Difficulties in recommending phosphorus fertilizers for soybeans in Argentina

In Argentina, soybean has been cropped without fertilization, although soil phosphorus (P) contents have decreased. Areas earlier considered well supplied are at present P‐deficient. Our objective was to determine the native and fertilizer P uptake and its relationship with yields. A trial was carried out using soils with different P content. The fertilizer efficiency was quantified using 32P. The results of biomass, yield and P uptake by the crop indicated that fertilization did not match the different native P availability. From this behavior the placement of the fertilizer appeared to us as a possibility to be taken into account. The fertilized band is near the roots in the first growth stages; in the stages of higher P uptake rate, the roots are in contact with a soil mass with lower P availability. The placement and depth of fertilization is suggested to be considered together with the soil analysis, to avoid difficulties in fertilizer recommendations.