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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

Forage Systems Update
Vol 13, No. 2

Soil testing is a vital tool for maintaining productive pastures and hay fields. At FSRC we sample about one third of the pastures each year in the early spring. In order to follow trends in soil fertility a three to five year sampling regiment is recommended. Soil testing, and adjusting soil fertility, is critical when establishing forages. There are variables you cannot control, but you can control the fertility level, giving the new seeding the best chance for success.

The soil test results you get back are only as good as the sample that you submit. A soil probe or soil auger is the best tool to collect the sample. When using one of these, the sample contains the same amount of soil from the top to bottom of each individual core and all the cores are the same size. The only other requirement is a clean plastic bucket. Metal buckets can contaminate samples with micronutrients. I also have made a useful little tool that looks like a nail with a large head that I use to push the soil sample out of the probe (a small wooden dowel would also work).

The next step is to determine where to collect the sample. Ideally a sample should not represent more than 20 acres. Separate samples should be collected from areas of the field that have been managed differently historically. For example, you may have a pasture where half of a field was grazed for several years and the other half was a hay field. Even though you graze the entire area as one unit now, historically the areas have been treated differently and the fertility levels will reflect that. Different topographic areas should also be sampled individually. Again, even if a pasture or hay field is managed as one unit, bottom areas of a field will have different fertility levels than the adjoining hillsides.

Be aware that areas in pastures near water tanks, shade trees and hay feeding sites will be much higher in fertility due to the fact that livestock spend much time in these areas loafing, therefore depositing nutrient rich manure. These areas should be avoided when sampling and applying the fertilizer. Another possible difference in fertility can result from old farmstead sites and areas where manure was applied, even 20 or 30 years ago.

Collect approximately 20 cores for each sample by zigzagging across the area. Each core should be the same depth, typically 6 inches deep. Thoroughly mix the sample and put it in the box or bag to be submitted to the laboratory.

A regular soil test will generally include the soil pH, phosphorus, potassium, calcium, magnesium, and organic matter levels, the cation exchange capacity (the ability of the soil to hold certain nutrients) and the neutralizable acidity (used to determine the amount of limestone needed to alter the pH). Fertility recommendations based on the yield goals you submit usually accompany the results as well.

The ranges of fertility that we aim for are: pH 6.0-7.0, phosphorus level of 30-40 pounds per acre, and potassium level of 300-400 pounds per acre. At the very least, fertilizer should be applied to replace the amount of nutrients removed from the field each year. This is especially important in hay fields. As a rule of thumb, every ton of alfalfa or red clover removes approximately 15 pounds of phosphorus and 50 pounds of potassium, no nitrogen is required since these crops fix their own nitrogen. For tall fescue, every ton of forage removes approximately 45 pounds of nitrogen, 15 pounds of phosphorus, and 50 pounds of potassium. The warm season grasses (switchgrass, big bluestem and indiangrass) require approximately 25 pounds of nitrogen, 5 pounds phosphorus, and 12 pounds potassium for every ton of forage produced. These are approximate figures, but may be used as a fertility replacement guide if current soil test levels are not available.

Listed below are some of the University of Missouri Extension Guide Sheets that are available that address soil fertility management:

These guide sheets can be viewed and/or printed from the internet or obtained from your local extension office. The web address is: http://muextension.missouri.edu/explore/agguides/. You can either use the search option and type in the guide sheet number or search the site manually.