Evaluation of alternative fertility management for ‘BG34’ and ‘Mara’ perennial ryegrass and ‘Stargrazer’ tall fescue

Jim Gerrish

Research methods: The experimental site consists of soils of the Armstrong-Lagonda association (fine, montmorillinitic, mesic) in north-central Missouri (W 93o04′:N 39o50′). Cultivars in the study include ‘BG34’ perennial ryegrass, ‘Mara’ perennial ryegrass, and ‘Stargrazer’ tall fescue. Grazing plots were established in a completely randomized design with four replications. Individual plots were 50 ft X 50 ft with a 10 ft buffer between each plot. Prior to seeding a uniform application of 36-92-62 was applied to the entire study area. Grass varieties were broadcast seeded at 30 pound/acre on a prepared seedbed on September 30, 1999. Plots were rolled with a cultipacker immediately after seeding. Soil conditions were extremely dry with less than 2 inches of precipitation falling in the 60 days after seeding and establishment was poor to fair. An additional 20 pounds/acre seed was broadcast March 7, 2000, and 4 pound/acre ‘Alice’ white clover was broadcast March 10, 2000.It is important to remember that in the discussion when references are made to ‘high’ and ‘low’ fertility, both treatments received equal amount of N/acre. The differences in fertility treatments are in the levels of P, K, and micronutrients applied. Initial fertilizer treatments were applied May 19, 2000. Low fertility plots received 75 pounds/acre as urea while the following materials were applied to the high fertility plots on a per acre basis:

45 pounds N as diammonium phosphate
30 pounds N as ammonium sulfate
34 pounds S as ammonium sulfate
115 pounds P2O5 as diammonium phosphate
93 pounds K2O as muriate of potash
2.1 pounds B as borax
1.0 pound Cu as copper sulfate
5.4 pounds Zn as zinc sulfate

Additional applications of 40 units of N/acre were made on June 14, July 20, August 18, and September 29 as urea and ammonium sulfate for low and high fertility treatments, respectively. These four applications of ammonium sulfate added an additional 184 pounds of sulfur/acre. On September 8, 0-30-60 was applied to all plots.

Ground cover by the seeded species was visually estimated on April 2. Plot grazing began on April 7 and concluded November 5. Plots were individually sampled and grazed whenever mean sward surface height reached 6 to 8 inches. Mean sward surface height is defined as the height below which an estimated 90% of the forage biomass occurs. Data collected included clipped yield estimate from six 0.25m2 quadrats in each plot with corresponding mean sward height at each quadrat. Clippings from all six quadrats were thoroughly mixed and a 100 g subsample was retained for forage quality analysis. Dry matter content of the forage sample was determined by oven drying at 130°F and forage dry matter yield calculated. Plots were grazed with 7 to 10 head of yearling heifers for four to seven hours to remove approximately 50% of the forage biomass. Grazing usually occurred between 6 AM to 3 PM but during the hottest part of the summer, cattle were placed on plots from 7 PM to 7 AM to encourage grazing. Stand density was evaluated during winter 2000 by step-point method with 100 points per plot.

All measured parameters were compared using the SAS GLM procedure and least square means calculated. Comparisons among treatment means was made using Fisher’s protected least significant difference procedure.

Results and discussion:

To evaluate uniformity of grazing treatment among all plots, pre- and post-grazing mean sward height and forage availability were compared (Figures 1 and 2). No significant differences existed among the cultivars or fertility treatments for any of these parameters indicating that plots had been managed uniformly through the grazing season. As would be expected based on similarity of pre- and post-grazing forage availabilities, temporal utilization rate was similar for all treatments and very close to our target of 50% (Figure 3). The forage dry matter yield per acre-inch was significantly greater for ‘Stargrazer’ and ‘BG34’ compared to ‘Mara’ (Figure 4). This may be due to the high level of annual ryegrass contamination in the ‘Mara’ plots through June. Annual crops tend to be lower yielding per unit of height compared to perennial grass crops.

Rest periods required for regrowth to the target grazing height were similar for all treatments (Figure 5), but Stargrazer had significantly more forage regrowth during each rest period compared to ‘Mara’, while ‘BG34’ was intermediate (Figure 6). There was a trend (p=0.09) toward lower daily growth rate for ‘Mara’ at both fertility levels (Figure 7) compared to either ‘BG34’ or ‘Stargrazer’.

Total pasture yield for the grazing season was significantly greater for ‘Stargrazer’ compared to all other treatments except ‘BG34’ at the low fertility level (Figure 8). At this point in the study, there appears to be no production advantage for the higher level of soil nutrient application. Forage quality analysis has not been carried out at this time and some increase in forage nutritive value may be found when the analysis are completed.

Stand persistence has been difficult to assess due to the unfavorable environmental conditions under which the trial was established. The annual ryegrass contamination in the ‘Mara’ plots has also been a difficult factor to deal with in the analysis and interpretation of the data. Stand density at the end of the growing season was significantly different among species (Figure 9), but no effect of fertility treatment was observed. Stand density of ‘Stargrazer’ increased through the grazing season while ‘BG34’ remained unchanged (Figure 10).

Initial observations from the first year of the study suggest that ‘BG34’ may be a viable forage option in this region. The difference in annual forage yield between ‘Stargrazer’ and ‘BG34’ are slight enough that a if ‘BG34’ exhibited higher forage quality, the net energy yield per acre might be similar. Given the annual ryegrass contamination of the ‘Mara’ seed lot, no conclusions can be drawn. The application of micronutrient and higher levels of P and K apparently had no benefit for production or persistence of either tall fescue or perennial ryegrass.