Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2009
Publication Date: 7/1/2009
Citation: Yuan, Y., Locke, M.A., Gaston, L.A. 2009. Tillage Effects on Soil Properties and Spatial Variability in Two Mississippi Delta Watersheds. Soil Science. 174 (7): 385-394. DOI 10.1097/SS.0b013e3181ac769c [online]. Interpretive Summary: The principal focus of the USDA Conservation Effect Assessment Project (CEAP) Watershed Assessment Study effort is to provide an assessment of environmental benefits derived from the implementation of USDA conservation practices. Conservation tillage has been recognized as an important conservation practice and has been studied across the county for their effects on soil and water quality. The Mississippi Delta (flood plain of Mississippi River) is an important agricultural region of the United States, and conservation tillage is slowly being adopted in this region, but relatively limited information is available concerning the effects of tillage on these soils. Therefore, the objective of this study was to measure differences in soil characteristics that could be attributed to conservation practices in Mississippi Delta alluvial soils. The paper presents results from analysis of soil data collected from two Mississippi Delta watersheds before and after conservation tillage implementation. Results showed that soils in these Mississippi Delta watersheds were enhanced with higher organic matter and nutrients such as P, K, Ca, and Mg. In addition, Data collected from three time periods 1996, 2000, and 2006 consistently showed high soil P levels in these soils although relatively low P fertilizer was applied. This indicates that these alluvial soils have relatively high native soil P levels, and farmers may be cautioned against adding fertilizer P to help lower the environmental risk of loss to surface water and groundwater. Reduced tillage is especially important in this area because of high sediment loss associated with conventional tillage systems.
Technical Abstract: This study evaluated changes in soil properties several years after implementation of conservation measures. Two approximately 50-ha fields within two Mississippi Delta oxbow lake watersheds (Deep Hollow and Beasley) were laid out in 60-m grids. Soil from a tilled cotton field in Deep Hollow watershed was sampled at each node in 1996 and again in 2000 after four years of reduced tillage cotton (Gossypium hirsutum) and winter wheat (Triticum aestivum L.) cover crops; soil also was collected from conventional tillage cotton in Beasley Lake watershed in 1996 and again in 2006 from the same grid nodes after four years of reduced tillage cotton and five years of reduced tillage soybeans. Organic matter levels in the soil surface were higher in both watersheds after conservation tillage was implemented, likely due to increased plant residue accumulation and limited soil mixing. Higher soil P levels in both watersheds under conservation management were attributed to less distribution in soil because of reduced tillage. Lower NO3-N in Deep Hollow in 2000 suggested N immobilization in the soil surface. Nitrogen was not analyzed for Beasley soil samples. Soil pH values were also higher in the later samplings for both watersheds, but since lime was applied in the interim, it is difficult to ascribe an effect from tillage. Potassium, calcium and magnesium were higher in 2000 after 4-year reduced tillage practice in the Deep Hollow watershed. However, potassium, calcium and magnesium were lower in 2006 than in 1996 at the Beasley Lake watershed because no fertilizer was applied to the field since 2001. Regardless of tillage system, relatively high P levels in soils from both watersheds are indicative of high native soil P levels in the Mississippi Delta soils. Similar to other studies, water soluble P was positively correlated with Mehlich III P. Spatial relationships of P examined using Kriging showed that P data were spatially dependent and their spatial dependence was impacted by tillage practices.