Soil sampling this fall
By David G. Hallauer
Meadowlark District Extension Agent
With most of the area now having a little bit of soil moisture, we can finally get a soil probe in the ground. I've been in a number of fields over the past month where it was difficult at best. Just one more reason to welcome that mid-November rain.
For forages, pull samples to a depth of four inches. Take plenty of samples, avoiding concentration in the best or worst areas of the field. Many of the soil samples we see from hay grounds are deficient in phosphorous that results in declining stands. A soil test makes it easier to determine where our fertilizer dollar should be spent on a crop with a pretty thin margin.
Crop field sampling can be a little more complicated. If you are in no-till, you may want to sample to a shallower depth than the 6-inch depth suggested for tillage systems. Nutrient concentrations from repeated surface applications may better show up if you do so. If you want to take it a step further, you may want to go ahead and sample to a 6-inch depth, then split each core into a 0- to 3-inch and three- to six-inch sampling depths. That will give you an even better idea as to how much nutrient stratification is occurring.
There are a number of options for how to go about sampling. Grid sampling can allow for variable rate fertilizer applications to "even out" portions of the field with lower testing levels. You can also use a more general sampling procedure, similar to that used in grassland sampling where you take a good cross section of the field and collect numerous samples with the intention of fertilizing everything the same. I like a combination of the two I'll refer to as zone sampling. You know your farms--where the best and worst areas are--so sample accordingly. In that way, you can fertilize the high production areas for high production, while not applying fertilizer to areas that simply don't have the soil type, or drainage, or are yield limited in some way.
No matter what, sample. It really is the best way to determine what your fertilizer needs are or to monitor your current program.