# Soil Test Results - Looking Good, So Now What?



## jeffjunstrom (Aug 12, 2019)

Received my results from Penn State, as follows:

pH: 7.2 (Optimum)
N: 1-4#/M per year recommended
P: 91 ppm (Above Optimum; no P recommended)
K: 200 ppm (Optimum; no K recommended)

So, basically they are recommending the typical amount (as I understand it after reading myriad posts here) of N applied each year, and no P or K. They recommend 2-4#/M per year for new lawns (<4 years old, which mine is), and then 1-2#/M per year for lawns 4+ years old.

I guess my question is, now what? Is it as simple as applying some form of X-0-0 fertilizer at appropriate times during the year (very light in spring, none in summer, majority in fall), or is there still some basic amount of P and/or K that I should be applying?

Or do you do a soil test every year (or multiple times), and adjust annually?


----------



## corneliani (Apr 2, 2019)

In a nutsehell, your soil was determined to have sufficient amount of the major nutrients at time of testing. Going forward you need to replenish whatever is being used by the plant during its growth cycle (N & K primarily). You can do so with Nitrogen-only ferts or with a more balanced N&K fert (24-0-4, 32-0-10, etc). This is where you choose what kind of program you like to implement. A simple 4-step plan will suffice. If no problems arise most recommendations are to test every 2-4 years.

There is no mention of micros, CEC, etc, to allow further insight in how efficiently/effectively those major nutrients can be expected to be utilized ... but if this is all you have then just roll with it and if any problems arise (such as not dark enough color, etc) you'll have to either trial & error a solution or get a more complete soil test with micros, etc.


----------



## ScottW (Sep 16, 2019)

I've been reading about MLSN (minimum levels for sustainable nutrition) and playing around with some spreadsheets to calculate nutrient usage & fertilizer stuff. Our forumites have created a Google sheet that you could play with if you get bored during the winter down time. See  this thread. There's a section where you can input your local climate info from the weather almanac and it will calculate growth potential and nutrient usage.

Grass uses N and K in about a 2:1 ratio.
You have enough K in your soil right now, but eventually it will get depleted.
Based on historical climate averages for my area, if I give my lawn 5 lbs N/M next year, and if I bagged and disposed all my clippings, about 90 ppm of K would be removed from the soil. The model I'm playing with assumes that returning the clippings to the lawn (mulching) cuts that nutrient loss by 80%, so only 18 ppm would be lost. So whether you bag or mulch is a big factor.
P is used much more slowly, like 1/8th the rate of N. My yard would lose 4 ppm if mulching or 20 ppm if bagging. You're probably stocked up on P for a while.
You could probably get away with N only (X-0-0) next year, but a more conservative approach would be to keep K well above minimum levels. So if you were planning for 4 lbs N/M then add 1 to 2 lbs K/M in 2020, and then stick with a general 2-0-1 ratio going forward until your next soil test.


----------



## Gilley11 (Nov 3, 2019)

Wow, how do you calculate those numbers?


----------



## ScottW (Sep 16, 2019)

The spreadsheet from that thread I linked does the calculations. I've used Excel enough that I can figure out what formulas it's using and which user input values they're based on.

The general idea is that the various nutrients/elements are used at known ratios based on grass tissue analysis. Everything is relative to nitrogen and it looks like this (pardon the crappy formatting): 
Element	Tissue ppm	Ratio:N
N	40000	1
K	20000	0.5
P	5000	0.125
Ca	4000	0.1
Mg	2500	0.0625
S	3000	0.075
Fe	200	0.005
Mn	75	0.001875

Target levels in soil seem to be taken from scientific literature with some safety margin to be above the minimum MLSN numbers:
Mehlich-3 target ppm
K	125
P	50
Ca	625
Mg	75
S	30
Fe	75
Mn	10

The actual rate at which your grass grows and uses those elements at those ratios out of your soil is calculated based on a "growth potential" value, which is based on your local climate data which you would input as monthly average temperature and rainfall.
If you then input your soil test results of ppm for the various elements, it will combine that with the growth potential based on your local climate averages to predict any shortfall in nutrients relative to the target values, which you'd compensate for in your fertilizing plan.
If you're like me, you already fertilize and soil test and have the greenest lawn on the block, but maybe you haven't cared to get as quantitative as this before. Me neither. This is a new level of nerdery that I'm going to play with next year.


----------

