Phosphorus Management for Continuous Corn-Cowpea Production in a Brazilian Amazon Oxisol
- T. J. Smyth and
- M. S. Cravo
Although Oxisols occupy extensive areas in the Amazon, few studies have addressed their fertilizer P requirements for sustained, long-term crop production. This field study was conducted to evaluate initial and long-term responses to P rates and placement by corn (Zea mays L.) and cowpea (Vigna Unguiculata L.) when grown in annual rotation during five consecutive years in a Xanthic Hapludox (clayey, kaolinitic, isohyperthermic) near Manaus, Brazil. Effects on yields of sole broadcast P rates of 0, 22, 44, 88 and 176 kg ha−1 in split-plot combination with subplot banded P rates of 0, 11, 22 and 44 kg ha−1 were evaluated over 11 total crops. Banded P at 11 kg ha−1 was applied to every crop and rates of 22 and 44 kg P ha−1 were only applied to the initial eight and four crops, respectively. Residual effect of broadcast P, as measured by both yields and Mehlich 1 soil P, were greater at high rates. Although cowpea yields were increased up to the highest band rate, no response in corn yields were observed beyond the rate of 22 kg P ha−1. At equal amounts of applied P, banded P provided greater yields than broadcast P during the initial crops. Total corn and/or cowpea yields, after 11 crops, were similar for all broadcast and band combinations at equal amounts of total applied P. The absence of a cumulative yield difference among placement methods indicated that banded placement of 22 and 44 kg P ha−1 to corn and cowpea, respectively, would be the best method of applying P to sustain long-term crop production under the manual tillage practices used in the region.
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