Soil phosphorus sorption capacity after three decades of intensive fertilization in Mato Grosso, Brazil

• Published in: Agriculture, ecosystems & environment Vol. 249; pp. 206 - 214
• Main Authors: Roy, Eric D., Willig, Edwin, Richards, Peter D., Martinelli, Luiz A., Vazquez, Felipe Ferraz, Pegorini, Lindomar, Spera, Stephanie A., Porder, Stephen
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2017; Elsevier BV
• Subjects: Agricultural intensification; Agricultural land; Aluminum; Amazon; Brazil; Cerrado; chronosequences; clay soils; Crop production; cropland; Crops; Farmers; Farming; Farms; Fertilization; Fertilizer; Fertilizers; Harvesting; inorganic phosphorus; Intensive farming; interviews; Oxides; Oxisols; Phosphorus; phosphorus fertilizers; prices; rock phosphate; Saturation; Soil types; Soils; Sorption; Soybeans; Tropical environment; Tropical environments; Tropical soils; Tropics; United States; Volatility; Western European region; Brazil; United States; Western European region; Agricultural intensification; Amazon; Cerrado; Oxisols; Tropics; Fertilizer
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/j.agee.2017.08.004

•We studied 31 plots cultivated for 0–31 yrs on soy farms in Cerrado & Amazon biomes.•We used farmer interviews and soil measurements to examine P dynamics.•Soil P is increasing with fertilization but most residual P is unavailable to crops.•Clayey soils show marginal decline in P sorption capacity after three decades.•High-P-fixing soils impose long-term soil P ‘tax’ where P input must exceed output. Soil phosphorus (P) availability commonly limits the productivity of tropical croplands. While large fertilizer inputs can alleviate P limitation, this strategy is costly and relies on finite phosphate rock resources subject to price volatility. Nevertheless, high-P-input agriculture on P-poor and P-fixing soils is spreading rapidly in some regions of the tropics, particularly in Brazil, where farmers on average add twice as much P to soils as they harvest to ensure high yields. Here we ask whether P fertilizer inputs to tropical soils in excess of harvested P outputs will eventually build up a residual pool of soil P that crops can tap into if fertilizer inputs are decreased – a phenomenon observed in the U.S. and Western Europe, albeit on very different soils. We pose this question in Mato Grosso, Brazil, where we quantified soil P input-output budgets, total P, Bray-extractable P, P sorption capacity, P saturation, and other characteristics from a chronosequence of 31 plots that had been in soybean production for 0–31 years. Farmer interviews revealed ongoing annual additions of P fertilizer greater than P removals in crops, with an average farm P balance in the most recent year, including soybeans and a second harvest, of +14kgPha−1y−1. Soil total P and Bray-P1 have increased, and P sorption capacity has decreased, with time in production. However, clayey soils rich in iron- and aluminum-oxides still have high P sorption capacity and low P saturation, even after three decades of intensive fertilization and residual P build-up. Our findings suggest that commodity crop producers farming on this soil type in Mato Grosso and other tropical regions may need to add annual inorganic P fertilizer inputs greater than the quantity of P recovered in harvests for up to a century or more before soil P budgets can be balanced without endangering yields. This result has implications for the sustainability of agricultural intensification in the tropics.