Seed Bed: When should you head to the field to start tillage and planting?

Tuesday, March 2, 2010

The key to 'picking the right day' is to know what is happening, not at the surface of the soil, but just below the depth of tillage

by KEITH REID

There are lots of resources to help you choose the right seed varieties, and to make sure your fertilizer and herbicide programs are optimized. Books have been written about the importance of equipment maintenance. Equipment salesmen stand at the ready to sell you the latest advances in tillage and planting technology.

But with all this expertise, there is silence on the one decision that will determine if you have the potential for an excellent crop, or only a mediocre one. When do you head to the field to start tillage and planting?

We cannot minimize the importance of this decision. With every crop that we grow, it has been shown that early planting gives higher yields than late planting (although the definition of "early" and "late" will vary for each crop). At the same time, planting into unsuitable soil conditions underlies many of the crop diagnostic calls every year.

What makes the soil unfit for planting? Most of the time, excess moisture is the culprit. 

Water around the soil particles acts as a lubricant, allowing them to slide past one another more easily and pack together more tightly when pressure is applied.

If there is much clay in the soil, the moisture will make it sticky, so the clods that are formed remain as solid blocks after the soil dries out and are very resistant to breakdown by further tillage. Smearing at the bottom of the tillage depth forms an impermeable layer that blocks the drainage of moisture down into the soil and also the growth of roots.

In a few cases, a lack of soil moisture can also render a soil unfit for planting, but this is generally only on soils that have already been damaged by tillage under wet conditions. These have been described as "minute soils" – one minute too wet and the next minute too dry. Rather than a fine, friable seedbed, these soils often work down into a blend of coarse clods and fine powder. They do not readily wick moisture to the seed, and they are more susceptible to crusting if there is rain after planting.

How can you tell the field is ready? Some will say, rather smugly, that this is part of the "art" of farming, and that it is impossible to quantify.  I would suggest that we could all do a better job of picking the right day by sharpening our observational skills.

The key to "picking the right day" is to know what is happening, not at the surface of the soil, but just below the depth of tillage. If all of the soils in the neighbourhood were identical, we could do this by watching the neighbours who are eager to be first on the land – every area has one. When they stop bringing up ribbons of wet soil with their disk or cultivator, then the ground is ready to go.

Since soils vary greatly, this is only a rough guide. A better approach is to head to the field with a shovel and see what your own land is like. Dig down five or six inches, and squeeze a handful of soil. It should crumble, rather than forming a solid ball. By checking a few areas in the field, you should get a good sense of how close the field is to workable condition.

A further challenge is that every field has areas that lag behind the rest, so the decision is whether to wait for the wetter areas to dry out, or to go ahead, knowing that these areas may suffer for the rest of the season. Factors that must be balanced include whether you are near the beginning or end of the ideal planting date for that crop, the weather forecast, and how much of the field is affected.

How can you widen the planting window? The obvious response is to invest in more drainage so the excess moisture is removed more quickly, but this is not the entire answer.

As important as more tile is improving the wet aggregate stability of the soil. A soil with stable structure will not only resist crusting and erosion, but it won't form hard clods as readily if it is worked too wet. Adding organic matter and maintaining a good crop rotation will make your soil much more "forgiving" on those springs when the number of planting days is limited. BF

Keith Reid is soil fertility specialist with the Ontario Ministry of Agriculture Food and Rural Affairs, based in Stratford. Email: keith.reid@ontario.ca