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Zone till great for wet clay soils

Zone tillage is the practice of cultivating a band of soil about 21 cm (eight inches) wide, while leaving the areas between these tilled zones as no-till. Zone tillage has been around since the early 1990s. Over the last five to 10 years, this tillage system has gained in popularity.

Dr. Craig Drury, research scientist with Agriculture and Agri-Food Canada’s Harrow, Ont., research station, and his colleagues have been studying the effects of different tillage systems for 20 years. No-till works very well in some medium and coarse textured soils and in some climatic regions.

In high clay content soils in Canada’s humid regions, cool and wet soils may delay row crop planting. This results in lower crop emergence rates and may also lower plant populations.

“When low emergence and reduced populations occur, yields and amounts of crop residue returned to the soil may be lower than when conventional tillage is used,” says Drury. “In such situations, zone tillage is an excellent compromise. It can improve seedbed conditions and also maintain many of the benefits of no-tillage.”

One example Drury noted is in the case of corn with 76 cm (30 inch) row spacing. The tilled zone is only 28 per cent of the whole area, with the majority of the soil (72 per cent) left as no-till.

The benefits

According to Drury, zone tillage has been found to reduce fuel consumption and labour costs compared to conventional tillage. “Zone tillage uses only about 6.7 litres per hectre compared to 21 l/ha for conventional moldboard plowing,” he said. That’s a difference of 14.3 l/ha, or almost six litres per acre.

“Using a mouldboard plough at a depth of six, seven inches differs widely with the no-till system, but zone till combines the two nicely — leaving 72 per cent of the field. This offers a warmer and drier seed bed plus all the benefits of no-till carbon management.”

While no-till produces a soil surface with very high carbon content, conventional till has the opposite effect, mixing the carbon into deeper depths, while some is lost via mineralization.

Drury and team have found zone till treatment of surface soil fairly similar to that of no-till systems, except the carbon levels at lower depth are similar to conventional till. “When you add up the carbon stored in the entire profile, we found 11 to 12 per cent more carbon storage with zone till than with either no-till or conventional tillage,” he said.

Although both conventional till and zone till systems produce similar crop yields, the overall carbon balance is higher in zone tillage as carbon sources are slower to break down.

“Our carbon inputs are the same (plant residues),” said Drury. “Our carbon dioxide losses tend to be lower and, as a result, we’re gradually building up carbon in soils with the zone till system.”

Nitrogen

In a 13-year southwest Ontario clay soil field study, zone till increased soil carbon storage by 11.2 per cent compared to no-till and by 12.5 per cent compared to conventional till.

Drury and team found that, with zone tillage, there is lower penetration resistance as well as improved aeration. Since denitrification occurs under anaerobic soil conditions (that is, where there are saturated soils with little or no oxygen), zone tillage’s improved physical conditions reduce nitrous oxide emissions.

“In particular, zone tillage resulted in 17 to 20 per cent lower nitrous oxide emissions compared to no-tillage and 38 to 44 per cent lower emissions than conventional tillage in two three-year field trials,” said Drury.

The cost of fertilizer is on the rise, especially when it comes to high nitrogen-demanding crops. “When you start losing it through gaseous nitrous oxide emissions (biological de-nitrification) or by nitrate leaching, it’s both an economic loss as well as an environmental problem,” explained Dr Drury.

When nitrogen was applied at planting alone, it had 33 per cent greater nitrous oxide emissions than when it was added as a side-dress application, especially with conventional till.

Nitrogen, of any source, consistently emits less nitrous oxide when used in zone tilled fields than when used with conventional or no-till, whereas zone till averaged 44 per cent fewer nitrous oxide emissions than conventional till, and more than doubled the reduction achieved by no till over conventional till.

“I firmly believe zone tillage is a viable practice and am now looking at what we can do to make it a more efficient system wherein more nutrients go into the crops, environmental losses are reduced, and farming practices make more efficient use of inputs,” said Drury.

“I believe zone tillage will continue to grow in popularity for row crop production in clay loam and clay textured soils. The improved soil quality, high yields, reduced nutrient losses, and improved fuel efficiency are some of the benefits that make zone tillage a management practice that should be considered. “There are several companies manufacturing zone tillage equipment and it may also be possible to modify existing equipment.” †

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