Solvita and Other Soil Measurements As Indicators for N Availability in Minnesota Soils.

In most corn (Zea mays L.) cropping systems, nitrogen (N) is the most limiting nutrient. Accurate estimation of potentially mineralizable soil N (PMN) is desired to predict the need for additional N fertilizer. Traditional laboratory aerobic incubation (Stanford and Smith, 1972) is recognized as the standard method for predicting PMN, but cannot supply in-season recommendations due to the long incubation time. Recently, two carbon fraction tests, Solvita CO₂-Burst test (Solvita) and permanganate oxidizable carbon (POXC), have been used for soil quality studies and compared to incubation tests for PMN determination. However, these two methods have not been tested for Minnesota soils and conditions. 

In this study, our specific objectives include: 1) Compare the Solvita test with standard laboratory aerobic incubation techniques, KCl-extractable nitrogen, organic matter content, and POXC; 2) Determine whether the Solvita test is a better measure of soil N supply and yield than soil OM and extractable N; and 3) Compare how different prior crops and soil textures affect the relationships among these soil variables.  

Both the Solvita test and POXC were significantly related to all other measurements used in this study. However, our results showed that both POXC and SOM were more strongly related to PMN than Solvita was. SOM, extractable N, and Solvita for the 0-15 cm depth were equally good at predicting corn grain yield. Solvita was well correlated with extractable N at sites previously in corn or soybean, but not alfalfa. Solvita has much stronger relationships with other soil measures in coarser textured soils than in clay loams and clays.