Evaluating Cotton Nitrogen Dynamics in the GOSSYM Simulation Model
- William E. Stevens ,
- Jac J. Varco and
- Joseph R. Johnson
Prediction 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.
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