Beyond NP&K, don’t forget lime and micronutrients
Adjusting soil pH is critical to nutrient availability. Manure is a good source of micronutrients to soils and crops.
The big three nutrients, Nitrogen, Phosphorus and Potassium, get most of the buzz when discussing soil nutrients. Lime is like the Maytag salesman—people forget to respect its importance in soil fertility. Especially on sandy loam soils of Michigan, low soil pH can often be a deciding factor on micronutrient availability to crops. The soils often are not truly deficient of the nutrient and it may be in the soil, but the pH of the soil keeps it from being readily available to plant growth. Sandy soils tend to suffer from low pH, which can be corrected with lime. Clay soils may be high in pH, a condition that is much harder to remedy and often necessitates the addition of the micronutrients, especially zinc and manganese.
If you spread livestock manure, you are adding free micronutrients. Manure samples can be tested for micronutrient content at an additional cost. Micronutrients are called “micro” because when needed, just several pounds per acre will correct a problem. Even if micronutrients are added with manure, if the pH is out of line, the nutrients may still not be available for plant growth. Legume crops that make their own nitrogen such as alfalfa and soybeans are sensitive to pH and prefer a 6.5 -7.0 to produce their own nitrogen. Corn is more tolerant of pH, but the 6.5-6.8 is still considered the range to achieve.
Rental ground is always a concern for pH. When pH is low, lime is recommended. Lime is considered slow to adjust pH but has several years of useful benefits. Producers with year to year land rental contracts may be hesitant to invest in lime.
Soil testing is the best way to determine pH, whether lime is recommended, and how much is needed per acre, based on the specific soil type and crop to be grown. If you are concerned about the availability of a certain micro nutrient, have the soil lab run a specific test on that nutrient.
Teaming up a soil test and knowing the analysis on manure will enable you to keep tabs on soil pH and micronutrient availability so that crops are not shorted nor money spent on unnecessary nutrients.