Comparing Soil Health Among Graminaceous Crops with the Solvita CO₂ Release System

A three year study compared microbial soil populations in six groups of grass crop production – field corn, sweet corn, equine pasture, turf, golf courses and a bio-energy site.  All sites had similar sandy loam soils and were located in Monmouth County, NJ within a 10 mile radius.  The Solvita CO₂ aerobic respiration test measured the release of carbon dioxide from the soil in the spring, summer and fall of 2013, 2014 and 2015.  Project objectives were to establish a baseline of soil health, compare carbon flux seasonally among various monocot species and estimate potential nitrogen mineralization in order to adjust fertility recommendations downward and determine effectiveness of any future changes in management practices.  Soil pH values ranged from 5.1 - 6.3 and organic matter 1-2%.  Soil temperatures in this growing zone 7A at a four inch depth ranged from 20-40⁰  F. in the winter, 55-64⁰  F. in the spring and 65 -84⁰ F. in the summer and fall.  

The bio-energy crop, Miscanthus giganteus, had the highest CO₂ burst of 23 ppm over a 24 hour period which was significantly different at P>.05 than the 11 ppm of golf course bentgrass greens, Agrostis stolonifera.  Farm soil results for field corn, Zea mays, and sweet corn, Zea mays convar. Saccharata var. rugosa were only slightly higher at 14.0 ppm than the bentgrass growing in an artificial sand mix.  Golf course fairways, equine pastures and residential lawns, all with bluegrass mixes, Poa pratensis, were similar the Miscanthus site yet consistently lower at an average of 21 and 22 ppm, respectively.  These higher levels of microbial CO₂ respiration can return 20-30 lbs. of naturally produced nitrogen per acre per year. For the lower rates found from sweet corn, field corn, and golf green sites, the potential nitrogen return ranged from 10-15 lbs/A/Yr.  Cultural practices as well as cultivar types may contribute to these differences among the grass crop groups.  The ¼ inch, low cut greens do not recycle grass clippings and have very high and frequent application rates of insecticides and fungicides. Furthermore, in contrast to the perennial bio-energy and bluegrass-mix crops, annual crops feature deep disking and frequent tillage practices common in this region that can reduce soil structure, organic matter and stability in the soil environment.