Development of modified maize stover for enhancing soil nutrients and functional microbes: Application of NPK-enriched techniques

Abstract

Returning maize stover (MS) to the soil can effectively enhance fertility by introducing organic matter. However, the slow degradation and nutrient deficiencies in MS potentially undermine soil quality. This study developed a method to synthesize NPK-enriched MS with the aim of improving soil nutrients and microbial diversity, as demonstrated in preliminary field trials. Under optimal conditions (8% urea, 4% KOH, and 8 freeze-thaw cycles), N and K were successfully grafted onto MS, forming MS-UK. This resulted in increased N and K content by 17.57% and 4.49%, respectively. The increase was due to urea interacting with fragmented lignin benzene rings to form C-N bonds, and KOH acting as a hydrogen bond acceptor to form C-K bonds. Following phosphorus adsorption with a K2HPO4 solution, MS-UK achieved a near-theoretical maximum adsorption capacity of 21.34 mg g−1, forming MS-UK-P. In field experiments, MS-UK-P showed a 29.11% higher degradation rate compared to unmodified MS. Notably, the MS-UK-P treatment group exhibited significant increases in soil organic carbon (SOC) and the availability of N, P, and K contents compared to the unmodified MS group, with SOC levels rising by 1.74 g kg−1, and N, P, and K contents increasing by 6.37 mg kg−1, 15.59 mg kg−1, and 18.7 mg kg−1, respectively. Furthermore, MS-UK-P promoted the growth of nitrogen and carbon-fixing microorganisms, including Bradyrhizobium, Gemmatimonadaceae, and Mycobacterium. This study highlights the urea-KOH and K2HPO4 modification as a novel and effective approach for converting MS into nutrient-rich fertilizer, offering new opportunities for enhancing the utilization of MS and similar agricultural residues to improve soil quality.