There are no "cookbook" guidelines for preparing cropland for planting, whether it's for half an acre of pumpkins or 500 acres of grain corn. Soils differ in their response to the various types of tillage, with some crops, especially those with small seed size, needing a fine seedbed to provide adequate seed-to-soil contact. In order to finish well - meaning high yield and quality - crops need a good start, and this begins with soil preparation.
Rows of young corn plants on a misty morning.
Photo by Smileus/Shutterstock.com.
There are a number of reasons for tillage, including insect, disease and weed control, but the main purposes of tillage are to dry and warm the soil, particularly in and around where the seed will be placed, and to provide an environment that will permit good seed-to-soil contact. One size does not fit all when it comes to tillage.
Know your soil types and their capability
Most counties have soil maps published by the USDA that indicate the soil type(s) for each field, as well as descriptions of the capabilities of each soil type for crop production and other uses. This information includes whether it's a sandy loam or a silty clay, for instance, plus the slope, the degree of stoniness, whether the topsoil is deep or shallow, and a description of natural soil drainage.
You can learn a lot about the capability of a particular soil by reviewing this information, and doing so might prevent some mistakes. For instance, you wouldn't want to put a crop requiring soils with good moisture-holding capacity in droughty soil, nor would you want to plant a deep-rooted crop like alfalfa on a soil with poor internal drainage that hasn't had any drainage improvements, such as the installation of subsurface drainage tubing.
In the heading of this section, note that it says types, not type. In the Corn Belt, entire farms may have only one or two soil types, but in the eastern U.S., parts of which were subjected to more recent glacial activity, it's not unusual to find several soil types in a 10-acre field. One 40-acre field at Miner Institute in northeastern New York, for instance, has at least eight soil types, ranging from a very well-drained gravelly loam to a poorly drained clay loam.
Don't over-till seedbeds for small-seeded crops such as alfalfa and grasses. In a properly prepared field, a soil imprint should be about half an inch deep-it shouldn't come over the sole of your work boot.
Photo courtesy of Everett D. Thomas.
In some cases, the soil types in a field may be so different that you may consider dividing the field according to soil type, especially if it's a large field. This is what Miner Institute did with a couple of fields where the soil type at one end of the field was very different from the soil at the other end. One end would grow alfalfa-grass just fine, with the alfalfa dominating the stand, while the other end of the field wouldn't hold alfalfa well, and an alfalfa-grass seeding would become mostly grass.
The soil type often dictates the most desirable tillage options, as well as when the tillage should be done - spring versus fall.
Many clay loam soils should be tilled in the fall to allow for the winter freeze-thaw cycle to break down clods and make it easier to achieve a good seedbed the following spring. Moldboard plowing or chisel plowing clay loam soils in the spring requires more patience waiting for them to dry out than many farmers apparently have. If these fields are tilled before they're dry enough, a common result is large clods that are very hard to break down. I've seen a number of crop failures that were entirely attributable to mismanagement of clay loam soils.
Other soils, including sandy loams, may have high erosion potential and should be tilled in the spring, if they're tilled at all, since some of these soils are particularly well-suited to no-till. The soil type often dictates tillage management, and woe to the farmer who ignores this fact.
A mound of bulk natural alfalfa seeds
Photo by Louella938/Shutterstock.com.
To till or not to till, that is the question
Miner Institute still does some fall moldboard and chisel plowing, particularly of its clay loam soils. There's no universal agreement on the need for clean tillage - tilling the entire field surface and burying crop residues. I occasionally get questioned about this practice, which is called "recreational tillage" by one farming friend, since he claims that the crops crew at the institute does it for the exercise and not because it's necessary. (Plowing isn't exercise, but stone picking sure is!)
Miner Institute also does some no-till planting every year and has for over 30 years, but on a selective, field-by-field basis. There's some land on the farm that's so stony - "two rocks for every dirt" - that without no-till it's unlikely that it would be economical to grow crops on it at all. In general, the stonier the field, the lighter the soil type (sandy loam versus clay), and the better the drainage, the more likely that it may be a candidate for no-till. That's why no-till is used on much of the sandy loam soil in the DelMarVa region (Delaware, Maryland and Virginia), and some farms in the area have long since sold their moldboard plows. In other parts of the country, though, to till or not to till is still a field-by-field decision.
