It’s soil test time.
As harvest progresses this fall, many fields will be in a rotation to have soil sampled. One very ‘illuminating’ procedure that growers might consider having done is to have an occasional sample drawn from a depth of greater than 6 inches. While it is true that applied P & K fertilizer tends to remain in the upper 6 inches of the soil, it is also true that plants roots are feeding much deeper than 6 inches when they reach full size and are producing grain. In the drier weather of late summer when top soils dry down, the strata of soil below 6 inches is where the roots do most of their feeding. Samples taken from depths of from 12 to 18 to 24 inches can provide an indication of where real deficiencies may exist. Because roots feed from very great depths of soil, those nutrient levels won’t change as often as the top 6 inches. So deep sampling need not be done often. However, a few samples from each field every 8 to 12 years or so can provide useful reference figures that may help you understand how crop yields can vary across a field. If you use zone sampling, taking two deep samples from each zone should be sufficiently instructive. If you use grid sampling, a deep sample from every 15 acres may suffice.
Many soil testing services are now offering a service to do deep soil sampling. Since many services are using truck mounted samplers, they prefer to sample before tillage operations have begun. Be sure to check Tractor Time for the best time to head out into the field, then don’t hesitate to call your testing service before you till those scheduled fields and let them know when you finish harvesting a field.