Abstract
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.
Highlights
Broadcast and incorporated application of rock phosphates can be used to enhance soil phosphorus (P) availability and reduce the doses of phosphate applied annually to crops as soluble fertilizer (Novais et al, 2007; Sousa et al, 2009)
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
In 2013, the leaf P concentration was affected by broadcast and incorporated phosphate application (p ≤ 0.01) and annual application of phosphate doses (p ≤ 0.01) independently, whereas in 2014 and 2015, it was significantly influenced by annual application of phosphate doses (p ≤ 0.01)
Summary
Broadcast and incorporated application of rock phosphates can be used to enhance soil phosphorus (P) availability and reduce the doses of phosphate applied annually to crops as soluble fertilizer (Novais et al, 2007; Sousa et al, 2009). Few studies have evaluated the suitability of this fertilization technique for annual crops (Vasconcellos et al, 1986; Lange et al, 2016) Owing to their higher solubility, sedimentary rock phosphates are more suitable for direct application to soils than igneous phosphates (Rajan et al, 2004). In the Brazilian Northeast, Souza et al (2014) observed that broadcast and incorporated applications of sedimentary phosphates to an Inceptisol soil (with an exchangeable Ca2+ equal to 13.5 cmolc dm-3 and pH value of 6.0) reduced the triple superphosphate dose required at maize sowing for two years after their application. A high exchangeable calcium concentration and pH value greater than 5.5 are potentially unfavorable to rock phosphate dissolution (Chien & Menon, 1995; Junio et al, 2013)
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