1. Simulated Sorghum Grain and Biomass Yield, Water Use, Soil Erosion and Carbon Evolution, and Potential Ethanol Production in Central and South Texas Manyowa N. Meki 1, Armen R. Kemanian 1, Evelyn Steglich 1, Wyatte Harman 1, Giovanni Piccinni 2 and Thomas Gerik 1 1 Blackland Research and Extension Center, Texas Agricultural Experiment Station, 720 East Blackland Road, Temple, Texas 76502-9622 2 Uvalde Agricultural Research and Extension Center, Texas Agricultural Experiment Station, 1619 Garner Field Road, Ulvalde, Texas 78801-6205  Bioenergy crops are an attractive alternative to traditional cropping systems with potential economic and environmental benefits.  Grain sorghum can be a suitable crop for ethanol and biomass production in central and south Texas because of its high yield potential, water use efficiency, tolerance to abiotic stresses, and because Texas growers have ample experience managing this crop.  One bushel of grain sorghum produces the same amount of ethanol as one bushel of corn (~2.6 gal bushel -1 ).  Currently about 12-20% of the US grain sorghum crop goes into ethanol production and its co-products. Introduction  Simulate grain sorghum and biomass production for typical central and south Texas sorghum cropping systems using the biophysical model EPIC;  Evaluate potential ethanol production for central and south Texas; and  Assess sorghum cropping systems environmental impact. Objectives EPIC Model Simulations – A total of 2398 simulations were made for several dryland and irrigated sorghum cropping systems, over a 45 year time series (1961-2005), 28 central and south Texas counties, and 148 soils, considering 73 weather stations. EPIC provides daily, monthly, seasonal, and yearly information for crop growth, yield, nutrients uptake, hydrological processes, carbon and nutrient cycling, and erosion. Management systems and conservation practices were selected using the NRI database. EPIC Model Testing – The Sorghum Variety Trials data from the Texas A&M Ag Program was used to test a unique set of crop parameters representing grain sorghum hybrids grown in Texas. Within each year and location, the average yield of the top three yielding hybrids was used for testing; management practices were as described for each trial. Methods Results: Simulated Environmental Impacts Results: Potential Ethanol Production in Central and South Texas Results: Model Testing Figure 1. Simulated and measured sorghum grain yield in dryland and irrigated systems. Future Activities  Compute the net energy value for grain- and biomass-based energy production systems.  Assess the global warming potential for each production system. Funds provided by the Great Plains Sorghum Improvement and Utilization Center at KSU. Project Director Michael Tuinistra, TAES representative Mark Hussey. Results: Simulated Sorghum Grain and Biomass Yield for Dryland and Irrigated Systems Figure 2. Simulated grain sorghum yield and biomass production.  Realistic estimates of sorghum grain yield and biomass production can be obtained from long-term simulation studies.  Additionally, the environmental impact of different cropping systems and their spatial and temporal variability can be obtained in a cost-effective way using comprehensive simulation models such as EPIC. Figure 3. Biomass and grain yield of sorghum in response to growing season evapotranspiration (ET) for dryland (left panel) and irrigated (right panel) crops. Figure 5. Average yearly change in soil carbon in 610 combinations of soils and cropping systems in Central Texas simulated with EPIC, which uses the Century soil carbon modeling approach. Conclusions Figure 4. Sorghum area simulated in each county (A), grain yield in dryland (B) and irrigated (C) conditions, and estimated ethanol production if 100% of the harvested grain were directed to ethanol production. RunoffLateral Sub-Flow PercolationNitrogen Volatilization DenitrificationNO 3 and NH 4 in Percolation mmKg N ha -1 Central TXAvg 42 81971812 24 Min 1 1 65 1 0 1 Max140484933231144 St Dev 29 7 85 5 8 26 South TXAvg 59 422918 5 16 Min 0 1 36 6 0 0 Max261295543428114 St Dev 53 3108 5 7 16 Valley TXAvg 26 213217 214 Min 0 1 5 8 0 1 Max 84 9252271795 St Dev 23 2 52 4 420 Table 1. Summary of hydrological and nitrogen related losses for three regions in Texas. Preliminary soil carbon simulation With the current parameter settings EPIC overestimates carbon turnover rate. The slow (passive) pool is at equilibrium for soils ~86 (0) Mg C ha -1 ; the model needs to be re-parameterized to properly simulate carbon and nitrogen processes. Blackland Research & Extension Center Texas Agricultural Experiment Station Texas A&M University System