Nitrogen use efficiency of cotton following corn in rotation and foliar fertilization of cotton using leaf blade analysis

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