Author
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Bartholomew, Paul |
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Submitted to: Forage and Grazinglands
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/15/2014 Publication Date: 6/26/2015 Citation: Bartholomew, P.W. 2015. Nitrogen application for spring growth of cool-season grasses overseeded into unimproved warm-season pasture. Crop, Forage and Turfgrass Management. doi: 10.2134/cftm2014.0105. Interpretive Summary: Since native and introduced warm-season grasses do not grow in the cooler months of the year many livestock producers in the southern Great Plains plant cool-season grasses to provide pasture for grazing animals, and to reduce or eliminate the need for purchase of winter feed. Nitrogen fertilizer application is usually required to ensure the nutrition and productivity of cool-season grasses, and this represents a production cost that offsets to some degree the reduction in purchased feed costs made possible by increased production from pasture. Efficient use of N applied is important for economic viability of grass production systems, and also because N that is not taken up and utilized by a growing crop is at risk of loss the broader environment, where it may have harmful effects on water and air quality. Experiments were carried out with annual ryegrass, a widely-used cool-season forage, to compare the efficiency of use of N applied in fall, in early spring or in late spring, for regrowth after a first harvest. Fall application of N was not essential for good establishment of annual ryegrass and it did not result in harvestable fall production in any year. Fall applied N increased forage yield in spring in 1 year out of 3, with an average production of 13.4 lb of dry forage for each 1 lb of N applied. In contrast, N applied in early spring increased forage yield in 2 years out of 3, with an average of 17.2 lb of dry forage produced for each 1 lb of N applied. Application of N for regrowth of ryegrass in late spring gave the least effective use of N with only 6.7 lb of dry forage for each 1 lb of N applied. Elimination of fall application will allow small producers to reduce the cost of nitrogen use by 25 to 33% of current recommendations for cool-season grasses. Technical Abstract: Successful production of herbage by cool-season forage grasses in the southern plains is heavily dependent on a sufficient supply of available N, and appropriate scheduling of N application is an important component of cost-effective fertilizer use. The effects of different combinations of fall, early-spring and late-spring increments of 25 kg N/ha on forage DM and N yields of annual (Italian) ryegrass (IRG) were tested over 3 years. Fall N application had minimal effect on IRG establishment, measured in plant or tiller counts in the following spring. Application of N in fall did not produce harvestable herbage DM in fall and provided significant increase in DM yield in the following spring in only one year out of three. Early-spring N application produced significant yield increase in two out of three years and provided a mean yield response of 17.2 kg DM/kg N applied. Application of N for regrowth after initial IRG harvest in early May produced a mean yield increment of 6.7 kg DM/kg N applied. There was no residual effect of fall or spring N application on warm-season grass production. Limited N supply (<75 kg N/ha) is likely to be most efficiently used when applied at the beginning of the spring growing season. |
