Energy crops and their environmental implications

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Source: Soil Science Society of America

Interest in producing cellulosic ethanol from renewable energy sources is growing. Potential energy crops include row crops such as corn, perennial warm-season grasses, and short-rotation woody crops. However, impacts of growing dedicated energy crops as biofuel on soil and environment have not been well documented. This review article looks at the impacts of growing warm-season grasses and short-rotation woody crops on soil properties, soil organic carbon (SOC) sequestration, and water quality, and (2) the performance of energy crops in marginal lands.

The author’s literature review shows that excessive (≥50%) crop residue removal adversely impacts soil and environmental quality as well as crop yields. Growing warm-season grasses and short-rotation woody crops can be potential alternatives to crop residue removal as biofuel. Warm-season grasses and short-rotation woody crops can improve soil properties, reduce soil erosion, and sequester SOC. Crop residue removal reduces SOC concentration by 1 to 3 Mg ha−1 yr−1 in the top 10 cm, whereas growing warm-season grasses and short-rotation woody crops increase SOC concentration while providing biofuel feedstocks.

Warn season grasses can store SOC between 0 and 3 Mg C ha−1 yr−1 in the top 5 cm of soil, while the short-rotation woody crops SRWCs can store between 0 and 1.6 Mg ha−1 yr−1 of SOC in the top 100 cm. The warm-season grasses, WSGs and SRWCs have more beneficial effects on soil and environment when grown in marginal lands than when grown in croplands or natural forests. Indeed, they can grow in nutrient-depleted, compacted, poorly drained, acid, and eroded soils. Development of sustainable systems of warm-season grasses and short-rotation woody crops in marginal lands is a high priority.

The review also reveals that gains in SOC and improvement in soil properties under warm-season grasses and short-rotation woody crops can vary, depending on soil-specific characteristics (e.g., drainage, slope, and texture), harvest cycles, addition of amendments, previous land use and management, plant species, and climate.

Impacts are often measurable with longer periods of management. Warm-season grasses and short-rotation woody crops as biofuel must be carefully managed to achieve the desired ancillary soil and environmental benefits. Growing warm-season grasses and short-rotation woody crops as biofuel cannot replace natural forest and native prairie lands, but they can provide a number of ancillary benefits when managed properly.

The potential benefits of growing energy crops on the environment will depend on how energy crops are grown and where they are grown. Mixture of plant species can be more effective than single species for controlling runoff, sediment, and nutrient loss. Well-managed energy crops can improve soil and environmental quality while supplying much-needed feedstocks for cellulosic ethanol production.

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