The Citizen Science Soil Health Project, Years 4-6

Our recommendations for sustainable agricultural production and future research:

1. More research into the causes of individual growers' soil health lab results' variability.
2. Much of Western Ag is supplied with Colorado River water, including our area, the Colorado Front Range.  We all know that water travels uphill to money, so as Colorado River water becomes more scarce, Ag-water will be gobbled up by urban areas, leaving Ag with less and less supplemental irrigation water.  Western research should be focused on how to maximize water yield for Ag in a time of dwindling supplies.

SOIL PH AND LOCATION: In previous years, we have found that as pH increases and becomes more alkaline, soil health decreases.  We wondered if geographical location could have anything to do with pH, and indeed it does.  We compared our sites’ soil pH with longitude (east-west location).  We found that sites further east out on the plains tend to have higher pH than sites closer to the Front Range foothills and up in the mountains.  This could be due to several things. 

Precipitation is higher in the mountains and foothills than further out on the plains.  Higher rainfall is associated with more acidic soils.  Also, a site’s original parent soil material is more acidic in the mountains and foothills than on the plains.  Furthermore, the pH of irrigation water can change soil pH with repeated applications.  Irrigation water becomes more alkaline as it travels further east, picking up tail-water, salts and minerals.  All this means that the location of a field might determine its soil pH as well as its soil health, since soil pH has a significant effect on soil health.

We wondered if certain kinds of sites might be located further east or west, thus influencing their soil pH.  We sorted our sites into 7 groups. Most groups include both organic and conventional fields.

• Dryland Grains : Dryland wheat and millet, no irrigation, using a crop-fallow system.
• Commodity Row Crops: Irrigated crops like corn, triticale, wheat, hemp, beans, sugar beets, barley, millet, silage.
• Commercial Vegetable/Flower/Fruit : Irrigated vegetables, flowers and fruit, sold commercially.
• Perennial Hay/Alfalfa/Pasture: Irrigated perennial pasture systems of grass, hay and alfalfa.
• Home Gardens: Vegetables, flowers and fruit trees for home consumption.
• Non-farm Grasslands : Dryland grasslands with no recent tillage or farming practices.
• Trees : Forests and tree farms. 

We then calculated each group’s average longitude, and calculated the average pH for each of the 7 groups, as shown in the next 2 graphs. No surprise, trees are located to the west in our forests, with dryland gains and commodity crops located to the east, where large sections of undeveloped agricultural lands remain. The order of the average pH of the 7 groups closely corresponds to their relative longitude.  These 2 graphs suggest that some crop groups face more of a disadvantage than others when it comes to soil health, since their location can determine their soil pH, which in turn can make improving their soil’s health more difficult.

SOIL HEALTH OF 3 DIFFERENT CROP GROUPS: In previous years, we learned that more supplemental irrigation water, more days of living cover, more organic matter inputs, more grazing days and more use of cover crops can all improve a site’s soil health.  We have also learned that lower tillage intensity and a lower soil pH improves a site’s soil health as well.  We decided to calculate the average use of each soil health practice for the 3 crop groups which most of our growers are in: 1) Hay/Pastures/Alfalfa, 2) Vegetables/Fruit/Flowers, and 3) Commodity Row Crops.  We wondered if each crop groups' average soil health practices could predict which crop groups would have the lowest and highest soil health scores.  See if you can predict which crop groups with have the best and worst soil health scores, just by looking at their relative rankings on soil health practices.  Remember that you are looking for HIGH water days, HIGH days of living cover, HIGH organic matter inputs and HIGH grazing days, but LOW tillage intensity and LOW soil pH to predict the highest soil health scores.

The following table has the average soil health scores of each of the 3 groups, for Soil Organic Matter, Soil Respiration, Organic Nitrogen, Organic Carbon, Soil Health Score, Total Microbial Biomass, and Number of Fungi, using the Haney and PLFA soil health tests. 

