Amending pasture soil to decrease weed presence while improving forage species composition and quality

Final Report for FNE11-714

Project Type: Farmer
Funds awarded in 2011: $10,706.00
Projected End Date: 12/31/2012
Region: Northeast
State: Maine
Project Leader:
Bill Errickson
Singing Nettle Farm
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Project Information


Many farmers in the Northeast have pastures or hayfields that, over time, tend to show a decline in desirable forage species and quality as weed species increase. Common practice for pasture renovation includes mechanical cultivation, reseeding, and sometimes the use of herbicides, resulting in greater soil erosion and compaction, higher costs, and compromised natural resources. Recognizing that weeds thrive in particular conditions of low soil fertility, three one-acre test plots were amended with custom formulated blends to address mineral deficiencies, and compared to three adjacent one-acre control plots. As soil nutrition in the field increased, an increase was observed in palatable forage species, such as fescue, orchard grass, quackgrass, timothy, red clover, and vetch. A decrease was observed in broadleaf weed species including aster, buttercup, chickweed, cinquefoil, goldenrod, hawkweed, daisy, strawberry, and yarrow. Forage species were also sampled and analyzed for nutritional content to compare forage quality in test and control plots, though no consistent differences were observed in plant tissue analysis.

This study took 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 Haflinger draft ponies to grow produce for a CSA (community supported agriculture) program, local restaurants, the Maine Organic Farmers and Gardeners Association (MOFGA) Common Ground Fair, and a farmers market.


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 hay 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.

Most weeds grow in a narrowly defined window of allowable soil conditions (Weeds and Why They Grow, McCaman 1994). Common problem weed species such as goldenrod, buttercup, bedstraw, asters, and thistles are examples of non-palatable species that are diminished by changing soil nutritional levels and generally indicate low soil pH, calcium, phosphorus, and trace element levels. Comparatively, desired forage species such as Kentucky bluegrass, timothy, smooth brome grass, perennial rye grass, ladino clover, red clover, alfalfa, reed canary grass, and tall fescue thrive in more alkaline conditions with higher soil fertility (University of Maine Cooperative Extension). On more than one farm, the effect using a full compliment of elements to amend the soil was approximately 60-70% reduction of bedstraw on the first year, accompanied by a show of over 50% red clover types (that were not seeded), by second cutting. The second year showed even greater improvements in desirable species composition (personal communication, Mark Fulford).

Because forages are quite competitive with weeds when provided with proper nutrition (Hay Crop and Pasture Weed Management, University of Tennessee Cooperative Extension), and because many of the desired species are already present in the fields, we anticipated that existing weed problems would be ameliorated with the application of custom soil amendment blends. By raising soil fertility, we expected to shift the species composition towards desirable forage species and away from undesirable weed species without the need for plowing, seeding, or applying herbicides. The result is a pasture renovation plan with reduced farm labor and seed costs, as well as reduced soil erosion and compaction that would otherwise occur during cultivation. Increased soil nutrition also results in extended forage stand life and persistence, and in higher nutrient quality of the forages, translating to optimum animal nutrition and reduced feed and supplement costs. These soil fertility improvement trials provide an example of shifting pasture species composition with methods that are not only ecologically and economically sustainable, but regenerative.

Previous work has illustrated that weak forage stands are a direct result of compromised soil nutrition (Pasture Management, Oklahoma State University; Managing Pasture Weeds, University of Massachusetts Cooperative Extension; Nutrient Cycling in Pastures, Bellows 2001), which allows weed species to grow in the space previously occupied by a thriving forage stand. Because low fertility and low pH are favored conditions for the weeds, they begin to thrive (Weeds and Why They Grow, McCaman 1994). Many studies have evaluated the role of grazing, reseeding, biocontrol, and disturbance in restoring forage species (Ecologically Based Integrated Weed Management to Restore Plant Diversity, Jacobs 2007, Sustainable Pasture Management for Horses, Williams 2007), while less research exists documenting the role of soil fertility, especially the role of micronutrient levels, in pasture species composition and hay quality. While there are anecdotal and on-field results that have been achieved by Maine farms optimizing soil nutrition to shift species composition and increase hay quality, this evidence has yet to be quantifiably documented (personal communication, Eric Gallandt; personal communication, Mark Fulford).

Project Objectives:

This study was conducted during the 2011 and 2012 growing seasons in mid-coast Maine on a six-acre section of 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 plot in spring 2011 to determine starting fertility levels and were repeated in spring 2012 to monitor progress and to make necessary nutritional adjustments. Approximately 3,900 lbs of custom blended soil amendments were applied to each experimental plot over the course of two years. The effects of this remineralization were measured with respect to species composition, in which field counts were obtained from transects throughout each field to indicate which species were growing in the field at a particular time (June and September). Plant forage samples were also obtained (June and September) to quantify the effects of applying the dry blended soil amendments on plant nutrition.


