Temporal Dynamics of Soil Nutrient Availability and Humic Substances under Continuous Rice Cultivation

Abstract

Temporal shifts in soil macro- and micronutrient availability and in humic fractions were evaluated in soils under continuous rice cultivation in Telangana State. Six sites that had been under paddy cultivation for more than ten years were sampled from the 0–30 cm soil layer in February 2023 and again in January 2024. Across the two sampling times, the major available nutrients increased significantly: mean N rose from 223 to 233 kg ha-1, P from 30.8 to 32.8 kg ha-1, and K from 340 to 352 kg ha-1. Mean Fe, Cu, Mn, Zn, B and Mo concentrations likewise rose from 42.8 to 45.8, 1.44 to 1.53, 9.22 to 9.67, 0.88 to 0.98, 0.44 to 0.47 and 0.30 to 0.32 mg kg-1, respectively. Most nutrients were consistently highest at Suryapet and generally lowest at Mallapur. Conversely, mean humic acid declined from 0.81 to 0.79 g kg-1, while mean fulvic acid decreased from 0.74 to 0.71 g kg-1. Repeated fertiliser inputs during successive rice crops may account for the observed nutrient enrichment, whereas intensive cultivation, repeated tillage and puddling, and inadequate organic matter replenishment may explain the loss of humic fractions. These results indicate that sustaining soil fertility and productivity under continuous rice cultivation requires balanced nutrient management together with sufficient organic matter inputs.