loss, content of different SON components, and soil microbial communities under different treatments.

Results

On average, straw return not only increased SON content by 33.8 kg N ha^-1 year^-1, but also optimize its composition. Specifically, it increases rapidly mineralized acid-hydrolysable nitrogen (AHN) by 124.6 kg N ha^-1 year^-1 while reducing slowly decomposed non-acid-hydrolysable nitrogen (N-AHN). CRNF decreased NH₃ volatilization by 19.0 % and N₂O emissions by 27.8 %. Combining straw return with CRNF exhibited synergistic benefits exceeding either practice alone, including a 6.7 % increase in yield, a 21.3 % reduction in the ratio of total gaseous N loss to applied N, a 3.1 % increase in harvesting index of nitrogen (HI_N), and annual SON sequestration of 40.3 kg ha^-1 year^-1. CRNF and straw return alter key soil microorganism traits that regulate AHN components and gaseous N losses. For example, ASN, AAN, and AHAN were related to the abundance of Sarcopodium, Bacillus, Botryotrichum and Vishniacozyma. NH₃ volatilization and N₂O emissions were mainly related to the abundance of Sporacetigenium, MND1, Panaeolus and Tomentella. Predicted metabolic functions also implies a potential synergistic effect: straw return could maintain soil nitrogen cycling activity, while CRNFs reduce associated losses.

Conclusions

Straw return combined with CRNFs synergistically enhanced soil fertility via SON accumulation, improved NUE by reducing gaseous N losses. The effects were related to alteration in soil microbial community.

Implication

This study provides useful information for how to enhance different SON components in wheat field with combined straw return and controlled release nitrogen fertilizer at high yielding levels.