Do you have current soil tests for your fields? Are you having problems with low crop yields, poor plant growth or difficulty managing weeds? Soil tests can provide a lot of information that can help guide you with what you should be putting on your fields.
Soil testing is important because the results give an idea of what the soil is lacking, or even what nutrients are high in the soil. There can be variability in soil test results which can be attributed to time of year the sample is taken, depth of the sample and where the samples are taken from.
Because of the potential variability, some people don’t trust soil test results, and choose to manage nutrients based on crop removal.
While it is possible to apply nutrients based on crop removal each year, this can present a problem. Even if you are applying the correct phosphorus and potassium based on crop removal, your soil pH level could be off, causing nutrients to be unavailable to the crop.
The solution to this is applying a ton per acre of lime every few years, right? At $30 or so a ton, it might not make financial sense to do that if the soil doesn’t need it, or worse, not applying enough to bring soil pH to an acceptable level. This can be critical for some popular crops, like alfalfa, which require a certain soil pH level to be most productive.
Also, soil test levels may be high enough that there is some wiggle room to draw down nutrient levels. According to the brand new Tri-State Fertility Guide, a 200 bushel corn crop removes 70 pounds of phosphorus and 40 pounds of potassium per acre.
Replacing these nutrients will require 152 pounds per acre of DAP and 67 pounds per acre of Potash. At current prices this would be $29.64 per acre for DAP and $11.73 per acre for Potash for a total cost of $41.37 per acre.
If these nutrients are not needed, the potential cost savings for a 20 acre field is $827.40. This works the other way as well if soil test levels are too low, crop yield response can be seen from a heavier application to build nutrient levels up in the soil.
The point is this: soil test results will show what the field needs to produce the maximum yield while using nutrient inputs as efficiently as possible. A soil test result can show you the pH level in standard pH, and also buffer pH or lime index, which will tell you if you need to apply lime to your field and how much.
In addition, it shows the plant-available phosphorus, potassium, calcium and magnesium levels. It will also show the soil’s cation exchange capacity and the percent base saturation for potassium, calcium and magnesium. Soil organic matter is also commonly tested for, although sometimes it is not included in a basic soil test.
We would recommend requesting that soil organic matter be included in your sample results if it is not included in the basic test. You can also request micronutrients (boron, copper, iron, etc.) to be included in the results and ask for a recommendation on the amounts of nutrients to apply in pounds per acre.
This information usually will involve an additional cost per sample, but is very useful information to have.
The Natural Resources Conservation Service considers a soil sample to be current for three to four years, as referenced in the 590 Nutrient Management Standard. Any tests that are older than four years should be updated.
To have a more accurate trend in the soil fertility, samples should be taken at the same time every sample cycle. The best time to take soil samples from cropland and vegetable production is in the fall of the year, after harvest. For pastures and perennial crops the best time is during the late summer period.
For pastures, the sample should be four inches deep. For plowed or chiseled cropland, the sample should be eight inches deep. Fields that are no-tilled every year is eight inches deep when you are looking for phosphorus and potassium, and four inches deep for pH.
When you take the samples, you should use a zigzag pattern across the field that you are sampling and collect 15-20 individual samples that will represent no more than 25 acres for one sample.
Some fields may need to be broken into sections for soil testing purposes. Avoid areas that may skew the overall results, such as where manure was stockpiled in the field or field corners that may not see the same nutrient application as the rest of the field. Remember, consistency is the key to getting the most out of soil test results.
Once you have all of your samples from the field, pour the individual samples on top of a plastic or paper bag for it to air dry. Then when the soil is dry mix it together and put it into the soil testing bag or box. Samples can then be taken to your local agriculture retailer or extension office to be sent to the lab for analysis.
Taking soil tests and making improvements on your fields you should see increased crop productivity and better yields. Arguably, the biggest benefit to soil testing is watching soil test nutrient levels over an extended period. It helps to really get to know individual fields and what they specifically need.
As a note, future cost-share programs through the soil and water districts are going to require current soil tests as a prerequisite for farmer participation. Having current soil tests on every field will ensure that you can participate in future cost-share programs, as well as giving you recommendations to improve the value and productivity of your crop, hay and pasture land.
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