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  • Mark Fulford


Materials and methods:

This study was conducted from spring 2011 through September 2012, providing two full seasons of data collection. A total of six acres of pasture was designated for research and 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 plot in spring 2011 to determine starting fertility levels; soil tests were repeated in spring 2012 to monitor any changes and make necessary nutritional adjustments. The soil tests revealed deficiencies in calcium, magnesium, phosphorus, potassium, nitrogen, sulfur, boron, zinc, copper, and manganese. Approximately 2,900 lbs of amendments per acre were spread on the three experimental plots with a drop spreader pulled behind a tractor in July 2011. The remaining three control plots did not receive any amendments. Each amended acre received: 800 lbs hi-cal lime, 750 lbs soft rock phosphate, 450 lbs dolomitic lime, 400 lbs gypsum, 150 lbs sul-po-mag, 100 lbs sodium nitrate, 100 lbs micronized humates, 50 lbs sulfate of potash, 25 lbs magnesium sulfate, 25 lbs zinc sulfate, 20 lbs calcium borate, 20 lbs mangaese sulfate and 1 lb myco-seed treat. In 2012, an additional application of Lancaster Agriculture's Fall Blend M was applied at a rate of 1,000 lbs per acre. Fall Blend M is a proprietary blend of limestone, marl, sulfate of potash-magnesia, humus, soft rock phosphate, gypsum, brown phosphate rock, calcium borate, copper sulfate, zinc sulfate, and humates. Fall Blend M nutrient analysis includes 1.5% phosphorus, 3% potassium, 26% calcium, 2% magnesium, and 2.7% sulfur. All ingredients in the blends were selected to meet USDA organic certification requirements.

Species composition was measured in each plot using the beaded string method (Northeast Cover Crop Handbook, Sarrantonio 1994), in which a string marked in three-foot increments is stretched across the plot in transects; the researcher records which species is growing beneath each mark. Weed and forage species composition was measured two times throughout the growing season: once in June during first-cut (of hay), and again in September during second-cut.

To measure hay quality, plant tissue samples from each plot were collected twice throughout the growing season, once in June and again in September, 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. September 2012 forage samples were sent to Lancaster Agricultural Products for analysis because previous nutrition data from the University of Maine contained anomalies and inconsistencies that were less pronounced in the Lancaster analysis. The Lancaster analysis also included sulfur and sodium data. 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, plots were mowed to simulate grazing and to prevent weed species from going to seed.

Research results and discussion:

Records were kept individually for each test plot and each control plot. The records included the initial soil tests and follow up soil tests, as well as the percent species composition in each plot, and forage nutrition data. Soil tests are illustrated in Table 1, depicting deficiencies in calcium, magnesium, phosphorus, potassium, nitrogen, sulfur, boron, zinc, copper, and manganese in 2011, with increased fertility showing in the experimental plots in 2012 after amendment application. Soil tests in 2012 indicated an increase in Ca, Mg, S, pH, conductivity, and P levels, with a slight increase in N and K in amended plots when compared to the control group. (Table 1).

Species composition data is reflected in Table 2, detailing the percentage of each of the thirty-four observed species in the research plots. Field counts were averaged for the three replications and calculated into a percentage of the total species counted for control and experimental plots during June and September of 2011 and 2012.

Species composition analysis in June 2011 presents base line data before the dry amendment blend was applied. In September 2011 we begin to see slight increases in amended plots for orchard grass, quack grass, red clover, and timothy, with decreases in aster, buttercup, goldenrod, and hawkweed when compared to control (Table 2). June 2012 continues to depict the trend in amended plots with increased fescue, orchard grass, quack grass, timothy, and vetch, and decreased aster, chickweed, cinquefoil, golden rod, hawkweed, june grass, oxe-eye daisy, and strawberry as compared to control (Table 2). September 2012 reflects some of the most dramatic changes in species composition, after two seasons of amendment application, resulting in experimental plots with increased levels of fescue, orchard grass, red clover, and timothy, and decreased levels of aster, buttercup, chickweed, goldenrod, hawkweed, and june grass when compared to control (Figure 1). All species that demonstrated a decrease in the pasture thrive in conditions of low calcium, and many of those species also favor low phosphorus environments. Comparatively, species that showed an increase thrive in soils with higher Ca, Mg, S, P, and pH.

Figure 2 depicts species composition categorized into two groups (Palatable Species and Non-Palatable Species) with percentages of palatable species compared to percentages of non-palatable or less desirable species in the experimental plots versus the control plots. Palatable species were categorized to include: fescue, june grass, orchard grass, quack grass, red clover, reed canary grass, timothy, and vetch. Non-palatable or less desirable species include alder, ash, aster, bedstraw, blackberry, burdock, buttercup, chickweed, cinquefoil, dandelion, fern, goldenrod, hawkweed, medic, milkweed, ox-eye daisy, plantain, scorzonera, sedge, sheep sorrel, speedwell, strawberry, sweet clover, thistle, wild carrot, and yarrow. While some of the species classified as non-palatable may be palatable to some animals, the parameters for this study are specified to give preference to optimum equine forage and hay. The values in Figure 1 are plotted across a time gradient (June and September) to identify changes throughout the season, as well as yearly comparisons from 2011 to 2012. Whereas the control and experimental counts are very similar in June 2011, with approximately 55% palatable species and 45% non-palatable, data for June 2012 suggests the control plots with 54% palatable species and 46% non-palatable species, while June 2012 amended plots had 67% palatable species and 33% non-palatable species. September 2011 control plots had 64% palatable and 36% non-palatable species, while experimental had 72% palatable and 28% non-palatable species. September 2012 control plots had 56% palatable and 44% non-palatable species, while experimental had 72% palatable and 28% non-palatable species.

