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    Which practices increase microbial life on the Front Range?

    Irrigation Water Microbial life Organic Matter Inputs Perennial & Annual cropping PLFA (Phospho-lipid Fatty Acid Test) Tillage Intensity

    Based on our analysis of PLFA scores over 7 years, we conclude:

    • Perennial cropping systems promote more microbial life than annual ones.
    • Supplemental irrigation promotes more microbial life than no irrigation.
    • Fields with lower Tillage Intensity scores have more microbial life than fields with higher Tillage Intensity scores.
    • More than 100 days of water availability promotes more soil microbial life.
    • Larger applications of organic matter promote more soil microbial life. 
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    Tillage Intensity Effects on Microbial Life

    Microbial life PLFA (Phospho-lipid Fatty Acid Test) Tillage Intensity
    Graph of Change in sample depth VS change in soil organic matter

    Tillage intensity also has a clear effect on soil microbial life, with less intense tillage correlated with more microbial life for all microbial groups.  For context, two passes with a rototiller equals a score of 36, one pass with a plow equals 42, and one pass with a hoe equals 4.

    The graph above suggests beneficial effects generally occur when total annual tillage intensity scores are <50, but this is the artifact of an over-weighting of 39 fields in the 10-20 tillage intensity range skewing results. When tillage groups are analyzed on a more granular level, and other practices are considered such as in the graph below, a much more complex picture emerges.  This second graph illustrates how comparing varied and stacked agricultural practices can skew results and how statistics can lie.

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    Characteristics of Fields with Increasing Soil Health

    Irrigation Water Organic Matter Inputs Progress Tillage Intensity
    Graph of Change in sample depth VS change in soil organic matter
    Graph of Change in sample depth VS change in soil organic matter

    We identified the fields in our 6 different crop categories which are making the most progress improving their soil health.  They are Stonebridge Farm (Vegetables, Flowers & Fruit), Olander Farms (Commodity Crops), Lehi Ranch (Commodity/Pasture rotation), Nine Mile Ranch (Pasture Grass & Hay), Longview Farm (Dryland Wheat), and Your Neighborhood Christmas Tree Farm (Home Garden).  These 6 sites share 4 characteristics which have helped them improve their soil’s health.

    1. Supplemental irrigation water: 5 out of 6 of these growers (all except Dryland Wheat) have supplemental irrigation water.  More water means more varied and bigger plants, healthier roots and soil microbes, and the ability to grow fall cover crops and to water grazing livestock year-round.
    2. Decreasing tillage intensity: All 6 growers decreased tillage intensity over 6 years, or maintained it at very low levels. Less tillage means more and healthier soil microbes, especially more fungi, which feed more nutrients to crops. 
    3. Organic Matter Inputs: All 6 growers have added or plan to add significant amounts of organic material to their soil, through imported amendments, grazing, cover crops and crop residues.  It may not matter how you get more organic matter onto your soil, just that you get it there. 
    4. Starting with soils in the “Poor” to “Good” range: None of these 6 growers started with soils that were in the “Excellent” range, where soils may have reached their carbon saturation point.  Some of our CSSHP growers who enrolled in the CSSHP with “Excellent” soils are discouraged because they aren’t seeing their soil health scores improve significantly, despite their best efforts.  It may be that their soils have reached their carbon saturation point, and now they can only build deeper “Excellent” soil, just maintain and make more of, but not improve significantly, the “Excellent” soil they already have.
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    Average Tillage Intensity has decreased, part 2.

    Progress Tillage Intensity
    Picture
    When we examine the Tillage Intensity of the 191 sites for which we have tillage data and group them into their 5 crop categories, we see that 4 crop groups have made very good progress in reducing their Tillage Intensity, with Commercial Veg/Flower/Fruit sites and Dryland Grains making the most progress.  Perennial Hay/Alfalfa/Pastures have held steady with quite low Tillage Intensity scores.  Home gardens also have low tillage intensity scores, because many of our home gardeners use mostly hand tools, which disturb the soil less and have lower intensity scores.
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    Average Tillage Intensity has decreased, part 1.

    Progress Tillage Intensity
    Picture
    When we examine just the 51 sites for which we have 5 years of data, we see that our growers have decreased their Tillage Intensity by 17 points over the last 5 years. This is very good news since lower tillage intensity is correlated with better soil health.  We use a Natural Resources Conservation Service soil erosion model to assign a soil disturbance score to all farm operations that compact or disturb soil.  For example, NRCS assigns a single pass with a subsoiler-chisel plow a score of 52.6, a disc harrow gets a score of 11.67, and hay cutting equipment gets a score of 0.15. We total all the scores from each implement used in a field in a calendar year to compute the tillage intensity score for each site.
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    Our Growers have made progress!!

    Cover Crops Days Of Living Cover Organic Matter Inputs Progress Tillage Intensity Variability
    Picture
    The variability we continue to see in our lab results has thrown a great big monkey wrench into our ability to assess progress using only our lab results. However, we can still assess the progress our growers have made in increasing their use of tried-and-true soil health practices, including:
    • Increasing their Days of Living Cover
    • Increasing their use of Cover Crops
    • Decreasing their Tillage Intensity
    • Increasing their Organic Matter Inputs
    Our growers have made excellent progress incorporating 3 out of 4 of these soil health practices in the last 5 years.