This project aims to engage and support farmers that are currently using cover crops and work with them to share information with other local farmers. There has been much research and discussion about implementing cover crops and the benefits to soil health, however, this study will measure and quantify some of the benefits of cover cropping. We will work with four farmers in southern Minnesota, all of whom are experienced in cover cropping. These four individuals, working with their local conservation districts, are key members of the Freeborn County Soil Health Team. Their group aims to promote beneficial soil health practices by hosting field days, collecting data, and educating other farmers who are interested in cover crops. These farmers are eager to learn how their cover cropping practices improve soil health, and want technical assistance to quantify soil health, plant health, and economic parameters. Participating farmers have asked for help collecting local data to guide them in quantifying the physical and economic benefits that the practice is providing. In this study, we will quantify one potential benefit that cover crops provide; their ability to scavenge, recycle, and release nutrients for subsequent cash crops.
- Monitor nutrient levels throughout the cover crop life cycle to establish a procedure for properly crediting cover crop nutrients for subsequent cropping years. If this can be done successfully, there is potential to reduce fertilizer inputs. Reduced fertilizer inputs would save the farmer money and could potentially reduce nutrient losses that are impacting water quality.
- Generate high quality data for this specific geographic area, soils, and climate.
- Provide education and outreach through field days, fact sheets, handouts, etc. This will help local farmers make more informed management decisions regarding cover crops.
The main goal of the study is to quantify the ability of cover crops to scavenge nutrients from the soil, and release those nutrients as “credits” for subsequent cash crops. Plant and soil parameters will be monitored in an attempt to quantify these values. Non-treatment, control areas will be monitored for the same parameters, providing baseline data for comparison.
– Each of the four participating farmers will select one corn field and one soybean field in each year of the study. There will be four corn fields and four soybean fields studied each year.
– Cover crops will be applied according to the farmers’ normal management methods. Each farmer
will utilize the same management methods from field to field and year to year, but application
method, application timing, and cover crop specie(s) selection may vary between farmers.
– Cover crops will be applied across the entire field, with strategically sized and placed control areas.
– The parameters measured will include:
o Cover crop biomass
o Cover crop nutrient content (tissue sample analysis)
o Soil nitrate
o Comprehensive soil nutrient levels (standard composite soil samples)
o Infiltration rates
o Cash crop stand counts
o Cash crop yield
o Management and financial information
The combination of biomass measurements and tissue sample analysis will provide an estimate on the
total amount of each analyzed nutrient assimilated in the cover crop stand. Periodic soil nitrate
samples will allow us to track when nitrogen is being released by the terminated cover crop. Other
parameters measured will help to gauge the effects on soil health and existing cash crop.
Participating farmers will share their results and experience through a minimum of four
individual or combined field days and outreach events. The Freeborn Soil Health Team, which
cooperating farmers participate in, has a presence in the local farming community and holds annual
spring and fall field days. Fact sheets and educational materials will be developed and distributed at
local and regional events. Lessons from this study will be shared through a number of local media
distributions including newsletters and newspapers.
Data was collected from three corn and three soybean fields that incorporated cover crops in the 2016-2017 season. Each of the six fields participating in the study had a cover crop planted in late summer or fall of 2016 and was terminated in the spring of 2017. Cover crop species, seeding rate, and seeding method was determined by the farmer operating the land. Each field left an untreated check strip where no cover crop was planted. This provided the opportunity to compare soil chemistry and crop yield on paired sites, with and without the presence of a cover crop. Plant data was collected and a number of parameters were analyzed to quantify cover crop growth and nutrient content. Cover crop samples were collected from eight randomly assigned locations within each field. The above ground biomass was collected from one square foot of ground surface and sent to Minnesota Valley Testing Laboratory (MVTL) for analysis. The cover crop samples were analyzed for their carbon, nitrogen, phosphorus, and potassium content, along with their dry matter yield. These analyses were used to calculate the total nutrient uptake in the above ground biomass in the cover crop at termination. The cover crop analysis also provided the C:N ratio to estimate when the decomposing cover crop could release its nutrients. All of the plant data was collected within three days of termination to maximize cover crop growth and nutrient uptake. Cover crop tissue samples prior to corn planting were collected on May 8-9, 2017. Cover crop tissues samples prior to soybean planting were collected from May 10 through June 7, 2017. Dates ranged based on weather and cover crop termination dates. Soil sampling was also conducted in these six fields. The first sampling period was planned before crops were planted, however, weather challenges prevented this from taking place. The first soil samples were collected in early June, just prior to the time farmers began side-dress nitrogen applications. Soil samples were collected from ten sites in each field and sent to MVTL for analysis. The ten samples were collected in a strategic manner to form five paired sites for comparison. The paired sites had one sampling location within the check strip where no cover crop was established, and one sampling location outside the check strip where a cover crop was present. The paired sites were located in close proximity, within a common soil mapping unit, and other management techniques held constant. Each soil sample was made up of twelve subsample soil core and combined to form a single composite sample. Soil cores were sampled to a depth of 12” to perform the pre-sidedress nitrate test (PSNT). Composite samples were also analyzed for routine chemistry including; pH, buffer pH, organic matter, phosphorus, and potassium. Soil sampling sites were geo-referenced and revisited later in the growing season for additional sampling. A second round of samples was collected in early August and analyzed for nitrate. In field where nitrogen fertilizer was banded, special attention was paid to collect subsamples both within the row and between rows.
