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Characterization of N Dynamics and Soil Microbial Communities as a Result of Biological Nitrification Inhibition by Brachiaria Grasses

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Brachiaria spp. are the most widely planted tropical forage with niches from Southeast
Asia, Sub-Saharan Africa, Latin American and the Caribbean. This tropical forage grass have a mechanism known as biological nitrification inhibition (BNI) able to inhibit nitrifiers activity. This study analyzes the behavior of inorganic N dynamics, microbial activity and CH4 and N2O in Brachiaria spp. on a tropical pasture.

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Characterization of N Dynamics and Soil Microbial Communities as a Result of Biological Nitrification Inhibition by Brachiaria Grasses

  1. 1. Introduction § The study is located on a 10 years long term field experiment in the International Center for Tropical Agriculture (CIAT) at Palmira Valle of Cauca, Cali, Colombia. Soil at the experimental site is classified as a Mollisol with a silt clay loam texture with clay content of 40–60% in the plough layer. § The experiment was and in situ incubation organized as a completely randomized block design with three replicates. § Bovine urine was collected, sealed and storage at 5oC until applied. Before application the urine was mixed, and applied at a rate of 1L. § Gas sampling- static chamber method § in 15 min interval 45 min. Samples were taken during 1 hr, and 1, 2, 3, 7, 10, 14, 17, 21, 25, 28, 32, 35, 39 and 42 days after urine application (AUA); and analyzed for CO2, CH4 and N2O using the Hutchinson-Mosier method and linear equations (Pedersen et al., 2010). § Biomass was harvested on a 15 days basis AUA. § Soil inorganic N (NH4 + and NO3 -) concentrations were determined at depth 0-5 during 2, 4, 7, 28 and 56 AUA. § Soil nitrification rates were determined within 0-5 cm soil depth before urine application (BUA) and 7, 28 and 56 AUA. § Phospholipid fatty acid analysis (PLFA) was extracted from the first 0-5 cm of soil, BUA and 28 AUA, using a modification of the Bligh and Dyer (1959) extraction (White and Rice, 2009). § Statistical Analysis System (SAS) 9.3 was used to analyze results using an analysis of variance (ANOVA) method (α=0.05) and a Post-hoc comparisons with Tukey at α=0.05. This study analyzes the behavior of inorganic N dynamics, microbial activity and CH4 and N2O in Brachiaria spp. on a tropical pasture in order to: 1. Determine an quantify soil inorganic N dynamics and soil microbial community as a result of the BNI on two Brachiaria grasses 2. Quantify BNI capacity for reduce N losses in the soil from cattle urine patches. Characterization of N Dynamics and Soil Microbial Communities as a Result of Biological Nitrification Inhibition by Brachiaria Grasses Johanie Rivera-Zayas1*, Ashly Arevalo2, Catalina Trujillo2, Sandra Loaiza2, Ngonidzashe Chirinda2, Jacobo Arango2, Charles W. Rice1* 1 Department of Agronomy, Kansas State University, Manhattan, KS; 2International Center for Tropical Agriculture, Cali, Colombia Corresponding author: johanie@ksu.edu, cwrice@ksu.edu Objectives Methodology Results Experiment Highlights Acknowledgements 50 150 250 350 450 DryBiomasskgha-1 Date BH CO BH UR MH CO MH UR Dr. Vara Prassad- Kansas State University Dr. Nelson Vivas and Dra. Sandra Morales - Universidad del Cauca in Popayán, Colombia Main Factor Secondary factor Bare soil (BS) Control (CO) Cattle Urine (UR) Brachiaria humidicola 16888 (BH) Control Cattle Urine (UR) Brachiaria mulato hybrid 1 (MH) Control Cattle Urine (UR) -2.000 0.000 2.000 4.000 6.000 8.000 gN2Oha-1day-1 Date BS CO BS UR BH CO BH UR MH CO MH UR -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 gCH4-Cha-1day-1 Date BS CO BS UR BH CO BH UR MH CO MH UR 0 2 4 6 8 10 12 14Nitrificationrates (mgN-NO3-kg-1soil /day-1) Date BS-CO BS-UR BH-CO BH-UR MH-CO MH-UR Brachiaria spp. are the most widely planted tropical forage with niches from Southeast Asia, Sub-Saharan Africa, Latin American and the Caribbean. This tropical forage grass have a mechanism known as biological nitrification inhibition (BNI) able to inhibit nitrifiers activity. On grazing systems were hotspots of nitrogen (N) concentration from bovine urine deposition generally exceeds plant N uptake rates resulting in environmental losses by leaching and gas emissions the BNI on the Brachiara enhances N utilization in soils, reduces NO3 - leaching and minimizes N2O emissions minimizing the environmental footprint of cattle grazing systems. Results 0.00 15.00 30.00 45.00 60.00 N-NO3 -mgkg-1soil Date BS-CO BS-UR MH-CO MH-UR BH-CO BH-UR Fig. 6. This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 2013-69002-23146 from the USDA National Institute of Food and Agriculture Subbarao et al., 2009 0 10 20 30 40 50 BH MH BS Totalmicrobialcommunity (nmolPLFA/gsoil) Soil Cover 0 10 20 30 40 50 60 70 80 90 0 5 10 15 20 25 30 35 40 45 Precipitation(mm) Temperature(C) Precipitation Temperature Fig. 1. Temperature and precipitation patterns during the incubation. Fig. 2. B. humidicola 16888 produce 20% more biomass compare to B. mulato hybrid 1. Drought for a 15 days period decrease biomass growth rate by 46%. Fig. 4. Fluxes of CH4 in Brachiaria sp. grasses showed higher CH4 emissions after precipitation, and high uptake after dry periods. B. humidicola 16888 CH4 were significantly higher than B. mulato hybrid 1 and bare soil . Fig. 3. Brachiaria grasses interaction with UR and time showed higher N2O emissions, specially after precipitation over time. 0.00 15.00 30.00 45.00 60.00 N-NH4 +mgkg-1soil Date BS-CO BS-UR BM-CO BM-UR BH-CO BH-UR Fig. 5 and Fig. 6. Highest NH4 + concentration was immediately after UR application, followed by a decrease of 48% over time. Soil cover interaction with UR and time showed highest NO3 - available during 28 days AUA on bare soil with UR, followed by a decreased of 87% on soil with Brachiaria sp. grasses with UR, with no significant difference between B. humidicola 16888 and B. mulato. Fig. 7. A significant interaction between soil cover, urine and time showed a decrease on 49% from the Brachiaria sp. Grasses, compare to bare soil after urine application. 0 0.5 1 1.5 2 2.5 BH MH BS Arbuscularmycorrhizal fungi (nmolPLFA/gsoil) Soil Cover Fig. 9. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 T1 T11 T1 T11 T1 T11 BH BS MH Actinomycetes (nmolPLFA/gsoil) Fig. 10. Fig. 8. Long term soil cover (10 yr) from Brachiaria grasses increase soil microbial community by 80% compare to bare soil. Fig. 8. Fig. 5. Fig. 9. Arbuscular mycorrhizal fungi is 32% higher in B. humidicola 16888 than in B. mulato, and than bare soil. Fig. 10. On Brachiaria grasses Actinomycetes showed a decreased over time, with higher values from the B. humidicola. ü The long term use of Brachiaria grasses as soil cover maintain microbial population. ü Brachiaria humidicola 16888 produce more biomass, have lower nitrifications rates, and create proper soil conditions for higher population of arbuscular mycorrhizal fungi and actinomycetes. ü Nitrogen from cattle urine affect N2O and CH4 dynamics over 35 days after applications; the variability is also affected by weather conditions and soil cover. This study was undertaken as part of the LivestockPlus project funded by CGIAR Research Program (CRP) on Climate Change, Agriculture and Food Security (CCAFS), which is a strategic partnership of CGIAR and Future Earth. In addition, this work was also done as part of the Livestock CRP. We thank all donors that globally support the work of the program through their contributions to the CGIAR system.

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