Soil N is not used to guide N fertilization of turfgrass due to a lack of soil test correlation and calibration research for this purpose. We could find only one paper in the literature that examined the reliability of soil NO 3 -N concentrations to estimate turfgrass response (Rieke and Ellis, 1974). The authors concluded that soil NO 3 -N was not a reliable estimator of turfgrass response, but the design of the experiment and the analysis of the data were completed using standard methods from the 1970s and not contemporary methods of soil test correlation and calibration.Methods to develop soil tests have changed greatly since the 1970s. Current methods require a three-step process of soil test correlation, calibration, and then interpretation of data to develop recommendations. Correlation and calibration are usually completed in one set of experiments and development of recommendations in another set of experiments if the correlation and calibration steps were successful (Dahnke and Olson, 1990).Soil test correlation is the process of establishing a relationship between the extractable concentrations of the soil nutrient of interest, in this case NO 3 -N, and the yield or quality of the plant of interest, in this case turfgrass (Dahnke and Olson, 1990

The Illinois soil nitrogen test (ISNT) and soil permanganate‐oxidizable C (POXC) concentrations have been used to estimate mineralization potential of agricultural soils, assess soil quality, distinguish differences between crop management treatments, and predict crop response to N fertilization. However, it is not known if these measures are correlated to growth and color quality responses of cool‐season turfgrasses. This study was conducted across 5 yr (2008–2012) in Connecticut to determine if a single spring measurement of Illinois soil nitrogen test‐N (ISNT‐N) and POXC concentrations could be used to estimate color and growth responses of Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) lawns. Randomized complete block field experiments were set out on the two species with varying rates of an organic fertilizer. Soil samples were collected in early May of each year and analyzed for concentrations of ISNT‐N and POXC. Turfgrass color, clippings yield, clippings total N concentration, and clippings total N uptake were measured from May through October. Turfgrass responses showed consistent positive linear responses (p < 0.05) as a function of ISNT‐N and POXC. Across species and years, ISNT‐N and POXC were generally greater under tall fescue than under Kentucky bluegrass. A single spring measurement of soil ISNT‐N and POXC shows promise in categorizing Kentucky bluegrass and tall fescues lawns as to their likelihood of N fertilization response. The data suggest a low probability of meaningful Kentucky bluegrass and tall fescues lawn responses to N fertilization when spring ISNT‐N and POXC concentrations exceed 250 mg kg−1 and 1300 mg kg−1, respectively.

Core Ideas There are limited data to determine if the Illinois Soil Nitrogen Test and Solvita Labile Amino Nitrogen test are correlated. Across a 6‐yr study, Illinois Soil Nitrogen Test and Solvita Labile Amino Nitrogen were significantly and positively correlated. Illinois Soil Nitrogen Test and Solvita Labile Amino Nitrogen concentrations increased linearly across organic fertilizer rates. Illinois Soil Nitrogen Test concentrations increased at a greater rate than Solvita Labile Amino Nitrogen concentrations. The Solvita Labile Amino Nitrogen test may offer an easy and rapid soil analysis to guide N fertilization. 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 < 0.05) correlated with ISNT–N concentrations. Correlations were strongest (r > 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.

Few correlation or calibration studies have been conducted to determine or validate sufficiency levels of N concentrations in the clippings of turfgrass for color and growth responses. In a series of field experiments conducted across six consecutive growing seasons (2007–2012) in Connecticut, clipping samples of Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) lawns were used to estimate yields and then analyzed for N concentrations. Chlorophyll and normalized difference vegetative index (NDVI) meters were used to quantify turf color before sampling. Macy's concept of three nutritional zones of plant tissue nutrient concentration was used to identify minimum and critical concentrations of N in the clippings that define sufficiency ranges for color and growth responses, in addition to luxury consumption. Averaged across all variables and seasons (spring, summer, and fall), the sufficiency ranges of N concentration in the clippings were estimated to be 32 to 46 g kg–1 for Kentucky bluegrass, and 28 to 42 g kg–1 for tall fescue. Differences in minimum and critical concentrations among seasons and between species were thought to be due to demand‐driven nutrient uptake. Luxury consumption of N was observed in both species. When used in context with local conditions, tissue analysis for N concentrations in cool‐season turfgrass clippings can provide an objective basis for guiding N fertilization.

Few correlation or calibration studies have been conducted to determine or validate sufficiency levels of N concentrations in the clippings of turfgrass for color and growth responses. In a series of field experiments conducted across six consecutive growing seasons (2007–2012) in Connecticut, clipping samples of Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) lawns were used to estimate yields and then analyzed for N concentrations. Chlorophyll and normalized difference vegetative index (NDVI) meters were used to quantify turf color before sampling. Macy's concept of three nutritional zones of plant tissue nutrient concentration was used to identify minimum and critical concentrations of N in the clippings that define sufficiency ranges for color and growth responses, in addition to luxury consumption. Averaged across all variables and seasons (spring, summer, and fall), the sufficiency ranges of N concentration in the clippings were estimated to be 32 to 46 g kg–1 for Kentucky bluegrass, and 28 to 42 g kg–1 for tall fescue. Differences in minimum and critical concentrations among seasons and between species were thought to be due to demand‐driven nutrient uptake. Luxury consumption of N was observed in both species. When used in context with local conditions, tissue analysis for N concentrations in cool‐season turfgrass clippings can provide an objective basis for guiding N fertilization.