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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

Forage Systems Update
Vol 8, No. 2

Forage production and yield distribution in diverse pastures

There is a lot of discussion these days about biodiversity in both agricultural and environmental communities. When I was an undergraduate in the 1970's, the common definition of a mixed pasture was one grass and one legume. A pasture that was any more diverse than this was considered too difficult to manage. Many of you know that I am very partial to diverse, mixed pastures. I would like to share the evolution of my appreciation for pasture diversity.

Grazing research began at the University of Missouri-Forage Systems Research Center in 1970. Through the first approximately 15 years of research, the basic grazing management was as 3-pasture rotational grazing systems. It was the researchers' belief that any Missouri cattleman should be able to implement and manage this system. The pastures were typically tall fescue monocultures receiving 100 lb-N/acre annually or binary mixtures of tall fescue, orchardgrass, or smooth bromegrass with red or ladino clover. During that same time period these pastures were invaded by bluegrass, white clover, and a few other perennial species as minor components. That early research clearly showed benefits of fescue-clover pastures over N-fertilized tall fescue.

In 1984 the basic grazing management was changed in many pastures to multi-paddock, short-duration grazing periods with flexible rest management. In the following five years, the pastures receiving this type of grazing management rapidly evolved from the binary or simple mixtures which had existed previously to much more diverse swards. A typical pasture at FSRC now consists of 8 to 12 desirable species making a significant contribution to total yield and animal intake. Pastures where tall fescue had provided >90% of the annual herbage in 1980 are typically 25 to 30% tall fescue now. This is in an environment where traditional grazing management has resulted in fescue dominance of nearly all pastures over the last 40 years. We saw the same trend occurring on many farms in the region where improved grazing management had been implemented. In many cases tall growing native warm season grasses, such as big bluestem indiangrass, and eastern gamagrass, that had not been observed for many years began to reappear in the pastures.

This evolution of diverse swards raised several comparative questions relative to the fertilized monocultures : 1) Were the diverse pastures more or less productive? 2) Was the distribution of available net energy and crude protein through the season more or less desirable? 3) How stable was the mixture that had evolved? 4) Would sowing a diverse seed mixture result in a diverse pasture? In 1994 we began a study to address these questions.

Research procedures: Sixteen grass or grass-legume mixtures were established in a completely randomized design with four replications. The grass components were seeded on September 5, 1994 on a prepared seed bed. Grass seed was broadcast and rolled in with a cultipacker. The legume components were frost seeded on March 10, 1995. Red clover and birdsfoot trefoil establishment with frost seeding was very good while alfalfa establishment was very poor. Due to the near absence of alfalfa in the designated plots, the plots identified as TF or SB + alfalfa are being used as 0 N treatments for comparative purposes. Individual plots are 50 X 50 ft with a 10 ft bluegrass alleyway surrounding each plot. Swards were uniformly managed to encourage establishment during the 1995 growing season. Tall fescue and smooth bromegrass monocultures receive 120 lb N/acre annually as three 40 lb applications applied in March, June, and September.

Each mixture was sown with a target seeding rate of 80 seeds/sqft. Mixtures were constructed in the following manner. First order pastures were monocultures of either tall fescue (TF) or smooth bromegrass (SB). Second order pastures were binary mixtures of each base grass with either red clover (RC), birdsfoot trefoil (BFT), or alfalfa (A) added. Binary mixtures were seeded at 40 seeds-m/sqft for each principal component. Third order mixtures contained the base grass (40 seeds/sqft) in combination with all three legumes (13 seeds/sqft for each component). Fourth order mixtures contained both base grasses (20 seeds/sqft for each component) with all three legumes. Fifth order mixtures contained both base grasses, all three legumes, plus orchardgrass (OG) and timothy (T) all in equal proportions. Sixth order mixtures contained all of the above plus big bluestem (BB). The mixtures are listed below. In the figures on the following pages, the numeral on the X axis refer to the mixture number given below.

Tall Fescue Base

1) TF + 120 lb N/acre
2) TF + 0 N/acre
3) TF + BFT
4) TF + RC
5) TF + A +BFT
6) TF + A + BFT + RC
7) TF + A + BFT + RC + OG + T
8) TF + SB + A + BFT + RC + OG + T
9) SB + 120 lb N/acre
10) SB + 0 N/acre
11) SB + BFT
12) SB + RC
13) SB + A + BFT
14) SB + A + BFT + RC
15) SB + A + BFT + RC + OG + T
16) TF + SB + A + BFT + RC + OG + T + BB

Beginning in 1998, plots were sampled and grazed according to the following protocol. Prior to grazing, six .25m2 quadrats were clipped from each plot. At the same site sward surface height was measured and the species composition was visually estimated. Plots were grazed with six steers for four to seven hours to remove approximately 50 - 60 % of the forage biomass. Following grazing, the same measurements were made. During the first grazing cycle, all fescue-based plots were grazed first followed by smooth bromegrass-based plots. In subsequent grazing cycles, plots were grazed strictly on an as needed basis. Total annual forage yield, yield by month, rest period to reach target grazing height, pasture daily growth rate, and forage utilization were all calculated. Laboratory analysis of forage quality is incomplete at this time.

