Effect of land-use change along altitudinal gradients on soil micronutrients in the mountain ecosystem of Indian (Eastern) Himalaya

Management of soil micronutrients for better crop production needs a sound understanding of their status and causes of variability. This is more relevant for acid soils of the mountain ecosystem of Eastern Himalaya (Northeast India). We assessed the status, and the effect of land uses along altitudinal gradients (14 to 4090 masl) on soil properties and micronutrient concentrations (DTPA extractable Fe, Mn, Cu, and Zn) across the region. Soils varied widely in micronutrient concentrations: Fe from 0.665 to 257.1 mg kg(-1) while Mn, Cu, and Zn from traces to 93.4, 17.1, and 34.2 mg kg(-1), respectively. On conversion of evergreen forests (EF) to upland agriculture (Shifting-SC and Settled-SA) and plantation (PH), Mn, Cu, and Zn concentrations decreased significantly from 30.5, 1.74, and 2.13 mg kg(-1) to 6.44-17.8, 0.68-0.81, and 1.06-1.42 mg kg(-1), respectively. Grassland (GL) and lowland paddy (LP) had comparable Fe, Mn, and Cu concentrations (except Zn). Degradation of EF to scrubland (SL) recorded the lowest Mn (5.91 mg kg(-1)), Cu (0.59 mg kg(-1)), and Zn (0.68 mg kg(-1)) concentrations. Fe concentration was however increased in degraded SL (+73%) over EF (48.7 mg kg(-1)). The distribution of micronutrients among the land uses was inconsistent and followed the order: (i) Fe: SL>PH>LP>EF>GL>SC>SA, (ii) Mn: EF>GL>LP>PH>SC>SA>SL; (iii) Cu: EF>GL>LP>SC>SA=PH>SL; and (iv) Zn: GL>EF>LP>SC>SA>PH>SL. Four micronutrients responded differently and followed a non-linear, 6th-order polynomial trend along the altitudinal gradients (<500 to 4100 masl). Peak concentrations of Fe, Mn, and Cu were recorded at 1001-2000 m while Zn was recorded at>4000 masl. The variability (54-64%) in soil micronutrients was mainly controlled by three key soil properties: acidity, clay, and organic carbon contents. Thus, altitude-specific land-use management holds significance in the distribution of available soil micronutrients in hilly ecosystems.