Nov. 20, 2012 -- Conservation management practices have become increasingly popular due to their potential for improving agricultural sustainability and soil quality. However, comparisons among management practices and their effects on soils are scarce. Understanding the ways in which soil quality can change in response to conservation management practices is necessary for further development of such practices.
Ten-year-old agroforestry (tree-grass) vegetative filter strips planted into a corn-soybean rotation at the Greenley Memorial Research Center, Missouri, USA.
In a paper in the Nov.-Dec. issue of the Soil Science Society of America Journal, researchers from the University of Missouri and the USDA-ARS compared soils from a no-till, corn-soybean rotation with soils from vegetative filter strips (VFS) installed in the no-till, corn-soybean rotation in north-central Missouri. Using measures of soil aggregate stability and water-extractable organic carbon (C), they found that no-till soils exhibited decreasing measures of soil quality relative to VFS, possibly due to the lack of perennial root biomass under no-till cultivation.
The primary functions of VFS are to reduce runoff and soil erosion, and no-till has been shown to improve soil quality over conventional tillage practices through several effects including retention of soil organic C. Previous work, however, found no differences in soil organic C quantity among these conservation management practices at the site of the current study. Therefore, more sensitive indicators of soil quality need to be used, such as soil aggregate stability and water-extractable organic C.
Aggregate stability reflects soil structure, soil erosion, and water infiltration. It is closely linked to soil organic matter, which acts as a binding agent between soil particles to form aggregates. Aggregate stability tests can be conducted using air-dried or field-moist soil. Field-moist samples have the advantage of representing more natural conditions found in the field but may only represent soil
behavior at the time of sampling. Air-dried aggregate stability is more commonly measured but does not necessarily reflect soil behavior under field conditions.
In the current study, Veum and colleagues looked at no-till fields with and without VFS. Researchers conducted aggregate stability tests using both air-dried and field-moist soil, and also measured water-extractable organic C, a highly mobile fraction of soil organic C that may play a role in aggregate stability.
Aggregate stability in air-dried soil samples was approximately double in the VFS fields compared to no-till fields without VFS, but no differences were found in field-moist samples. Researchers also saw an almost 2-fold increase in the amount of water-extractable organic C in the VFS compared to no-till soil.
The results of this study suggest that even though no-till offers many benefits over conventional tillage, the lack of a continuous, living root biomass leads to reduced soil organic matter when compared to soils with perennial vegetation in VFS. Under no-till cultivation, strong soil aggregates are less likely to form, soil organic matter is more susceptible to microbial decomposition because it is not protected within aggregates, and overall soil quality is reduced.
Sensitive indicators of changing soil quality are critical for effective agroecosystem management. The current study found that air-dried aggregate stability and water-extractable organic C can serve as rapid, cost effective indicators of short-term (10 year) changes in soil quality under conservation management practices. The observations also suggest that field conditions (i.e., differences in soil moisture content) can have dramatic effects on aggregate stability. More work is needed to fully understand the relationships among these soil properties and the effects of conservation management practices on soil quality.
Kristen S. Veum, Keith W. Goyne, Robert Kremer and Peter P. Motavalli. 2012. Relationships Among Water Stable Aggregates and Organic Matter Fractions Under Conservation Management. Soil Sci. Soc. Am. J. 76 (6): 2143-2153. View abstract