Nutritive value of fall-stockpiled tall fescue in response to N and P fertilization

Authors: Franzluebbers, Alan; POORE, MATTHEW - North Carolina State University

Submitted to: Crop, Forage & Turfgrass Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2020
Publication Date: 1/20/2021
Citation: Franzluebbers, A.J., Poore, M.H. 2021. Nutritive value of fall-stockpiled tall fescue in response to N and P fertilization. Crop, Forage & Turfgrass Management. 113:610-622.

Interpretive Summary: Fall stockpiling of tall fescue pastures is a viable strategy to stretch the grazing season towards more year-round grazing to lower the cost of cow-calf production. How forage nutritive value is affected by nitrogen and phosphorus fertilization in mature pastures has not been a major focus of research, and yet many pastures in North Carolina and surrounding states are well matured. A scientist from USDA-Agricultural Research Service in Raleigh NC collaborated with a ruminant livestock specialist from North Carolina State University to evaluate forage nutritive value responses to fertilization on 92 fields in the region. Only small increases in forage nutritive value were observed in response to nitrogen fertilization and essentially no response occurred to phosphorus fertilization. Forage nutritive value was not affected whether tall fescue had novel or wild endophyte association, but was typically greater when pastures were historically grazed than when cut for hay. Older stands of tall fescue pastures were similar or greater in nutritive value as young pastures. Soil texture did not affect forage nutritive value. A gradient of greater forage yield and lower forage nutritive value occurred from the highland Blue Ridge region to the lowland Coastal Plain region. This study demonstrated that fall-stockpiling of tall fescue can be considered an efficient nutrient cycling strategy on many well-established pastures in the eastern US and many mature pastures may have sufficient nitrogen cycling through mineralization of organic matter that exogenous nitrogen and phosphorus fertilization may not always be profitable. Research demonstrated in another report indicated that soil biological testing would be a reasonable method of discerning responsive and non-responsive sites.

Technical Abstract: Fall-stockpiling of tall fescue (Schedonorus arundinaceus) is an approach to overcome fescue toxicosis, as well as to reduce winter hay feeding costs of beef cattle grazing systems. We analyzed the nutritive value of fall-stockpiled forage in response to N and P fertilization on three dozen fields throughout North Carolina in 2018, as well as on several more dozen fields in North Carolina and neighboring states in 2015 and 2016 (n = 92 fields total). Our goal was to understand how inherent soil nutrient cycling might supplement the need for exogenous N and P fertilizer recommendations. Nutritive value of stockpiled tall fescue was generally improved with N fertilization, but not at all with P fertilization. Although increasing N fertilization led to (a) greater crude protein, macronutrient concentrations (i.e. K, Ca, and P), moisture content at time of harvest, and relative feed value and (b) lower acid-detergent fiber and insoluble protein, neutral detergent fiber, and lignin, the changes were not dramatic. For example, crude protein increased from an average of 111 g/kg without N fertilization to 127 g/kg with 100 kg N/ha. Small changes in nutritive value may have been a consequence of trials conducted on fields with relatively high soil biological activity and net N mineralization potential. Therefore, continued exogenous N and P fertilizer inputs were not always needed to enhance forage nutritive value. These results suggest that fall-stockpiling of tall fescue can be considered an efficient nutrient cycling strategy on many well-established pastures in the eastern US.