Respiration Is Not an Accurate Predictor of N Mineralization Across California Agricultural Systems.

The use of soil testing to predict soil nutrient status is imperative for proper fertilizer prescriptions. Many current tests lack information about the biological components of soil, which can lead to inconsistent and inaccurate results. Utilizing the burst of respiration on the rewetting of soil can provide insight into soil microbial community size and activity. Recently, it has been used to predict net N mineralization in agricultural soils, representing a potentially viable commercial soil test. This test, coupled with other soil chemical and biological assays, was tested across four growing regions and two management strategies in California. Univariate relationships between respiration and N mineralization were moderate, yet mostly statistically significant in cover cropped fields (R²=0.01-0.30) and weak and not significant in fields that did not receive cover crops (R²=0.001-0.12). Respiration did not represent a better sole predictor of N mineralization than total C or total N for either cover cropped or non-cover cropped fields. When best-fit models were constructed, respiration was coupled with chemical indicators in cover cropped fields to predict N mineralization across growing regions. These models were slightly more accurate than univariate relationships, yet were inconsistent in their efficacy across growing regions. This lack of strong relationships shows that respiration upon rewetting does not serve as a valid predictor of N mineralization in California agricultural regions. However, it has the potential to be used in tandem with other indicators for relative measures of soil fertility.