Agronomic Effectiveness of Mixtures of Triple Superphosphate and Phosphate Rock for Soybean

IPNI-2006-BRA-52

20 Jan 2009

2008 Annual Interpretive Summary


Phosphorus is considered the most limiting nutrient for soybean production in Brazil. It is necessary to add P fertilizer to most soils to obtain good economic yields. Nearly all P fertilization is carried out using acidulated phosphate ... e.g. triple superphosphate (TSP). However, the co-application of acidulated phosphate, which has high water solubility and less soluble phosphate rock (PR), is thought to be a feasible alternative. Two field experiments were carried out, one in Maranhão State (Balsas) and another in the State of São Paulo (Palmital), to evaluate the agronomic effectiveness of mixtures of TSP and Arad PR for soybean. In both experiments, the P sources were: i) applied separately, but in the same treatment ... i.e, broadcast PR application and banded TSP, and ii) applied as compacted, granular mixtures obtained through different proportions of TSP and PR. Thus, the relative agronomic effectiveness (RAE) of the P sources, calculated on a percent basis related to the standard source of P (the banded TSP), was evaluated under different P placement methods and water solubilities.

The RAE of sources with lower solubility was generally higher when they were broadcast and incorporated into the soil. For example, the RAE of broadcast PR was 77% (average of the three harvests), while banded-PR resulted in a RAE of 44%. The use of broadcast PR and banded TSP were a feasible alternatives which delivered high yields in the first harvest and provided a good residual effect in the next 2 years. Compared to TSP alone, similar soybean yields could be obtained with granulated mixes of TSP and PR having a water solubility that was 60% of TSP alone. Combining of P sources, with the objective to obtain lower P fertilizer solubility, seems to be a feasible agronomic and economic alternative for soybean crops. Brazil 52