Zero tillage: lime it occasionally

Acidification of the top few inches may inhibit cereal growth

Anything we do these days often comes with a meaningless label. For example, people say, “I am a Catholic, a Baptist, a Methodist …” but haven’t been near a church in many years. Some say, “I am right wing, left wing, green, a socialist, conservative …” but when questioned, most individuals have no definition or firm concepts about their beliefs or ideologies.

The same goes for farmers. “I am zero till, minimal till, I work up my soil every few years whether it needs it or not …” they say.

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What you have to remember is if you adopt an agricultural procedure or system, you will need to check out and examine this system periodically to ensure that it still works or functions effectively.

I first ran into this problem as a plant disease diagnostic specialist. I was asked to figure out why lawn and golf greens deteriorated over time. The time frames were anything from 10 to 25 years, sometimes more.

Lawn and golf green deterioration

In a typical city lawn that was more than 20 years old, I dug up slices six inches deep with a very sharp spade. You could distinctly see the turf thatch (i.e. the buildup of dead grass roots that looked like a two-inch (five centimetre) layer of peat moss.

Below the thatch the soil looked fairly normal but with less grass roots than I expected. Grass roots, such as those on perennial grasses like bluegrass (Poa pratensis) and fescue always die off in winter but regrow annually, grass roots are annual and not perennial like quack grass rhizomes. You have all likely seen rolls of turf being laid down on bare ground every spring with no roots in sight on the turf squares.

When I had the soil and thatch on these vertical turf slices analyzed at zero to two inches (five centimetres), two to four inches (five to seven centimetres), and four to six inches (10-15 centimetres), there were distinct differences. The thatch had a pH of just under 4, the two- to four-inch layer a pH of around 5, and the four- to six-inch layer a pH of 6. The subsoil below the six-inch layer had a pH of around 8.

A remedy

This pH stratification was a consequence of annual and regular fertilizer application, regular watering and a surface buildup of dead organic roots that formed thatch. Past correction was to dig up the high pH-loving blue grass lawn or golf area and reseed. My remedy was to apply around two pounds of fine, crushed limestone per square yard (one kilogram of crushed limestone per square metre).

By the next season, the blue grass lawn looked as good as new and would likely stay that way for many more years. The crushed limestone raised the pH on the top few inches probably to 6 or more. Blue grass lawns need high pH soils.

Minimal or zero tilled cropland

Cropland that has been minimal or zero tilled for the past 15 or 20 years, especially with a pH of less than 6.5 and shows a buildup of organic duff, may get acidified in the top few inches. An appreciable amount of your soil-available potash and phosphate may also be in these top few inches of soil.

This acidification of the top few inches, particularly if the pH drops below 5, may well inhibit cereal growth, such as wheat, but it also may block or inhibit the availability of molybdenum.

Molybdenum is not available in soils with a pH of 5 or less. This micronutrient essential for nitrogen metabolism in all crops may delay emergence of all crops and establishment. Release of molybdenum, only trace amounts are needed, may well be the reason why many crops respond to crushed limestone applied in the drill rows of known acidic soils. There are Prairie soils, by the way, that are naturally devoid or very low in molybdenum, even at neutral pH levels. Get a soil test done for the element molybdenum.

In conclusion, I can expect acidic soils, at a pH of 6 or less that have been zero or minimally tilled, could benefit greatly from an application of crushed limestone at around two to three tons an acre. Other benefits from a lime application are it’s a known fact that below pH 5.5 you can lose 10 to 15 per cent of your expected wheat yield as well as yields of other field crops. Raising the pH also greatly speeds up the breakdown of persistent soil-applied herbicides, such as imidazolinone herbicides.

I live in Parkland county just west of Edmonton, where most farmers practice zero or minimum till in a soil pH average of around 6 or so. Many potato farmers and I have noticed that after potatoes appear in cropland and greatly disturb the soil, the following cereal or canola crop is particularly vigorous. Is this due to residual potato fertilizer or is it tantamount to deep ploughing of the soils and a redistribution of surface nutrients such as nitrogen, phosphorus and potassium?

I would certainly advise farmers on acidic cropland to at least lime 10 to 20 acres and calculate the crop yield benefit over application cost for a five- or 10-year period. Wood ash available in many areas could also be an alternative to liming on acidic soils. Crop yields due to the higher pH and nutrients in the ash will be significantly improved.

Why were British sailors called limeys? Because they were fed lime juice loaded with vitamin C aboard long ship voyages to avoid a disease called scurvy — vitamin C deficiency.

About the author

Contributor

Dr. Ieuan Evans is a forensic plant pathologist based in Edmonton, Alta. He can be reached at [email protected]

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