Soil microbial responses to cover crop use

• 2014 annual report

Commodities

• Agronomic: corn, soybeans, wheat
• Additional Plants: native plants
• Animals: bovine

Practices

• Animal Production: grazing - rotational, winter forage
• Crop Production: cover crops, no-till
• Education and Training: on-farm/ranch research
• Farm Business Management: whole farm planning
• Production Systems: agroecosystems, holistic management
• Soil Management: soil analysis, soil microbiology, soil quality/health

In the sustainable farming literature, there seems to be a consensus that cover crops and rotational grazing can result in better soil quality, but how long does it take for these practices to show a benefit and what is the best way to measure the differences? Studies tracking crop yield can be unreliable since there are so many factors that influence crop growth, and common measurements of soil quality such as soil organic matter, infiltration, and nutrient content (nitrogen, phosphorus, and potassium) can be slow to detect changes. My hypothesis is that soil microbial life is the first soil attribute to benefit from land use improvements. Diverse vegetation and the addition of nutrients from animal manure can increase the diversity and activity of soil biology, including bacteria and fungi. Until recently, it was difficult to test for soil microbial activity, but two new tests (the Solvita CO2 burst test and the Solvita soil life test) are now on the market that collect the CO2 given off by the respiration of soil microbes and record the amount as a color change on a specially designed gel pad. High levels of soil respiration are closely related to the ability of the soil to store and release soil nutrients to plants, so soil respiration can be a good indicator of overall soil health. I propose to add both grazed (site 1) and ungrazed (site 2) cover crops into a conventional corn/soybeans rotation and compare soil respiration and traditional soil quality tests across three additional land uses: a conventional corn/soybean field with winter fallow (site 3), a field with a long history of cover crops, seasonal grazing, and no-till corn/soybeans (site 4), and a grazed perennial grass pasture (site 5), as a control. Quantifiable short-term benefits are necessary to convince more farmers to implement cover crops and grazing on crop land. Additionally, a better understanding of soil function could help reduce the amount of excess fertilizer spread on crop ground, thereby benefiting water quality.

In the time period between summer, 2013 and spring, 2015 I will run soil tests six times: summer, fall, and spring for each of the two years. During each sample season, I will visit all five test sites and study three soil samples at each site. Using the USDA soil test kit, I will investigate soil quality through measurements of soil nitrates, phosphorus, potassium, water infiltration rate, soil aggregate stability, compaction, and pH. I will also count the number of earthworms in a volume of soil as a measure of soil health. Soil organic matter will be tested with the loss on ignition method at the University of Kansas soil testing lab. Finally, I will collect soil samples for the Solvita CO2 burst test to characterize microbial activity at each site. These samples will be dried in the oven and then rewetted with distilled water to uniformly activate soil microbes. After the designated wait time, the color change of the CO2-reacting gel pad will be read with a colorimeter. I will keep all of this data in a spreadsheet and produce graphs and analysis of each measurement at the conclusion of the study.

With the results of this study I hope to answer the following questions:

1. What is the best way to characterize soil quality and soil health?

2. Is the Solvita CO2 burst test (and the producers version, the Solvita soil life test) useful in tracking soil health changes with land use?

3. Assuming that cover crops and rotational grazing can both benefit soil quality, how long does it take to see measurable differences: one season, one year, two years, or only after many years?