Pasture Renovation and Grazing Management Impacts on Cool-Season Grass Pastures

Legumes have been shown to increase production in cool-season grass pastures. However, they are included in relatively few acres of pasture. A split plot experiment with six replications was conducted to evaluate the impact of pasture renovation and grazing management on forage production and species composition of cool-season grass pastures. Grazing management main plots were grazed to leave low (2-4 in.), medium (4-6 in.), or high (6-8 in.) residue levels. Main plots were intensively grazed (SO 000-70 000 lb of cows per acre) five or six times per grazing season by lactating Holstein cows. Subplot pasture renovation treatments were (i) an untreated check, or sprayed with glyphosate and interseeded with (ii) alfalfa (Medicago sativa L.), (iii) red clover (Trifolium pratense L.) and birdsfoot trefoil (Lotus corniculatus L.), or (iv) “graziers mix” (a mixture of legumes and grasses). Areas that were grazed to leave low residue level produced less forage mass (4.7 ton/acre) than areas grazed to medium (5.4 ton/acre) or high (5.5 ton/acre) residue levels. When averaged across years and grazing management treatments, renovated areas produced 1.8 ton/acre (46%) more forage than the control. Of interseeded species, alfalfa, red clover, and orchardgrass persisted through the study (more than 25% of the dry matter in at least one of the pasture renovation treatments). By June 1998, thistle (Carduus and Cirsium spp.) was present in all treatments. Fewer thistle was present in areas that were grazed to leave low residue (10 sq yd) than high residue (18 sq yd) and in renovated areas (9 sq yd) than the control (22 sq yd). The additional forage produced as a result of pasture renovation cost from S8.07/ton to $12.81/ton. This study indicates that pasture renovation can be a valuable tool for increasing forage production in cool-season grass pastures. Problem and Literature SummaryCool-season grass pastures in the North Central Region often do not produce to their potential. Renovation of pastures with legumes and productive grasses can increase pasture productivity. The addition of legumes to pastures provides N, increases forage quality and intake of forage, and increases summer growth. In spite of all the potential benefits from legumes, they are included in relatively few acres of pasture. The inclusion of adapted cool-season grasses can also increase pasture productivity. One of the challenges in maintaining renovated pastures is grazing management. This experiment addressed two pasture renovation issues: (i) does residue height left after grazing impact forage production and/or the persistence of desirable species, and (ii) identification of species which are adapted, productive, and have relatively good persistence under grazing in the north central region. Study DescriptionIn June of 1994 a split plot experiment with six replications was planted in an old bromegrass pasture. From 1995 through 1997 the area was grazed with 50 000 to 70 000 lb of lactating Holstein cows per acre five or six times per approximate 5-mo grazing season. Grazing management main plots were 120 by 100 ft. and designed to leave low (2-4 in.), medium (4-6), or high (6-8 in.) residue levels after grazing. Pasture renovation subplots consisted of (i) an untreated control; or were sprayed with 0.75 lb/acre glyphosate and interseeded with a no-till pasture drill with (ii) 10 lb/acre of alfalfa, (iii) 4.5 lb/acre of red clover and birdsfoot trefoil, or (iv) 2.1 lb/acre of alfalfa, birdsfoot trefoil, red clover, smooth bromegrass, orchardgrass, and timothy, and 0.5 lb/acre of alsike and ladino clover. Experimental areas were grazed each time forage reached 10 to 15 in. in height. Forage production estimates were taken prior to each grazing. In July of each year, species composition was estimated by hand clipping and separating. In addition, areas were evaluated for thistle infestation in June 1998. Applied QuestionsDoes residue level left after grazing affect forage production and stand composition? Grazing to leave 2 to 4 in. of residue resulted in less forage production (4.7 ton/acre) than grazing to leave 4 to 6 (5.4 ton/acre) or 6 to 8 (5.5 ton/acre) in. of residue. Grazing management did not affect species composition. This may have been because the rest periods between grazing events was sufficient for the species used in this study to recover. Which species are best suited for pasture renovation in the north central region? All pasture renovation treatments produced more forage than the bromegrass dominated control in all 3 yr of the study (Table 1). In 1995, the graziers mix, which contained many species, was the most productive treatment. This may have been the result of the species in that mix being more responsive to the abundant moisture in 1995. In 1996 and 1997, the alfalfa pasture renovation treatment was the most productive. Alfalfa annually produced about 60% more Full scientific article from which this summary was written begins on page 564 of this issue. forage than the control. Of the species planted, only alfalfa, red clover, and orchardgrass still comprised a substantial component of the forage (over 25% of the dry matter) in at least one pasture renovation treatment by the end of the study. Did residue level after grazing or pasture renovation treatment affect thistle populations? No mowing or thistle control measures were taken during the study, and by 1998 thistle was prevalent in all grazing and renovation treatments. Areas that were grazed to leave 2 to 4 in. of residue had fewer thistle (10/sq yd), than areas grazed to leave 6 to 8 in. of residue (18/sq yd). Areas grazed to leave 4 to 6 in of residue were intermediate (13/sq yd). It appeared that in the areas that were grazed to leave 2 to 4 in. of residue, there was more trampling and grazing of thistle (personal observation). There was fewer thistle in areas that were renovated (9/sq yd, averaged over the renovation treatments) than in the control (22/sq yd). The additional N supplied from the legumes may have resulted in more vigorous growth and competitive stands of forage plants in renovated areas. What was the economic benefit of the additional forage production? The additional forage produced from the renovation treatments over the 3 yr compared with the control was 7.0 ton/acre for the alfalfa treatment, 5.5 ton/acre for the graziers mix, and 3.8 ton/acre for the clover/trefoil treatment. The cost of the additional forage ranged from $8.07/ton for the alfalfa treatment to $12.81/ton for the clover/trefoil treatment. The cost to produce that additional forage is about 10 to 15% of the cost of purchasing that forage as hay, indicating that pasture renovation is very cost effective. Table 1Pasture renovation treatment by year interactions for season total forage mass for four pasture renovation treatments in 1995 through 1997. Means presented are averaged over grazing management treatments.† YearPasture renovation treatment199519961997---------- ton/acre ----------Alfalfa5.27.95.4Red clover/trefoil4.46.44.3Graziers mix5.76.44.9Control3.15.03.4†LSD (0.05 = 0.48 ton/acre) is suitable for comparisons within and between columns.