ORIGINAL PAPER Enhancing Wheat and Soybean Yields in a Subtropical Oxisol Through Effective P Fertilization Strategies Jessé Fink 1 & Gianluca Borga 1 & Gustavo Frosi 1 & Clovis Pierozan Junior 1 & Christiano Santos Rocha Pitta 1 & Antonio Rafael Sánchez-Rodríguez 2 Received: 1 November 2019 /Accepted: 17 March 2020 # Sociedad Chilena de la Ciencia del Suelo 2020 Abstract Phosphorus (P) deficiency limits agricultural production in tropical and subtropical soils, where soil mineralogy is dominated by kaolinite, iron, and aluminum oxides. The aim of this work was to compare two application methods of P, to the soil surface and to the sowing line, to determine the most effective strategy to increase wheat and soybean yields on an oxidic subtropical soil in Brazil under field conditions. Additionally, four inorganic P fertilizers (monoammonium phosphate (MAP); single superphos- phate (SS); triple superphosphate (TP); and natural rock phosphate (NP)) in a wheat crop and four different P rates (zero, 0; low, 45; medium, 90; and high, 180 kg ha -1 of P 2 O 5 ) of TP in a soybean crop were tested after being applied to the soil surface and to the sowing line. A significant increase in yield (54%) was only found when TP was applied to the sowing line in comparison with the soil surface in wheat plants, probably due to its high solubility. However, the application method did not produce a significant effect in soybean yields, probably because this crop has a different P requirement and root distribution pattern than wheat. In the case of P fertilizers applied to the soil surface, higher wheat yields were observed with NP and MAP in comparison with TP. Finally, a linear increase was observed in soybean yields while increasing the P rate, finding significant differences between the plants fertilized with the highest P rate and the non-P-fertilized plants (24% yield increase in the first case). Our results highlight the need for specific P fertilization strategies for the different crops grown on subtropical regions where soil mineralogy curbs P availability. Keywords P fertilizers . P application method . P rate . P adsorption . Plant nutrition 1 Introduction Tropical and subtropical soils mainly are acid soils whose mineralogy is dominated by the presence of clay minerals like kaolinite and iron and aluminum oxides/hydroxides (Kämpf et al. 2012). These factors contribute to the limited availability of certain essential nutrients for plants, for example, phosphorus (P) that is strongly adsorbed onto the soil mineral surfaces (Johnson and Loeppert 2006; Santos et al. 2008; Fink et al. 2016a). As a result, P deficiency limits plant growth and agricultural production in these areas (Novais et al. 2007; George et al. 2018). Phosphorus fertilization in soils with a limited P availabil- ity is fundamental to enhance plant yield. However, it requires a deep understanding of soil reactions after P addition. Most of the total P added (up to 90%) is quickly adsorbed onto mineral surfaces (fast adsorption, 1 h), and slowly later (Barrow 1983). Williams and Reith (1971) found that only a small fraction of the P applied to the soil remained available 1 year after its application (8–20%) and it was reduced to a lower amount (2.7%) 6 years later. Furthermore, this situation is aggravated in soils with oxidic mineralogy. Fink et al. (2016b) assessed P desorption in subtropical soils incubated for 30 days and ob- served that soils with a high goethite content desorbed 30% less P than soils with the same Fe oxide contents but with the predominance of hematite. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42729-020-00232-y) contains supplementary material, which is available to authorized users. * Jessé Fink fink1j@gmail.com 1 Laboratory of Soils, Federal Institute of Paraná – Campus Palmas, Palmas, Paraná CEP 85555-000, Brazil 2 Agronomy Department, University of Córdoba, Campus de Rabanales, 14071 Córdoba, Spain Journal of Soil Science and Plant Nutrition https://doi.org/10.1007/s42729-020-00232-y