Agronomic effectiveness of rock phosphate combined with nitrogen sources in spot application: A pot experiment

• Published in: Journal of plant nutrition and soil science 2017-10, Vol.180 (5), p.585-593
• Main Authors: Valadares, Rafael V., Cantarutti, Reinaldo B., Mattiello, Edson M., Vieira, Rogério F.
• Format: Article
• Language: English
• Subjects: Agronomy; Ammonium; Ammonium sulfate; Apatite; Bioavailability; compound fertilizer; Compound fertilizers; Corn; Dissolution; Fertilizers; Granulation; Limestone; Minerals; monoammonium phosphate; Nitrogen; Nitrogen sources; P uptake; pH effects; Plants (botany); Potassium nitrate; Rock phosphate; Rocks; Soil chemistry; Soil pH; Soils; Solubilization; Sulfates; Urea; Zea mays
• ISSN: 1436-8730; 1522-2624
• DOI: 10.1002/jpln.201600037

Rock phosphate (RP) shows reduced dissolution in soils amended with limestone and when applied through spot application. A simple way to improve RP efficiency under these unfavorable conditions may be the combination with nitrogen (N) fertilizers which can increase the solubilization of apatite minerals and/or stimulate P uptake. In this context, we evaluated the agronomic effectiveness of a RP from Bayóvar, Peru (BY), combined with different N sources in spot application, in a clayey Oxisol (Typic Hapludox). The pot experiment consisted of a factorial scheme (3 × 2 × 2+4) in randomized block design with four replications. Treatments consisted of BY combined with three N sources (ammonium sulfate–BY+AS; urea–BY+U; potassium nitrate–BY+KN), in two forms (granulated or powdered), and in two N : P molar ratios (0.5 : 1.0 or 1 : 1) and four additional treatments [control: without P; monoammonium phosphate (MAP); powdered BY; granulated BY]. The products were incorporated into a 50 cm3 cylindrical soil volume (central and upper position in the pot: diameter 17 cm and height 15 cm) with three maize plants (Zea mays L.). Above‐ground biomass was sampled after 42 d after sowing, analyzed for N and P concentrations to calculate N and P uptake. Soil samples were taken from the cylindrical soil volume and measured for RP dissolution (ΔCa index), P availability (P‐resin index), and soil pH. Application of MAP increased soil P availability about 11 times compared with BY treatments. As a result, maize plants grew 3.8 times and absorbed 7.3 and 3.3 times more P and N compared to those fertilized with BY combined with N fertilizers. Compound fertilizers BY+AS and BY+KN had the same effect on N and P uptake, presenting an effectiveness about 12 and 19% greater than pure BY, respectively. Compound fertilizers with BY+AS were more effective in powdered form (with no N/P ratio effect), while BY+KN was more effective in granulated form and in 1 : 1 N : P ratio. BY+U combinations were less efficient in promoting plant P bioavailability than the other N sources. We conclude that Bayóvar RP has a low agronomic effectiveness for spot application, even when combined with N.