Nitrogen Fertilization of Stockpiled Tall Fescue in the Midwestern USA

Abstract

Stockpiled tall fescue ( Festuca arundinacea Schreb.) has been shown to extend the grazing season in the mid‐Atlantic states and upper‐South, but has not been widely used in the Midwest. A 3‐yr field study examined the effects of N fertilizer management strategies on stockpiled tall fescue yield and quality in the northern zone of tall fescue adaptation. Varying levels of four treatment factors, including sward growth stage at the time of N application, N fertilization date, N fertilization rate, and harvest date were imposed on a low‐endophyte ‘KY 31’ tall fescue sward. Maximum dry matter (DM) accumulation of stockpiled tall fescue (2800 lb/acre) occurred in mid‐November. Early‐August N fertilization increased ( P &lt; 0.01) stockpiled tall fescue yield by 30% compared with late‐August fertilization. Stockpiled tall fescue yield increased ( P &lt; 0.01) as fertilization increased from 0 to 120 lb N/acre, with summer precipitation determining the extent of the yield response. Nitrogen conversion efficiency was greatest ( P &lt; 0.05) for the first 40 lb N applied, then decreased about 60% and was similar for additional 40 lb/acre increments. Fertilization date did not affect forage quality. Increasing N from 0 to 120 lb/acre increased crude protein (CP) and lowered neutral detergent fiber (NDF) ( P &lt; 0.01) 2 out of 3 yr. Spring yield of tall fescue following fall stockpiling averaged 4000 lb/acre and was often higher ( P &lt; 0.05) with later and heavier N application the previous fall. We conclude that early‐August N fertilization of tall fescue produces favorable yields of high quality stockpiled forage for late season grazing in the Midwest. Research Question The practice of accumulating summer and fall growth of tall fescue as stockpiled feed for winter grazing has been widely investigated and adopted in the Southeast and lower Midwestern regions of the USA. The applicability of this practice to the more northern and western zone of adaptation for tall fescue has not been studied. This research was designed to determine appropriate N fertilization management for stockpile production in the Midwest. Literature Summary Research from the Upper South indicates that tall fescue is very responsive to N fertilization in the fall. Most researchers recommend N rates of 40 to 60 lb/acre. While stockpile yield tends to be greatest when accumulation begins in early to mid‐summer, forage quality tends to be higher as the date of stockpile initiation is delayed until autumn. Stockpile quality tends to be affected more by N application timing than by rate of N. Study Description A small plot study was conducted from the summer of 1989 through the spring of 1992 in north central Missouri to determine the impact of rate and timing of N fertilization on the yield, botanical composition, and nutritive quality of tall fescue. Effect of fall production on spring yield also was evaluated. Treatments: Sward state: 0, 14, or 28 d of regrowth at N application N application date: 1 August, 15 August, 29 August N rate: 0, 40, 80, or 120 lb N/acre Harvest dates: Every 21 d beginning in early October Cultivar: Kentucky 31 tall fescue (&lt;5% endophyte infected) Soil type: Lagonda silt loam (fine, montmorillinitic, mesic Aquic Argiudoll) Growing season moisture: Extremely variable across 3 yr of study Applied Question When is the appropriate time to begin stockpiling tall fescue in the Midwest? Within the month of August, higher yields for fall grazing will be obtained by beginning stockpiling early in the month. Potential yield drops off rapidly when initiation of stockpiling is delayed beyond mid‐month. Averaged across 3 yr and four N rates, 1 August N application produced 2923 lb dry matter (DM)/acre while 29 August application yielded 2277 lb DM/acre (Table ). There appears to be very little difference in forage quality between early August and late August initiation dates (Table ). Other research suggests that beginning stockpiling earlier in the summer will significantly lower quality, whereas delaying initiation until September or later will produce higher quality forage but dry matter yield will decline substantially. What is the optimal economic N application rate for stockpiling tall fescue? Even though tall fescue produced a growth response to N rates up to 120 lb N/acre, it is unlikely that an economic response occurs much beyond the 40 to 60 lb rates that are recommended in other regions of tall fescue use. The conversion rate of pounds of forage DM produced per pound of N applied declines from 19.0 lb DM/lb N for the first 40 lb N increment to 9.3 lb DM/lb N for the third 40 lb N increment. Given an N fertilizer cost of 23C/lb, the cost of each additional grazing day gained from higher N application rates would not be cost competitive with other feeding alternatives. Three‐year average yield across N application dates ranged from 1988 lb DM/acre for 0 lb N up to 3062 lb DM/acre for 120 lb N. Stockpiling tall fescue for winter grazing by livestock can have several potential economic and environmental effects. Reducing the need for harvested feedstuffs by extending the grazing season will lower equipment, storage, and labor costs associated with hay or silage feeding. Frequently, when ruminants are fed harvested feed, they are fed in a smaller area, resulting in manure concentration that must be dealt with from both an economic and environmental perspective. Transporting and redistributing manure mechanically can be costly. Allowing the animals to graze and carry out the distribution of manure themselves makes economic and environmental sense. Feeding in concentrated areas during the winter frequently denudes the land and results in increased erosion potential. Keeping livestock on grazable swards should protect soil integrity and water quality. Main effect means for forage yield of tall fescue stock‐piled with varying sward state at initiation of stockpiling, N fertilization date and rate, and harvest date in 1989, 1990, and 1991. Factor Treatment 1989 1990 1991 ‐‐‐‐‐‐‐‐‐‐lb/acre‐‐‐‐‐‐‐‐‐ Sward state 0 2532 2536 2161 (days) 14 2608 2857 2234 28 2938 3153 2359 N fertilization 1 August 2954 3190 2626 15 August 2721 2943 2113 29 August 2402 2414 2016 N fertilization 0 1896 2260 1809 rate (lb/acre) 40 2656 2766 2179 80 2922 3034 2463 120 3294 3337 2556 Harvest date 4 October 2388 2939 1826 25 October 2898 2717 2564 15 November 2968 2849 ‐ 6 December 2515 2892 2365 Crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) concentrations of stockpiled tall fescue at varying N fertilization rates in 1989,1990, and 1991 (averaged for sward states, N application dates, and harvest dates). Year N rate CP NDF ADF lb/acre ‐‐‐‐‐‐% DM‐‐‐‐‐‐‐ 1989 0 15.7 52.7 31.6 40 16.0 52.3 31.8</j