Course: BFM 101 Biofuels Fundamentals

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Life Cycle Assessment
Ground and Surface Water

Sustainable Management for Biomass Production
Sustainable Management for Biomass Production

There are environmental benefits and challenges associated with the utilization of biomass for energy and other bio-based products. For example, while the use of biomass for energy can help moderate greenhouse gas emissions, protect soil, water and air quality, and enhance habitat for many species, improper practices can reduce these benefits or even place these resources at risk. Recognizing these concerns, various strategies, generally labeled as best management practices (BMPs) or guidelines, have been developed to mitigate these impacts. Here we review environmental concerns and mitigation strategies associated with the management and harvesting of biomass on soil productivity, water quality and quantity, and biodiversity and wildlife.

Soil Productivity

Soil is a fundamental resource essential to plant and wildlife productivity. Growing and harvesting biomass can impact soil physical, chemical and biological properties.

Soil physical properties. Growing and harvesting biomass may alter soil structure, texture, porosity, density, drainage, and surface hydrology. Equipment traffic on unfrozen soil tends to compact the soil (increase its density), which reduces its porosity, aeration, and drainage and can impact surface hydrology. Soil compaction also can reduce root survival and growth. Mechanical site preparation can change the soil structure and texture.

Soil chemical properties. The nutrient status and pH of soils may be altered by removing biomass, as it takes away material that would have decomposed and provided nutrients to the soil. When biomass is removed, the amount of organic matter in soil (the residues of dead plants and animals in various stages of decomposition) is also reduced, thereby affecting the soil pH and nutrient availability.

Soil biology. Soil contains many organisms, such as bacteria and fungi, which improve its quality by breaking down organic material to smaller particles and releasing nutrients. Soil organisms are also important links in many nutrient cycles. Mechanical site preparation techniques such as tillage, raking, windrowing, disking and piling can reduce soil organic matter, which is important for soil microbes, soil structure, soil carbon storage, nutrient cycling and regulation of soil hydrological processes [2]. A reduction in soil organic matter and soil carbon storage will reduce the availability of nutrients, especially nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca).

Best Management Practices

The most important way to maintain soil productivity while growing biomass is to retain organic matter on lands where bioenergy crops are being harvested. Organic matter (including field crop residue and slash from woody crops) reduces soil erosion and helps maintain favorable soil temperatures and moisture relations.

Some residue management considerations:

- While there is no consensus about the amount of residue that should be retained, the soil surface does not have to be completely covered with residue in order to help prevent erosion [3]. Studies suggest that at least 2.3 tons per acre should be retained in a no-till continuous corn system and 3.5 tons per acre in a corn-soybean rotation system.
- For woody crops, recommendations are that 1/6 to 1/3 of the residue should be retained.
- It may be possible to increase the residue removal rate if other management practices are implemented, including establishment of cover crops; using no-tillage, narrow row spacing; growing higher plant populations; increasing fertilization rates, or applying bio-char or other organic amendments.
- Harvesting methods that leave enough crop residues to keep soil loss to a minimum can be used for perennials such as switchgrass or Miscanthus spp. [4]. Surface cover is especially important during the establishment of these perennial crops, which may take several years.
- It is important to limit the removal of crop residues to rates that will sustain long-term soil health and ecosystem services. Of the soil ecosystem services affected, soil carbon sequestration seems the most sensitive. For example, substantially more crop residue must remain in the field after harvest to maintain carbon levels than to prevent soil erosion [5].

Resources provided by the eXtension Farm Energy Community of Practice at http://www.extension.org/ag+energy

Life Cycle Assessment
Ground and Surface Water