Nitrogen anticipation in tropical grasses and 15N recovery by upland rice

Author(s)

Isabô Melina Pascoaloto

• Document type: Doctoral Thesis
• Press: Botucatu. 2020-12-01.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agronômicas. Botucatu
• Defense date: 2020-11-17
• Advisor: Carlos Alexandre Costa Crusciol; Carlos Antônio Costa do Nascimento

Abstract

Rice is one of the most consumed cereals globally and upland rice production has gained prominence due to its low demand for water resources. Nitrogen is one of the main nutrients influencing rice yield, but despite extensive study, the N soil dynamics in different crop systems are still poorly understood. In this work, the technical and economic feasibility of the early application of nitrogen fertilizer, (15NH4)2SO4, for upland rice in grass-rice succession under a no-till system were evaluated. Upland rice was sown in areas previously occupied by Urochloa brizantha or Urochloa ruziziensis. The experimental design was split-plot in a completely randomized block design with four replications in a 4 x 2 factorial scheme: four nitrogen fertilization management strategies and two grass species. The four nitrogen fertilization management strategies were N fertilization (90 kg N ha-1) applied to the living cover crop 10 days before chemical desiccation (A1), N fertilization (90 kg N ha-1) applied 1 day before rice sowing (A2), N fertilization (90 kg N ha-1) applied at rice tillering (C), and no extra N applied (0 kg N ha-1) (T). Soil physical and chemical characteristics, nitrate and ammonium ratios, soil mineral and organic N, soil total N and C, N in microbial biomass, straw decomposition and N release, rice productivity, N content in grains and aerial part of rice and the Urochloa straw, and 15N recovery in the system were analyzed for the two years of the experiment. For these analyses, soil samples were collected at five different times each year: before the beginning of the experiment, at the time of grass desiccation, at rice sowing, at rice tillering, and at rice harvest. Rice yield did not differ among treatments A1, A2, and C. Rice yield was higher in succession to U. brizantha. N fertilization in advance resulted in higher N availability to rice during its initial development. Nitrate and ammonium accumulation in the soil were higher when upland rice was sown over U. brizantha. N immobilization by the soil microbiota was not consistently increased by N fertilization before rice sowing, but it was influenced by Urochloa species. 15N recovery was not affected by Urochloa species but was higher in rice plants in treatment C than in treatments A1 and A2. (AU)

• FAPESP's process: 17/10226-7 - NITROGEN FERTILIZATION ANTECIPATION IN FORAGE AND 15N RECOVERY BY UPLAND RICE.
• Grantee: Isabô Melina Pascoaloto
• Support Opportunities: Scholarships in Brazil - Doctorate