Computation of soil quality index after fifteen years of long-term tillage and residue management experiment (LT&RE) under rice wheat system

Abstract

CONTEXT

Maintaining the optimal soil quality stands a fundamental determinant for sustained yield of rice-wheat system (RWS) in Indo Gangetic plains (IGP) of India. To uphold soil quality, implementing minimum/no tillage along with addition of crop residue are required.

OBJECTIVE

To evaluate the long-term (15 years) impact of tillage and residue management experiment (LT&RE) initiated in 2006 on soil quality index (SQI) and to establish the quantitative relationship between the SQI and crops yield under various crop establishment practices.

METHODS

Experiment consisted of six treatment combinations including LT&RE namely, (i) conventional tillage without residue (CT − R), (ii) conventional tillage with residue incorporation (CT + R), (iii) reduced tillage without residue (RT − R), (iv) reduced tillage with residue incorporation (RT + R), (v) zero tillage without residue (ZT − R), and (vi) zero tillage with residue retention (ZT + R). The SQI was used as an instrument based soil physical [bulk density (BD), soil penetration resistance (SPR) and infiltration rate (IR)], chemical [soil pH (pH_1:2), electrical conductivity (EC_1:2), soil organic carbon (OC) available nitrogen (N), phosphorus (P), potassium (K), iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn)], and biological [microbial biomass carbon (MBC), alkaline phosphatase activity (ALP), and dehydrogenase activity (DHA)], properties as these are very useful indicators of soil's functions, fertility and agronomic productivity. Soil samples were collected from 0–15 and 15–30 cm soil depth from each treatment after harvesting of wheat in 2021 and 2022.

RESULTS AND CONCLUSIONS

The ZT + R treatment exhibited the lowest bulk density (1.45 Mg m⁻³) and soil penetration resistance (1306.02 KPa) at surface soil, resulting in higher infiltration rates (7.80 mm h⁻¹). Adoption of LT&RE led to a notable increase (15.8–25.7%) in soil organic carbon (SOC) stock across all the treatment combinations compared to CT-R. The enhanced SOC and better physical soil conditions increased microbial activities. The ZT + R treatment had the highest levels of MBC (271.63 mg kg⁻¹ soil), alkaline phosphatase (187.08 μmol p-nitrophenol g⁻¹ h⁻¹), and dehydrogenase activity (122.00 μg TPF g⁻¹ 24 h⁻¹). Despite a significant increase (3.8 and 6.9%) in wheat yield, a notable decrease in rice yield (10.5 and 16.7%) was recorded, leading to 2.9 and 6.2% yield reduction in RWS under RT and ZT treatments, respectively.

SIGNIFICANCE

Addressing the decline in rice yield, improved management of direct seeded rice (DSR) in RT/ZT system, or the crop diversification of long-term DSR with suitable alternative crops in rainy season under LT&RE are recommended strategies.