Carbon Management (Sep 2021)
Spatial distribution of soil organic carbon in apple orchard soils of Kashmir Himalaya, India
Abstract
Apple orchards constitute an important agro-ecosystem across Kashmir Himalayan Region (KHR), but estimates of their soil organic carbon (SOC) are unavailable. We investigated 174 apple orchards for estimating SOC spatial distribution across KHR at regional scale and evaluate accuracy of five interpolation methods. The selected orchards were representative of varied size, age, and management practices prevalent across KHR. Soil samples were collected from both tree rows and alleys between tree rows by digging pits at three depth intervals of 0–10; 10–20 and 20–30 cm. A total of 1044 soil samples were collected. The interpolation methods used included, ordinary kriging (OK), inverse distance weighing, empirical bayesian kriging, radial basis functions and local polynomial interpolation. Cross validation was used to assess the comparative performance of each method by measuring interpolation bias and accuracy. The soils were structurally less stony, with weak granular to moderate crumb at surface and sub-angular to angular blocky structure at sub-surface. The soils exhibited lowest co-efficient of variation for soil acidity and highest for soil electrical conductivity. With mean value of 12.33 ± 3.98 g kg−1 on concentration basis and 48.45 Mg C ha−1 on stock basis, the SOC declined with increasing soil depth, so much that near surface (0–10 cm) SOC content could explain well over 64% and 35% of second (20–30 cm) and third layer (20–30 cm) variation respectively. Exponential model best described SOC content across all depths. Semi-variograms of SOC at topsoil exhibited larger nugget effect while nugget sill ratios of 43% suggested moderate SOC spatial dependence. Cross validation exhibited better accuracy for OK in terms of indicating good match between observed and predicted SOC. This study exemplifies that apple orchards across KHR are significant carbon pool, improves our understanding of spatial distribution of SOC and help in evaluating soil health by providing site specific maps.
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