A European acquaintance quizzed me recently about crop rotation and tillage practices for major crops in Ontario. I’ve prepared the following. And, since it might be also of interest to others too, I am posting it on the web. This is a very simplified overview of Ontario cropping systems. Readers should recognize that each farmer does things somewhat differently, and farming practices continue to evolve quickly.
The principal field crops in Ontario are corn, soybeans and perennial forages – about 2 million+ acres of each. This column is mainly about corn and soybeans, and also wheat which is grown on about 1 million acres – and mainly about those farmers who are primarily grain growers. Perennial forages are mostly grown by farmers who raise cattle, sheep, goats and horses.
Although corn has been grown by Ontario farmers since about 500 AD, its production by farmers of European origins did not really become dominant across most of Southern Ontario until the 1960s following the introduction of better-quality, early-maturing hybrids. After that, Ontario agriculture experienced a period of about 15-20 years when many farmers grew only corn. This, coupled with intensive tillage which buries all crop residues after harvest, resulted in some serious soil erosion and other soil structural and insect/disease problems. The soil problems were worse when the entire above-ground plant was harvested to make ‘corn silage.’ (Corn silage once represented up to half of Ontario corn acreage; it’s about 10% now – usually on dairy and beef farms which also have soil-building perennial crops in their rotations.)
Soybeans have been grown in extreme southwestern Ontario (warmest part of the province) since the early 1900s. Production blossomed across the rest of Southern Ontario during the 1980s. This was because of the availability of better early-maturing varieties and the need for a profitable cropping alternative to break the pattern of continuous corn production. (This is sometimes called ‘mono-cropping,’ though ‘mono-cropping’ can have other meanings too and is an ambiguous term).
Many Ontario grain farmers add a third crop to the rotation – fall-seeded wheat, which is commonly called winter wheat. While wheat is usually not as profitable a ‘cash crop’ as corn and soybeans, farmers grow wheat because it spreads out their annual work load, provides diversity and stability (weather-vulnerable growth stages for wheat occur at different times of the year than for corn and soybeans), and because research data have shown that corn yields benefit significantly from having wheat in the rotation. (Wheat has a fine root structure which contrasts with the generally coarser roots of corn.) Wheat also represents an over-winter cover crop, to help limit soil erosion in early spring runoff (lots of water runs off the soil surface because of melting snow and rainfall).
Corn rootworm larvae are commonly a serious problem when corn follows corn. This necessitates the use of insecticides or the use of Bt-corn-rootworm-resistant corn hybrids. Corn rootworm has also become a problem in corn-soybean rotations in the United States. However, the problem does not occur with corn-soybean-wheat rotations.
Farmers are concerned about protecting their soil from erosion (primarily water erosion in Ontario), and in maintaining/improving soil organic matter levels and soil structure. Good soil structure makes root growth easier and facilitates internal water and air movement.
Reduced soil tillage (often this means no tillage at all except for the possible preparation of a very small mini ‘seed bed’ right around the planted seed) is one means of doing that. It also reduces the cost of farming (less equipment, less time for field operations, and less fuel usage). Corn crop residues are especially valuable for protecting soil from erosion (i.e., if left on the surface and not plowed under). This is because of both their high quantity (about 9 tonnes/ha for a good average corn crop) and their slow rate of decomposition. They can stick around on the soil surface for 2-3 years.
By contrast, soybean crop residues decompose quite quickly after harvest time and in the following spring. This is one reason why farmers commonly plant winter wheat immediately after soybean harvest to protect the soil surface.
Winter wheat presents its own soil problems – mainly because it is harvested during midsummer (commonly in July), leaving the soil surface ‘unprotected’ for many months to follow. Wheat straw residue helps. But, at least in North America, it is not as plentiful as what remains after corn. Many farmers plant special cover crop species. The most common is red clover for which the seed is spread on winter wheat fields in early spring. This allows red clover plants to germinate and then subsist until the wheat is harvested; after harvest they usually flourish until growth stops with the arrival of colder weather in October. Red clover cover crops protect the soil surface from erosion while adding soil organic matter and nitrogen fertility (red clover is a legume). The crop which follows wheat/red-clover is usually corn.
Some farmers will plant other cover-crop species after the wheat is harvested, usually using ‘no-till’ seeders for reasons of speed and minimal soil disturbance.
Early spring planting presents some challenges – and a need for compromise. Complete surface coverage is best for erosion control but it can mean slower drying of soil in spring. (Most Ontario soils begin each spring fully saturated with water, because of late-autumn and early-spring rainfall, and snow melt.) This is a special problem for corn which generally yields best when planted early. This is especially true for slow-drying clay soils. If residue coverage is really dense, some farmers will try to incorporate some residue into the soil with autumn tillage. Some farmers use strip tillage equipment to work a narrow strip (either in the fall, or a day or two before spring planting), thus allowing soil in the strip to dry out faster to permit early planting. If soil is planted when too wet, it ‘smears’ during planting operations and this can have a very negative effect on corn seedling growth and final yield.
GPS technology allows farms to plant corn into the centre of the tilled strips.
In addition most no-till planters have attachments which move residues a few cm to either side of the planted row. This permits sunshine penetration to the soil above the planted seed, and quicker germination. In some countries (notably north-western Europe), garden slugs will flourish with abundant soil surface organic matter coverage. Slugs eat the emerging crop plants. This is occasionally a problem in Ontario too.
Emerging plants in springtime in Ontario are also vulnerable to occasional late frosts, and this risk is magnified with lots of soil residue cover. It’s a trade off, with most farmers considering that the increased risk of frost damage is more than off-set by better soil quality and higher yields with ample soil residue cover, over a period of years.
Pest control is very important to the success of reduced and no-till cropping programs which allow for the abundant presence of soil surface residues. Fungicide and (usually) insecticide treatments are generally needed to protect planted seeds and emerging seedlings from diseases and insects which flourish in conditions of cool, damp soil and surface residue cover. Herbicides are needed for the weed control which was traditionally done by soil tillage. Organic farmers, who cannot use synthetic pesticides, often counter these insect and disease challenges by planting a little later and by using tillage implements for weed control which penetrate the soil only shallowly. While a few organic farmers and researchers are currently exploring options for the elimination of tillage, no-till organic farming remains largely unknown.