Forage nutrition analyses is depicted in Table 3, with data for nitrogen, calcium, potassium, magnesium, phosphorus, sulfur, aluminum, boron, copper, iron, manganese, zinc, and sodium levels obtained from forage samples in each plot, with mean values calculated for test and control plots during peak haying times (June and September) for 2011 and 2012. No major, consistent differences were observed between amended and unamended plots. These results do not suggest any discernible correlations between palatable species composition and forage nutrition at this time, with the exception of evidence of elevated Boron levels in the September 2011 and 2012 samplings. More accurate forage nutrition data may be obtained in the future by only sampling palatable species along the transect, providing a better indication of the nutrition that an animal might actually consume.

Research conclusions:

Two complete growing seasons of data have now been collected, and approximately 3900 lbs per acre of custom blended soil amendments have been applied in order to investigate the influence of increased soil fertility on species composition and forage nutrition. Farmers have walked the fields to see the results, and a graphical and photographic slideshow has been presented off-site. Increased fertility in the amended plots demonstrated a correlation to an increase in some palatable forage species and a decrease in some non-palatable species. Weed species that thrive in soils with low Ca and low P showed a decrease in overall field composition after the addition of an amendment blend containing Ca and P. Palatable forage species that thrive in soil conditions high in Ca, Mg, S, and P demonstrated an increase in overall field composition after the addition of Ca, Mg, S, and P. While some change was observed in the forage species composition of the pastures studied, weed species are still present and soil fertility levels are still low to moderate.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

In September 2012, Singing Nettle Farm hosted an on-farm presentation to allow other farmers to come and see the demonstration plots. Bill Errickson and Mark Fulford spoke about the project and the importance of proper soil nutrition on herd health to a collection of farmers representing beef, dairy, equine, and grass farmers, in addition to faculty from Unity College. In February 2013, an off-site presentation was given at the MOFGA Common Ground Education Center in Unity, Maine, as part of a day-long, free Winter Session Workshops series. Sponsoring organizations included the Western Mountains Alliance, the Maine Federation of Farmers' Markets, Maine Farmland Trust, and the Maine Organic Famers and Gardeners Association (MOFGA). Errickson and Fulford presented a slideshow with photographs from the research fields and graphs to clearly articulate the results of this study. The audience was predominantly made up of farmers and members of the agricultural non-profit sector. A written report has been sent electronically to The Grass Farmers Network, Acres USA, and Cooperative Extension of Maine, New Hampshire, and Vermont.

Project Outcomes

Assessment of Project Approach and Areas of Further Study:

Potential Contributions

This study demonstrates the early effects of pasture soil fertility on species composition. Because animals in the field, or those in the barn who are fed hay, find certain species more palatable than others, it is important that the field contains a high percentage of palatable, desirable species. The implications for shifting the species composition utilizing soil fertility allows the farmer to focus his or her labor and financial resources on nutrition, as opposed to disturbing the ground to reseed or creating further nutritional imbalances by using manure alone on the fields. Even if there is a tight nutrient cycle, with the majority of fertility being returned to the fields, if there are essential nutrients lacking, they must be added to correct the imbalances from years of crop removal. Only when the soil nutritional levels are brought to optimum fertility will we see a truly thriving field in which vigorous grasses have naturally outcompeted less desirable species. As this nutrition improves, we believe it will be further perceived in the nutritional content of the plant, resulting in more efficient feeding, less need for mineral supplements, and lower veterinary expenses.

Future Recommendations

Farmers' feedback from the September presentation reinforced the need for low-cost, fast-acting solutions to the challenges of declining pasture fertility, which may be achieved with the use of liquid amendments in conjunction with a dry blended application. Anecdotal evidence from experienced farmers suggests that liquid amendments applied to a field that has previously received a dry blend is the most effective and long term solution to achieving high fertility and high productivity in the field. Yield data, in which amended and non-amended fields are cut, baled and compared, is also important in determining the economics of a pasture remineralization program. Many farmers are reluctant to invest financial resources into soil fertility without solid evidence that their profit margin is going to increase at the end of the first or second year after application. If a higher yield can be delivered with a degree of confidence, the investment in soil fertility will be paid off, despite the challenge of replenishing fields that have seen declining fertility as a result of years of crop removal without restocking the mineral reserves. Future research is essential to continue this investigation into the effects of increased soil fertility on species composition, forage nutrition, and yield, with a focus on the most cost-effective, long-lasting, and sustainable solutions.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.