Vertical distribution of soil aggregates and associated organic carbon fractions under conventional vegetable- and rice-based tillage operations

Abstract

Context Vegetable- and rice-based cropping systems are the dominant agricultural practices across South Asia, but the conventional tillage method associated with their cultivation is responsible for soil degradation in terms of aggregates and organic carbon in the surface layer. However, knowledge of its impact on the deeper layers is needed because the aggregate and organic carbon dynamics in deeper soils are little understood. Aims This study analysed the effects of conventional rice-based tillage (RBT) and vegetable-based tillage (VBT) operations on the vertical distribution of aggregates and aggregate-associated organic carbon fractions. Methods Soil samples were collected from 10 vegetable and rice fields, where conventional tillage systems were applied, and analysed for the vertical distribution of aggregates, soil carbon stock, aggregate-associated total organic carbon (AATOC), the relationship between mean weight diameter (MWD) and AATOC, and intra-aggregate particulate organic carbon (iPOC). Key results Soil macroaggregates, MWD, AATOC, and iPOC for the surface soils under RBT were less than for soils under VBT, indicating that soils under RBT had weaker aggregate stability compared to soils under VBT. The relationship between MWD and AATOC was significant (P < 0.01) for the top layers of VBT, but this relationship was non-significant for RBT. Conclusions The study suggests that wet rice cultivation has an adverse effect on soil aggregate stability and its associated organic carbon fractions. Implications Alternative tillage operations for rice-based cultivation are necessary to avoid soil degradation in rice fields.