The decision isn't simply whether or not to till, but the amount of tillage needed. That's why minimum or reduced tillage has become so popular in many parts of North America, and it's likely that the trend toward less tillage will continue. Reduced tillage is particularly common with large-seeded crops, such as corn and soybeans, and there are many tillage tools that can be used to prepare an adequate seedbed for these crops. However, there are excellent minimum-till and no-till grain drills and seeders on the market, and in recent years the acreage of reduced-tillage small grain production has increased considerably.
Seed-to-soil contact is the bottom line
Regardless of whether you use no-till, reduced tillage or a moldboard plow, the goal is to provide a seedbed resulting in good seed-to-soil contact. If you plant corn, for instance, you should be able to walk the rows after planting and see very few exposed kernels. This is particularly important with no-till planting. If you can see even a small part of the kernel, chances are that kernel will never result in a plant, but will be eaten by insects or birds or simply sit there until it rots.
This is seldom a problem with reduced or conventional tillage, providing the soil wasn't tilled when it was wet. As previously noted, plowing soils with high clay content when they're wet results in lots of clods, making it almost impossible to prepare a good seedbed. I've seen farmers tow heavy rollers and cultipackers across such fields in an often futile attempt to reduce the football-size clods to something more manageable.
The term "no-till" is something of a misnomer, since some tillage is done, but only in a narrow strip rather than across the entire soil surface. In recent years, there have been some variations on no-till, including strip tillage. While no-till corn and soybeans involve a tilled area only about 2 inches wide, strip tillage equipment produces a band 8 or 10 inches wide into which the crop is planted.
Large seeds, such as corn and soybeans, need somewhat less seedbed preparation than small seeds, like alfalfa and timothy. Corn, for instance, is usually planted about 2 inches deep, so it doesn't need as fine a seedbed as alfalfa, which is planted .25 to .5 inch deep.
Since small-seeded forage crops need a fine seedbed, there may be the temptation to over-till. A handy rule of thumb to indicate a proper seedbed for small-seeded crops is the sole of your shoe or boot. If you walk across the seedbed just before seeding, the imprint you make in the soil shouldn't come over the sole of your footwear - in other words, an imprint half an inch or so deep. We sometimes get into trouble by overworking seedbeds, resulting in a fluffy top few inches of soil that can make it hard to achieve a uniform planting depth. That's why prior to an alfalfa-grass seeding, the crops crew at Miner Institute tows a cultipacker (essentially a corrugated roller) just ahead of the grain drill, which has a set of packer wheels to firm the soil right over the row of seed, so the soil is firmed twice, once right before seeding and a second time right after. The result: No alfalfa-grass seeding failures in over a quarter century.
Get on your knees
During corn or soybean planting you should get off the tractor and get down on your knees in the field. To pray for a good crop? Not a bad idea, but there's another, more immediate reason: to check on soil depth. This is especially important if you've done anything new and different, including a change in tillage or planting equipment, but you should do it on a routine basis as well.
Using a pocketknife or other probe, carefully remove the covering soil from the planter row until you locate several soybean seeds or corn kernels to confirm that they're planted at the desired depth. It doesn't cost any more to plant crops at the correct depth, but improper planting depth can make the difference between a good crop and a poor one.
Plant corn too deep, and the seed can take longer to germinate and emerge (if it does so at all), while planting corn too shallowly can result in uneven emergence, especially if a period of dry weather follows planting.
Research in New York found that corn planted at a depth of 1.5 inches resulted in considerably lower yields than the same corn hybrid planted 2 inches deep. The goal of soil preparation and planting is to get the crop out of the ground as quickly as possible and with a good root system, since only then will it begin converting energy from the sun and nutrients from the soil into feed and food.
Ev Thomas has worked as an agronomist in New York for 45 years, first with Cornell University Cooperative Extension, then with the William H. Miner Agricultural Research Institute in Chazy, N.Y., including managing its 680-acre crop operation. He continues to work part-time for Miner Institute and is now an agronomist at Oak Point Agronomics. He has written our Forages column for 15 years and has been an expert contributor on a number of other topics.