RESUMO Avaliou-se o efeito residual de fosfatos sedimentares associado a doses anuais de fósforo em milho cultivado em um Cambissolo com elevado teor de cálcio trocável e pH 6,0. O delineamento experimental foi em blocos casualizados com parcelas subdivididas em faixa. As parcelas principais foram o fosfato de rocha de Bayóvar, o fosfato de rocha Itafós, o superfosfato triplo e um tratamento controle, sem aplicação de fosfatos. Estas fontes foram aplicadas a lanço e incorporadas no solo dois anos antes do presente estudo, com dose equivalente a 200 kg de P2O5 ha-1 e não houve preparo de solo nos anos subsequentes. Nas subparcelas, foram aplicadas as doses de 0, 60 e 120 kg de P2O5 ha-1 ano-1 através de superfosfato triplo no fundo do sulco de semeadura. O teor foliar de P, a produtividade de grãos e fósforo no solo pela resina de troca iônica foram avaliados. As diferenças na concentração de fósforo foliar entre os tratamentos com as fontes fosfatadas e o tratamento controle reduziram de 2013 a 2015. Em 2013 e 2014, os efeitos residuais dos fosfatos de rocha influenciaram a produtividade quando não houve aplicação anual de fósforo. Em 2015, a produtividade nos tratamentos com os fosfatos de rocha não foi superior ao controle, mas também não diferiu significativamente do superfosfato triplo. O teor residual de P no solo, extraído pelo método da resina, foi maior no tratamento com Itafós, entretanto, para esta fonte, a correlação entre o teor de P no solo e a produtividade foi fraca.
ABSTRACT It was evaluated the residual effects of sedimentary phosphates associated with the annual application of phosphate on maize grown in Inceptisol soil with a high exchangeable calcium concentration and pH value of 6.0. The experiment was conducted based on a completely randomized block design with strip-split plots. The main plots were treated with Bayóvar rock phosphate, Itafós rock phosphate, or triple superphosphate, while the control received no additional phosphate. The phosphate sources were applied by broadcasting and incorporated in the soil two years prior to the current study at 200 kg of P2O5 ha-1, with no tillage in subsequent years. In the sub-plots, phosphate doses of 0, 60, and 120 kg of P2O5 ha-1 year-1, as triple superphosphate, were applied at the base of the sowing furrows. Leaf phosphorus (P), grain yield, and soil P by ion exchange resin were evaluated. Differences were observed between the leaf P among the plots treated with phosphate sources and the control plot, which declined from 2013 to 2015. In 2013 and 2014, rock phosphate residuals influenced the grain yield when there was no annual application of phosphate. In 2015, grain yields in rock phosphate treatments without annual phosphate application were not superior to those in the control treatment and did not differ significantly from the plots receiving triple superphosphate. Furthermore, it was found that the soil P content extracted by ion exchange resin was higher in the Itafós treatment; however, for this source, the correlation between soil P and grain yield was relatively weak.
