Contribution of forest fine roots in reclamation of semiarid sodic soils

Abstract

Fine root biomass (<2 mm diameter) was estimated to a depth of 0.3 m in a 40‐year‐old rehabilitated forest on sodic wasteland at Lucknow, India (26°45'N, 80°53'E). The mass of live fine roots was estimated to be 166 g m‐ 2 (75% of total) on an ash‐free dry weight basis. Spatial and temporal variation in fine root biomass (11% and 17%) was not significant. Classification of fine roots into three diameter classes revealed that the proportion of very fine live roots <0.5 mm increased with soil depth. A significant negative correlation of fine roots (0.5–2.0 mm) with time was observed during 20 months of regular sampling (r2 = 0.71, P < 0.01). Fine root production was measured as 194 g m−2 a−1 by an in‐growth core technique including the decomposition loss during this period. Production differs significantly under different species (P < 0.05) and time (P < 0.01). Fine root mortality was 86 g m−2 a−1. Fine root decomposition rate declined through time and accounted for approximately 77% mass loss per year. Nutrient concentrations (N, P, K, Ca, Na) of live and dead roots were almost similar except for C, indicating almost no resorption. Nutrient inputs to the soil from fine roots were less than that of litter, corresponding to their lower turnover rate. However, the contribution of fine roots was apparently greater in the reclamation of soil structure, pH, and water permeability. The net change in soil nutrient pool on afforestation increased the soil C pool to 13 times and total N twice through the regular inputs from fine roots and litter fluxes. In forested soil, Na content was decreased by 74% and Ca elevated by 33% from the surrounding barren soil, whereas, P and K were not significantly different between sites.