Water productivity of irrigated corn in Nebraska

1. Water productivity of irrigated corn in Nebraska Patricio Grassini Research Assistant Professor University of Nebraska-Lincoln “This cornfield, and the sorghum patch behind the barn, were the only broken land in sight. Everywhere, as far the eye could reach, there was nothing but rough, shaggy, red grass” Willa Cather (My Antonia, 1918), novelist from Red Cloud NE Water roundtable meeting Oct 9, 2013

2. Water and stability 2000-2009 average yields and coefficient of variation by county for maize and soybean in Nebraska (USDA-NASS) Grassini et al., In Press Grassini, unpublished Assured water supply greatly increases yield and reduces year-to- year variation in yield. Irrigated agriculture attracted investment in livestock feeding operations, biofuel refineries, and manufacturing of irrigation equipment.

3. Water-food nexus • We need water to produce high and stable grain yields • Appropriate metrics that account for both crop production and water use are needed in the discussion about water & agriculture. • Water Productivity (WP, kg grain per inch of water supply) provides a good framework for the discussion

4. Rainfed Irrigated Developing a WP benchmark for corn in NE • Yields were simulated over 20-y for 18 locations in western Corn Belt using Hybrid-Maize model. • Crops assumed to grow under optimal conditions (no nutrient deficiencies and no incidence of pests, diseases, weeds). • Model inputs based on actual sowing date, plant population, weather, and soil properties at each of the 18 locations. Grassini et al. (2009) *Available soil water (0-5 ft) at planting + planting-to-maturity rainfall + applied irrigation

5. Validation of Mean Water Productivity Function Crops grown with adequate nutrient supply and without loss from diseases, insect pests, and weeds Grassini et al. (2011)

6. 225 bu/ac 3) Higher yields with less irrigation water 1) Higher yields, same water supply with better crop mgmt 160 bu/ac 2) Less water, same yield with improved irrigation mgmt 24 in 33 in Framework to diagnose and identify options to improve water productivity in farmers’ fields 270 WP boundary slope =11 bu ac-in-1 225 180 Grain yield (bu ac-1) 135 90 Mean WP function slope = 8 bu ac-in-1 45 0 0 10 20 30 40 50 Seasonal water supply (in)

7. 777 field-year observations from irrigated maize fields in central Nebraska (2005-2007) Tri-Basin Natural Resources District Stars indicate weather stations ( ) or rain gauges ( ) Each circle represents a producer field Grassini et al. (2011)

8. 280 PIVOT n = 516 240 200 160 Maximum yields WP = 6.0 bu ac-in-1 ~245 bu ac-1 120 15 25 35 45 55 Grain yield (bu ac-1) SURFACE 280 n = 261 240 200 Water requirement for maximum yield ~ 36 in 160 WP = 5.3 bu ac-in-1 120 15 25 35 45 55 Seasonal water supply (in) Water productivity (WP) in the Tri-Basin NRD Producer-reported yields in Tri-Basin NRD, 2005-2007. Each data point corresponds to an irrigated corn field. 280 n = 777 240 200 WP boundary 11 bu ac-in-1 160 Grain yield (bu ac-1) 120 Average farmer’s WP = 5.8 bu ac-in-1 80 40 Mean-WP function slope = 8 bu ac-in-1 0 0 5 10 15 20 25 30 35 40 45 50 55 Seasonal water supply (in)

9. Optimal irrigation 33,252 ac-ft yr-1 20,639 ac-ft yr-1 Limited irrigation Actual Surface Actual Pivot 37,819 ac-ft yr-1 Opportunities to reduce applied irrigation water substantially without reducing productivity 288 Reported yield and actual water supply under pivot (  ) and gravity ( Δ ) irrigation systems. 11 bu ac-in-1 8 bu ac-in-1 256 ■ Simulated yield under fully-irrigated conditions (irrigation based on ETO and phenology) 224 Grain yield (bu ac-1) ● Simulated yield under limited-irrigation management (75% of fully-irrigation except during the interval around silking when the crop was fully-irrigated) 192 160 Total saving: 91,710 ac-ft y-1 (~32% of current water use in corn!) Energy saving equivalent to annual electrical use of 4,300 houses in NE! 128 16 24 32 40 48 56 Grassini et al. (2011) Seasonal water supply (in) Large scope to save irrigation water, without hurting yield, through replacement of existing surface systems by pivots and fine tuning adjustment of irrigation schedule

10. Benchmarking yield and efficiency of corn & soybean cropping systems in Nebraska Patricio Grassini, Jessica A. Torrion, Kenneth G. Cassman, James E. Specht Collaborators: Jenny Rees (UNL Extension Educator) & Daryl Andersen (Little Blue NRD)

11. Nebraska Natural Resources Districts (NRD) data Data on yield, N fertilizer rate, and irrigation water annually reported from 10,000+ fields since 2004 20 of 23 NRDs collaborating on this project

12. On-farm data survey Data from 1030 dryland and irrigated fields in NE planted with corn and soybean in 2010, 2011, and 2012 Collected data include: field coordinates, yield, applied NPK fertilizer, lime and manure and time of application, irrigation, type of irrigation system, tillage system, crop rotation, planting date, crop maturity, plant density, pesticide rates and time of application, incidence of diseases and insects.

13. Website:www.yieldgap.org

14. Thanks! Questions?