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United States Department of Agriculture

Agricultural Research Service

Research Project: SOIL ORGANIC CARBON AND NUTRIENT DYNAMICS IN TALL FESCUE PASTURES Project Number: 6612-11120-003-02
Project Type: Reimbursable

Start Date: Dec 01, 2006
End Date: Jan 14, 2011

Objective:
Link soil organic carbon sequestration, soil quality, and soil microbial community structure with nutrient dynamics and water runoff quality in tall fescue pastures varying in endophyte association, fertilizer source input, and harvest management. Plant and animal productivity will be determined to relate environmental responses to production responses. Specific objectives will be to: (1) Measure a suite of soil physical, chemical, and biological properties that could contribute to soil quality assessment in response to management, animal behavior, and landscape characteristics, (2) Quantify the rate of soil organic C and total N sequestration in response to tall fescue-endophyte association, fertilizer source, and harvest management, (3) Separate the influences of management, landscape features, and animal behavior on the physical, chemical, and biological components of soil quality, (4) Define the volume and quality of water runoff, both seasonally and yearly, in response to fertilizer source and harvest management of tall fescue pastures, (5) Assess botanical composition of pastures with time and management, (6) Differentiate cattle production responses to tall fescue–endophyte association and fertilizer source, (7) Ascertain the factors (management, landscape position, animal behavior, soil properties) that might contribute to variations in nutrient runoff, and (8) Integrate soil, water, plant, and animal responses into a recommendation for producers to balance productivity and environmental quality.

Approach:
A 20-ha tract of land operated by the USDA-Agricultural Research Service in Watkinsville GA will be used as a long-term field experiment for this experiment to link soil and water quality. The land lies on a typical Southern Piedmont landscape with 0 to 10% slope. Soils at the site are sandy loam to sandy clay loam (fine, kaolinitic, thermic Typic Kanhapludults) composed of: 80% Cecil, 12% Pacolet, and 8% Appling. Significant soil loss occurred in the past during cropping and the site would be considered typically eroded for the region. Fourteen experimental paddocks (1.00 +/- 0.05-ha each) were created with 0.4-m-high and 1-m-wide soil berms along the edge of each experimental unit. An H-flume water outlet was constructed in berms at the lowest elevation of each paddock. Good stand of all tall fescue (‘Jesup’)-endophyte associations was obtained by Spring 2002. The experimental design consists of a randomized arrangement of seven treatments in two blocks. Six of the seven treatments are grazed by yearling Angus heifers whenever sufficient forage is available. Grazing of paddocks was initiated in April 2002. The six grazed treatments are a factorial combination of three tall fescue-endophyte associations (A) and two fertilizer management (B) variables. Harvest management (C) is either with cattle grazing or as hay removal. (A) Tall fescue-endophyte association--(1) Wild-type E+ producing high concentration of ergot alkaloid, (2) Novel E+ selected with very low production of ergot alkaloid, and (3) E- having no ergot alkaloid production. (B) Fertilizer management--(1) Inorganic fertilizer applied at a rate recommended for the region (180-45-90 kg N-P2O5-K2O/ha/yr) in split applications of 90-45-90 (spring) and 90-0-0 (autumn) and (2) Broiler litter applied twice yearly (spring and autumn) to supply similar available N as with inorganic fertilizer (6.6 Mg/ha/yr, estimated to supply 270-100-140 kg N-P2O5-K2O/ha/yr with 67% of applied N considered available). (C) Harvest management--(1) Grazing of paddocks with a variable stocking rate of yearling Angus heifers to consume forage to approximately 1 Mg/ha. Variable stocking is based on an available pool of 50 weaned heifers (8-month old) beginning in October each year. (2) Haying occurs 2 to 3 times each year with commercial equipment, depending upon quality (dictated by season) and quantity (>1 Mg/ha) of forage available to cut. Soil, water, plant, and animal response variables will be individually determined and initially analyzed to ascertain the effects of management within a disciplinary approach. Results will be integrated across disciplines to understand controls on ecosystem productivity and changes due to management inputs. Individual paddocks will be routinely subdivided into three zones for soil and plant determinations to account for assumed variability due to animal behavior, but also sampled on a grid basis to account for inherent soil and landscape differences.

Last Modified: 11/21/2014
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