Impact of organic residues and mineral fertilizer application on soil–crop system: II soil attributes

The effects of crop residues alone (Cr+) or combined with inorganic fertilizer (FCr+) sewage sludge (SS) and humentos (H) on soil properties were studied in a five-season wheat–guar rotation. Incorporation of Cr+ and SS significantly decreased pH by 5–9%. Highest organic carbon (OC) was observed in SS plots, whereas Cr+ resulted in values threefold that of the control. The added effect of Cr+ (46%) combined with fertilizer on total nitrogen (TN) was greater than Cr+ by 28%. The fraction of total residue N mineralized was 71%, whereas net N mineralized in Cr+, SS, H and FCr+ plots at 0–20 and 20–40 cm depths were 39.8, 52.3, 11.4, 66.7 mg kg−1 and 21.2, 27.9, 8.2, 41.2 mg kg−1, respectively. Integrated application of Cr+ with fertilizer had a synergistic effect on P content (3.49–3.69 units), but soil levels has never exceeded 13 mg P kg −1. Sole Cr+ significantly increased topsoil cation-exchange capacity (CEC) compared with the control treatment (9.39–21.59%). Application of SS, FCr+ and Cr+ significantly increased water-holding capacity and decreased bulk density by 9–15% and 8–9%, respectively, suggesting that such practice can restore the productivity of degraded soils and improve crop yields.