Correlations between Two Alkali Extractable Amino-Nitrogen Tests and Response to Organic Fertilizer in Turfgrass Soils

The Illinois soil nitrogen (N) test (ISNT) and the Solvita Labile Amino-Nitrogen (SLAN) test are chemical analyses that estimate the concentrations of soil labile N. The SLAN uses the same reagent as the ISNT but is a relatively new test with limited field data available. This study was conducted across 6 yr (2008–2013) to determine if concentrations of SLAN–N and ISNT–N are correlated in soils under predominantly Kentucky bluegrass (Poa pratensis L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] lawn turf and to compare the response of SLAN–N and ISNT–N concentrations in relation to varying organic fertilizer rates. Separate randomized complete block field experiments were established in Connecticut on the two species with varying rates of an organic fertilizer to create a wide range of labile soil N concentrations. Soil samples were collected in the spring of each year and analyzed for concentrations of ISNT–N and SLAN–N. For all years and each species, and for pooled years and species, SLAN–N concentrations were positively and significantly (P 0.80) at Year 6 of the study. Furthermore, SLAN–N and ISNT–N concentrations increased linearly (P < 0.05) in response to organic fertilizer rate, but the rate of change was greater for ISNT–N. The data suggest that the SLAN test is generally well correlated with the ISNT and may offer an easy and rapid soil analysis to guide N fertilization.