Effects of soil flooding on phosphorus transformations in soils of Mesopotamia region, Argentina

CESAR E. QUINTERO; FLAVIO H. GUTIERREZ BOEM; MARÍA R. BEFANI; NORMA G. BOSCHETTI

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE-ZEITSCHRIFT FUR PFLANZENERNAHRUNG UND BODENKUNDE

Wiley-VCH Verlag GmbH

Año: 2006

1436-8730

In the Mesopotamia region (Argentina), rice is cropped on a wide range of soil types, and the response of rice to fertilizer application has been inconsistent even in soils with very low levels of available phosphorus. Phosphorus transformations in flooded soils depend on soil characteristics that may affect phosphorus availability. This study was conducted to determine which soil characteristics were related to the changes in phosphorus fractions during soil flooding. Soils were chosen from 10 sites within the Mesopotamia region that are included in five different soil orders: Oxisols, Ultisols, Alfisols, Mollisols and Vertisols. Soil phosphorus was fractionated by a modified Hedley method before and after a 45-day anaerobic incubation period. Changes in the inorganic P extracted with resin depended on soil pH, and were related to the exchangeable iron concentration of soils (extracted with EDTA). Inorganic P extracted with alkaline extractants (NaHCO3 and NaOH) increased due to soil flooding. This increase was related to the organic carbon (OC) percentage of soils (r2=0.62, p<0.01), and ranged from 13 to 55 mg kg-1. Even though previous studies showed that phosphorus associated with poorly crystalline iron played an important role in the phosphorus nutrition of flooded rice, in this study there was no relationship between ammonium oxalate extractable iron and phosphorus changes in soils due to flooding. Our results suggest that in the Mesopotamia region, changes in phosphorus fractions due to soil flooding are related to soil OC, soil pH, and soluble and weakly adsorbed iron.