Abstract
Fertilizer is one of the most important tools in turfgrass management, and soil testing should help turf managers use it skillfully. The conventional soil test guidelines, however, have little connection to surface performance. They were developed decades ago from research on other crops grown in agricultural soils, they placed turfgrasses in high P and K requirement categories for economic rather than agronomic reasons, and they date from an era of much higher nitrogen rates. This article traces the author’s path from superintendent in Shanghai and Japan, through doctoral research on soil testing at Cornell, to the development of the minimum levels for sustainable nutrition (MLSN) with Larry Stowell and Wendy Gelernter beginning in 2011. MLSN guidelines were derived from Mehlich 3 soil test results of sand-based and other low-CEC soils with pH 5.5 to 8.5 that were all producing good turf. A probability distribution was fit to the data for each element, and the MLSN value was set at the level below which only 10% of those results fall, which builds in a safety buffer against deficiency. To use MLSN, a turf manager supplies enough of each element to keep the soil above its MLSN value, based on how much of that element the grass is expected to use, and then checks soil tests over the years to adjust rates up or down. This approach supplies all the nutrients the grass can use, avoids problems associated with overapplication (such as excess P favoring Poa annua invasion and excess K increasing snow mold and dollar spot), and keeps fertilizer decisions linked to surface performance.