Perennial Hay/Alfalfa/Pastures : The Pasture group has the highest average soil health scores of these three crop groups. Although the Pasture group has lower supplemental water days and lower organic matter added, their very high days of living cover and very high grazing days, along with their very low tillage intensity and lower soil pH seem to more than make up for their water challenges, in terms of soil health.
Commodity Row Crops : The Commodity crop group has the lowest average scores of these three groups. Although they have done an excellent job of reducing their tillage intensity, that fact alone cannot make up for their high soil pH, lowest days of living cover and lowest organic matter added. They have only 2/3rds of the water availability as the Commercial Veg/Flower/Fruit group, which explains their lower days of cover crops that often require fall seeding and fall water. Inter-seeding cover crops aerially or when the main crop is still small are work-arounds but not always practical. Low commodity prices mean the cost of additional organic matter inputs like compost and manure are hard to justify.
Commercial Veg/Flower/Fruit: The Commercial Veg group has the highest tillage intensity by far, but also triple the organic matter inputs of the other 2 groups. These huge organic matter inputs, along with their longer water season, greater use of cover crops, and lower pH overpowers their intense tillage and boosts their average soil health scores above the commodity crops’ averages. Their longer water season means they can plant more fall cover crops and string together succession plantings for a longer growing season. Their high value vegetables mean that they can afford organic matter input costs and hauling fees.

VARIABILITY: We continue to be plagued with a great deal of variability in our lab results when we compare sites with themselves year-to-year. Last year we determined that grazing animals contribute to variability in lab results. This year we asked, “Does adding organic matter like compost, manure and mulches to a site also make lab results more variable year-to-year?” The answer: It seems to.
In the first graph below, 71 sites with both grazing animals and organic matter inputs (OMI) are each represented by a quadruplet of data points connected by a vertical black line. Each square-circle-triangle-diamond-black-line combo represents the Soil Organic Matter (SOM) values for one site for 4 years. According to the literature, SOM is supposed to be quite stable and very difficult to change, and yet we are seeing large swings in individual sites’ SOM data, especially when grazing animals are present or organic matter is imported to the site, as is the case in the first graph below.  We only have 12 sites in our study which have no grazing animals or imported organic matter for 3 or more years. The second graph shows that the variability in SOM values for these 12 sites is much less than for sites in the previous graph.

We then sorted our sites into 3 groups and calculated the average variability for each group.  The bar graph below shows that the groups which grazed animals or added organic matter to their sites for 2 consecutive years have approximately three times as much variability in their lab results as the group with NO grazing animals and NO organic matter inputs.

Finally, we examined the 28 sites which have the most variability in their soil health scores.  We call these sites our “Swingers”, and they are evenly split between organic and conventional growing methods.  Over half the “Swinger” sites are pastures with the rest split evenly between home gardens and commercial vegetable sites.  Their most common crop is grass hay with mixed vegetables coming in second. Their average water season is 127 days long.  “Swinger” sites have an average soil health score of 27.6, which is very high, especially for Colorado.  The growers of these “Swinger” sites are all Soiley Award winners or nominees.  They have adopted many soil health practices, as you can see in the following graph.

The lesson here seems to be that no good deed goes unpunished.  It seems that one result of adopting good soil health practices may be a great deal of variability in soil health lab results.  If you see your Haney test results bouncing around a lot, year-to-year, it does not necessarily mean that you are doing anything wrong.  It may mean that you are doing many things right!  We will explore this hypothesis further in coming years as we gather more data.

GRANTS AND COLLABORATORS: We secured a generous partnership grant from St. Vrain and Lefthand Water Conservancy District, and a small grant from the Boulder County Sustainability Food and Agriculture Fund, which we have used to expand our educational outreach.  We have also received 2 very generous anonymous private donations.  We added 6 growers to our 47 growers and lost 2.  We now have 51 growers participating in the project and will not accept any more growers unless others drop out.