Time and time again producers attest to the benefits of winter bale grazing out on pastureland. Not only does it eliminate the cost of starting a tractor to feed bales and clean corrals, but they see that the manure and urine deposited by the animals, along with litter from the bales is greatly improving the organic matter in the soil, resulting in a marked increase in forage production.
As of yet, there have been no best management practices established for in-field winter feeding systems, largely because there hasn’t been enough research carried out to determine the long-term impact of the nutrient load on the land, groundwater and surface waterbodies in the watershed areas near in-field winter feeding sites.
Trials at two locations in Saskatchewan are assessing the concentrations and export of nitrogen and phosphorus nutrients as well as coliform bacteria in snowmelt run-off water. The studies are being carried out at the Western Beef Development Centre (WBDC), situated on light black soil near Lanigan, and at AAFC’s Semiarid Prairie Agriculture Research Centre (SPARC) in the brown soil zone at Swift Current.
On behalf of the numerous cooperators and researchers involved with the nutrient export study at both locations, WBDC research scientist Bart Lardner presented some of the preliminary findings from the first year of the studies at the WBDC field day earlier this summer.
Because snowmelt increased the potential for nutrient loss from winter bale grazing sites at both locations, the early recommendation is to situate bale-grazing areas so that run-off doesn’t enter sensitive surface and subsurface waterbodies.
The winter bale-grazing site at the WBDC was set up in the fall of 2008 on rolling perennial pastureland that had not previously been used for winter bale grazing. This three-year study involved two bale-grazing sites, with the cattle returning to the first site in the third year of the study.
The bales were placed 30 feet apart on centre to average 23 bales per acre. During the first winter, a group of 80 to 105 cows was bale grazed from Dec. 8 through Mar. 6. The bales were mostly bromegrass with five to 10 per cent alfalfa.
The bale-grazing density of 887 cow days per acre added an estimated 248 tons of manure to the site during the first winter grazing period. Of that total, 1.26 tons would have been in the form of nitrogen, for an application rate of 281 pounds per acre. Phosphorus totalling 0.42 tons was deposited at the rate of 94 pounds per acre.
A number of low-lying areas in the pastures where water tends to gather during run-off times (micro-watershed basins) have been established to monitor surface run-off water on the bale-grazed sites, in non-bale-grazed control sites, and outside of the bale-grazed and control sites.
Piezometers have been installed in low and high areas to capture samples of water from eight to 10 feet underground and to monitor the depth of the water during the snow melt. Interestingly, during the high rainfall experienced this past summer, the water in some of the piezometers rose almost to the surface. The piezometer stations are equipped with solar-powered data loggers to monitor surface water levels, rainfall, and temperatures.
In the fall of 2008, soil samples from a depth of six inches were taken across a large grid in the area to be used for bale grazing. Soil samples from the same depth were collected after the first winter of bale grazing in the spring of 2009.
Compared with the control grid, winter feeding had no significant effect on soluble and exchangeable soil phosphate, suggesting that winter feeding on the land reduces the potential for phosphate transport. In fact, the soluble and exchange phosphate measurements were lower in the spring compared to the previous fall. This may be due to plant and soil microbial uptake of phosphate in the spring.
Piezometer water samples collected weekly from the beginning of April until the end of June indicated that the average concentration of orthophosphate in the groundwater was slightly higher, but not significantly higher than that collected from the piezometers in the control areas. Orthophosphate is a basic form of phosphate that is readily available for plant uptake.
Overall, the total coliform bacteria count was higher at both piezometers in the bale-grazed sites compared with the control sites. But again, the difference wasn’t statistically significant.
Surface Water Samples
Surface run-off samples were collected during spring melting from Mar. 31 to April 19, 2009. The two parameters measured were the concentration of nutrients in samples from within the bale-grazed and control sites, as well as the export of nutrients in samples collected outside of the study and control sites.
The concentration of nitrogen in the form of ammonium was significantly higher in the run-off collected in the bale-grazed site compared with that in samples from the control site. The average ammonium exported from the bale-grazed site was elevated in comparison with the control site as well.
The concentration of nitrogen in the nitrate form in the run-off water was similar for the bale-grazed and control sites. More nitrate nitrogen was exported from the control site than from the bale-grazed site. The cool early-spring temperatures in the field may have limited the microbial conversion of ammonium to nitrate in the bale-grazed site.
Average orthophosphate concentrations were significantly elevated in the run-off water collected in the bale-grazed sites. The average amount of orthophosphate exported from the bale-grazed site was higher than that exported from the control site as well.
The total coliform count as well as theE. colicount in the run-off water from the bale-grazed area was elevated compared to total coliforms and E. coliin the run-off water from the control site.
The effect of winter bale grazing on forage production and soil nutrient levels on 10-year-old stands of Russian wild ryegrass (RWR) and crested wheatgrass (CWG) are being evaluated for a period of three years at AAFC-SPARC. The study is also incorporating the use of natural micro-watershed basins to monitor the nutrients in run-off water.
Each of the 2.5-acre RWR and CWG pastures was split in half. Each replicate has two micro-watershed basins to capture run-off water from the bale-grazing area, and another to capture run-off water from a non balegrazed control area.
The herd bale grazed the RWR pasture during the winter of 2008-09, the CWG pasture last winter, and will return to the RWR pasture this winter. In this way, they hope to assess whether bale grazing on the same pasture every second year is too soon in terms of nutrient loading on the pastures.
Targeting a bale-grazing density similar to that of the WBDC study, the cows were restricted to bale grazing in the sites with micro-watershed basins for four days in December and another four days in January as bale grazing progressed up the study pasture over the course of 93 to 96 days during each of the past two winters.
In the fall of 2009, two additional micro-watershed basins were incorporated into the study. Manure was spread on the new control sites at a phosphorus rate comparable to that achieved by bale grazing. No bale grazing occurred on the new control sites.
During four days of snowmelt in early March, 2010, run-off samples were collected from the micro-watershed basins on the bale-grazed pastures, non bale-grazed control sites, the manured controls sites and the sites that had been bale-grazed the previous winter.
The run-off samples from the balegrazed sites were significantly higher in total coliform bacteria, total nitrogen and total phosphorus than the run-off samples from the control areas. Most of the nutrients were in the dissolved forms, while particulate concentrations of nitrogen and phosphorus were the same in the run-off from the balegrazed and control sites.
Similar to the findings at WBDC, most of the nitrogen in the run-off water from the winter feeding sites was in the form of ammonium, while most of the nitrogen in the run-off water from the non-bale-grazed sites was in the nitrate form.
Most of the phosphorus in the runoff water was in the orthophosphate form. Most of the particulate phosphorus was in organic forms, including phytate.