Comparison of Obsolete and Modern Cotton Cultivars at Two Nitrogen Levels

Increase in cotton (Gossypium hirsutum L.) yields have been the result of both improved crop management and breeding. However, there is little information on how both management and breeding have interacted to produce higher yields. The objective of this study was to determine to what degree yield improvements and maturity changes which have taken place in the last 54 yr are due to using higher N rates and new cultivars. Eight modern cultivars (MC) and eight obsolete cultivars (OC) were grown on two soil types near Stoneville, MS, in 1992 and 1993. The year of cultivar release ranged from 1938 to 1992. Two N rates of 22 and 112 kg ha⁻¹ were used. The field design was a randomized complete block with five replications. Five hand harvests were made on all tests to measure yield and maturity differences. A significant N × cultivar interaction was detected. The average yield for MC was 914 and 1021 kg ha⁻¹ for the low and high N rates, respectively, or a 12% increase. However, average yield for OC was 743 and 799 kg ha⁻¹, respectively, or an 8% increase. The slope of the equation predicting yield from year of cultivar release was 6.1 and 4.8 kg ha⁻¹ yr⁻¹ for the 112 and 22 kg ha⁻¹ N rates, respectively. The higher N rate resulted in a 4-d delay in maturity, measured as days after planting (DAP) until 65% of the crop was harvestable. The maturity range for MC was 6 d, ranging from 136 to 142 DAP. The range for OC was three d, 138 to 141 DAP. Cultivar × environment interactions were small. This study shows that high yields can be obtained with both late and early maturity cultivars. However, early maturing culfivars escape some late season insect buildups and allow for greater harvesting flexibility. The regression coefficient of yield increase on year of release was significantly lower in this study than that detected in two previous studies. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product or service, and the use of the name by USDA implies no approval of the product or service to the exclusion of others that may also be suitable.