Abstract
Organic residue application is a low cost alternative to reduce the use of inorganic fertilizers and correctives. In order to study the effect of organic residues, limestone and gypsum application on phosphorus adsorption by lowland soils, four experiments were carried out. A Mesic Organosol (OY), a Melanic Gleysol (MG), a Haplic Gleysol (GX), and a Fluvic Neosol (RU) were used in a completely randomized design and factorial scheme (3 x 2), with five replicates: three soil amendment practices (limestone, gypsum and no corrective) and two levels of organic residue (with and without corral manure). Soil samples were incubated for 60 days, with and without organic residue incorporation. After this period, we applied the corrective and incubated the soil for 30 days, then P and basic fertilization (macro and micronutrients) were applied and the soil was incubated for additional 60 days. Equilibrium phosphorus, maximum phosphate adsorption capacity, pH, exchangeable Al and phosphorus-buffering index were measured. Organic residue and limestone application increased soil pH and reduced exchangeable Al, decreasing P adsorption. Gypsum application did not increase the pH but reduced exchangeable Al and P adsorption.
Highlights
Application of organic residues to soils reduces phosphorus adsorption and increases phosphate fertilizer efficiency (Hue, 1990)
Flooded soil conditions influenced phosphorus dynamics, raising its availability, which is attributed to: ferric phosphate reduction to ferrous phosphate, phosphates and organic anion hydrolyses, phosphorus displacement from iron and aluminum phosphates by chelate agents produced by anaerobic decomposition of organic matter, phosphorus release from organic matter, phosphorus release in limestone soils and removal of hydrated iron oxide that recovers phosphates due to iron reduction (Ponnamperuma, 1972)
Mg a(MmgoSuOnt4.th7aHt 2wOasp.aad.dfeodrmb)y was added in limestone, to avoid the same nutritional unbalance in bean plants
Summary
Application of organic residues to soils reduces phosphorus adsorption and increases phosphate fertilizer efficiency (Hue, 1990). This is an interesting practice, specially for developing countries, due to its low cost and to the fact that it reduces expenses with inorganic fertilizers and correctives (Iyamuremye et al, 1996). For soils in flooded-drained conditions, organic residue addition decreases phosphorus adsorption and alteres phosphate fractions; mainly organic fractions, which correspond to more than 50 % of total P in these soils (Sah et al, 1989). When a flooded rice field is drained, a reoxidation of soil components that were reduced occurs due to changes in oxidation-reduction potential, pH and Fe2+ concentration, which decreases the solubility of background and added phosphorus (Sayal & De Datta, 1991). The lower P availability in drained soils is associated to P adsorption increase owing to iron oxide activity increase (Willett & Higgins, 1978)
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