Irrigated cotton lint yields as affected by phosphorus fertilizer and landscape position

Phosphorus (P) is the second most limiting nutrient in cotton (Gossypium hi rsutum L.) production after nitrogen. Response to P fertilizer, however, is often hard to predict in the Southern High Plains, even with soil test-bas ed applications. Landscape position has a strong influence on yields and pe rhaps on fertilizer response as well. The objective of this 5-year study (1 994-1998) was to determine P fertilizer response in irrigated cotton in dif ferent landscape positions. We used an 825-m transect of end to end 15-m pl ots across a broad swale in an Amarillo fine sandy loam in Lamesa, TX that included three landscape positions, sideslope, bottomslope and drainageway. A randomized complete block design was used with 11 replicates and 5 P rat es (0, 22.4, 33.6, 44.8, and 56 kg P ha(-1)). Analysis of variance showed a linear or quadratic response to P fertilizer in 3 of 5 years, and an effec t of landscape position in 4 of 5 years. Four-year lint yield averages, exc luding 1997, were 1355 kg ha(-1) in the bottomslope position in the landsca pe, and 1210 and 1226 kg ha(-1) on the sideslopes and in the narrow drainag eway, respectively. Cross-correlation using the 55 plots as a tran sect rev ealed few effects of soil properties on lint yield, but negative correlatio n between yield and elevation. In 1997, the one year without a landscape ef fect on yield, more rain fell during the growing season than in the other 4 years. This suggests that yield potential is higher in lower landscape pos itions because of more favorable soil water relations. Cotton lint response to P fertilizer was evident only in the bottomslopes and in the drainagewa y, and was absent in the sideslopes, meaning that variable rate fertilizer applications could be linked to management zones based on landscape positio n.