1) The study analyzed the effects of bovine urine and two varieties of Brachiaria grass on soil nitrogen dynamics, microbial activity, and greenhouse gas emissions over a 10-year field experiment in Colombia. 2) Results showed that Brachiaria humidicola produced more biomass and maintained higher populations of beneficial soil microbes like arbuscular mycorrhizal fungi and actinomycetes, compared to Brachiaria mulato and bare soil. 3) The presence of Brachiaria grasses, especially B. humidicola, led to lower nitrification rates and reduced nitrogen losses from urine patches through decreased nitrous oxide and ammonium levels over time.

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.