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Title: Soil-test biological activity with the flush of CO2: IV. Fall-stockpiled tall fescue yield response to applied nitrogen

Author
item Franzluebbers, Alan
item PEHIM LIMBU, SMRITI - North Carolina State University
item POORE, MATT - North Carolina State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2018
Publication Date: 8/16/2018
Publication URL: https://handle.nal.usda.gov/10113/6471006
Citation: Franzluebbers, A.J., Pehim Limbu, S., Poore, M.H. 2018. Soil-test biological activity with the flush of CO2: IV. Fall-stockpiled tall fescue yield response to applied nitrogen. Agronomy Journal. 110:2033-2049.

Interpretive Summary: Fertilization of perennial pastures with nitrogen may not always be cost-effective, due primarily to stored nitrogen in soil organic matter that can be released for plant uptake. Scientists from USDA-ARS in Raleigh NC and at North Carolina State University evaluated tall fescue yield response to fall-stockpiled nitrogen application in a series of 55 field trials throughout Georgia, North Carolina, Virginia, and West Virginia. Yield response was either nil, modest, or high among various sites. Those sites predominantly with high soil-test biological activity and associated high nitrogen mineralization potential led to no yield response. Those sites with low soil-test biological activity and low nitrogen mineralization had high yield response. These results support the use of soil-test biological activity as an indicator of nitrogen availability so that producers can fine-tune nitrogen applications for greater production and profit, as well as to limit nitrogen losses to the environment. These results will be valuable for farmers, agricultural advisors, and applied agricultural scientists.

Technical Abstract: Fall stockpiling of tall fescue (Lolium arundinaceum) in the southeastern US is promoted as an ecologically favorable cattle management approach to avoid financial and environmental burdens of winter hay feeding. We hypothesized that soil N mineralization should be an important factor controlling forage yield response to N fertilizer. We conducted 55 N fertilizer trials in combination with analyses of soil C and N fractions at multiple locations in Georgia, North Carolina, Virginia, and West Virginia during two seasons. Plant available N, as a combination of residual inorganic N + mineralizable N at depth of 0-10 cm, was significantly negatively related with extent of forage dry matter response to N fertilizer input. Large variations in economically optimum N fertilizer requirement (EONR) occurred among fields, but when several fields were averaged along a gradient of soil biological activity, a strong negative yield response with increasing soil-test biological activity emerged. With moderate soil-test biological activity of 200 mg CO2-C/kg/3 d, EONR was 20 kg N/Mg forage dry matter (a value similar to current N fertilizer recommendations). However, with progressively greater soil-test biological activity up to 600 mg CO2-C/kg/3 d, EONR declined in a non-linear manner to near zero. These results illustrate that N fertilizer recommendations for fall stockpiled tall fescue pastures should be a function of soil-test biological activity, as an indicator of biologically active N. Greater economic and environmental sustainability would likely be attainable with a shift to recognizing soil biological activity in an ecologically oriented fertilization paradigm.