A new research report from the Great Lakes Bioenergy Research Center (GLBRC) finds that perennial crops grown on marginal land for biofuel use could use comparable water to that of corn. The report looked at how these crops could affect the balance of water between rainfall inputs, evaporation losses, and movement of soil water to the groundwater. The report cites that in humid climates such as the U.S. Midwest, evaporation returns more than half of the annual precipitation to the atmosphere, with the remainder available to recharge groundwater and maintain stream flow and lake levels.
The study, led by GLBRC scientist and Michigan State University professor of ecosystem ecology Stephen Hamilton, is a multi-year effort to compare the water use of conventional corn crops to the perennial cropping systems of switchgrass, miscanthus, native grasses, restored prairies, and hybrid poplar trees, feedstocks currently under review for use as biofuel crops.“When we established the different cropping systems in 2008,” said Hamilton, “we installed soil-water sensors at various depths through the root zone. We’ve been continuously monitoring the soil water content ever since.”
To measure the rate of evapotranspiration occurring within each cropping system, soil-water sensors are used. Evapotranspiration refers to the sum total of water lost while the plant is growing, either from evaporation through the plant stem itself (a process called “transpiration”), or from water evaporated off of the plant’s leaves or the ground. By measuring the amount of precipitation that has fallen against actual soil water content, Hamilton said it’s possible to quantify the water lost to evapotranspiration while each crop is growing.
In a finding that contrasts sharply with earlier modeling studies that found particularly high perennial water use in areas with high water tables, the report finds that the perennial system’s evapotranspiration did not differ greatly from corn. Hamilton’s study, however, took place in Michigan’s temperate humid climate and on the kind of well-drained soil characteristic of marginal farming land.
Hamilton and his team also measured the water use efficiency (WUE) of each crop, calculating which plants grew the most biomass with the least amount of evapotranspiration. Miscanthus had the highest WUE, then corn, followed by poplar, native grasses, and prairie.