Minimum soil nutrient guidelines for turfgrass developed from Mehlich 3 soil test results

Conventional soil nutrient guidelines are higher than needed to produce high quality turfgrass. Although there have been repeated calls for more turfgrass soil calibration research, it is not practical to conduct conventional soil test calibrations for this global crop. Turfgrass comprises more than 10 common species and hundreds of cultivars, grown in a multitude of soils and climates. We took an indirect approach to identify universally applicable guidelines by studying a large sample of 16,163 Mehlich 3 soil test results collected from good-performing turf. We modeled a subset (n = 3,683) of those results, specifically from soils with low nutrient holding capacity, as 2 parameter log-logistic distributions. We take these continuous probability distributions to be representative of soils in which good-performing turf is being produced. The minimum levels for sustainable nutrition (MLSN) guidelines were selected as the value \(x\) at which the probability of a random sample \(X\) drawn from the distribution being less than or equal to \(x\) is \( 0.1\). That is, we identified the level \(x\) where \(P (X ≤ x) = 0.1\). We propose the MLSN guidelines as minimum levels for all turfgrass sites, with fertilizer recommendations suggested as the quantity sufficient to prevent each element from dropping below the MLSN guideline. The MLSN guidelines from the Mehlich 3 data used in this paper are, for K, P, Ca, Mg, and S respectively, 37, 21, 348, 47, and 7 mg kg^-1.