Increased Late Spring Fescue Yield from Late Fall N Application the Previous Year

Classically, tall fescue stockpiling starts with 40 to 80 lb N/acre (Ritchey and McGrath, 2020) in August/September. With good management before and after the stockpiling interval, and typical fall weather, stockpiling produces significant forage yield (10 to 30 lb dry matter/lb N; Poore and Drewnoski, 2010) and lower winter feed costs. However, the question of what to do, soil fertility-wise, with remaining cool season grass pastures and hay fields to improve their productivity next year, remains.

One observation, from a turfgrass professional (A.J. Powell, pers. comm.), was that a late fall (November/December) N application caused improved cool season grass tillering and competitiveness in the spring of the next year. More recent tall fescue research, from China (Han et al., 2014), supports that observation. These observations were the focus of a field trial begun in the fall of 2020 at the UK Research and Education Center near Princeton. Here, some of the first year’s results are reported.

An established stand of tall fescue (Jesup MaxQ), managed for hay (2 previous cuttings earlier in 2020) was used. Three N sources (ammonium nitrate, 34-0-0; ammonium sulfate, 21-0-0-24S; SymTRX 20S, 16-1-0-20S) and 4 N rates (0, 30, 60, 90 lb N/acre) were used. SymTRX 20S is a product of Anuvia Plant Nutrients Inc. There were four replications of each of the 12 treatments. Fertilizer treatments were hand broadcast on 2 December 2020. On 1 April 2021, an application of ammonium nitrate, at 80 lb N/acre, was made across the entire field trial – to simulate usual spring N management for tall fescue.

Early growth and tillering were monitored weekly, starting on 15 March, with a rising plate meter. The N rate treatment differences were visible on that date (Figure 1a) and were even greater at the start of the third week (29 March, Figure 1b). The rising plate data supported the visual observations. No differences due to the N sources were apparent until the sixth week.

The first harvest was rain-delayed until 13 May, so the grass was somewhat beyond the desired boot stage of growth. There were large differences due to the late fall 2020 N rate (Figure 2a, averaged across the three N sources) and small differences due to N source (Figure 2b, averaged across the four N rates). There was no N rate by N source interaction.

Regardless the 80 lb N/acre applied on 1 April, the late fall N application increased dry matter yield at least 22 lb per pound of N. This value is well within the range of values for lb DM/lb N reported for fall fescue stockpiling followed by August/September N applications. The response indicates that the late fall N application caused the crop to emerge from the winter with greater capacity to respond to favorable early spring conditions. The response appears to ‘taper off’ a bit at the 90 lb N/acre rate, suggesting that 60 lb N/acre was more optimal in causing forage dry matter formation.

Averaged across all N rates, the SymTRX 30S source gave significantly (p < 0.10) less forage dry matter (3460 lb DM/acre) than the other two N sources (average of 3875 lb DM/acre). Given the lack of difference between ammonium nitrate and ammonium sulfate, there was no value to added S.

Figure 2. Fescue dry matter yield response to: a) fertilizer N rate; b) fertilizer N source.

On average, a 60 lb N/acre application of one of these three N sources in very early December returned 20 to 25 lb DM per lb applied N. We caution the reader that these are the results of a single trial, for a single year. This research needs to be repeated. That said, the preliminary results are both surprising and quite promising, potentially giving producers another window of opportunity to push greater cool season grass productivity when additional forage is needed.

~ John H. Grove, Chris Teutsch and Josh Duckworth

References:

Han, Y. et al. 2014. Effects of seeding rate and nitrogen application on tall fescue seed production. Agronomy Journal 106:119-124. doi:10.2134/agronj2013.0326

Poore, M.H. and M.E. Drewnoski. 2010. Utilization of stockpiled tall fescue in winter grazing systems for beef cattle. Prof. Anim. Sci. 26:142-149.

Ritchey, E. and J. McGrath. 2020. AGR-1: 20-21 Lime and Nutrient Recommendations. Univ. Kentucky Coop. Extn. Svc. Lexington. http://www2.ca.uky.edu/agcomm/pubs/agr/agr1/agr1.pdf