Impacts of reclaimed water irrigation on mulch decomposition, microbial activity, and soil nutrient availability in the Brazilian semi-arid

Abstract

Knowledge gaps persist regarding mulch decomposition, nutrient dynamics, and microbial responses in semi-arid soils under reclaimed water irrigation. This is a critical issue for water-scarce regions like the Brazilian semi-arid. This study evaluated these processes in cactus-sorghum intercropping systems with mulch under irrigation depths with reclaimed water. The study employed a randomized block design with four replicates, testing irrigation depths of 0 %, 80 %, 100 %, and 120 % of sorghum ETc. Mulch decomposition was monitored for 165 days using litter bags, with subsequent C/N analysis of residual biomass. Soils at 0–0.10 m and 0.10–0.20 m depths were sampled to determine the contents of NO₃⁻, NH₄⁺, P, and microbial biomass C (MB-C), basal soil respiration, and aromatization index (ALIFS). Decomposition revealed the highest rates at 10 days (16 %) under 80 % ETc and at 25 days (24 %, 22 %, and 21 %) under 80 %, 100 %, and 120 % ETc, surpassing non-irrigated soils. Residue half-life was 182–196 days. Mulch N content declined most sharply at 10 days (1.2–1.8 g kg⁻¹ in irrigated treatments). Soil NH₄⁺ and NO₃⁻ peaked in the 0–0.10 m layer, but nitrate decreased by 15–62 % at 65 days, signaling microbial disruption from water excess. MB-C dropped >90 % at 65 days but recovered by 165 days, with the 80 % and 100 % treatments showing the highest MB-C in surface soils. These treatments also increased available P₂O₅ by 46–216 mg kg⁻¹ versus 0 % and 120 % ETc. The ALIFS was higher in irrigated soils, especially at 120 % ETc (0–0.10 m). Reclaimed water irrigation enhanced nutrient supply, decomposition, and microbial activity, reducing synthetic fertilizer dependency while improving soil health in semi-arid agroecosystems.