Influence of cover crop and tillage management practices on soil physical and hydraulic properties
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Several agricultural land management practices, such as cover crops and tillage, can influence soil physical and hydraulic properties, soil health indicators and crop productivity. This study evaluated the influence of cover crops, tillage and perennial biofuel crops on soil physical and hydraulic properties. The objectives of this study included: (i) evaluate hydraulic properties for soils managed by cover crops and tillage, (ii) assess the influence of cover crops and tillage management on in situ water infiltration parameters, and (iii) evaluate thermal conductivity (λ), volumetric heat capacity (C[subscript v]) and thermal diffusivity (D) for soils managed by perennial biofuel and cover crops. Two field sites were used for the study; the first and second objectives were conducted at Lincoln University’s Freeman Research Center while the third objective was conducted at University of Missouri Bradford Research Center. The cover crop grown at Freeman Research Center was Cereal rye (Secale cereal L.), while Cereal rye, Hairy vetch (Vicia villosa subsp. villosa) and Austrian winter pea (Pisum sativum subsp. arvense) were grown at Bradford Research Center. The perennial biofuel crops at Bradford Research Center included giant miscanthus (Miscanthus x gigantus J.M. Geef & Deuter ex Hodkinson & Renvoize) and switchgrass (Panicum vergatum L.). The tillage treatments at Freeman Research Center included tillage using a moldboard plow to a depth of 15 cm and no-till. The soil at Bradford Research Center was managed with no-till. Intact soil samples (76 by 76 mm) were collected for objectives one and three with samples taken in 2014 and 2015, respectively. Infiltrometers were used to measure infiltration rates for objective two during 2014 and 2015. The physically-based Parlange and Green-Ampt infiltration models were fit to estimate saturated hydraulic conductivity (K[subscript s]) and sorptivity (S) parameters. Results showed that bulk density values for tillage were 13% lower compared with no-till management right after tillage. At the 0-10 cm soil depth, water content was significantly higher at the 0.0 and -0.4 kPa pressures for tillage compared with no-till management, right after spring tillage. However, this effect did not persist over time probably due to soil consolidation after some rainfall events. Tillage improved coarse mesopores by 32% compared with no-till; and this effect resulted in 87% higher saturated hydraulic conductivity values in tillage compared with no-till management, right after spring tillage. Cover crops improved macropores by 24% compared with no cover crop; this can potentially increase water infiltration and reduce runoff. As a result of higher macroporosity, saturated hydraulic conductivity was higher in the cover crop compared with no cover crop management. This study demonstrated that the effects of tillage in improving some soil hydraulic properties may not persist over time. The Parlange and Green-Ampt model appeared to fit measured infiltration data well with coefficient of variation (r[superscript 2]) ranging from 0.92 to 0.99. The K[subscript s] parameter value estimated from the Parlange and Green-Ampt models in 2014 were 42% and 54% higher in no-till compared with tillage management, respectively. In 2015, the S parameter values estimated from the Parlange and Green-Ampt models were 82% and 90% higher in cover crop management compared to no cover crop management, respectively. This study showed that cover crops can improve water infiltration and may reduce water and nutrient runoff which can lead to enhanced agricultural productivity. Results of the third objective showed that perennial biofuel crops (giant miscanthus and switchgrass) had 11% higher C[subscript V] at saturation compared to row crops (cover crops and no cover crops). Cover crops compared to no cover crop had 18% higher volumetric water content at saturation and 26% higher soil organic carbon; this led to 13% higher C[subscript v] compared to no cover crops. Row crops had significantly higher λ and D compared to perennial biofuel crops. This study showed that perennial biofuel and cover crops can change soil thermal properties by reducing λ and D and increasing C[subscript v]; this indicates that these management systems can improve the ability of the soil to buffer against rapid heat change and better handle a more variable climate. Results from these studies showed that tillage may influence some soil properties temporarily; however, these influences may diminish over time. Cover crops can improve soil physical and hydraulic properties and soil health indicators and this can lead to improved productivity. However, longer-term studies are needed to evaluate these effects over time, especially with an increasingly changing climate.
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