One of the debates since the early days of precision farming and variable rate spreading is whether you should apply more lime and fertilizer to build up areas that don't yield as well, or divert those resources to the areas that yield the best instead, helping those yields rise even higher. Some agronomists think there's another step that needs to be taken before you even get to that point where you can ask that question. First you need to document where yields aren't as high, and why they aren't as high there.
Maybe it's low soil fertility. Or maybe it's a pocket of soil different from the surrounding area that has lower organic matter contest, is shallower to sand or gravel, making it droughty, or both. Unless you pursue low-testing areas to pinpoint the cause, you won't know. And if you don't know, you won't be able to decide if it's worth investing money to improve yield potential on those areas. If the yield drag is due to a natural factor, such as gravel at a shallow depth or a fragipan, then all the fertilizer in the world may not help in certain situations. On the other hand, if it's soil compaction that can be reversed by ripping and a change in tillage management, then it might be worth concentrating on that area in an attempt to raise yields to new plateaus.
Lloyd Murdock, a University of Kentucky researcher, says now is the time to determine if you have a soil compaction layer that could be limiting yields. Do it while soils are saturated. Ironically, the time to fix the problem won't come until soils are dry enough that they will shatter. That will likely be next fall in most cases, not this spring. If soils aren't dry enough for the compacted layers to shatter during mechanical ripping, and instead the soil just smears as a knife passes through the soil, it's possible that you could actually make the situation worse by ripping, he notes.
Plots observed during the two years of Corn Illustrated plots on a farm near Edinburgh, Ind., provided lots of opportunities to find spots that didn't yield as well as others. Ideally, you can trace the cause as soon as you either see difference in growth in early summer, or notice yield differences at harvest in the fall. The one advantage today is that if you use GPS and a yield monitor to make yield maps, you can still determine where low-yielding areas were, even if you've already tilled the field. So you could still go back there and test for soil compaction when soils are saturated using a soil penetrometer. Or you could pull soil samples this spring, when soils are somewhat drier than saturated, and have a lab analyze the results. Be sure to check for pH, potassium and phosphorus for sure. These results may help you determine if soil fertility is a limiting factor. If so, you may need to do some pencil pushing to see if you could improve yields enough at today's fertilizer prices to stand a reasonable chance of seeing a return on your investment in fertilizer through increased yield and higher dollar-volume grain sales. That will also depend somewhat upon what grain prices do between now and next fall, unless you use a marketing tool such as forward contracting to lock in a price.