What is MLSN?

Selected excerpts from ‘Minimum soil nutrient guidelines for turfgrass developed from Mehlich 3 soil test results’.

Micah S. Woods, Larry J. Stowell, and Wendy D. Gelernter

Asian Turfgrass Center, Bangkok, ailand
PACE Turf, San Diego, California

High quality turfgrass is often produced in soils that don’t have enough nutrients to produce high quality turfgrass.  That’s the paradoxical conclusion one arrives at when using conventional soil nutrient guidelines to interpret turfgrass soil tests.  

There are two primary reasons for this result.  One is the increased use of sand as a growing medium for high traffic turfgrass areas, and another is the development of the conventional guidelines themselves.  The guidelines for turf have been adapted from those of forage or agronomic crops (Carrow et al., 2004), and have in some cases been knowingly set high – not because the grass requires those quantities of nutrients, but because fertilizer cost was considered a minor issue for turf (Carrow et al., 2001, p. 164).

These conventional guidelines, and the resultant soil test interpretations, are recognized as problematic.  There have been repeated calls for more soil test calibration research across a wide range of turfgrass species and cultivars, climates, and soils (Turner and Hummel, 1992; Carrow et al., 2001; Frank and Guertal, 2013). 

Considering the more than ten species of turfgrass in common use around the world, the many cultivars of each species, and the wide range of soils in which these grasses are grown, it seems unlikely that such extensive calibration research will ever be conducted.  However, if improved guidelines were available, the same turf conditions could be produced with lower nutrient inputs.  

Nutrient use on United States golf courses has decreased over the past decade (Gelernter et al.,2016) with no indication of turf performance problems.  We developed new soil test interpretation guidelines which we call minimum levels for sustainable nutrition (MLSN).  

Turf grows well in a wide range of soils.  When the soil contains enough of an element, adding more of that element provides no benefit to the grass (Dest and Guillard, 2001; Johnson et al., 2003; Kreuser et al., 2012; Raley et al., 2013; Rowland et al., 2010, 2014; Snyder and Cisar, 2000; St. John et al., 2003; Turner and Waddington, 1983; Woods et al., 2006).  

Rather than classify soils into low, medium, and high categories, or sufficiency ranges, one can ensure the soil remains above the level at which enough of an element is supplied to the grass.  To identify the minimum guideline levels, we analyzed Mehlich 3 soil test data from 3,683 soil test results, drawn from a larger set of 16,163 samples collected from professionally-managed and good-performing turf. 

We propose the MLSN guidelines as a single soil test value to stay above for K, P, Ca, Mg, and S, applicable for all soils and all types of turfgrass.  The quantity of an element required as fertilizer to stay above the MLSN guideline will be dependent on the grass use of the element, which is site specific.  

The advantages of this approach are extensive. One can produce the same quality of turf with lower nutrient inputs.  The guidelines can be updated with ease as new data become available.  

A single soil nutrient level is identified for each element – a minimum level that we want to stay above.  Thus, this approach can answer the simple question, do we need to add fertilizer, or do we not need to add fertilizer? 

Also, we can classify soils by the SI, giving a comparison of the current soil nutrient level to the MLSN data.  This MLSN approach corresponds well to the large body of turfgrass nutrition research and we look forward to continued testing and refinement of these values in field research.

Woods MS, Stowell LJ, Gelernter WD. (2016) Minimum soil nutrient guidelines for turfgrass developed from Mehlich 3 soil test results. PeerJ Preprints 4:e2144v1 https://doi.org/10.7287/peerj.preprints.2144v1