Evaluating Cotton Nitrogen Dynamics in the GOSSYM Simulation Model

Abstract

AbstractPrediction of cotton (Gossypium hirsutum L.) N requirements would be useful in preventing excessive vegetative growth and negative environmental effects from overapplication of fertilizer N. Field research studies were conducted at Holly Springs, MS, to evaluate early‐maturing and full‐season cultivar effects on N nutrition and yield. Cotton was grown across a range of N application rates and results were compared with simulations of the cotton model GOSSYM. Cotton cultivars Stoneville 825 and DES 119 were grown on a Grenada silt loam soil (fine‐silty, mixed, thermic Glossic Fragiudalfs) in 1989 and 1990, and Deltapine 20 on a Loring silt loam soil (fine‐silty, mixed, thermic Typic Fragiudalfs) in 1990, all with N rates of 0, 45, 90, 135, and 180 kg ha−1. Rainfall in May through September 1990 was only 52% of the rainfall during the same period in 1989. Cultivar effects on yield and cotton N nutrition were minimal. Averaged across cultivars and N rates, 24% of total plant N on the Grenada soil and 20% on the Loring soil in 1990 was in ground litter at first open boll, compared with 13% in 1989 on the Grenada soil. GOSSYM accurately predicted litter N for the Grenada site in 1990, but overpredicted N in litter in 1989 at this site and in 1990 for the Loring site. On the Grenada soil in 1989, an average of 61% of the total plant N at first open boll was in seed and burrs, while in 1990 it was 41%, due to a lower boll load. For both soils, N availability without fertilizer ranged from 68 to 77 kg N ha−1. GOSSYM overestimated soil N availability by 10 to 30 kg N ha−1. Averaged across cultivars on the Grenada soil in 1989, GOSSYM underpredicted yield on cotton with no fertilizer N by 463 kg lint ha−1. Fertilizer N recovery was overpredicted by the model. These results point to the need for more accurate prediction of N dynamics if the model is to be used for N management on fragipan soils.