Ecohydrology of irrigated silage maize and alfalfa production systems in the Upper Midwest US

Authors: Gamble, Joshua; Baker, John; Dalzell, Brent; Wente, Christopher - Chris; Feyereisen, Gary

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2022
Publication Date: 6/1/2022
Citation: Gamble, J.D., Baker, J.M., Dalzell, B.J., Wente, C.D., Feyereisen, G.W. 2022. Ecohydrology of irrigated silage maize and alfalfa production systems in the Upper Midwest US. Agricultural Water Management. 267. Article 107612. https://doi.org/10.1016/j.agwat.2022.107612.
DOI: https://doi.org/10.1016/j.agwat.2022.107612

Interpretive Summary: Greater usage of silage corn, an annual crop, has increased dairy productivity but the corresponding loss of perennial alfalfa acreage may result in trade-offs with on-farm water balances and water quality. Alfalfa and corn have contrasting growth and water-use patterns, which may have impacts on soil water storage, and tile drainage. As an annual crop, corn requires more frequent tillage, which disturbs the soil surface and may result in increased sediment and phosphorus loss in runoff. In this study, we monitored water balance components, water-use efficiency, and water quality for alfalfa and silage corn crops for 8 years at a large dairy farm in Minnesota. We demonstrated that crop water usage was similar between crops, but water-use efficiency (yield per unit of water used) was 70% greater for corn than alfalfa. Estimates of fall soil water storage (crop water balance) were similar for alfalfa (25 mm per year) and silage maize (27 mm per year). Cumulative tile drainage loss over three paired years was 326 mm for silage corn and 214 mm for alfalfa. Alfalfa reduced drainage losses of nitrate-nitrogen, dissolved reactive phosphorus, and sediment by 72%, 33%, and 37%, respectively, compared to silage corn. Collectively, these results highlight the value of alfalfa for managing on-farm water flows and water quality during heavy spring and summer precipitation. As is often the case, the challenge comes in weighing these environmental benefits against the production gains that have driven the increased use of silage corn in the dairy industry. This information will enable researchers, industry, and agency personnel to design additional research aimed at improving water-quality outcomes from silage corn and improving water-use efficiency of alfalfa. This information will also aid industry, producers, and crop consultants in evaluating trade-offs between yield, water, use, and water quality achieving environmental quality targets.

Technical Abstract: Increased reliance on maize silage as a primary dairy forage in place of perennial crops like alfalfa may result in trade-offs with on-farm water balances and water quality. This study utilized year-round measurements of precipitation, irrigation, evapotranspiration (ET), soil water storage, subsurface tile drainage, and drainage concentrations and loads of nitrate (NO3-N), dissolved reactive P (DRP), and total suspended solids (TSS) to calculate annual water balances, water-use efficiency, and water quality impacts of silage maize and alfalfa production systems. Mean annual ET and tile drainage were similar between crops, due in part to high variability, although cumulative drainage over three paired years was 326 mm for silage maize and 214 mm for alfalfa. Estimates of annual soil water storage suggest that water budgets were balanced for these two fields and were similar for alfalfa (25 +/- 44 mm/yr) and silage maize (27 +/- 50 mm/yr). Inherent water use efficiency (IWUE) was 70% greater for maize than alfalfa. Paired-watersheds analysis indicated alfalfa reduced NO3-N but increased DRP concentrations in drainage compared to silage maize, but total loads of NO3-N, DRP, and TSS were reduced by 72%, 33%, and 37%, respectively, with alfalfa compared to silage maize. Results highlight the value of alfalfa for managing on-farm water flows and water quality during critical periods of the year, and suggest that increased usage of maize silage has facilitated gains in dairy productivity at the expense of water quality.