Solvita and Other Mineralizable Nitrogen Tests As Indicators of N Response in Minnesota Soils.

Extractable and mineralizable nitrogen (N) is the N pool that can be accessed for plant uptake. Thus accurate estimation of soil potentially mineralizable N (PMN) is desired to predict optimum N fertilizer rate recommendations for farmers. Percent organic matter (OM) was formerly used to adjust N rate recommendations for corn production in Minnesota, but is no longer considered. Traditional laboratory incubations are recognized as the standard for predicting PMN, but they are labor intensive, expensive, and cannot supply in-season recommendations due to long incubation times. A new test from Solvita that determines the burst of soil respiration after rewetting is a relatively low cost tool being marketed as an easy way to estimate soil N response. Previous studies have shown high correlations between soil respiration rate from this 24-hour test and the estimated mineralizable N pool from incubation experiments, but this test has not been evaluated for Minnesota soils and conditions.  

The objectives of this study were to: 1) compare the Solvita test with standard laboratory incubation techniques; 2) determine whether the Solvita test is a better measure of soil N supply than soil OM level; and 3) use existing corn N response studies in Minnesota to determine whether fertilizer N recommendations can be improved based on the Solvita test.  For 160 soil samples from control plots in several N response trails, the Solvita test was compared to KCl-extractable N, OM, laboratory incubation and EONR results to determine whether this can be a useful tool for predicting N rates. Overall, the correlation between the Solvita test and OM had an r² of 0.49, with a better relationship observed for soils with OM less than 5%. Solvita results were not correlated with EONR.