Dynamics of Soil Cationic Micronutrients in a Chronosequence of Poplar (Populus deltoides Bartr.)-Based Agroforestry System in India

Abstract

Soils of India are generally deficient in micronutrients. The Fe, Mn, Zn, and Cu are present in different chemical fractions, and the extent to which each fraction is present is sensitive to cultivation and management practices. The inclusion of trees in major cropping systems may ameliorate micronutrient deficiencies to some extent as they increase mobilization of micronutrients in the soils. Depthwise dynamics of total, DTPA-extractable, water-soluble plus exchangeable (WSEX), specifically adsorbed (SpAd), carbonate bound (CARB), Mn-Oxide bound (MnOX), amorphous Fe-Oxides bound (AFeOX), crystalline Fe-Oxides bound (CFeOX), organically bound (OM), and residual (RES) fractions of cationic micronutrients (Fe, Mn, Zn, and Cu) were observed on the sites having poplar (Populus deltoides Bartr.)-based agroforestry system (AFS) for 10, 20, and 30 years, fodder-fodder (F-F) rotation and fallow land (FL). Total and DTPA-extractable micronutrients followed the order AFS > F-F > FL, and in chronosequence of AFS, the total content of Fe, Mn, Zn, and Cu increased by 9.8, 24.8, 50.8, and 9.2%, respectively, in 0–15 cm soil depth on the sites having AFS for 30 years over 10 years of AFS. All the micronutrients were highest in residual fraction than their other fractions in each land use system. Adoption of poplar-based AFS led to buildup of total micronutrients and their various pools in the soil. Chronosequence of AFS resulted in increase and redistribution of micronutrients from unavailable (CARB and CFeOX) to readily available (WSEX) and potentially available (OM, MnOX and AFeOX) forms in the soil.