In a long-term experiment on a mollisol in North India, the availability of Ca, Mg and S nutrients was enhanced under integrated nutrient management (INM) conditions, but depleted in the case of continuous rice-wheat-cowpea cropping for 28 years without nutrient input (control), suggesting the need for the regular estimation of these macronutrients in soils under intensive cropping. The soil was still able to supply crop needs for Ca and Mg, but the soil became S-deficient (8.9 mg kg−1) when S-free diammonium phosphate (DAP) fertilizer was applied. Its availability increased 5-fold (45.3 mg kg−1) after the application of S-containing single superphosphate (SSP) fertilizer and improved further when this was combined with farmyard manure (FYM) in an INM system. The wheat response to S was 0.36 and 0.45 t ha−1 for the grain and straw yields, respectively. The highest removal of Ca, Mg and S was observed with INM (21.36, 27.52 and 13.38 kg ha−1, respectively) and the lowest in the unfertilized control.
The properties of humic (HA) and fulvic acids (FA) isolated from a 27-year-old long-term experiment with rice-wheat-cowpea on a Mollisol in northern India were evaluated for elemental composition and functional groups. As compared to fallow, C, H and N decreased, while O increased in the control, but the use of NPK+FYM over the years enhanced the C and N of humic substances. The carboxylic (-COOH) and phenolic-OH groups declined in the control, but improved with NPK+FYM in comparison to fallow. Carboxylic groups (-COOH) contributed about 2–3 times more in HA and 4–5 times more in FA than the respective phenolic-OH groups to the molecular weights of these fractions of soil organic matter. The results suggested the role of integrated nutrient management in maintaining active soil humus over the years.
In a twenty five years old long-term fertilizer experiment with rice-wheat-cowpea system on a mollisol at Pantnagar; rice and wheat responded well to applied N, Zn and FYM over the years; whereas, responses to other applied nutrients are improving with the passage of time owing to decline in their availability in soil. Uptake of micronutrients by the entire cropping sequence of rice-wheat-cowpea varied from 143 to 597, 2274 to 6169, 384 to 1234 and 119 to 521 g ha
for Zn, Fe, Mn and Cu, respectively. The highest removal of Zn by crops was observed under 100%NPK+Zn, while that of Fe, Mn and Cu was under 100%NPK+FYM. Removal of micronutrients by the annual cropping cycle depleted the availability of Zn, Fe, Mn and Cu in soil in the range of 0.02–.0.37, 0.1–1.8, 0.1–1.6 and 0.1–0.2 mg kg
, respectively under different treatments.