Phosphorus availability to corn and soybean evaluated by three soil test methods for southern Brazilian soils

Authors: BORTOLON, LEANDRO - University Of Rio Grande Do Sul; GIANELLO, CLESIO - University Of Rio Grande Do Sul; Kovar, John

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2009
Publication Date: 2/1/2011
Citation: Bortolon, L., Gianello, C., Kovar, J.L. 2011. Phosphorus availability to corn and soybean evaluated by three soil test methods for southern Brazilian soils. Communications in Soil Science and Plant Analysis. 42:39-49.

Interpretive Summary: Soil tests are used by growers to prevent yield losses due to insufficient fertility levels and to ensure wise use of their fertilizer dollars. Efficient use of nutrients, such as phosphorus (P), also lessens the risk of environmental degradation. Systematic evaluation of phosphorus soil tests is necessary to maintain the accuracy of fertilizer recommendations. In this greenhouse study conducted under natural rainfall conditions, we evaluated the ability of three phosphorus soil tests to accurately predict phosphorus availability to corn and soybean plants grown in 49 Brazilian soils. We found that soil phosphorus extracted by the three methods was similar, but that the amount of clay in the soil affected the results. As the clay content increased, the amount of phosphorus by an exchange-resin method also increased, whereas P extracted by the Mehlich-3 method decreased. Because soil clay content influences extractable P values, this soil property needs to be considered to properly interpret soil phosphorus status and to develop more accurate fertilizer recommendations for corn and soybean grown on these soils. This information is a valuable resource for any laboratory that analyzes these or similar soils for phosphorus content.

Technical Abstract: In order to select and evaluate the effectiveness of multielement soil test methods for extracting plant-available phosphorus (P), correlation studies are needed. Under natural conditions, corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) were sequentially cultivated in 9-L microplots for 45 days to determine the amount of P that would be absorbed from 49 diverse soils of Rio Grande do Sul state in southern Brazil. Before planting, soil P was extracted with Mehlich-1 solution, Mehlich-3 solution, and ion exchange resin. The ability of Mehlich-1, Mehlich-3, and resin to extract plant-available P was then compared. The coefficients of determination obtained between plant P and the amounts extracted by Mehlich-1, Mehlich-3, and resin were 0.59, 0.45, and 0.59, respectively, for corn, and 0.57, 0.57, and 0.52 for soybean. Soil P extracted by the three methods was highly correlated; however, the amount of P extracted by the methods was affected by the clay content of the soils. As the clay content increased, the amount of P extracted by the resin also increased, whereas P extracted by the Mehlich-3 solution decreased. Because soil clay content influences extractable P values, soil clay classes are needed to properly calibrate soil P status and fertilizer recommendations for corn and soybean grown on these soils.