Environmental enhancement of U.S. biomass crop technologies: research results to date1

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Abstract

The U.S. continues efforts to develop genetically superior short-rotation woody crops (hybrid poplar and willow) and herbaceous crops (switchgrass). These biomass crops can provide multiple environmental benefits as well as energy and fiber. This paper focuses on results of site-specific studies that are quantifying the environmental potential and ramifications of converting agricultural croplands to biomass crop production.

At research-scales, no differences have been found in erosion and movement of nutrients from annual row crops, switchgrass, and tree crops with and without a cover crop in the initial year of establishment. Research- and watershed-scale studies on different soil types, in different regions, and to match tree species with specific site characteristics and management regimes will help determine whether research-scale results can be used to predict effects at larger scales and to identify best management practices to minimize environmental effects while maximizing yields.

Studies in different regions of the U.S. are evaluating the habitat value of biomass crops compared to agricultural row crops, grasslands, or natural forests. Results to date from both research- and larger-scale plantings show that SRWCs support greater bird diversity than row crops, but less diversity than natural forests. Switchgrass plantings extended habitat for grasslands birds compared to row crops. Surveys on industrial tree crop plantings in the south-eastern U.S. are addressing the relationship between site characteristics (planting acreage, species, landscape context, and age of plantings) and breeding bird use. The environmental studies of water and soil quality and wildlife diversity are being used to identify management strategies for biomass crops to increase productivity while increasing agricultural sustainability.

Introduction

Short-rotation woody crops (SRWC) and perennial grasses when used as biomass feedstocks for energy and fiber have the potential to provide both economic and environmental benefits while meeting energy production needs. These renewable feedstocks when converted to liquid transportation fuels, directly combusted for production of electricity, or co-fired with fossil fuels as alternative sources of energy can provide broadscale environmental benefits by reducing the overall contribution of fossil fuels to global warming. The benefits of using biomass crops to replace conventional fuels can accrue from the global scale (reduction in greenhouse warming) to site-specific (e.g. decreases in erosion and the need for chemicals for production). These benefits will vary from region to region because of the differences in the demand, land available, and production costs for the different biomass crops among regions. However, the environmental benefits from including biomass crops in the mix of energy feedstocks are additive both nationally and globally.

Meeting projected energy needs using biomass feedstocks could require a shift of tens of millions of hectares from crop or pasture lands to production of these dedicated feedstocks.[1] Production of these biomass crops as energy sources currently will not generate profits competitive with production of annual row crops such as corn and soybeans on the most productive lands. Perennial biomass crops have the potential to achieve profitable growth rates on more marginally productive croplands where erosion is a concern and soil stabilization is needed.

The type of land base on which biomass crops are planted will determine their environmental risks and benefits. Economic evaluations of biomass crops assume that these crops will be grown on agricultural croplands.[2] Graham[3] estimated that there are 74 million ha of cropland that are not required for agricultural production in the U.S. Of this total, only 16 million ha were in regions well suited for energy crop cultivation. This 16 million ha includes croplands currently in long-term set-aside programs such as the U.S. Department of Agriculture's Conservation Reserve Program (CRP). These set-aside lands have generally been removed from production because they are subject to either wind or water erosion and can result in environmental degradation when used to produce annual crops. In Minnesota, CRP lands, eligible for 5 year extensions in program participation, have been approved for tree crop production. This approval enables farmers to continue to participate in the conservation program while planting hybrid poplar, cost-sharing establishment expenses (up to $30–35/acre), and producing a marketable crop in 7–10 years.

The U.S. Department of Energy (DOE) is funding research through the Bioenergy Feedstock Development Program (BFDP) to quantify the environmental aspects (soil erosion, nutrient availability and retention, water quality changes, and wildlife habitat) of biomass crop production.[4] The environmental research is being conducted in conjunction with collaborative research through individual universities, industries, cooperatives, and research centers on both tree and grass crops. This collaborative research, with the objectives of developing and testing genetically improved clones appropriate to the different regions of the U.S. and development of disease and pest resistance, offers the opportunity to identify crop production strategies that the BFDP, individual, and industrial-scale growers can incorporate into management regimes to ensure environmentally sound production of energy and fiber. Production of biomass crops must occur in an environmentally sustainable manner to insure their acceptance in the agricultural crop mixture. A goal of the BFDP is to integrate environmental research and monitoring into most, if not all, crop production and scale-up projects sponsored by the U.S. DOE over the next 10–15 years and to answer questions by potential growers and the public at national, regional and local scales to increase the potential for sustainable production of biomass crops. Results of the environmental research to date and current directions based on ongoing research are the focus of this paper.

Section snippets

Approach

The DOE has increased emphasis on environmental aspects of biomass crop production in the past 3 years as larger-scale woody crop production trials have been established and commercialization of woody crops has expanded as a source of pulp fiber. Specific studies have been designed to address questions about how biomass crops can provide environmental benefits on former agricultural lands and whether these crops can contribute to reclaiming erosion-prone lands. Studies of the ability of biomass

Biodiversity studies

The first BFDP funded studies of wildlife use of biomass crop plantings were initiated in 1992. These site-specific studies were conducted on eight hybrid poplar clonal trials that were 4–5 years in age. These 4 or 8 ha plantings of 10 clones each were located in the north-central U.S. (Minnesota, Wisconsin, and South Dakota). Results from these research scale plantings showed that avian abundance and species richness were consistently higher in SRWC plantings than in rowcrop/small grain fields.

Soil nutrient/water quality studies

Studies funded by DOE began in 1994 and 1996 to address how biomass crop production affects soil and water quality. The studies reported here provide an overview of the research directions being taken and the results to date that can help quantify environmental effects associated with nutrient application, uptake, and loss for biomass crops compared with annual row crops.

A study in the south-eastern U.S., conducted cooperatively between the BFDP, the Tennessee Valley Authority (TVA), the

Discussion

Although Christian et al.[5] concluded, based on results of small-scale studies that there appeared to be positive environmental effects for wildlife from including biomass tree crops in the landscape, it is important to remember that different species have different environmental requirements and that the positive habitat provided for one species by including trees in the landscape may have a neutral to negative effect on other species. For example, placement of short-rotation tree plantings

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