Influence of Organic and Inorganic Amendments on Aggregate Development in a Sodic Dispersive Soil

Abstract

Improvement of soil structure is critical for efficient nutrient and water transport to plants, particularly in sodic, dispersive soils. In addition to inorganic amendments such as gypsum, organic amendments (OAs) can enhance soil aggregation and stability through biochemical processes, but it is unclear how OAs composition [carbon (C) content, C: nitrogen (N) ratio and C functional groups] influences aggregation in sodic subsoils. To address this, we conducted a 17‐month soil incubation study in which 19 organic and inorganic amendments were vertically banded in an alkaline sodic subsoil (collected from 20 to 40 cm depth). The study examined how OA properties and their decomposition affected aggregate formation and stability (indicated by wet mean weight diameter; WMWD), via changes in soil physiochemical and biological properties at 3 and 17 months. At 3 months, aggregate stability correlated positively with total C content and C quality of the OAs (i.e., aliphatic C, C/N ratio), and soil microbial biomass C. The highest increase in aggregate stability (2–2.5‐fold) was observed in soils amended with plant residues, including reed ( Phragmites australis ), faba bean ( Vicia faba L.) and wheat ( Triticum aestivum L.). By 17 months, these beneficial effects on aggregation largely diminished. Chicken manure improved soil aggregation in the short term (3 months) and maintained higher N availability in the long term (17 months), indicating its potential use to address multiple subsoil constraints. In contrast, neither gypsum nor polyacrylamide improved soil aggregation. Our findings support the use of vertically banded plant and animal manure‐based OAs to improve sodic subsoil structure and biological functions of sodic subsoils, with implications for soil function and agricultural productivity.