Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/24/2007
Publication Date: 5/1/2007
Citation: Haan, M.M., Russell, J.R., Powers, W.J., Kovar, J.L., Benning, J.L. 2007. Effects of forage management on pasture productivity and phosphorus content. Rangeland Ecology and Management. 60:311-318. Interpretive Summary: Developing appropriate grazing strategies is important because in addition to providing feed for animals, forages protect the soil surface from raindrop impact, bind soil particles together, and slow runoff, thus allowing more time for infiltration and reducing loss of sediment and nutrients [especially phosphorus (P)]. Three grazing strategies, harvesting forage for hay, and a non-grazed control were compared for three years in Iowa. We found that when the pastures were not grazed or harvested, forage and root production were lower and annual P uptake by the forage was also decreased. There was also a seasonal response with P concentrations in the forage being higher in spring than autumn. The percentage of surface cover had the largest effect on sediment and P losses, which agreed with a previous study. By managing grazing so that surface cover is maintained, neither sediment nor P loss will exceed non-grazed grassland. This research provides useful information for cattle producers, local environmental groups, Cooperative Extension, and NRCS personnel.
Technical Abstract: The objectives of the current study were to determine the amounts of above- and below-ground plant biomass production, phosphorus (P) uptake by forage, and P concentration of cool-season grass forage as influenced by management and season. Five forage management treatments were evaluated over three years in smooth bromegrass (Bromus inermis Leyss) pastures. Management practices were: ungrazed (U), hay harvest/fall stockpile grazing (HS), rotational stocking to residual forage heights of 10 (10R) or 5 (5R) cm, and continuous stocking to maintain sward height at 5 cm (5C). Forage samples were hand-clipped within and outside grazing exclosures monthly from April through November of each year and analyzed for mass and P concentration. Root samples were collected at the initiation and completion of the study for determination of root length density (RLD) and root surface area density (RSAD). Phosphorus concentration of forage outside of grazing exclosures did not differ between 5C, 5R, and 10R treatments which were greater than U paddocks in April and August and less than HS paddocks in June. Mean annual forage productivity was greater in HS, 10R, 5R, and 5C paddocks (6744+ 890 kg ha**-1) than in the U paddocks (1872+ 890 kg ha**-1). Mean P concentration of forage outside exclosures was greatest during the spring (0.21+ 0.02%), and lowest during the fall (0.13 + 0.02%). Mean annual P uptake by forage followed the same trend as forage production, being greater in the HS, 10R, 5R, and 5C paddocks (13.9+ 2.1 kg ha**-1) than in the U paddocks (3.7+ 2.1 kg ha**-1). After three years, both RLD and RSAD decreased in the ungrazed paddocks, but were unchanged in the HS, 10R, 5R and 5C paddocks. Above- and below-ground forage production and P uptake by forage were stimulated by forage harvest, either by grazing animals or hay harvest.