Impact of long term nutrient management practices on ferrolysis induced soil transformations in an acid alfisol

Abstract

The present investigation was carried out in an on-going long term fertilizer experiment, initiated during 1972 at the experimental farm of the Department of Soil Science, CSK HPKV Palampur, to study the effect of fertilizers and amendments on ferrolysis, its impact on maize-wheat yield and soil fertility in an acid Alfisol. The experiment was laid out in a randomized block design with eleven treatments replicated thrice. The soil of the experimental site was silty loam in texture and taxonomically classified as Typic Hapludalf . Grain and stover/straw yields of maize and wheat during the 50th and 51st cropping cycles (kharif 2022, 2023 and rabi 2022-23, 2023-24) were recorded after their harvest and nutrient uptake was calculated. After the 51st wheat harvest, soil samples were collected at six depths (0-0.05, 0.05-0.1, 0.1-0.15, 0.15-0.2, 0.2-0.25 and 0.25-0.3 m) and analyzed for physical, chemical and biological properties The occurrence of ferrolysis was evaluated based on particle size distribution, soil pH and iron and aluminium forms under different treatments. The results revealed that the balanced fertilization of 100% NPK along with FYM and lime significantly enhanced macro- and micronutrient uptake, thereby, sustaining higher maize and wheat yields compared to other treatments. A sub-optimal dose of NPK (50%) combined with FYM outperformed the optimal (100%) and super-optimal (150%) NPK doses without FYM. In contrast, imbalanced fertilization, particularly the sole application of nitrogen resulted in crop failure. The omission of sulphur or potassium, also significantly reduced crop productivity. The balanced fertilization along with amendments (FYM and lime) stabilised soil texture and reduced bulk density while imbalanced nitrogen inputs (150% NPK, 100% N, 100% NPK ( S) and 100% NP) increased sand and silt content and reduced clay content, indicating ferrolysis triggered by acidification from excessive or unbalanced fertilization. The amendments also raised soil pH and enhanced organic carbon, with the highest levels under 100% NPK + FYM. Balanced fertilization with amendments increased macro- and micronutrient availability and significantly enhanced microbial biomass carbon, nitrogen and populations of bacteria and actinomycetes, whereas fungal populations were highest under the sole application of nitrogen. Pertaining to iron and aluminium forms, higher concentrations of water-soluble plus exchangeable and organically bound Fe were recorded under 100% NPK + FYM. Carbonate-bound Fe increased with lime application, whereas the sole application of nitrogen resulted in significantly higher Fe-Mn oxide-bound Fe, likely due to soil acidification and ferrolysis. Soil mechanical separates variably affected wheat yield and nutrient uptake, with sand and clay content positively correlated to micronutrient uptake and straw yield, respectively. Conversely, silt content showed a negative relationship with both yield and nutrient uptake. Soil pH, organic carbon, exchangeable Ca and Mg and organically bound and amorphous Al were positively correlated with grain and straw yield. Similarly, water-soluble plus exchangeable and organically bound Fe were positively correlated with Fe uptake and yield. In contrast, bulk density, Fe-Mn oxide-bound Fe and exchangeable/sorbed Al negatively affected crop productivity. These findings highlight the importance of balanced fertilization with FYM and lime in sustaining soil fertility in Alfisols, mitigating the adverse effects of ferrolysis and improving soil resilience under continuous cropping. newline