In June, the Agro-One lab added the Solvita? CO2 Burst and SLAN soil health monitoring tests to our lineup of test offerings.
The Solvita? CO2 Burst Test
This test measures the amount of CO2 released from the soil after it is rewetted as an indicator of the level of microbial activity in the soil. The rate of CO2 release is generally regarded as an indicator of soil health, which can be favorably improved with practices such as cover cropping, manure application, and reduced tillage.
Results reported as:
Very Low Biological Activity (0 - 20 mg/kg CO2-C): Low in microbes and microbial activity, associated with depleted and dry sandy soils, and little or no organic matter
Moderate Biological Activity (21 - 60 mg/kg CO2-C): Moderate microbial life and activity, soil is moderately balanced and has likely been receiving organic matter additions
High Biological Activity (61 - 20 mg/kg CO2-C): High microbial life and activity, soil will range from well supplied to excessive amounts of organic matter
The SLAN Test
SLAN can reveal soil quality factors by revealing forms of organic nitrogen that are held in root and plant debris. This indicates recent biological activity and potentially mineralizable nitrogen.
Results reported as:
Results will be reported at mg/kg of Amino-N and usually range from 75 to 400 mg/kg.
Low: < 100 mg/kg NH3-N
Moderate: 101 - 200 mg/kg NH3-N
High: >200 mg/kg NH3-N
Sampling Needs and Timing
One or both tests can be run on the same sample as is submitted for standard soil nutrient analysis. The most activity for the tests is seen in July and August; however, the most important part of using the test is to be consistent with the time of year when samples are taken so that results can be compared across years.
We have been working with the University of Vermont Extension Champlain Valley Crop, Soil, and Pasture Team to look at test results on fields with known management histories (Table 1).
Vergennes clay (with some Covington Panton silty clay) - tile drained, Fall injected manure with 7" wide sweeps on injector, Winter cover crop, and reduced till corn
Vergennes clay (undrained), Fall injected manure with 2" wide sweeps on injector, Winter cover crop, reduced till corn
Vergennes clay (with some Livingston clay) - tile drained, Broadcast fall manure, Winter cover crop, and No-till corn
Vergennes clay (with some Livingston clay) - tile drained, Injected late fall manure after cover crop established, Winter cover crop (reduced yields due to later injection through established plants), reduced till corn
Elmwood Fine Sandy Loam, Spring injected manure, and no-till corn
Elmwood Fine Sandy Loam, Spring broadcast manure, no-till corn
On the six fields in VT, it was found that the no-till fields generally had higher PSNT values and that the clay fields generally had higher SLAN values. Field 2, the only undrained clay field, and had generally lower values on all tests.
In June, when SLAN was measured on clay and sandy fields a the clay fields had higher SLAN values than the clay. There was no difference between the 6" and 12" depth samples for SLAN in the clay and sandy soils. The lower values of SLAN in the clay could be indicative of N losses early in the season from rainfall, and also related to the organic matter in the soil. The difference in the SLAN values in the sandy soil at the different depths may also be related to the method of manure application, injected vs. surface applied. However, more data to compare these manure application methods is needed.
There does not seem to be any relationship between the SLAN results and the PSNT results. All PSNT results call for N application, and SLAN numbers are not lower where more N side dress is called for from the PSNT.