Author
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Martens, Dean |
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Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/19/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Agricultural soils on a world-wide basis have been reported to have lost a majority of their initial productivity due to our current farming practices. The loss of productivity has many implications, but with the large increase in the world's population, we have an even greater need to produce even more food on an ever shrinking land resource. This has prompted a research effort to convert our current farming practices to more sustainable practices. Due to the lack of pristine or original noncultivated lands, our understanding of the initial state of soil before farming occurred is limited. It is very important to understand the changes that occur when soils are converted to agricultural practices before we can suggest management practices that will reverse soil degradation, improve sustainability and increase food production. This study monitored identical soils that remain in native prairie or have been exposed to greater than 90 years of cultivation, to determine the changes in erodability and productivity that has resulted from agricultural management. The results noted that tillage is the greatest force degrading our soil resource basis, but the study also found that growth of soybean results in an increased degradation of soil structure when compared to the growth of corn. It was determined that the chemical composition of the corn and soybean residue influences soil degradation and that better varieties of crops will need to be introduced that will limit this increased destruction of our soil resource. Agricultural scientists will be able to more accurately monitor the improvement or degradation of soil management systems with the methods demonstrated in this study. Technical Abstract: Soil management is one of the most important factors influencing the structure of soils. The interaction of management (including tillage and crop rotation history) with soil biochemistry, soil aggregation and soil humus composition was determined in a native prairie and a producer field situation in 1997. A comparison of a native prairie and an adjacent conventional corn-soybean rotation on the same soil type found that the Webster soil after soybean (C3 plant) was lower in monosaccharide content and protein content as determined by ion chromatography, and phenolic acid content than the Webster soil after corn (C4 plant) or in native prairie as determined by gas chromatography. A wet, nested sieve aggregate stability measurement determined that the prairie soil had a higher mean aggregate size (1.85mm) when compared with the soil in the presence of decomposing corn (1.0 mm) or soybean (0.34 mm) residues. Mean aggregate size was found to be correlated with soil monosaccharide content (r=0.75), total soil protein content (r=0.995***), total soil phenolic acid content (r=0.997***) and alkaline extractable humic substance content (r=0.98**), and alkaline extractable humic substances were correlated with phenolic acid content of the humic substances (r=0.996***). The results suggest that the decrease in soil stability after soybean growth was due to a decrease in the content of soil humic substances caused by the substantially lower phenolic acids content (humic acid precursors) in the soybean residue. |
