Nitrogen dynamics and balance under organic and inorganic nutrient management in cotton

Abstract:

Nitrogen is the nutrient cotton demands most, yet applying it efficiently remains a persistent challenge. This research compared organic and inorganic nitrogen sources at four rates (0, 40, 80, 120, and 160 kg N ha⁻¹) to track nitrogen dynamics and construct a field-scale N balance for irrigated cotton near Shiraz, Iran. Inorganic urea produced higher total N uptake than composted cattle manure at every non-zero rate, but the gap narrowed at 160 kg N ha⁻¹ (78.6 vs 62.1 kg N ha⁻¹). Apparent nitrogen recovery was consistently lower under organic management (31-39%) than under inorganic (42-49%). Soil residual mineral N at harvest was 27-44% greater in urea-treated plots, raising concerns about post-season leaching risk. The N balance showed that organic treatments retained more N in soil organic pools, while inorganic treatments lost a larger fraction to gaseous and leaching pathways. These results suggest that combining a moderate organic base with a small inorganic supplement may balance productivity with long-term soil-N conservation in arid-zone cotton.