Cotton lint yield responses to nitrogen fertilization are diverse in South Carolina

Abstract Optimizing nitrogen (N) management in cotton ( Gossypium hirsutum L.) production across diverse environments in the southeastern United States remains a challenge. We examined cotton yield responses to N fertilization on multiple commercial farms with different management histories in four physiographic regions of South Carolina. Field experiments were conducted using a randomized complete block design with four N rates (0, 45, 90, and 135 kg ha −1 ) replicated three times at 50 trials from 2021 to 2023. Field management varied by previous crop, type of tillage, water regime, and history of conservation practices. Cotton lint yield was responsive to N fertilization in 52% of the trials. Economic optimum N rate (EONR) had an interquartile range of 0–135 kg ha −1 , with 68% of trials having values <78 kg ha −1 (below the recommended rate). The physiographic region influenced EONR ( p < 0.05), with higher EONR values at Coastal Plains and Sandhills compared to the Piedmont region, reflecting differences in soil types and the history of management. Sites with long‐term conservation practices had greater yield without N input, higher relative yields, and lower N factor (fertilizer N required per unit of lint) than conventionally managed sites. These sites exhibited greater residual soil N content, thereby reducing N fertilizer requirements. Current‐season management had varying impacts, and tillage primarily influenced how efficiently cotton used N (affecting EONR and N factor), while water regime affected yield potential indices (control, maximum, and profit‐maximizing yield) as well as EONR. These findings emphasize the need for site‐specific N recommendations that should consider physiographic characteristics, current‐season management practices, and the long‐term history of conservation practices. This study provides a foundation for developing more sustainable and efficient N management practices for cotton production.