Legacy phosphorus and no tillage agriculture in tropical oxisols of the Brazilian savanna.
Crop production in the Brazilian Cerrado is limited by soil phosphorus (P) supply without large inputs of inorganic P fertilizer, which may become more costly and scarce in the future. Reducing dependency on fertilizer P requires a greater understanding of soil P supply in the highly weathered soils in this important agricultural region. We investigated the impact of no tillage (NT) and conventional tillage (CT) agriculture on accumulated (legacy) soil P and P forms in four long-term sites. Compared to the native savanna soils, tilled soils receiving regular annual P fertilizer inputs (30-50 kg P ha(-1)) increased all forms of inorganic and organic P, except highly recalcitrant P associated with the background lithology. However, 70-85% of the net added P was bound in moderately labile and non-labile forms associated with Fe/Al oxyhydroxides rather than in plant available forms. Under NT agriculture, organic P forms and labile and non-labile inorganic P forms were all significantly (P<0.05) increased in the surface soil, except for one site with maize residues where labile inorganic P was increased more under CT agriculture. The contribution of organic P cycling in these tropical soils increased after conversion to agriculture and was proportionally greater under NT. The results highlight the large amounts of unutilized legacy P present in Brazil's Cerrado soils that could be better exploited to reduce dependency on imports of finite phosphate rock. No tillage agriculture confers a positive albeit relatively small benefit for soil P availability and overall soil function.
University of São Paulo, "Luiz de Queiroz" College of Agriculture, Soil Science Department, Pádua Dias Av., 11, Box 9, Zip code 13418-900 Piracicaba, SP, Brazil.
Marcos
M
Rodrigues
University of São Paulo, "Luiz de Queiroz" College of Agriculture, Soil Science Department, Pádua Dias Av., 11, Box 9, Zip code 13418-900 Piracicaba, SP, Brazil. Electronic address: pavinato@usp.br.
Paulo Sergio
PS
Pavinato
School of Environment, Natural Resources and Geography, Bangor University, Bangor LL57 2UW, UK.
Paul John Anthony
PJ
Withers
University of São Paulo, "Luiz de Queiroz" College of Agriculture, Soil Science Department, Pádua Dias Av., 11, Box 9, Zip code 13418-900 Piracicaba, SP, Brazil.
Ana Paula Bettoni
AP
Teles
University of São Paulo, "Luiz de Queiroz" College of Agriculture, Soil Science Department, Pádua Dias Av., 11, Box 9, Zip code 13418-900 Piracicaba, SP, Brazil.
Wilfrand Ferney Bejarano
WF
Herrera
Brazilian savanna; Cerrado; Inorganic P; No tillage; Organic P; Phosphorus fractionation