Results and discussion: The mean sward height at initiation of grazing was approximately 10.5 inches which was slightly taller than our target of 8 to 10 inches (Figure 1). Rapid growth early in the season allowed some plots to exceed target height before they could be grazed the second time. The mean dry matter availability at initiation was slightly less than the expected target level of 2700 lb/acre (Figure 2). The expected forage availability level was based on height:yield relationships previously developed at FSRC. In this study, quadrats were clipped above the thatch layer rather than at ground level as was done in the calibration study.

Figure 1. The mean sward height at grazing initiation was slightly above the target level of 8 to 10 inches.

Figure 2. Forage availability at turn in was less than what was predicted by mean sward height.

Mean rest period required to reach the target grazing height was greater for SB-based pastures than for TF-based pastures (Figure 3). Mean rest period was 28 days for SB pastures while only 22 days for TF pastures. Nitrogen fertilized TF had the shortest mean rest period at 19 days. The range in length of rest period for TF + N pastures was 15 days in May to 28 days in July-August. The longest mean rest period was required by SB + RC at 31 days with a range from 25 days in May to 41 day in July-August. Excluding the N-fertilized TF and SB treatments, SB-based pastures usually required about five days additional rest through the summer months compared to TF-based pastures (Figure 4). The shorter rest periods in August are a reflection of the summer annual grass component, primarily crabgrass, in the swards.

Figure 3. Mean length of rest period required to reach target grazing height of 8 to 10 inches for sixteen pasture mixtures.

Figure 4. Smooth brome based pastures typically require a longer rest period than tall fescue based pastures.

While it has been easy to maintain OG as a strong component in TF-based pastures with rotational grazing, maintaining SB in a TF mixture has been much more difficult. If a pasture is grazed using TF condition as the guide for initiating grazing, the SB will likely not be adequately rested. Basing turn-in on SB condition may reduce palatability and quality of the TF component which may result in selective grazing of the SB component. Based on these observations, pasture mixtures should not include both smooth bromegrass and tall fescue. Based on relative length of rest period, daily growth rate for TF-based pastures was significantly greater than SB-based pastures (Figure 5). Mean daily growth rate was similar for TF + N, TF + BFT, and TF + BFT + RC, however, there were very notable monthly differences among the three treatments (Figure 6). Daily growth rate of TF + N increased very markedly following N applications in early April and mid-June and was significantly greater than the TF + legume mixtures during April, May, and July. During June and August, the TF-legume mixtures exhibited significantly greater daily growth. Daily growth rate of TF + N pastures fluctuated from 33 to 89 pounds/acre/day while the range for TF-legume mixtures was from 47 to 70 pounds/acre/day. The range for TF + N is 270% compared to only 50% for TF + legumes. Greater flexibility in management is required to accommodate the larger changes in daily growth rate associated with N fertilization. Either stocking rate, size of paddock, or amount of forage harvested as hay or silage should be adjusted more often and to a greater extent for TF + N compared to TF + legumes. There was less variance in daily growth rate among SB-based pastures than among TF-based pastures (Figure 7).

Figure 5. Mean daily growth rate of sixteen pasture mixtures during April through August growing period.

Figure 6. Monthly variance in daily pasture growth rate between tall fescue + 120 lb N and tall fescue + legumes.

Figure 7. Monthly variance in pasture daily growth rate for tall fescue (TF) or smooth bromegrass (SB) based pastures.

The low relative variance in monthly mean daily growth rate is in stark contrast to the growth curves for cool season forages that are often presented to producers. The typical growth curves represent either unmanaged growth or what might be expected in a hay management system. The data presented here indicate that seasonal variance in growth distribution in managed pastures is much less than many graziers believe. The variance occurring in mixed grass-legume pastures is much less than that occurring in grass monocultures. The inclusion of warm season annuals such as crabgrass and lespedeza in the mixture are also very likely contributing to the higher level of growth observed during July and August. The summer annual species present in these plots were not sown as part of the mixtures but are volunteer components. Many pastures in this region contain these or other summer annual species which may contribute significantly to summer carrying capacity. Forage dry matter production is presented for the April through mid-September period Figure 8) and also for the total growing season (Figure 9). All pastures were rested from their final grazing in mid-August or early September and allowed to stockpile growth for winter grazing. Stockpile forage yield was measured after the end of the growing season in early November. During the spring-summer period, forage yield was similar for most of the pastures, although yield distribution varied. Only six mixtures were significantly lower yielding than the highest yielding mixture. When the stockpile phase is included, TF + 120 N was the highest yielding pasture and it was significantly greater than ten other treatments. Previous studies at FSRC have shown TF + RC to produce fall stockpile yields comparable to TF + 60 lb N/acre with N applied in mid-August. Because there was over 30 days variance, both within and among treatments, in the beginning of the stockpiling phase in this study, that data is not presented as a single component.

Figure 8. Forage dry matter yield produced from April to late August-early September.

Figure 9. Total season forage dry matter yield produced from April through October.

This project is offering some very interesting insights into the relative performance and merit of mixed pastures. We hope to be able to continue this project for a number of years. The Forage Systems Update has historically been either four or six pages and will not accommodate the full report on this project. Additional results from the study can be found by visiting our website at http://aes.missouri.edu/fsrc/ and browsing under the research button. Additional data on yield distribution, predicting growth rates, changes in species composition are all posted.