Soil P Diffusion and Availability Modified by Controlled-Release P Fertilizers
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ORIGINAL PAPER
Soil P Diffusion and Availability Modified by Controlled-Release P Fertilizers Marcelo R. Volf 1 & Ciro A. Rosolem 2 Received: 6 July 2020 / Accepted: 29 September 2020 # Sociedad Chilena de la Ciencia del Suelo 2020
Abstract Slow-release fertilizers have been proposed as tools to increase P fertilizer use efficiency in tropical acidic soils with high P adsorption, low P availability, and mobility. However, results have been controversial since soil diversity and the fertilizer itself may influence the results, which is not completely understood. Soil P diffusion and availability were studied in soils with different P fertilization histories, where triple superphosphate (TSP) and single superphosphate (SSP) coated with a polymer or with humic acid and complexed with humic acid were applied under laboratory conditions. No difference in soil P availability and diffusion was observed between humic acid–complexed, polymer, and humic acid–coated TSP and conventional TSP. For SSP, soil P availability was 15 to 30% lower in the region of application for the polymer and 0 to 16% for the humic-coated fertilizer. For the polymer-coated SSP, P diffusion was lower in some soils. With both base fertilizers, the soil adsorption capacity was more determinant of P diffusion than the protection of the fertilizers. Coating P fertilizers with polymer and complexing or coating the fertilizer with humic acid does not increase P availability or diffusivity in soil since these processes are driven mainly by the soil characteristics. Therefore, the potential of these controlled-release P fertilizers in increasing P use efficiency is low. Keywords Phosphate fertilizer . Slow release . P adsorption . Polymer . Humic acid
1 Introduction The orthophosphate ion H2PO4- is the main form of P taken up by plants; however, its availability and mobility in tropical, acidic soils are very low due to the physical-chemical mechanisms binding it to the colloid surface. As plants take up the nutrient which is closer to the roots and P movement in soil is very slow, a depletion zone is established in the rhizosphere and plant nutrition is impaired (Hinsinger 2001). Therefore, to overcome these constraints, phosphate fertilizer is applied in higher amounts than the plant requires, leading to low P utilization efficiency. Furthermore, the use of high rates of fertilizer is not advisable for a critical nutrient with potential environmental risk and volatile prices (Withers et al. 2018). A
* Ciro A. Rosolem [email protected] 1
Department of Agronomy, Western São Paulo University, Rod. Raposo Tavares, km 572, Presidente Prudente, SP 19067-175, Brazil
2
Department of Crop Science, School of Agricultural Sciences, São Paulo State University, Av Universitária, 3780, Botucatu, SP 18604-034, Brazil
strategy proposed to improve phosphorus use efficiency (PUE) is the use of controlled-release or slow-release P fertilizers (Shaviv 2001). The slow release of the nutrient as the crop cycle progresses in synchrony with plant demand minimizes th
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