Based on our analysis of PLFA scores over 7 years, we conclude:
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.
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.
We use the PLFA (Phospho-lipid Fatty Acid) test to measure microbial life in CSSHP fields. Only when comparing dryland VS irrigated fields, annual VS perennial fields and fields with various levels of tillage intensity, did we see significant differences in microbial life among these groups. Grazed VS ungrazed fields, fields with organic matter amendments VS fields with none, and fields with different soil types did not show significant differences in microbial life measurements.
Comparing dryland VS irrigated and perennial VS annual systems, PLFA results clearly show that irrigated and perennial fields have more microbial life than dryland and annual fields. Irrigated perennial fields had the highest average scores and dryland annual fields had the lowest. This bar graph also suggests that perennial systems with their lack of soil disturbance are more beneficial for microbial life than supplemental irrigation water alone.
