Evaluation of Potential Water Conservation Using Site-specific Irrigation Kenneth Stone and Phil Bauer USDA-ARS, Florence, SC

JanFebMarAprMayJunJulAugSepOctNovDec ET Total Rain Effective Rain Summer ET exceeds rain mm in Monthly Averages, Water fell behind 228 mm (9 in) from April to July DefIcItDefIcIt 50% Probability of a 20 day drought Why is Irrigation needed in the Southeastern US?

Site-Specific Irrigation Research Fine-scale (1:1200) soil survey in 1984 CP2 on quite variable soil: 12 soil map units CP1 on fairly uniform soil for ¾ of circle

Objective Evaluate the potential water savings using Site-Specific / Variable-Rate Irrigation (VRI) management compared to uniform irrigation management.

Approach Determine the water holding capacity of the 12 soil types. (top 300 mm, 12 in) Gather the weather parameters for calculating crop evapotranspiration (ET c ) Calculate a water balance for each soil type during a corn growing season.

Water Balance S i+1 = S i + Rain i – ET ci – Runoff i - Drainage i If S i > WHC excess is Drainage If S i > Saturation excess is Runoff Where: S = soil water storage ET c = calculated daily evapotranspiration

Treatments Corn –Planting date 3/31 (doy 90) –Ending date 8/6 (doy 218) Weather Data –Florence historical data –ET c calculated using ASCE method. Irrigation –If WHC < 50%, irrigation 12.5 mm Spatial Management Zones –Individual Soils (12 zones) –1 Zone (based on dominate soil type) –Soils grouped based on WHC 2 Zones 4 Zones

Soil Map Units SymbolSoil Classification BnABonneau loamy fine sand (lfs), 0% to 2% slopes CxCoxville loam DnDunbar lfs DoDunbar lfs, overwash ErAEmporia fine sandy loam (fsl), 1% to 2% slopes GoAGoldsboro lfs, 0% to 2% slopes NbANoboco lfs, moderately thick surface, 0% to 2% slopes NcANoboco lfs, thick surface, 0% to 2% slopes NfANoboco fsl, 1% to 2% slope NkANorfolk lfs, moderately thick surface, 0% to 2% slopes NoANorfolk lfs, thick surface, 0% to 2% slopes NrANorfolk fsl, 1% to 2% slopes

Soil Water Holding Capacity 65% difference in WHC between Bonneau to Goldsboro

12 Soil Map Units

Twelve Management Zones Based on Soil Map Unit

Four Management Zones Based on WHC

Two Management Zones Based on WHC

One Management Zone – Uniform Irrigation Based on dominate soil

Soil All Years and Weather Conditions Bonneau 271 A Coxville 240 B Dunbar 249 AB Emporia 249 AB Goldsboro 239 B NbA 252 AB NcA 271 A NfA 261 AB NkA 263 AB NnA 259 AB NoA 265 A NrA 271 A # of Zones 2 Max Diff. 32 Significant Management Zones

Soil Drought (% of ET ref ) All Conditions <50%50 to 60%60 to 75%> 75% Irrigation (mm) Bonneau 318 A290 A277 A213 A271 A Coxville 294 E258 F243 EF177 E240 B Dunbar 301 D268 E249 DE189 D249 AB Emporia 303 D268 E249 DE189 D249 AB Goldsboro 294 E258 F241 F177 E239 B NbA 303 D271 DE251 D196 C252 AB NcA 318 A290 A277 A213 A271 A NfA 313 BC279 BC260 BC205 B261 AB NkA 313 BC283 B260 BC207 AB263 AB NnA 311 C275 CD254 CD205 B259 AB NoA 316 AB283 B264 B208 AB265 A NrA 318 A290 A277 A213 A271 A # of Zones Max Diff Significant Management Zones

Irrigation depth per Management Zone All Years and Weather Conditions Zone # of Management Zones OneTwoFour Irrigation (mm) Difference2636

Irrigation depth per Management Zone Under Drought Conditions Mgt. Zone Drought (% of ET ref ) <50%50 to 60% 60 to 75%>75% # of Mgt. Zones On e Two Four OneTwo Four OneTwo Four OneTwo Four Irrigation (mm) Difference

Conclusions The 20-year overall analysis indicated that only 2 spatial management zones were needed. However, when divided into Drought and non-Drought years, 5 to 6 spatial management zones were identified. Irrigation by spatial management appears to save water, especially in fields with highly variable soils.

Future Evaluation Additional research is needed. Add additional field sites to the analysis Use Crop Simulation Models to evaluate both Yield and Water

Thank You