Water Resources Research Act Program

Details for Project ID 2013IL268B

Hydrologic Impacts of an Alternative Agricultural Land Use: A Woody Perennial Polyculture

Institute: Illinois
Year Established: 2013 Start Date: 2013-03-01 End Date: 2014-02-01
Total Federal Funds: $6,000 Total Non-Federal Funds: $12,288

Principal Investigators: Evan DeLucia, Kevin Wolz

Abstract: Conversion of the Midwestern U.S. from native vegetation to intensive row crop agriculture dominated by the com-soybean rotation has severely altered the region's hydrologic cycle. The physiological and physical properties of the vegetation, along with soil moisture properties, affect the weather and climate by altering the transfer of energy and water from the land surface to the atmosphere. The primary physiological properties of the vegetation that drive this influence are leaf and stem area, stomatal conductance, seasonality, and rooting depth, while the primary physical properties are albedo and surface roughness. The once-dominant matrix of oak savanna contained a diverse mix of perennial plants, which had very different physiological and physical properties than the now-dominant monocultures of annual crops. This conversion has reduced leaf and stem area, increased stomatal conductance, shortened growing season, decreased rooting depth, and reduced surface roughness. The hydrologic consequences of land use conversion in the Midwest has been shown to extend both high into the atmosphere and laterally well beyond the region. Increased surface water runoff has caused extensive soil erosion throughout the Midwest, now eroding around 1 billion tons of soil per year from sheet and rill erosion alone.3 The excess nutrients, herbicides, and pesticides present in this runoff have also led to a continental-scale non point source water pollution problem. The excess nutrients contribute to a eutrophication-induced "dead zone" in the Gulf of Mexico, and the excess chemicals contaminate drinking water supplies. Reduced stomatal resistance has moistened the near-surface atmosphere by 0.5 to 1.5 g kg- 1 over much of the Midwest, but the relatively short growing seasons of annual row crops limit this effect to the srring and summer, thereby creating a sharp discontinuity in the evapotranspiration of the region. Furthermore, the relatively shallow rooting depth of annual crops leaves them more susceptible to drought than perennial species. Restoring the hydrologic cycle of the region, along with other valuable ecosystem services, has important implications for climate change adaptation and mitigation5, water quality, and agricultural production. Therefore, the potential positive effects of a novel land use conversion impact everyone from farmers implementing new management strategies on the ground to policy makers negotiating climate change mitigation strategies. At the heart of the nation's "bread basket", Illinois is at center stage in this issue. While complete reversion to native ecosystems would likely eventually restore the Midwest's natural hydrologic cycle and other ecosystem services, this option is clearly not viable given the growing population's ever-increasing need for calories (of both food and fuel). Here, we propose an alternative land-use option for the U.S. Midwest that maintains current economic and agricultural capacity while substantially altering hydrologic and ecological processes. This system is a woody, perennial polyculture (WPP) that has the macrostructure and function of a Midwestern oak savanna, the once-dominant ecosystem of the region, but has the composition and management of a modem agricultural system. Instead of the native oaks, crabapples, wild hazelnuts, sour grapes, and understory of prairie grasses, typical of the native oak savanna6, each niche in the WPP would be filled with a complementary, agriculturally relevant species. The replacement species/varieties would also constitute the industry's latest advancements in breeding for disease/pest-resistance, hardiness, crop quality, and growth. Chestnut (Castanea mollisima x dentata), containing approximately 90% starch3, and American hazelnut (Corylus americana), containing approximately 80% oil and 10% protein3, form the core of this system and are good compliments to com and soybean, respectively. The woody and perennial growth habit, extended growing season, low-chemical requirements, heterogeneous structure, and diverse composition give the WPP the potential to ameliorate the hydrologic and environmental impacts described above. While this is a significantly more complex land use than the current system, long-term studies have repeatedly shown that both productivity and stability increase with species richness.7 Other studies have shown that more diverse agricultural systems can meet or exceed the performance of less diverse systems while utilizing significantly less chemical inputs, thereby reducing runoff contamination and increasing economic stability.8 While profitable, large-scale examples of this type are already in place on once degraded farmland across the Midwestern U.S.9, there has been no direct comparison of the hydrologic impacts of a WPP to the corn-soybean rotation. Our project will study the potential of a WPP to alter the hydrologic cycle in a side-by-side comparison to a com-soybean rotation.