A comparison of laboratory, greenhouse, and field indicators of nitrogen availability

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Abstract
In the past, greenhouse and field results have been used individually to test the predictive capacity of laboratory indexes of soil nitrogen availability. The field results are the most reliable measure of field available N, but greenhouse experiments can be conducted more easily and over the whole year. A comparison of the laboratory, greenhouse and field indicators of N availability was therefore needed to determine if greenhouse data could be substituted for field results in this capacity. In a study of ten Pennsylvania soils there was no significant correlation between field relative N uptake and greenhouse relative N uptake which suggested that greenhouse results could not be substituted for field results in testing the reliability of laboratory indexes. There was no significant correlation between the field results and the five laboratory indexes tested (total N, total organic matter, Fox‐Piekielek Test, MacLean Test, and Keeney‐Bremner Test). However, the latter three tests did correlate with the field relative N uptake when one of the soils was deleted from analysis. All five laboratory indexes were significantly correlated with greenhouse relative N uptake. Total organic matter content of the soil would explain 72% of the variation in greenhouse relative N uptake and only 23% of the field relative N uptake.