Study of a toposequence for variability in micronutrients from the moist subhumid Siwalik agro-ecological subregion of Punjab

A toposequence from the moist subhumid Siwalik agro-ecological subregion ofPunjab was studied for available and total micronutrient variability. The toposequence showed the least developed soils with only an A–C horizon sequence on steep slopes and a well-developed profile with an argillic horizon on moderate slopes. The soils consist of a variety of minerals and thus belong to the mixed mineralogy class. There were higher levels of DTPA-extractable micronutrients in the surface horizon than in the subsurface horizon due to their association with organic matter through chelation and adsorption. The surface horizons have relatively lower total micronutrient contents than the subsoil horizons. Soils from moderate slopes and lower terraces showed higher total micronutrients contents in the middle horizons, suggesting some redistribution of the constituents due to the illuviation process of pedogenesis. DTPA-extractable and total micronutrients showed an irregular increasing trend from the steep slope to the lower terrace soils. The DTPA-extractable micronutrients showed relatively greater variability (8–107%) than the corresponding total micronutrient contents (2–34%), suggesting the relatively dynamic nature of the former. Variability in DTPA-extractable and total micronutrients within and among the different soils was caused by several processes involved in the differentiation ofmicronutrients. DTPA-extractable micronutrients show the influence of organic matter through the processes of chelation and adsorption, whereas total micronutrients varied due to differences in pedogenic processes of eluviation/ illuvial on different landscapes and textural variation.