Articles | Volume 7, issue 3
Research article
07 Jun 2016
Research article |  | 07 Jun 2016

Estimations of soil fertility in physically degraded agricultural soils through selective accounting of fine earth and gravel fractions

Mavinakoppa S. Nagaraja, Ajay Kumar Bhardwaj, G. V. Prabhakara Reddy, Chilakunda A. Srinivasamurthy, and Sandeep Kumar

Abstract. Soil fertility and organic carbon (C) stock estimations are crucial to soil management, especially that of degraded soils, for productive agricultural use and in soil C sequestration studies. Currently, estimations based on generalized soil mass (hectare furrow basis) or bulk density are used which may be suitable for normal agricultural soils, but not for degraded soils. In this study, soil organic C, available nitrogen (N), available phosphorus (P2O5) and available potassium (K2O), and their stocks were estimated using three methods: (i) generalized soil mass (GSM, 2 million kg ha−1 furrow soil), (ii) bulk-density-based soil mass (BDSM) and (iii) the proportion of fine earth volume (FEV) method, for soils sampled from physically degraded lands in the eastern dry zone of Karnataka State in India. Comparative analyses using these methods revealed that the soil organic C, N, P2O and K2O stocks determined by using BDSM were higher than those determined by the GSM method. The soil organic C values were the lowest in the FEV method. The GSM method overestimated soil organic C, N, P2O and K2O by 9.3–72.1, 9.5–72.3, 7.1–66.6 and 9.2–72.3 %, respectively, compared to FEV-based estimations for physically degraded soils. The differences among the three methods of estimation were lower in soils with low gravel content and increased with an increase in gravel volume. There was overestimation of soil organic C and soil fertility with GSM and BDSM methods. A reassessment of methods of estimation was, therefore, attempted to provide fair estimates for land development projects in degraded lands.

Short summary
Three nutrient stock estimation methods, generalized soil mass (GSM), bulk-density-based soil mass (BDSM) and the proportion of fine earth volume (FEV) method, were compared to estimate organic C and major available nutrient stocks in physically degraded agricultural soils of southern India. The stocks were lowest using FEV method followed by GSM and BDSM method. The study highlights the importance of estimation methods to obtain realistic estimates for the development of degraded land areas.