Cultivation-driven Soil Degradation in Rice Based Systems in Nalbari District, Assam: RSQI Thresholds for Sustainable Yield Maintenance

Abstract

Aims: The present investigation was carried out to assess Relative Soil Quality Index (RSQI) for grouping of soils of two land use system viz. rice-fallow and rice-oilseed as good, medium and poor categories. Place and Duration of Study: Assam Agricultural University, Jorhat, Assam during 2016. Methodology: Geo-referenced soil samples were collected from rice-fallow and rice oilseed (toria) cropped field continuously cultivated for last ten years. In total 60 composite soil samples were collected from each of cultivated and uncultivated soils of rice- fallow system and 63 composite soil samples were collected from each of cultivated and uncultivated soils of rice- oilseed cropping system and from adjacent uncultivated soils in Nalbari district of Assam. The soils of the study area belong to the orders Inceptisols and Entisols. The sampling was done using core sampler and focused on the plough layer (0-15cm) and analyzed for selected physical, chemical and biological properties of soils following standard procedures. Soil management practices and crop yield data were recorded from identified farmers. The RSQI based on 14 soil parameters (Water Holding Capacity, Soil texture, Bulk density, soil pH, CEC, OC, Available N, Available P, Available K, Available S, DTPA-Zn, Available B, Available Fe and MBC) were computed. Results: Results indicated that in rice-fallow system, 100% of the soils transformed to medium categories (RSQI value 50 – 70%) whereas 43% and 57% soils remained as medium (RSQI value 50 – 70%) and good category (RSQI value >70%) respectively in adjacent uncultivated soils.  In rice-oilseed crop sequence, the RSQI values exhibited that 93% and 7% soils remained as medium and good category (RSQI value>70%) respectively as compared to 29% medium category and 72% good category soils under adjacent uncultivated soils. The regression lines were drawn between RSQI and % Relative yield of rice in rice-fallow system and yield of rice –oilseed system expressed in terms of equivalent yield of rice and RSQI values obtained were above 51.8% (rice-fallow) or 51.15% (rice-oilseed) to maintain 80% crop yields. Conclusion: It was evident that continuous cultivation without proper soil management practices shifted the good quality soils towards medium quality soils. The RSQI study is important in reviewing the current fertility status of the soil as it indicates either the management or activities conducted is sustainable or not. Hence proper management practices are essential to maintain optimum RSQI values to sustain soil quality and agricultural productivity for increasing   farmers’ income.