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Private: Evaluation of The Solvita Test to Estimate Mineralizable Nitrogen in Minnesota Soils

Start Date: 2013
Principal Investigator: Deborah Allan
Organization: University of Minnesota
Status: Complete

Background Info

An accurate estimation of soil’s potentially mineralizable nitrogen (PMN) would assist farmers in predicting optimum N fertilizer rate recommendations. 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 from this 24-hour test between soil respiration rate and the estimated mineralizable N pool from incubation experiments, but this test has not been evaluated for Minnesota soils and conditions. This study compared the Solvita test with standard laboratory incubation techniques, examined whether the Solvita test is a better measure of soil N supply than soil organic matter (SOM) level, and explored whether fertilizer N recommendations can be improved based on the Solvita test.

Objectives

Compare Solvita test results with standard laboratory aerobic incubation results for potentially mineralizable nitrogen (PMN), and with other potential measures of N availability, including extractable nitrate-N, organic matter content, N mineralized after 32 and 64 days laboratory incubation and permanganate-oxidizable carbon (POXC)

Assess how prior crop and soil texture affect the relationship among these soil variables

Determine which soil N availability measures are most strongly related to crop agronomic performance, such as corn grain yield, corn total N uptake, and corn grain N uptake.

Key Findings

When the results for the CO2-burst test from all the data points for soil at 0–6 inches depth (n = 110) are considered together, there is a significant relationship with organic matter, but with a large amount of variation in the Solvita test results.

At this point, the results indicate that the Solvita kit results may show significant relationships with SOM and PMN, but the kit is no better at predicting mineralizable N than SOM is.

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