By Dennis Frame, Emeritus Professor, UW-Extension
Last year, I collected data from eight farms that are part of Peninsula Pride Farms. I wanted to determine the effectiveness of cover crops in the region and to see if the membership was achieving the organization’s goal of “continual improvement of practices that improve the environment.”
This was not a scientific experiment with randomized sampling or selection based on farm size, acres or farming system. This was more a sampling of farms that were willing to provide data.
Cover crop analysis
Here is what I learned about the impact of cover crops.
The top portion of Figure 1 shows the data from the farms. It is based on 160 fields and 4,675 acres of cropland. On average, planting a cover crop reduced the risk of phosphorus loss by 1.3 lbs./acre. However, the range was from 7.8 to minus-1.1 lbs./acre. This means that on some fields, planting a cover crop can increase the risk of phosphorus loss, while on others it can have a dramatically positive impact. Another important piece of information is that the mean (the mid-point of the 160 fields) was 0.7. This means there were some very high fields bringing up the average.
For comparison, I looked at the 2019 annual phosphorous report I developed for Yahara Pride Farms in the Dane County area. In the bottom portion of the chart is the YPF data. The average reduction in the risk of phosphorus loss from planting a cover crop was 2.2 lbs./acre, with a range of 22.2 to minus-1.1.
There could be a number of reasons why the average is higher on the YPF farms, but one factor is that we have been working to educate farmers on what fields and under which conditions cover crops have the greatest positive impact. Do not assume that planting a cover crop will always reduce soil and nutrient loss. For the first year of analysis, PPF is on the right track. YPF has been doing this analysis for seven years; when they first started it was a lower reduction.
Continual environmental improvement
For the second analysis, the Peninsula Pride Farms board of directors decided to identify how farmers were doing in regard to soil erosion and the risk of phosphorus loss (the Phosphorus Index – PI). They asked farmers to send me copies of their nutrient management plans in SnapPlus so that I could create a benchmark for the group
In 2016, we had data from most of the membership, totaling 50,096 acres in 2,021 fields. The average PI on all the acres was 2.33 with 62.3 percent of the acres having a PI of 0, 1 or 2; 37.1 percent having a PI of 3, 4, 5 or 6; and 0.6 percent having a PI of 7 or greater. The nonpoint rules require farms to have a rotational PI of 6 or less on all fields.
In 2019, I received SnapPlus plans from the eight PPF farms with a total of 1,215 fields and 31,167.5 tillable acres. Of these farms, two were new to the organization and did not participate in the 2016 study.
I broke the analysis into three data sets:
- Two farms that did not participate in the 2016 study,
- Three farms comparing the phosphorus index from 2016 and 2018, and
- Three farms – 2016 data was updated from the 2016 SNAP program to 2018 SNAP and then compared.
Since the two new farms were not part of the original group, they cannot be measured for continual improvement. However, Farm 7 (in Figure 2) has an overall farm average PI of 1.06, which is the lowest of any of the farms evaluated. Farm 8 is well below the 2016 average. These two members are doing an excellent job of implementing conservation farming practices.
Figure 3 shows the comparison of the SnapPlus plan generated in 2016 v. 2018. All three farms have a lower PI in 2018 than they did in 2016. This is important but not as telling as comparing the percentage of fields with low PI’s to the fields with higher PI’s. As shown in the data, Farm 1 increased the percentage of fields with a PI of 0, 1 or 2 from 77 percent to 86 percent. Farm 3 also had a big improvement in the percentage of low PI fields, but Farm 2 had a decrease in low testing fields but also a decrease in the overall farm phosphorus index.
All farms in this table show improvement. Two of the farms were above the 2016 average of 2.33.
The final analysis is probably the most important and, in my opinion, the best way to measure improvement. That said, it is more work. In Figure 4, we evaluate Farm 4 to understand what the data means. The first column is the 2018 whole farm PI of 2.06/acre. The second column is the 2016 SnapPlus file updated into the 2018 SnapPlus program; this had a PI of 2.33. The final column is the 2016 PI from the old version of SnapPlus and shows 2.03.
When the 2016 data is updated into the 2018 program, the PI increased. All the data in the file is exactly the same; the only difference is the program. This means when using the updated version of SnapPlus and the phosphorus index is the same between 2016 and 2018, you have adopted practices that reduced your risk of phosphorus loss.
All farms showed improvement from 2016 to 2018, but the smaller improvements in Figure 3 are not accurate because the original data was not updated to the new version. The three farms with updated plans (Figure 4) saw an average reduction in the risk of phosphorus loss of 0.21. That is impressive.
This data answers the question of whether PPF members are showing continual environmental improvement. These six farms have.
The question on the impact of cover crops is that when planted on fields under farming systems that have a higher potential for soil and nutrient loss, cover crops can reduce the risk of phosphorus loss.
