Influence of landscape position, soil series, and phosphorus fertilizer on cotton lint yield
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Cotton (Gossypium hirsutum L.) response to P fertilizer can vary within fields, making P recommendations difficult. Phosphorus response may be more predictable with variable-rate fertilization, which matches soil test P and P fertilizer rate on a site-specific basis. Our first objective was to determine the effect of landscape position and soil series on cotton P accumulation, lint yields, and P fertilizer response on two irrigated cotton sites in the Southern High Plains of Texas. The second objective was to compare variable-rate P, blanket-rate P, and zero P applications. Mehlich-3 P levels ranged from 8 to 25 mg P kg-1at Lamesa, and from 12 to 23 mg P kg-1at Ropesville. Phosphorus fertilizer was not recommended when Mehlich-3 P >33 mg P kg-1. In both years at Lamesa, P accumulation at early squaring and lint yields were greater in the bottomslope than in the south-facing sideslope. Phosphorus fertilizer did not affect lint yields at Lamesa in 2000. In 2001, Lamesa lint yields responded to variable-rate and blanket-rate P in the south-facing sideslope only, which had just 8 mg P kg-1. At Ropesville in 2000, early P accumulation, biomass and lint yields responded to P on a calcareous soil but not on a noncalcareous soil. In all cases, yields were similar between variable-rate and blanket-rate P. Thirty-eight percent less P was applied with variable-rate than blanket-rate treatments in 3 of 4 site-yr. However, more research is needed to determine if fertilizer savings are consistent enough to offset the greater costs of variable-rate P fertilization.
