We compared 20 fields which had increased their total microbial biomass, total fungi and total mycorrhizal fungi over the last 7 years with 11 fields with falling PLFA scores for their total microbial biomass, total fungi and total mycorrhizal fungi.  Both groups contained a mix of vegetable crops, annual row crops and perennial crops.  We then calculated the percentage change between the averages of each group’s use of various soil health practices.

While our analysis shows that decreasing tillage intensity, increasing cover crops and increasing grazing days all are associated with increasing microbial life we found that the most significant drivers of microbial increases are the availability of more than 100 days of supplemental irrigation water annually and large organic matter inputs.

The group of 20 fields with rising PLFA’s contains over 50% more fields with more than 100 days of annual water availability.  However, the 11 fields with falling PLFA’s contain more dryland and poorly irrigated fields which have been significantly affected by the droughts and rising heat indexes the Front Range has experienced over the last 5-6 years.

The rising scores group also applied 570% more tons/acre/year of organic material to their fields per year than the falling scores group.   Organic matter such as manure and compost inoculates soils with the huge numbers of microbes they contain.  Wood products and carbon-rich mulches, hay and leaves provide structures for microbial life and additional food as they break down.  It makes sense then that large organic matter inputs will increase PLFA scores.

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.