Evaluating the effect of pasture type and grasing intensity
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2018 SWCS International Annual Conference July 29-August 1, 2018 Albuquerque Convention Center
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Evaluating the effect of pasture type and grasing intensity
- 1. Evaluating the Effect of Pasture Type and Stocking Rate on the Hydrology of Southern Great Plains R Niraula, A Saleh, N Bhattarai, R Bajgain, N Kannan, E Osie, P Gowda, J Neel
- 2. Background • Grassland occupy ~40% of the world's land surface and one of the largest land cover types in the United States. • Native grassland are managed by introducing new forage species for enhancing pasture productivity to feed millions of cattle in the Great Plains of the US. • Water: Fundamental resources that drive the growth of grasses. • Important to understand how the conversion of native to introduced pasture affect the water balance and biomass to ensure both the forage production and water demand in the region.
- 3. Objectives • Validate NTT/APEX for estimating evapotranspiration and biomass of grassland ecosystem • Compare the average annual hydrologic fluxes from native and introduced pasture • Analyze the effect of stocking rate on the hydrologic fluxes of grassland
- 4. Study Area m 0 1000200 600 Introduced Native
- 5. Pasture 11 Pasture 13 Grass type Introduced Native Species Old world bluestem Little/big bluestem Area ~ 64 ha ~ 64 ha Soil type Norge silt loam Norge silt loam Slope 1-3% 1-3% Grazing Yes Yes Fertilizer Yes No Burn Yes Yes Plot Characteristics
- 6. Nutrient Tracking Tool (NTT)
- 7. APEX(Agricultural Policy/Environmental Extender) Spatial Scale: Field/Farm/Watershed Temporal Scale: Daily Figure Source : Wang et al. 2014 Major components of APEX
- 8. Remote Sensing Application • Operational simplified surface energy balance (SSEBop) (Senay et al. 2013) • Spatial Resolution: 1 km • • Automatically calibrated Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC) model (Allen et al. 2007, 2013) • Spatial Resolution: 30 m
- 9. Scenarios Stocking rate class Stocking rate (head/ha) Native Introduced 1 Low 0.25 0.5 2 Medium 0.5 1 3 High 1 2 4 Very High 2 4 Stocking Rate Scenarios • Four stocking rate scenarios (namely low ,medium, high, and very high) on both pastures to understand its effect on the hydrological fluxes
- 10. ET Validation • NTT/APEX was able to simulate the grassland ET with high accuracy at the monthly time scale.
- 11. Biomass Validation R² = 0.74 NSE:0.72 PBIAS:-2% 0 2 4 6 8 10 12 0 2 4 6 8 10 12 SimulatedBiomass(tons/ha) Measured Biomass (tons/ha) Biomass_Native_Pasture R² = 0.74 NSE:0.60 PBIAS=2% 0 2 4 6 8 10 12 0 2 4 6 8 10 12 SimulatedBiomass(tons/ha) Measured Biomass (tons/ha) Biomass_Introduced_Pasture • NTT/APEX was also able to simulate the daily biomass of native and introduced grasses
- 12. 0 100 200 300 400 500 600 700 800 ET Q R WaterFlux(mm/yr) Planting & Harvest Native Introduced 0 100 200 300 400 500 600 700 800 ET Q R WaterFlux(mm/yr) Current Mgmt. Operations Native Introduced Effect of Pasture Type: Hydrology Relatively lower ET and higher Water Yield for Introduced Pasture compared to Native Pasture
- 13. 0 100 200 300 400 500 600 700 800 ET Q R WaterFlux(mm/yr) Low Stocking Rate Native Introduced 0 100 200 300 400 500 600 700 800 ET Q R WaterFlux(mm/yr) Medium Stocking Rate Native Introduced 0 100 200 300 400 500 600 700 800 ET Q R WaterFlux(mm/yr) High Stocking Rate Native Introduced 0 100 200 300 400 500 600 700 800 ET Q R WaterFlux(mm/yr) Very High Stocking Rate Native Introduced Effect of Pasture Type: Hydrology Relatively lower ET and higher Water Yield for Introduced Pasture compared to Native Pasture
- 14. Pasture Average annual ET (2015/2016) Measured APEX METRIC SSEBOP Native 802 797 956 1044 Introduced 711 718 982 1027 (Introduced-Native)% -11% -10% +3% -1.6% ET Comparisons • Both Measured and NTT predicated ET agreed that Introduced pasture loss at least 10% less water through evapotranspiration compared to native pasture.
