Date of Award
12-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Plant and Environmental Science
Committee Chair/Advisor
Dr. Bhupinder S. Farmaha
Committee Member
Dr. Alan J. Franzluebbers
Committee Member
Dr. Michael A. Jones
Committee Member
Dr. William C. Bridges
Abstract
Nitrogen (N) plays a critical role in promoting vegetative growth, yield, and fiber quality in cotton (Gossypium hirsutum L.). However, over- or under-application of N can negatively affect cotton’s performance and environmental sustainability. The current N recommendations are based on targeted yield goals, leading to an imbalanced application of N fertilizer in a significant fraction of fields. To refine current N fertilizer recommendations, it is essential to consider site-specific factors such as agricultural management factors, field crop history, conservation practices, regional effects, and soil properties. We hypothesize that sites with a history of conservation practices and improved soil fertility levels will require less N fertilizer compared to the current recommendation system. A series of 50 N-rate response trials was conducted across South Carolina from 2021 to 2023. A randomized complete block design with three replications of four N rates (0, 45, 90, and 135 kg ha-1) was implemented at each site. Study sites were established across four physiographic regions, and 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 to 135 kg ha-1, with 62% of trials having values < 78 kg ha-1 (below the recommended rate). Physiographic region influenced EONR (p< 0.05), with higher EONR in Coastal Plains while lower in Piedmont region, reflecting differences in soil types and history of management. Nitrogen fertilization had inconsistent effects on cotton fiber properties; micronaire decreased while uniformity and strength increased with increasing N application rates. Among all crop management practices, the history of conservation practices had the most substantial effect on all fiber properties and net return. Cotton yield response parameters were determined from N rate trials and associated with soil properties using correlation and Random Forest modeling. Both analyses identified that net N mineralization (Nmin), total soil N (TSN), Illinois soil N test (ISNT), cation exchange capacity (CEC), and soil test biological activity (STBA) were the primary variables associated with relative yield and EONR. Random Forest modeling was moderately successful (validation R² = 0.23-0.39) for both basic and extended soil properties. Sites with higher Nmin, TSN, ISNT, CEC, and STBA, i.e., >CSTV values, had a low requirement of EONR, approximately below 20 kg ha-1. Long-term conservation practices as no-tillage, cover crops, and poultry litter, significantly had higher Nmin, TSN, ISNT, and CEC, and lower EONR. This research supports the development of site-specific N management strategies for cotton by integrating conservation practices that enhance soil health and accounting for existing soil N reserves. The new soil-based recommendation tool in the soil testing routine can improve economic benefits and environmental sustainability.
Recommended Citation
Dubey, Shikha, "Optimizing Site-Specific Cotton Nitrogen Recommendations Based on Soil Properties" (2025). All Dissertations. 4188.
https://open.clemson.edu/all_dissertations/4188