Location: Global Change and Photosynthesis Research
Project Number: 5012-21000-030-005-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Jun 1, 2016
End Date: Feb 15, 2020
Objective:
Test three hypotheses comparing Patch Burn Grazing (PBG) and Lost Residue Grazing (LRG) in Subtropical Humid Grasslands (SHG): H1 forage production and quality will increase under PBG; H2 the greenhouse gas (CO2, CH4, N2O) sink strength will be greater under PBG; and H3 water use efficiency will be higher under PBG. These hypotheses will be tested in two pasture types' improved pasture (Paspalum notatum) and semi-native pasture with mixed C4 native grasses.
Approach:
The 4-year study will be conducted in experimental pastures at the MacArthur Agro-ecology Research Center (MAERC), a 3,000-head cattle ranch in south central Florida recently designated as part of a USDA Long-Term Agro-Ecosystem Research LTAR site. We will utilize four existing eddy flux towers (CO2 & CH4) installed in February, 2013, in four LRG improved and semi-native pastures. Two pastures of each improved (~40 ha) and semi-native (~ 64 ha) will be assigned to PBG or LRG. Semi-native pastures will be grazed during winter dry seasons and improved pastures during summer wet seasons. PBG treatment: burn spatially distinct patches (~30% of eddy tower footprint/annum) + free access cattle grazing. LRG treatment: burn before experiment then no burning + free access cattle grazing. Stocking density will be 1.0 ha AU-1 in improved and 1.6 ha AU-1 in semi-native. A flux tower with CO2 & CH4 sensors will be located strategically in each of the four pastures. The eddy covariance technique will be used to assess greenhouse gas (GHG) balance and water use efficiency; pretreatment data will be collected prior to PBG or LRG implementation. N2O data will be collected using the static chamber method and will be gap filled to obtain annual N2O estimates. Plant species composition and forage production will be measured using moveable-cages in each tower footprint. Biomass will be analyzed for crude protein and in-vitro dry matter digestibility. The performance and financials of cattle herds allocated to each treatment will be analyzed using Standardized Performance Analysis metrics. The potential interactions between management practices (PBG vs. LRG) and variation in climate will be determined with a process-based biogeochemical model.
