Soil quality indices following long-term conservation pasture management practices

Authors: AMORIM, HELEN - University Of Arkansas; Ashworth, Amanda; Moore, Philip; Wienhold, Brian; SAVIN, MARY - University Of Arkansas; Owens, Phillip; JAGADAMMA, SINDHU - University Of Tennessee; CARVALHO, TEOTONIO - Universidade Federal De Lavras; SUTIE, XU - University Of Tennessee

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2020
Publication Date: 6/15/2020
Publication URL: https://handle.nal.usda.gov/10113/6995158
Citation: Amorim, H., Ashworth, A.J., Moore Jr, P.A., Wienhold, B.J., Savin, M.C., Owens, P.R., Jagadamma, S., Carvalho, T.S., Sutie, X. 2020. Soil quality indices following long-term conservation pasture management practices. Agriculture, Ecosystems and Environment. 301. Article 107060. https://doi.org/10.1016/j.agee.2020.107060.
DOI: https://doi.org/10.1016/j.agee.2020.107060

Interpretive Summary: The USDA-Natural Resources Conservation Service (NRCS) recommends that farmers adopt conservation practices, such as rotational grazing, buffer strips, and riparian zones, to improve overall soil and water quality within pasture systems, thus increasing the sustainability of cattle production. To test whether the recommended practices improve soil quality (SQ), a framework named SMAF (Soil Quality Management Framework) was applied to calculate soil quality indices (SQI), which can be used to compare management practices. For that, researchers collected information on soil physical and chemical properties at the surface soil layer (0-15 cm) and calculated SQI in distinctive pasture systems: hayed (H), continuously grazed (CG), rotationally grazed (R), rotationally grazed with an unfertilized buffer strip (RB), and rotationally grazed with an un-grazed, unfertilized riparian strip (RBR). These pastures were consistently managed for 15 years and received annual poultry litter applications, except for the riparian buffer strips. Researchers also investigated the relationship between SQI and nutrient runoff using runoff water samples collected after 15 years of consistent management. Researchers found soil structure in pasture systems was not degraded, regardless the intensity of grazing (CG or R). They also demonstrated that conventional (CG) and conservation systems (R and RBR) had similar increased SQ. At the CG and R systems, increased SQ resulted from improved soil fertility, whereas at RBR systems resulted from the lower soil P concentrations and reduced risk of pollution of water bodies. A positive relationship between SQI and nutrient runoff suggested that pasture systems with increased soil fertility had greater nutrient runoff. The applied framework identified the impacts of long-term pasture management practices on SQ, demonstrating that conventional systems, when well-managed, can contribute to improved SQ as much as recommended conservation practices.

Technical Abstract: Monitoring long-term grazing management practices influence on soil quality (SQ) is essential to ensuring pasture sustainability, which is the largest land use in world agroecosystems. The aim of this study was to quantify SQ based on long-term (15-years) conservation pasture management and landscape position using the Soil Management Assessment Framework (SMAF). Treatments were setup in 15 watersheds (0.14 ha each, 8% slope) in a completely randomized design with five pasture management practices: continuously grazed (CG), hayed (H), rotationally grazed (R), rotationally grazed with an unfertilized buffer strip (RB), and rotationally grazed with an un-grazed, unfertilized riparian strip (RBR). Each watershed was divided in three zones (A, B, and C), with the riparian buffer strip (RBS) corresponding to the D zone. Selected soil chemical, physical, and biological properties were determined on soil samples collected in 2017 (0-15 cm depth) per zone. Total P, organic C, and total suspended solids (TSS) were measured in 2017 runoff samples. The SMAF SQ scores were evaluated individually and as an overall SQ index (SQI). Exponential models were used to investigate the relationship between SQI and total P, organic C runoff, and TSS loads. Continuously grazed watersheds had improved soil fertility, with greater nutrient concentration at the shoulder landscape position (zone A). Therefore, degradation of soil physical properties was not observed for this practice. After 15 years of continuous management, CG, R, and RBS watersheds had the greatest SQI (7.07, 7.05, respectively), not differing from RBR (6.93); likely owing to cattle manure deposition for these treatments. Increased SQI in RBS (7.33) improved SQI for RBR watersheds. Differences in SQI were mostly driven by changes in soil P, pH, electrical conductivity (EC), and K. The exponential models indicated that 34 and 28% of the variation in P and TOC runoff loads, respectively, can be explained by the SMAF SQI (p<0.05). Overall, SMAF identified the impacts of long-term pasture management practices on overall SQ and the contributions of individual indicators, thus identifying potential benefits of conservation practices.