Effects of length of forest fallow on fertility dynamics in a Mexican ultisol |
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Authors: | G. Wadsworth H. M. Reisenauer D. R. Gordon M. J. Singer |
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Affiliation: | (1) Department of Land, Air and Water Resources, University of California, 139 Hoagland Hall, 95616 Davis, CA, USA |
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Abstract: | Changes with time in the fertility of a Mexican ultisol were evaluated from analyses of soil samples from fields representing 50 years of pineapple slash-and-burn agriculture. Sixteen fields with similar soil profile charactersitics representing eight ages of forest fallow were sampled. The fields, within an area of 5 km2 of nearly level tropical forest, had been cleared by hand, initially intercropped with corn and manioc, followed with 3 to 4 y of pineapple, and then abandoned. The surface soils contained relatively high levels of C and N (5% and 0.3% respectively), were strongly acid (pH 5 to 5.5), and supplied very low levels of available P and K. Soil contents of both C and N declined rapidly after clearing to levels approximately 20% lower at 10y, then increased steadily during the fallow period to values not different from their initial levels. Since little of the N released was utilized by the low-yielding, P-deficient crops, this loss of C, N and accompanying cations is a most serious consequence of this rotation. Both the exchangeable and reserve K levels of these ultisols are low. Thus, K is identified as second to P as a growth limiting factor and the most difficult fertility management problem. |
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Keywords: | agro-ecosystems nutrient leaching rain forest shifting cultivation soil organic matter slash-and-burn agriculture tropical soils |
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