Asked October 2, 2018, 2:22 PM EDT

Hello My soil sample indicated that I am lacking nothing accept periodic Nitrogen. I fertilized over Memorial day and I aerated and slit seeded on the 9th of September. I was thinking about putting down one more Nitrogen treatment ( I have done three this year for a total of 3Lb/1000 sq. ft.) I was thinking about putting down a treatment of Milorganite next week to act as a slow release, late fall fertilizer and last treatment of the year. Is there any benefit from Cu or Fe? Below is my soil analysis as per your lab. Phosphorus (P) 59 ppm Potassium (K) 272 ppm Magnesium (Mg) 216 ppm Calcium (Ca) 1616 ppm CEC 10.6 meq/100 g Soil Type Mineral (Loamy sand) Soil pH 7.4 Lime Index 0 Organic Matter 3 % Should I just leave it alone or would you recommend another 20-0-10 treatment to get that last 1 Lb/1000 ft. sq. of Nitrogen? Thanks in advance.

Midland County Michigan

1 Response

Let's first look at your soil pH. Ideal pH for lawns is 6.5. Your 7.4 is a little alkaline to be ideal. Your pH can be reduced by adding sulphur. Understand that this will be a slow process. Please see the link below for information re. understanding your soil test. Follow the 7.5 up the line to see how well your soil is able to uptake the various nutrients:

The soil test does not measure Nitrogen because it varies significantly throughout the year by leaching through the soil. Your test makes a recommendation based on the fact that your are growing grass, but it doesn't measure. One way to increase your lawn's N is to mulch your fallen leaves into your lawn each fall. A late fall (I aim for Thanksgiving just before the ground freezes) is good. The nutrients will go into developing stronger roots rather than green tops.

Essential Nutrients: N - Nitrogen Supports overall plant health and above-ground growth. Accelerates growth, deepens green color in grasses and plant foliage. Too much makes plants grow quicker than their roots can support, weakening plants. P - Phosphorus Essential for strong root development. Improves flowering, blooming, fruit growth and seed production. Proper amounts promote disease resistance. K - Potassium Necessary for optimum plant health. Plays more of a behind-the-scenes role compared to nitrogen or phosphorous. Improves water retention and disease resistance, and protects plants from cold.

The State of Michigan has mandated that homeowners no longer apply phosphorous to their lawns. You will notice that the middle number of the N-P-K on today's fertilizer bags is now typically zero--due to that mandate. That is because our soil in MI contains enough phosphorous for your lawn's needs. Also phosphorous and nitrogen runoff are greatly contributing the large algae outbreaks on our streams and lakes. The third number (K) is potash. Potash is not biologically hazardous, so you cannot over apply it. But NEVER over-apply phosphorous.

The chemical makeup of Milorganite is 5-4-0 (in N-P-K order), a very small % of N. Your soil test probably recommended 3lb/1000 sq. ft. which is typical need for lawns. (Remember it wasn't actually measured.) 5% N is a very small amount. To get 3 lb/sq. ft. of N with Milorganite, you would need to apply 60 lb/1000 sq. ft.

Re. Iron and copper. Yes, these micronutrients play a role in your lawn's health. Copper is required for lignin synthesis which is needed for cell wall strength and prevention of wilting. Deficiency symptoms of copper are dieback of stems and twigs, yellowing of leaves, stunted growth and pale green leaves that wither easily. Grasses don't require a lot of iron, and it's generally not needed unless your soil test indicates an iron deficiency. that I've given you probably TMI, if your lawn is not green enough, you need more N. Use a typical lawn fertilizer, i.e., 12-0-12. That will give it a shot of N. You can always apply your slow release Milorganite later in the fall. I think the most important help you can give your lawn is trying to reduce the alkalinity. Your lawn will thank you!