Comparing Fields with Rising PLFA Scores VS Falling PLFA Scores

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.