Cotton Nitrogen Management on Clay Soil: Petiole Nitrate Monitoring Versus GOSSYM/COMAX

E.D. Vories, D.M. Oosterhuis, and C.M. Bonner


 
ABSTRACT

In response to concerns by area cotton producers, extension personnel and gin operators, a field study was initiated to investigate the suitability of GOSSYM/COMAX (GIC) as a management tool in northeast Arkansas. Cotton (Gossypium hirsutum L. cv. Deltapine 50) was planted on May 18, 1989, in a Sharkey silty clay - Steele loamy sand complex soil. The cotton received 100 lb N/acre, split between preplant and early squaring, as recommended by the University of Arkansas Cooperative Extension Service (CES) for the particular soil and location. After bloom, N on half of the plots was managed with GIC and the other plots were enrolled in the CES petiole nitrate monitoring program (petioles were sampled weekly and N recommendations based upon nitrate concentration). The G/C simulations indicated that the plants were never under a N stress, while the petiole analyses suggested N stress from mid-July through the end of the season. An additional 10 lb N/acre was foliar applied to the G/C plots on August 18, 1989. The petiole-nitrate plots received an additional 83 lb N/acre in seven increments, with 30 lb N/acre applied to the soil on July 27, 1989, and the remaining 53 lb N/acre applied over six foliar applications during August. Average yields were 3110 and 3370 lb seed cotton/acre for the G/C and petiole treatments, respectively, although the difference was not statistically significant. One possible reason for the small difference in yield is that most of the additional N was foliar applied and the cool, cloudy conditions may not have been favorable for foliar uptake.

The GOSSYM simulation model did not appear to accurately predict the status of the plants in this study. Squaring dates were later than predicted, which necessitated using a false emergence date on simulations. Soon after the final mid-season adjustment in late July, the computer simulations again differed from observations in the field. The field observations showed shorter plants than predicted and the actual cotton was produced over a shorter period of time. Predicted yield (2890 lb seed cotton/acre) was lower than the total mechanical harvest (3110 lb seed cotton/acre) for the G/C-managed plots even without considering picker losses and insect damage. In an adjacent study, yields for the same cultivar and planting date increased with N rate up to 200 lb N/acre, while GOSSYM simulations for that study predicted maximum yield at the 100 lb N/acre rate.

These results suggest that, at present, care should be exercised in the interpretation of G/C simulations on the clay soils of northeast Arkansas. Additional research is needed under a variety of environmental conditions. Furthermore, the G/C program is constantly being updated, so shortcomings observed in one season may be solved by the next. It also appears that research is needed to determine what conditions may inhibit plant uptake of foliar M to increase the utility of the petiole nitrate monitoring program.



Reprinted from 1990 Proceedings: Beltwide Cotton Production Research Conferences pg. 488
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998