Amending pasture soil to decrease weed presence while improving forage species composition and quality
On many farms in the Northeast, pastures tend to decrease in appropriate forage species for grass-fed animals while increasing in weed species over time, likely in response to decreasing soil fertility. When soil nutrition is compromised, the vigor and stand density of desirable forage species decline, allowing weed species to establish as forage quality diminishes. Because animals tend to graze species they find palatable while avoiding weed species, farmers with weed-dominated pastures need to increase the amount of hay fed to pastured animals, thus increasing their operational costs. Additionally, in weed-dominated fields with low soil fertility levels, nutrition available to the animals may be compromised, necessitating the feeding of often-expensive supplements to maintain optimum animal health.
Many recommendations for pasture renovation suggest mechanical cultivation, chemical weed suppression, and reseeding. While these methods may produce the desired results, they also have ramifications of increased soil erosion and compaction, environmental degradation, and cost, while failing to address the underlying nutritional deficiencies that are promoting weed growth in the field.
Recognizing that weeds thrive in particular conditions of low soil fertility, we are using custom soil tests and recommendations to amend the pasture soil to promote forage species desirable for horses and increase nutritional quality. We expect that with the proper balance of soil nutrients, the percentage of forage species in the field will increase along with an increase in nutritional quality, while weed species decline, without the need for cultivation, reseeding, or herbicide application. We are quantifying our results by measuring weed and forage species composition in three one-acre amended test plots and three one-acre unamended control plots. Forage species are sampled and analyzed for nutritional content in test and control plots. This study began in 2011 and will continue through the 2012 growing season in Mid-coast Maine. The results will be shared with other farmers via an on-farm workshop, an off-site presentation, and a written project summary in 2012.
This study is taking place on Zephyr Hill Farm, which consists of 130 acres of fields and woodlands in Waldo County, Maine. The farm includes three acres of organically managed vegetables with integrated flowering, fruiting, and medicinal perennial species, approximately twenty acres of pasture, and over one hundred acres of woodlands. Singing Nettle Farm operates on this land, working with a team of Halflinger ponies to grow produce for a CSA (community supported agriculture) program, local restaurants, the public school system, the Maine Organic Farmers and Gardeners Association (MOFGA) Common Ground Fair, and a farmers market.
This study began in spring 2011 and will continue through September 2012, providing two full seasons of data collection. We have established research plots in the Zephyr Hill Farm pasture arranged in a randomized complete block design, consisting of three replications of one acre test plots and three replications of one acre control plots. Initial soil tests were obtained from each section in spring 2011 to determine starting fertility levels; soil tests will be repeated in spring 2012 to monitor any changes and make necessary nutritional adjustments. Based on the soil tests, the three test plots received custom blended soil amendments (applied with a drop spreader) in summer 2011. The remaining three control plots did not receive any amendments. Amendment blends were formulated with the assistance of technical advisor, Mark Fulford, and supplied by Lancater Agricultural Products.
Species composition was measured in each plot using the beaded string method (Northeast Cover Crop Handbook, Sarrantonio 1994), in which a string marked in one-meter increments is stretched across the plot in transects; while the species growing beneath each mark is documented. Weed and forage species composition was measured twice throughout the growing season: in June, just before first-cut (of hay), and again in September, just before second-cut. To measure forage quality, plant tissue samples from each plot were collected twice throughout the growing season, once in June and again in Septermber, and sent to the University of Maine Analytical Laboratory and Maine Soil Testing Service for nutritional analysis that includes nitrogen, phosphorus, potassium, calcium, magnesium, aluminum, boron, copper, iron, manganese, and zinc levels. Plant tissue samples were obtained by cutting every tenth plant (whether a weed or forage species) along the beaded string and bulking the cuttings as a representation of the entire plot. After plant sampling, all plots were mowed to simulate grazing and to prevent weed species from going to seed.
In 2011 initial soil tests were obtained, revealing deficiencies in calcium, magnesium, phosphorus, potassium, nitrogen, sulfur, boron, zinc, copper, and manganese. Based on these results a custom soil amendment blend was formulated to address the nutrient deficiencies in the soil. The amendment recipe included hi-cal lime, gypsum, soft rock phosphate, magnesium sulfate, sulfate of potash, manganese sulfate, dolomitic lime, sul-po-mag, humates, zinc sulfate, sodium nitrate, myco seed treat, and copper sulfate. Approximately 2,900 lbs of amendments per acre were spread on the three experimental plots with a drop spreader pulled behind a tractor. All ingredients in the blend were selected to meet USDA organic certification requirements. Species composition and forage nutrition samples were collected before amending (prior to first-cut) and again later in the season (prior to second cut).
Impacts and Contributions/Outcomes
Late season species composition samples showed slightly more grasses in the experimental plots when compared to control, indicating that the soil nutrition may be beginning to shift towards favoring grasses over weeds. However, it is still early to detect any major differences. Forage nutrition analysis also revealed no major differences between control and experimental samples in 2011, suggesting that the plants have not yet begun to take up the amendments. We anticipate the observation of greater changes of both species composition and forage nutrition in the 2012 season, as the soil microbiology continues to assimilate the nutrients into the system. Follow-up soil tests will be gathered in early 2012 to identify any remaining nutrient deficiencies, with corresponding amendment recipes to be formulated and applied.
In 2012 the results of this project will be shared with the agricultural community through an on-farm workshop discussing the purpose, methods, and results of this study while observing the field plots. Written summaries of the project will be distributed to all participants. An off-site presentation illustrating our findings will also be proposed for an educational event at the MOFGA education center.