Eficiência agronômica de fontes alternativas de fósforo

Abstract

Brazil has an important role in the production of phosphorus (P) sources since phosphate minerals are finite. Moreover, the raw materials for the production of phosphate fertilizers present low quality, demanding the use of technologies that can turn fertilizers more expensive; however, there are some options to reduce this cost, making viable the use of alternative sources. Therefore, this study evaluated the agricultural efficacy of alternative sources of phosphate fertilizers in savanna soils cultivated with maize and of alternative sources in sugar cane. Two experiments were done in the greenhouse, in clayey and sandy soils. Treatments were P sources (triple superphosphate standard treatment, decanted phosphate, precipitate phosphate, mealed partially calcinated acidifyed phosphate and the and granulated one, and natural phosphate alvorada), and P doses (200 or 400 kg ha-1 P2O5) plus a control treatment, consisting in no phosphate fertilizer application. Most of the alternative P sources applied in total area presented higher soil P contents, dry matter and P accumulation than triple superphosphate in maize. Decanted phosphate, precipitate phosphate, mealed and granulated partially calcinated acidified phosphate presented greater relative agricultural efficacy (RAE) than triple superphosphate in both maize crops and soil types evaluated. The extractors Mehlich1 and Resin super estimated P availability for plants, in soils fertilized with mealed and granulated partially calcinated acidified phosphate and with natural phosphate alvorada. For the field experiment with plant cane, treatments consisted of P sources (triple superphosphate standard treatment, decanted phosphate, precipitate phosphate, mealed partially calcinated acidified phosphate, and the granulated one), and doses (200 or 400 kg ha-1 P2O5) plus the additional treatment (control), consisting of the lack of phosphate fertilizer. It was observed that the P sources evaluated (triple superphosphate, decanted phosphate, precipitate phosphate, mealed partially calcinated acidified phosphate, and the granulated one) when applied at the bottom of plant cane furrow did not resulted in differences in stalk and sugar production in the first harvest of cane; however, there was an increase in relative agricultural efficacy with inceasing P dose with decanted and precipitate phosphates, mealed partially calcinated acidulated phosphate, and the granulated one. Application of P2O5 at 200 kg ha-1 via triple superphosphate resulted in greater profitability per hectare in comparison to the alternative P sources. However, when applying P2O5 at 400 kg ha-1, the treatment of greater profitability per hectare was decanted phosphate.