Water Quality and Production Potential Effects of Cellulosic Biofuel Crops Grown on Marginal Land
With an increasing global demand for fossil fuels, there is a growing amount of concern about greenhouse gas releases. Concurrently, interest in alternative sources of energy, including bioenergy has expanded considerably in the recent years. The Energy Independence and Security Act of 2007 mandates that 136.3 billion liters of biofuels must be produced, with 60.5 billion liters coming from cellulosic biofuel crops by 2022. Potential sources of cellulosic biomass are: maize residue, sorghum, switchgrass, Miscanthus, and woody crops. The increase in biofuel crop production required to meet the mandate raises questions regarding the additional amount of agricultural land area needed, as well as the potential competition for land with food and feed production. The utilization of marginal lands, lands not suitable for crop growth due to infertility, slope, soil degradation or poor yields of common annual crops such as corn, is an alternative, but could come at a higher environmental cost. There has been little field research investigating the environmental consequences of using marginal land for biofuel crop production. The objectives of this research were to quantify surface and subsurface nutrient losses and determine production potential of six crops (Miscanthus, switchgrass, maize, sorghum, poplar, and native prairie) when grown on marginal lands with varying rates of nitrogen (N), and varying phosphorus (P), and potassium (K) fertilizer rates or residual soil P and K levels. This study used previously-established research plots at the Throckmorton Purdue Agricultural Center (TPAC), in West Lafayette, IN. Switchgrass plots were established in 2007, Miscanthus in 2010, and maize and sorghum plots were established in 2011 at one site. Other plots were established in 2011. Yields were assessed in 2013 and 2014. Suction cup lysimeters permitted soil profile leachate to be sampled at a depth of approximately 30.5 cm. in a small subset of plots, and nutrient loading in surface water runoff was sampled during 2014. Surface samples were collected in tanks at the bottom of the plots. Subsurface water samples were analyzed for nitrate-N (NO 3-N) concentration and soluble reactive phosphorus (SRP) concentration, while surface runoff water samples were analyzed for NO3-N, SRP, total nitrogen (TN), total phosphorus (TP) and total suspended solids (TSS). Subsurface leachate concentrations of NO3-N from the perennial grass plots were significantly lower when compared to those extracted from the annual row crops. Miscanthus showed some leaching of phosphorus when fertilized with P fertilizer. One year of surface monitoring data indicated that surface nutrient loads were not significantly affected by crop. However, switchgrass had significantly lower nitrate loads than sorghum and Miscanthus. Many of the nutrient and TSS loads were higher at the start of the growing season (May) when planting and fertilization occurred as compared to later in the season after full plant growth. Miscanthus yield was significantly higher than all other crops in this study, averaging 22.6 t ha-1 on the dry weight basis. Fertilizer rate did not make a significant difference in biomass production within a crop treatment on the plots with fertilizer trials. This study indicates perennial grasses may have markedly lower nutrient losses and can help reduce soil erosion, while also producing a significant biomass yield when grown on land considered marginal because of lower fertility and high erosivity.^
Indrajeet Chaubey, Purdue University, Sylvie M. Brouder, Purdue University.
Agricultural engineering|Environmental engineering
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