Ammonium-fertilizer application increases phosphorus use efficiency in maize

Author(s)

Elialdo Alves de Souza

• Document type: Doctoral Thesis
• Press: Botucatu. 2017-07-04.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agronômicas. Botucatu
• Defense date: 2017-02-13
• Advisor: Ciro Antonio Rosolem

Abstract

Ammonium application can improve phosphorus use efficiency (PUE) and the development of maize plants, especially in tropical soils, usually acids and P-limiting. The aim of this study is evaluate how ammoniacal fertilization impacts the P use efficiency (PUE), the biochemical conditions of the rhizosphere, the root morphology and the development of maize plants. Two initial experiments were carried on greenhouse, the first one in pots of 20 L and the second one in Plant Growth Containers (PGCs), using soil after liming and fertilized according to the following treatments: 3 (nitrogen fertilization: ammonium only, nitrate only and both) x five doses of phosphate (0, 40, 80, 120 and 160 mg P kg-1 of soil). At 35 days after emergence the roots were removed from the containers and pots and the plant and soil samples were collected for analysis. The rhizosphere soil in experiment I was obtained by "shaking-washing" and in the experiment II by "layer slicing". Four of the eight soil replicates were fresh frozen (analyzes: ammonium, nitrate, organic C and microbial P) and four of them were dried (analyzes: chemical fractionation of P and pH). Plant samples were weighed and analyzed for P content. The experiment III was carried on a system of nutrient solution scanners according to the treatments: 2 (ammonium or nitrate) x (high or low dose of P), with 10 replicates. Images were obtained in daily basis for the evaluation of root development. At the end of the tests, fresh and dry weights and P content were obtained. Data of different root traits were used to draw the average plant on the RootBox. The treatments with ammonium and nitrate + ammonium, plus the highest dose of P in the experiment I or at all doses in the experiment II, resulted in higher dry matter yield, lower root ratio: aerial part, root development adequate for P absorption, higher P recovering, higher ammonium, nitrate and N-mineral accumulation in the nearest layersto the rhizoplane, lower pH, greater mobilization of less labile P forms, higher mobilization of geochemical and biological P. There were differences between rhizospheric and bulk soils and between the different layers of the rhizosphere, for all parameters and treatments. Ammonium and nitrate + ammonium resulted in higher organic C water soluble organic C, and higher dose of triple superphosphate resulted in higher amount of P in the microbial fraction. Ammonium resulted in a branched root with a greater number of lateral roots. Ammonium improves the use efficiency, solubility, mineralization and uptake of P, due to chemical and biological changes in the rhizosphere and root architecture in the early stages of corn development. (AU)

• FAPESP's process: 13/18870-1 - LOCALIZED APPLICATION OF AMMONIA FERTILIZER AS STRATEGY TO IMPROVE THE EFFICIENCY OF THE USE OF PHOSPHORUS IN CORN.
• Grantee: Elialdo Alves de Souza
• Support Opportunities: Scholarships in Brazil - Doctorate