Ways to make your soil easier to work

Thursday, May 1, 2014

By incorporating manure into your cropping system, you can count on benefits from preserving or building good soil structure in your fields

by KEITH REID

As a youth, I was not always interested in the farm broadcasts my father listened to, but one radio ad did catch my attention. It was for a tractor that would "turn your toughest dirt into easy plowin' ground" thanks to its improved horsepower and traction.  

Even back then, this approach seemed rather silly. Wasn't it more sensible to make the soil easier to work than to put a bigger tractor in front of the plow?

So what is it that makes the ground hard? The simple answer is poor soil structure, because the aggregates in the soil have been broken down. In a well-aggregated soil, there are many joints where the soil can break apart easily into smaller granules, but those granules hold together firmly enough that they can move easily around tillage implements. If the soil doesn't have these planes of weakness, the only way for a tillage implement to move through the soil is by brute force.

At the other extreme, if the soil breaks down completely into individual particles, these fine particles will pack together as the implement moves through the soil, increasing the energy required. These fine particles are also susceptible to forming hard clods when they are wetted and then dried.

Virgin soils under either forest or prairie are generally well aggregated so, aside from the difficulty in slicing through tough roots, these soils are easy to till. Good soil structure also allows plant roots to grow easily through the soil, forming a large network to absorb water and nutrients. We break down this structure in two ways – through tillage and organic matter depletion.  

Excessive tillage, or tillage at the wrong time, breaks down the natural aggregation in the soil. We pulverize the aggregates, breaking off fine particles, or we squeeze the aggregates together with such force that they form large clods. Driving over the soil with heavy equipment when it is too wet can cause much the same damage, but not as pervasive as that caused by tillage.

Organic matter acts as both the glue that holds aggregates together and the skin that separates aggregates from each other. Soil with high organic matter content will resist the damage caused by tillage much better than a soil with low organic matter.

Unfortunately, many of our common farming practices deplete the organic matter in the soil. Erosion by wind and water selectively removes the organic particles from the soil. Air mixed into the soil by tillage speeds the breakdown of organic matter and crop harvest removes more organic material than it leaves behind. This leaves the soil highly susceptible to poor aggregation.

How can we make the ground easier to work? The first step is to stop doing any more damage. This doesn't necessarily mean stopping tillage completely, but it does mean minimizing the number of tillage passes and staying off when the soil is wet.

The next step is to rebuild the organic matter content of the soil. Retaining crop residues will help, as will growing cover crops, but the most common organic amendment is livestock manure.

Dr. Neil McLaughlin at the Eastern Cereals and Oilseeds Research Centre in Ottawa was part of a team testing the effectiveness of dairy manure as a soil amendment for reducing soil resistance by measuring the energy required for mouldboard plowing in continuous corn plots in an ongoing long-term crop rotation field experiment.

Comparing plots that had received manure annually for 18 years to plots that had received only mineral fertilizer he found that, in the former, the draught required to pull the mouldboard plow during fall tillage was reduced by up to 41 per cent, and fuel consumption was reduced by 22 per cent. That is the difference between pulling 10 furrows instead of six behind the same tractor.

This same reduction in energy inputs would apply no matter which tillage system is being used, but more important is the impact on plant roots. A soil that is easier to till will also be easier for roots to penetrate, resulting in larger, healthier crops.

Not every farm will show differences as big as this. The manure rate used was quite high (100 tonnes per hectare, or 40 tons per acre). In this study, rotted manure showed greater benefit than stockpiled manure, but the amount of dry matter added with the rotted manure was 25 per cent higher.  A parallel study on corn grown in rotation showed smaller benefits, but in this case the manure was only applied every second year.  However you incorporate manure into your cropping system, you can count on benefits from preserving or building good soil structure in your fields. BF

Keith Reid is Soil Scientist, Agriculture and Agri-Food Canada, Guelph. He is also the author of "Improving Your Soil," a new book for serious gardeners.