Dynamics of phosphorus in five acid Colombian soils

Jose Orlando Blanco, Purdue University

Abstract

Most Colombian soils, classified as Andosols and Oxisols, are characterized by being slightly to strongly acid, low in available P, high in exchangeable Al, and high in P adsorption capacity. These properties are considered to the principal limiting factors for their agricultural use, so that lime application and phosphate fertilization are very important practices in the management of these soils. To study the soil P supply characteristics, several rates of P, as Ca(H$\sb2$PO$\sb4)\sb2 \cdot$H$\sb2$O, were applied to each soil. Soils with pH below 5.0 were limed with CaCO$\sb3$ prior to P application. Soil samples were analyzed for pH, P, Ca, K, Mg, and Al both in the displaced solution (C$\sb{\rm li}$) and in the solid phase (C$\sb{\rm si}$). Exchangeable or labile P was determined by using the anion-exchange resin method. A pot experiment was conducted in a controlled climate chamber to verify the Barber-Cushman nutrient uptake model for predicting P uptake by twelve-day-old corn plants from these soils. The initial P concentration in soil solution (C$\sb{\rm li}$) for the Colombian Andosols and Oxisols is very low compared to that for U.S.A. Mollisols. The high P adsorption capacity of Andosols and Oxisols seems to be the principal reason for their low C$\sb{\rm li}$ values. The soil buffer power (b) was similar for Andosols (122) and Mollisols (118) but much higher for Oxisols (150). The effective diffusion coefficient (D$\sb{\rm e}$) values were highest in Andosols and similar for Oxisols and Mollisols. This result was related to the water retention capacity of the soils. The relationship between C$\sb{\rm li}$ and the rate of P added to soils resulted in an exponential function, whereas that between C$\sb{\rm si}$ and P addition resulted in a linear function. As a result, the soil buffer power showed a downward trend with P additions. The soil bulk density and the P application rate greatly affected root growth parameters. In Andosols the root length was greater than in Oxisols and Mollisols. Mean root radius was also less in Andosols. Increasing P rate significantly reduced most root growth parameters, except root radius. Good agreement was found between observed and predicted P uptake for both P rates and soils. This indicates that the Barber-Cushman nutrient uptake model accurately predicted P uptake by twelve-day-old corn plants from the soils used in this study.

Degree

Ph.D.

Advisors

Barber, Purdue University.

Subject Area

Agronomy|Agricultural chemicals

COinS