SOIL CARBON AND CLIMATE CHANGE NEWS
From Kansas State University's:
Consortium for Agricultural Soils Mitigation of Greenhouse Gases (CASMGS)
Charles W. Rice, K-State Department of Agronomy, National CASMGS Director
(785) 532-7217 email@example.com
Scott Staggenborg, K-State Department of Agronomy (785) 532-7214 firstname.lastname@example.org
Steve Watson, CASMGS Communications (785) 532-7105 email@example.com
Evaluating Long-Term Impacts of
Harvesting Crop Residues on Soil Quality
A special section in the January 2011 issue of Agronomy Journal contains several papers from a symposium titled “Residue Removal and Soil Quality—Findings from Long-Term Research Plots.” Presentations at this symposium examined residue removal impacts in the context of various management practices including crop rotation, tillage, applied fertilizer, and irrigation. The seven papers from the symposium that are published here primarily focus on residue harvest and input effects on soil organic carbon (SOC) over time.
David R. Huggins, USDA-ARS in Pullman, Washington, and colleagues provide the following introduction and summary of these papers:
* Powlson et al. reviewed 14 long-term studies from Europe, Australia, and Canada that examined straw removal effects on SOC. They concluded that residue removal resulted in small decreases in SOC; however, these small changes could have disproportionately large negative effects on microbial activity and related soil physical properties such as aggregate stability. Powlson et al. (2011) cautioned against annual removal of straw and recommended that studies be coupled to areas where residue harvest is being considered due to the site-specific nature of soil response to straw removal.
* Machado evaluated long-term dryland cropping system studies located near Pendleton, OR, with respect to effects on SOC. Here, removal of crop residues in winter wheat–summer fallow rotations which predominate in the region will increase SOC depletion, whereas continuous cropping, particularly in combination with no-tillage could maintain adequate SOC and soil productivity. Machado concluded that residue harvest may be sustainable if the wheat–fallow system was replaced with continuous cropping and no-tillage.
* Nafziger and Dunker reported on the long-term SOC trends under different crop rotation and fertilizer treatments at the University of Illinois Morrow Plots. Significant SOC decline occurred during the first half of the 20th century under annual residue removal with no fertilizer additions. Since then, however, SOC response to various treatments including residue removal have been inconsistent, although it is apparent that adequate nutrient levels are important for maintaining SOC.
* Miles and Brown found that long-term plots at the University of Missouri Sanborn Field also showed significant SOC decline with treatments that removed residues; however, retaining field residues was positively related to SOC.
* Gollany et al. evaluated five long-term field experiments in North America and simulated SOC dynamics under a wide range of biophysical factors with the CQESTR model. They concluded that increasing soil C inputs through manure additions and/or crop intensification as well as reducing tillage were important strategies for mitigating residue harvest impacts on SOC levels.
* Tarkalson et al. reviewed small grain residue management effects on SOC and specifically on SOC changes for six irrigation studies where wheat straw was removed or retained. They reported that SOC either increased or remained constant when wheat residues were removed and hypothesized that below-ground biomass production was important for maintaining or increasing SOC under irrigation. Tarkalson et al. point out that irrigated cropping systems in the Pacific Northwest and elsewhere tend to be diversified and include crops such as alfalfa, potato, and sugarbeet in addition to wheat and corn and that very little data on residue removal effects on SOC are available for these situations.
* Karlen et al. reported on the initiation of a U.S.-based multi-location study to: (i) evaluate the effects of harvesting corn stover on soil quality; (ii) assess potential trade-offs between short-term economic returns to growers harvesting residue and long-term benefits to soil, air, and water from retaining residues; and (iii) develop management strategies that support the sustainable harvest of crop residues. They reviewed issues surrounding the use of corn stover as a bioenergy feedstock and demonstrate the usefulness of the Soil Management Assessment Framework (SMAF) as a tool to monitor and evaluate soil responses to land-use changes associated with the developing biofuel industry. Initial study results included a SMAF analysis that identified SOC as a critical soil indicator with respect to monitoring residue removal effects on soil quality.
Summary and Conclusion: It is clear from the articles in this special section that residue harvest will impact SOC and associated soil properties and that residue removal effects cannot be evaluated in isolation. Factors such as initial site characteristics (e.g., soil, water, air, and wildlife resources), the suite of management practices that comprise the cropping system and the economic returns from residue harvest must be integrated into any analysis and likely trade-offs assessed. This situation shifts evaluation to the farm scale where emphasis should be placed on providing science-based decision aids that growers can practically apply to their unique farms. These might include technologies that measure site-specific residue loads and define threshold levels for residue removal that occur under different management scenarios. Management scenarios should include economic and environmental evaluation of alternative practices that could enable the sustainable harvest of residue feedstocks for a given location and situation.
-- Agronomy Journal, January 2011, Vol. 103 No. 1, p. 230-233