Soil Remediation Guidelines
You got your soil tested. They gave you some high level recommendations that you need to increase X or Y, but how do we do that? This article will try to address the techniques or approach to remediation based on your soil test and soil needs.General
For most cases, don't try to remediate the soil during the winter if your soil freezes. Products applied to frozen soils might not travel deeper into the soil and get washed away. Try to focus in the months the grass is actively growing. Also avoid applications in the peak of summer under drought conditions since it might lead to more plant stress. This is a marathon and unless you are deficient (rare) most of the amendment we do is to get the soil to an ideal condition.
The recommendations are for soil modifications to be applied monthly. Do not use these rates for foliar applications unless you immediately run the irrigation to wash the product off the leaves into the soil.
pH
We need to start with the pH. Most of the recommendations depend on your soil pH. As previously discussed, a pH around 6.0-7.0 is in the sweet spot. If pH is less than 6.0, then it will need lime. Your soil test should tell you how much lime to apply per ksqft. The guideline is no more than 50lb/ksqft every 6 months, unless you are using a fast acting lime. For a fast acting lime, follow the bag recommendations. There are 2 types of lime, dolomitic and calcitic. Dolomitic limestone is a mix of calcium and magnesium; while calcitic is mostly calcium. Most soils do not need magnesium, too much can cause the soil to become too hard and it cannot be removed from the soil. Unless the recommendation was to also increase the magnesium in your soil, use calcitic to increase your pH. For nitrogen, a low pH soil will benefit from using ammonium nitrate (34-0-0) at no more than 3lb/ksqft/month. Avoid applying other products for 2 weeks.
If soil pH is above 7.0, then the best way to reduce it is with elemental sulfur at 5lb/ksqft per hot weather season (once a year in northern states vs twice in Houston, TX). Why? Elemental sulfur needs a microbial breakdown to convert it to sulfuric acid and release the hydrogen which is what reduces the soil pH (more info in this Ohio State article). Too much elemental sulfur without the microbial activity can lead to accumulation and too much being released at once (hurt your lawn). There are other ways to reduce soil pH and this Purdue article describes it and this Iowa State article.
But (there is always a but), lowering pH in the soil might not be possible/cost effective. If the soil has enough calcium carbonate, the quantities needed of elemental sulfur are too much. This article describes a study that tilted 240lb/ksqft of elemental sulfur. It dropped the pH by 0.5, but it increased over the years. Continuous application might keep it there (but at 5-10lb/year?) and using other techniques (citric acid) will help.
High pH techniques
Having a high pH is not the end of the world. You can have a nice lawn with a high pH, as many of us do. It just needs some adjustments. The main issue with high pH is that iron is not as available via the soil. When iron is not available, then chlorosis starts (yellow lawn) due to the lack of chlorophyll. We work around it using foliar application of iron (FAS) so it is absorbed by the leaves (bypass the soil). The other option is to use a chelated source of iron. It is more expensive and might not work too well in the really high pH. Using Ammonium Sulfate (21-0-0) at no more than 4.7lb/ksqft/month as the nitrogen source will also help due to a slight acidifying effect.Phosphorous
If your phosphorus is low, then you can use:Triple superphosphate (TSP) 0-46-0 - Apply at 2lb/ksqft every month the soil is growing
For low pH soils you can use:
Diammonium phosphate (DAP) 18-46-0 Apply at 2lb/kqft but account for the nitrogen being applied 0.36lb N/ksqft. It will slightly increase the pH.
For high pH soils you can use:
Monoammonium phosphate (MAP) 11-52-0 - Apply at 2lb/ksqft, but account for the nitrogen being applied at 0.22lb/ksqft. It will slightly decrease the pH.
Another option is to use biosolids (eg. Milorganite). They will take longer to break down and be part of the soil, but they do work.
Last option is to use a fertilizer called "starter fertilizer". These normally have a higher percent of P than N and can be used to increase the P levels without too much nitrogen feeding.
Potassium
For potassium there are two main options:Sulfate of Potash (SOP) 0-0-50. Apply at 2lb/kqft/monthly. This will also provide some sulfate sulfur the plant needs too. It can be hard to find. Go to the hometown folders in the forum to ask someone local to your state for sources.
Muriate of Potash (MOP) 0-0-60. Apply at 1.6lb/ksqft/monthly. MOP can be harsh into the soil(chloride), but it is widely used by most fertilizer blends (eg. Scotts). Try to find the SOP since it is better, but don't sweat it.
Potassium Nitrate 13-0-44. Apply at 0.5lb/ksqft. The nitrogen is in the nitrate form, so it moves fast and leaches thru the soil. It is applied in liquid form and needs irrigation after to avoid foliar (4oz/ksqft foliar max). Thanks Greendoc for the info.
Iron
Once the soil pH goes above 7.0, iron is not as available. Soil applications of iron are just a waste of money. As explained above, use FAS or chelated irons for the high pH soils.For soils below 7.0, you can also use FAS. You can also use any other source of iron per the bag rate. Avoid applications with moist/wet lawn, since it can be absorbed via the leaves and cause a black lawn. After sweeping the concrete, run your irrigation after application to clean the leaves if the lawn was moist.
This article from Harrells is a great read on soil iron in general. The irony in iron
Warning
Iron stains. It will stain your concrete driveway, patio, etc. Be careful how you apply it and where you mix it. Chelated sources of iron stain less or not at all.
Sulfur
Sulfur in the form of sulfate is an essential nutrient the plant needs. If you need to increase it, then Sulfate of Potash or Ammonium Sulfate will be good options. Elemental sulfur can also be good, if your soil pH can handle it.Gypsum
Sometimes there is a desire to adjust the calcium without impacting the pH. We use gypsum for this. You can put down 20-30 lbs/M of gypsum every 60 days. Keep the applications of P and K apart. Gypsum is 21% Ca by weight.Micros
Research on micros is very limited. Even research on how low Phosphorus levels can be an issue is currently on going. Most of the micros ranges were extrapolated from the ag side (eg. corn). I normally recommend to leave them alone, unless you are seeing a lawn problem (eg. yellow lawn) and all of your other soil items are in range.Balanced fertilizer
Sometimes we refer to a balanced fertilizer. This means that the ratio of Nitrogen, Phosphorus and Potassium is equal. It is a mix of the products listed here (check the label) and ready to be applied from a bag. These products are easy to find in most stores. Applications rates (maximum per month)
10-10-10 - 10lb/ksqft
12-12-12 - 8.3lb/ksqft
13-13-13 - 7.7lb/ksqft
16-16-16 - 6.25lb/ksqft
20-20-20 - 5lb/ksqft
