Doctor of Philosophy (PhD)
Plant, Environmental Management and Soil Sciences
Research is needed to ensure proper cotton N fertilization in various production practices without the detrimental effects of excess fertilization on yield and the environment. The objectives were i) to evaluate the effect of residual N on the uptake efficiency of cotton-applied N when following corn in rotation, ii) evaluate the potential for using leaf blade analysis and preset N thresholds to trigger foliar applications of N to cotton grown on clay soils and iii) evaluate the effect of preplant N on early root and shoot growth and N assimilation of cotton grown on a clay soil. Nitrogen rates of 0, 56 and 112 kg N ha-1 as double labeled 5 atom% 15N NH4NO3- were applied to cotton grown on Commerce silt loam (fine-silty, mixed, nonacid, thermic Aeric Fluvaquent) following previous corn N rates of 0, 168 and 280 kg N ha-1. Total dry matter accumulation, total N assimilation and seedcotton yield on the upper third of the plant increased as corn- and cotton-applied N increased. Recovery of labeled N ranged from 40-53% in 1999 and 30-58% in 2000 and was highest following 0 or 168 kg N ha-1 previous corn-applied N in both years. More plant N assimilation was soil-derived in both years following 280 kg corn-applied N ha-1. Application of 112 kg N ha-1 resulted in the most 15N assimilated but uptake efficiency was the lowest. Seedcotton yields of cotton grown on Sharkey clay (very fine, montmorillonitic, non-acid, thermic, Vertic Haplaquepts) using 44 or 67 kg soil-applied N ha-1 along with foliar N as needed averaged 622 kg ha-1 less than the recommended soil-applied rate of 134 kg N ha-1 although N use efficiency was 34% higher. The lower yield occurred because of fewer bolls on the second and third fruiting positions of upper sympodial branches. Preplant N rate increased dry matter partitioning to shoots with potentially larger N reserves. This provided ample vegetative growth, more branching and production of fruiting sites, and provided adequate assimilate to meet this increased demand. Increased cotton yield appeared to be the result of N accumulation and not greater root growth.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Craig, Charles Chism, "Nitrogen use efficiency of cotton following corn in rotation and foliar fertilization of cotton using leaf blade analysis" (2002). LSU Doctoral Dissertations. 4087.