Location: National Soil Erosion Research2012 Annual Report
1a. Objectives (from AD-416):
1) Mitigate the impacts of soil drainage conditions on soil quality, soil erodibility, nutrient cycling and pesticide dynamics. 2) Develop control practices for soil erosion and specifically ephemeral gully erosion. 3) Optimize the benefits of innovative farming systems, including biofuel production, on soil water dynamics, soil and water quality, soil erosion and greenhouse gas emissions.
1b. Approach (from AD-416):
Conduct laboratory and field experiments to quantify the impact of soil drainage on soil and water quality, erodibility, nutrient cycling and pesticides dynamics. Develop practices to control soil ephemeral gully and other forms of water erosion. Develop through experimentation new innovative farming systems that reduce greenhouse gas emissions while optimizing benefits to production, soil and water quality and reducing erosion.
3. Progress Report:
Measurement of soil cohesion with the fluidized bed technique was further refined by using pressure transducers to precisely measure the actual point of fluidization. Four additional soils were tested with the new technique and the measured soil inherent cohesion correlated well with the field measured critical shear stress. New experiments are under way to quantify the development of soil cohesion due to aging, i.e., the duration that soil aggregates are saturated with water, and drainage. Experiments on seepage effects on channel initiated were conducted in a 3.7 m wide and 9.7 long laboratory hillslope. In this experiment, progression of channel development was quantified by analyzing time-lapsed 3-dimentional photogrammetric images. Zones of channel cutting and sedimentation on the experimental hillslope were clearly delineated from the photogrammetric analysis. Experiments are underway to identify suitable sorption materials that can sequester agricultural pollutants, i.e., mainly pesticides and fertilizers. Materials tested include granulated rubber (or shredded tire chips), zero-valent iron and gypsum. The suitable sorption material will be tested in a laboratory scale blind-inlet prototype to further identify the design criteria for field implementation. Greenhouse gas sampling from cropped fields at Purdue Research Farms, as a part of the GRACENet project, continued into the 9th year. Two traditional corn-soybean rotation plots were converted to corn-soybean-winter wheat with mixed cover crops such as annual ryegrass, oilseed radish and hairy vetch. The intent is to use a diverse cropping system to sequester carbon and to minimize the greenhouse emission. Soil quality analyses for soils from ARS Conservation Effects Assessment Project (CEAP) watersheds continued. The analyses were completed for 11 of the 17 CEAP watersheds.
1. Soil quality assessed at South Folk Watershed of Iowa. Soil and crop management practices on agricultural fields may cause changes in soil quality which in return affects the sustainability of the land for future crop production. Soil quality assessment is a proactive process for understanding the long-term effects of crop and soil management practices within agricultural watersheds. ARS researchers from West Lafayette, IN, and Ames, IA, studied soil quality parameters from fields with both well-developed and poorly developed corn plants in the Iowa River’s South Fork Watershed and used the ARS soil quality model, i.e., Soil Management Assessment Framework (SMAF), to distinguish differences within fields. The mean SMAF indicator scores for soil organic carbon, bulk density, water-filled pore space, electrical conductivity, and microbial biomass carbon were significantly lower in the poor canopy areas; however there was no single indicator that scored lower across all 50 fields sampled. A majority of fields had multiple indicators with SMAF ratings at least 0.10 lower in the poor areas than in the corresponding well-developed canopy areas. Soil quality assessment on a field-by-field basis thus provides an approach for identifying potential specific soil-based causes for the poor canopy development. The SMAF is a tool for famers to use in evaluating the impact of their management practices on their soil resources.
2. A new technique to measure soil cohesion. Soil erodibility is a term that describes the soil’s resistance against erosive forces before the soil can be detached. A common way of measuring soil erodibility is to apply different levels of erosive forces and empirically fit the measured erosion data through a soil detachment equation to come up with the value of soil erodibility. Nevertheless, soil erodibility is often affected by the condition when the measurement was made. The ARS research team and a Purdue University scientist at West Lafayette, IN, developed a fluidized bed technique that can measure intrinsic soil cohesion and tested this technique on four soils with varying soil properties. The results showed that the fluidized bed measured soil cohesion correlated well with empirically measured critical shear stress from a field experiment. This method is a simple alternative to traditional rainfall or runoff experiments with the advantage of being independent of external factors, hence is a true measure of soil cohesion. Erosion researchers now have a simple technique to measure soil cohesion.
3. Subsurface hydrology controls gully and channel initiation. Ephemeral gully erosion contributes to a significant amount of sediments on the landscape. Yet, current erosion assessment technologies are inadequate in predicting where the gully channels initiate and how fast these channels deepen and expand on the hillslope. To test the hypothesis that gully channel development is controlled by a combination of surface and subsurface hydrology, an ARS scientist, in cooperation with a Purdue University researcher, at West Lafayette, IN, designed a laboratory hillslope which has controls for different amounts of surface and subsurface water going through this hillslope segment. Results showed that if the soil had subsurface seepage, i.e., soil is over-saturated and water flowing out of the soil, erosion rate is 2.1 to 1.6 times higher when compared to the soil that water is allowed to drain through the profile. From photographs taken during the experiment, the research team found erosion from channel incision is about 1.5 times higher for the seepage condition. This study demonstrated that subsurface hydrology is a controlling factor in the development of rills channels and ephemeral gullies. Farmers, erosion control specialists, and soil conservationists can use soil drainage practices to minimize or control gully formation in agricultural fields or hillslopes.
Mello, C.R., Norton, L.D., Curi, N., Yanagi, S.N., Silva, A.M. 2012. Sea surface temperature (SST) and rainfall erosivity in the Upper Grande River Basin, Southeast Brazil. Science and Agrotechnology of Lavras. 36(1):53-59.