Plant Tissue Analysis
Cover crop yields were calculated for five of the six fields where plant tissue samples were collected. Cover crop yield was not able to be calculated on the Mower North farm, due to incomplete analysis from MVTL. Cover crop yields varied widely both within individual fields and between field sites. In field variability seemed to vary due to soil type, landscape position, and moisture availability. Low lying areas with wet soils seemed to inhibit cover crop growth, to the extent that cover crop yield was zero in some areas. Variability between fields can be attributed to a number of factors based on management factors like cover crop seeding mix and rate, establishment method, seeding and termination dates, as well as environmental considerations like soil texture, rainfall, and fertility. The Steele East and Steele West farms had average yields of 206.5 lb/ac and 902.7 lb/ac, respectively. Individual sample site yields ranged from 0 lb/ac to 1968.7 lb/ac. Meanwhile the Freeborn East and West farms had average yields of 153.7 lb/ac and 139.3 lb/ac, respectively. Individual site yields here ranged from 19.2 lb/ac to 1267.6 lb/ac. The final site, Mower South, had extremely high biomass yields. This farm had individual site yields ranging from 2131.9 lb/ac to 4628.8 lb/ac, with an average yield of 3178.8 lb/ac. Cover crop tissue analysis, in combination with cover crop biomass yields, was used to calculate the quantity of nutrients contained in the above ground portion of the cover crop. Looking specifically at nitrogen, there seemed to be a direct correlation between the cover crop biomass yield and the amount of nitrogen scavenged and contained within the above ground biomass. There was relatively little variability in nitrogen concentrations of the various tissue samples, so the highest amounts of plant nitrogen were found at sample sites with the highest cover crop biomass yield. Another trend was noted when considering C:N ratio and biomass yield. There appears to be a relationship between the two parameters; as biomass yield increased, C:N ratio also increased. This indicates that a mature cover crop with a high biomass yield would break down and flush nutrients more slowly than a cover crop with less vegetative growth, and likely, an earlier termination date. Further statistical analysis will be performed to test these hypotheses.
There appears to be some trends in the soil sample analysis from paired sites mentioned above. The pre-sidedress sampling period showed average soil test nitrogen levels were lower where a cover crop was growing when compared to the check strip. Steele East had average soil nitrate levels of 84.6 lb/ac within the check strip and 76.6 lb/ac where a cover crop was present. The Steele East farm had an average soil nitrate level of 24.8 lb/ac within the check strip, while outside the check strip soil nitrate measured 18.2 lb/ac. The Freeborn County farms showed even more marked differences between treatments. Freeborn West showed soil nitrate levels of 54.3 lb/ac within the check strip and 32.2 lb/ac where the cover crop was present. Likewise, Freeborn East had average soil test nitrate levels of 21.0 lb/ac in the check strip and 11.8 lb/ac in the cover crop. The Mower County sites were consistent with findings at other locations. The Mower South farm had average soil nitrate levels of 53.6 lb/ac and 43.6 lb/ac within the check strip and outside the check strip, respectively. Finally, the Mower North farm had an average soil nitrate level of 31.2 lb/ac within the check strip and 15.8 lb/ac where the cover crop was present. In every case, the average soil nitrate levels were lower where there was a cover crop growing. The August soil nitrate sampling results were much less conclusive. Further statistical analysis will be performed to both confirm hypotheses from the pre-sidedress sampling period and identify any trends from the August sample results.