Soil health and pasture productivity under mob grazing and fertility management
CSANR Project 146
Grazing cattle may be managed in such a way to improve the productive capacity and/or health of the land that supports them. This study assessed and continues to assess the soil health and productivity of a certified organic ranch pasture under a variety of grazing and fertility treatments. Two different strategies of planned grazing management are being used, differing by the density and timing of grazing cattle. These strategies represent a sustainable low-density stocking rate, and a very high density but brief stocking approach. These two grazing strategies are overlaid with four soil fertility treatments to address pre-existing fertility limitations. The fertility treatments are: none (control), organic P and S (at rates recommended by soil analysis), supplemental manure, and compost tea.
The two factors in this study, grazing management and fertility management, address two of the FY15 BIOAg priorities:
- Biologically-intensive and organic approaches to sustainable management of soil quality –
- Novel approaches to weed, disease, pest and/or fertility management that transcend traditional conventional or organic approaches.
The study site was established in 2015. Initial soil and plant communities were assessed. High and low density grazing and the fertility treatments have been applied in 2015 and 2016. Forage productivity and quality, and soil fertility and biological activity were analyzed in 2016. Forage production will be assessed annually going forward, with a full repeated forage and soil analysis in 2019.
Fact sheets on pasture amendment and grazing are still planned but cannot be written until results are firmer. The key change predicted by the research hypothesis is soil microbial activity increase and this was not expected to change inside a 2-year grant cycle. Preliminary results indicate that high stock density does make a difference in soil health and forage yield; further, that high stock density with long recovery periods combined with soil amendments improves measurable indicators of soil health. However, canonizing this partially tested hypothesis would be premature and would lack necessary detail for good guidance to farmers and ranchers.
Additional Funds Leveraged
Western SARE Professional + Producer grant, applied December 2015 and December 2016.
Graduate student Adel Almesmari has been funded by an outside scholarship, value $120,000.
Impacts and Outcomes
• Short-Term: Significantly greater awareness of pasture fertility concepts and the role of soil microorganisms in mediating nutrient availability. Researchers expect to learn over the next 3-5 years whether an additive or synergistic relationship exists between high-density grazing and organic fertility treatments. Pastured land commonly suffers from low soil nutrient levels and consequent low productivity. These conditions, combined with poor grazing management which inhibits full expression of the plant community, result in a relatively unproductive land base for commercial cattle production. During this study and related outreach, researchers and ranchers will gain knowledge and improve overall management of nutrient cycling for long-term pasture productivity.
• Intermediate-Term: Increased understanding of how grazing variables (duration of grazing bout, timing of grazing relative to plant phenology and season, animal density within paddock, frequency of grazing events, length of recovery period within plant growing season) affect the ratio of trampling to grazing (which relates directly to soil cover), severity of defoliation (how much of the plant is removed). Improving productivity of pastures through means other than synthetic fertilizer, which is already viewed as prohibitively expensive by livestock producers, could significantly increase the profitability of livestock production. Washington livestock producers, at least early adopters, if presented with a low-cost method of enhancing soil fertility and pasture production, will implement on a small scale to test the concept on their own, likely in the first growing season following publication and promotion of the research results. This research will have applicability to crop farmers as well.
• Long-Term: Throughout the Pacific Northwest there is increasing interest in integrating livestock with cropping systems. This is driven, in part, by volatile petroleum prices and the direct effects on synthetic fertilizer input costs for crop farmers; integration is motivated also by increasing awareness of the importance of soil health for water-holding capacity, nutrient availability, and soil conservation (avoiding erosion). Success in this project could prompt, within 5-10 years, a shift toward management that 1) optimizes profit rather than maximizing yield, 2) conserves nutrients through low-input application, and 3) utilizes alternative nutrient sources and methods that enhance nutrient availability using verified promoters of soil health, and 4) integrates livestock with crop production for improved long-term agroecosystem sustainability.