- 15. Effect of Stocking Rate : Hydrology ET decreases (and thus water yield increases) with increased stocking rate (with in carrying capacity) both the Introduced Pasture and Native Pasture
- 16. 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 Planting & Harvest Current Mgmt. Conditions Sedimentloss(tons/ha) Sediment loss (tons/ha) Native Introduced Native vs Introduced Pasture: Sediment Loss Relatively lower sediment loss though erosion from Introduced Pasture compared to Native Pasture: was one of the primary reason why Introduced pasture was first brought to US because these grasses are more tolerate to erosion from animal grazing
- 17. 0 2 4 6 8 10 12 Pasture Type Yield(tons/ha) Yield Potential (tons/ha) Native Introduced Native vs Introduced Pasture: Forage Yield Higher yield potential for Introduced Pasture compared to Native Pasture
- 18. Conclusions • NTT/APEX can simulate the grassland ET with high accuracy at the monthly time scale. • NTT/APEX makes a reasonable estimates of biomass. • Slightly lower ET from introduced pasture compared to native pasture. • Slightly higher runoff and recharge introduced pasture compared to native pasture. • Decrease in ET (thus increase in runoff and recharge) with increase in stocking rate within pasture’s carrying capacity.
- 19. Thank you Questions, comments and suggestions are welcome
- 20. Grazing limit: 0.01 tons/ha Grazing rate per unit animal: 9.1 kg/day
Editor's Notes
- The three major objectives of the study are to: …………………..I’ll give a brief description of NTT and Apex in the next slide.
- The study sites are located at the United States Department of Agriculture—Agricultural Research Service (USDA-ARS) Grazing Lands Research Laboratory (GRL) in El Reno, Oklahoma. The right plot (aka Pasture 11) is planted with native pasture and the one on the lest aka Pasture 13 is planted with introduced pasture.
- Here are the similarities and dissimilarities in the properties of the two study plots. As I already mentioned Pasture 11 is planted with the introduced gasses (namely old world bluestem) and Pasture 13 is planted with native grasses. Both plots have a similar area of about 64 hector. Both plots are dominated by same soil type which is norge silt loam with aslope of 1-3%. While both the pastures are managed by occasional burning and regular grazing, fertilizers are applied only to introduced pasture.
- The Nutrient Tracking Tool aka NTT an enhanced version of Nitrogen Trading Tool, a user-friendly web-based computer program originally developed by the USDA. NTT is developed by Texas Institute of Applied Environmental Research (TIAER) at Tarleton State University in collaboration with USDA-NRCS. The tool estimates nutrients (nitrogen and phosphorus) and sediment losses from fields managed under a variety of cropping patterns and management practices through its user-friendly linkage to the Agricultural Policy Environmental eXtender (APEX). NTT is evolving and in the current framework it includes suite of models like APEX (Agricultural Policy/Environmental Extender) , FEM (Farm Economic Model) and APLCAT (Animal Production Life Cycle Analysis Tool) which can interact among themselves.
- APEX is a continuous-time, spatially distributed model developed for whole farm and watershed management. The model typically operates on a daily time step. Spatially, farms and/or watersheds may be subdivided into hydrologically connected subareas based on terrain attributes, fields, soil types, landscape positions, or any other desirable configurations. APEX uses watershed information on weather, soils, topography, vegetation, and land management practices such as crop rotation, fertilization, tillage, furrow diking, pesticide application, grazing, terraces, buffer strips, and waterways to simulate watershed processes. The major components in APEX include climate, hydrology, erosion/sedimentation, crop growth, soil temperature, carbon cycling, nutrient cycling, pesticide fate, and routing components. Simulation of liquid waste applications from feeding waste storage ponds or lagoons is also a key component of APEX.
- We also applied two remote sensing approach to compare the ET estimates from APEX and measured ET for the study plots
- We tested four stocking rate scenarios (namely low ,medium, high, and very high stocking rate) on both pastures to understand its effect on the hydrological fluxes. We assume double the stocking rates for Introduced compared to Native pastures based on on the current management practices and literatures.
- Based on measured data, averaged over the two years period of 2015 and 2016, we can see that Introduced has 11% less evaporation compared to native pasture. NTT/APEX was able to simulate the difference pretty well. The average values matches too. But in the case of remote sensing products, While MATRIC showed slightly higher ET for Introduced pasture , SSEBOP showed slightly lower ET for Introduced pasture. And Both the models significantly overestimate the average annual ET for both the pastures when compared to Measured and APEX estimated ET.