2 similar approaches to fertilization, with 1 notable difference
Slides for TurfNet webinar on MLSN

Soil test phosphorus in turf soils: 2 datasets

Selection_090Landschoot et al. wrote about a large dataset of Mehlich 3 phosphorus data in Summary of Mehlich-3 P Data from Home-Lawn Soil Tests in Pennsylvania.

How are the data distributed? The median of the Pennsylvania data is 57 ppm, and 40% of the samples are less than or equal to 45 ppm, which is the cutoff level for P fertilizer recommendations to home lawns by the Penn State Agricultural Analytical Services Laboratory (AASL). Home lawn samples greater than or equal to 45 ppm P will not receive a fertilizer recommendation from AASL. For golf course putting greens the recommendation is different; P fertilizer is recommended by the AASL for putting greens when the soil test P is less than 90 ppm.

I looked at the Global Soil Survey (GSS) Mehlich 3 P data through August 2014. For these GSS data, the median value is 76 ppm, compared to 57 ppm for the Pennsylvania data, and only 35% of the GSS samples are less than or equal to 45 ppm, compared to 40% falling below that value in Pennsylvania lawns. Here is a histogram of the GSS data collected through August 2014:

Histogram_gss_m3pIn the GSS data, 11% of the samples were below the MLSN guideline of 21 ppm for P. The average expected P use by grass on putting greens is about 22 ppm, based on the average nitrogen application rate to putting greens in the US. Using the MLSN interpretation of the GSS data, and assuming P use at an average level, 33% of the GSS samples would receive a P fertilizer recommendation, compared to 40% of the Pennsylvania samples.

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