Evaluation of Soil Tests for Predicting Nitrogen Mineralization in Temperate Grassland Soils

Improving nitrogen (N) fertilizer‐use efficiency (NfUE) in temperate grassland soils is important for agronomic and environmental sustainability. Nitrogen supplied from soil N reserves through N mineralization processes need to be accounted for when prescribing additional N fertilizer applications. Therefore a rapid and reliable soil N testing procedure for predicting mineralizable N (MN) needs to be identified for temperate grassland soils. In this study, the MN across 35 mineral grassland soils (depth 0–10 cm) from Ireland, with varying physiochemical properties, was investigated using a 7‐d anaerobic incubation (AI‐7) as a reference method. The soil N pools measured using seven relatively rapid chemical N indices were also examined and compared with the AI‐7 values. The Illinois Soil N Test (ISNT), total N (TN), and total C (TC) correlated strongly with MN, (r > 0.81) across these 35 soils. There was no distinct improvement when soils were grouped according to soil textural class. Although TN and TC displayed strong relationships with MN, these N indices may be less sensitive to short‐term changes due to soil management practices and climates and consequently may be less suitable as an indicator. The ISNT was the best predicator of MN, explaining 69% of the variability in MN, suggesting that it was measuring a similar labile soil organic N pool to that released by AI‐7. The ISNT shows potential to replace AI‐7 as a more rapid and reliable soil N test for routine analysis across temperate soil types, however, further field based studies are required.