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Dirt poor or soil rich?

Long-term tillage and rotation plots at Ridgetown, Ont.     Photo by Adam Hayes, OMAFRA.

It’s no secret agricultural practices have changed over the years. Producers have moved away from livestock-based operations with perennial crops. They’ve put fewer crops into rotation and have adopted intensive tillage practices. And all this has taken its toll on soil health.

Adam Hayes, a soil management specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) in Ridgetown, Ont. says the change in cropping has greatly reduced organic matter levels in soil, impacting the physical and biological aspects of soil health, and even the chemical aspect, to some extent.

“The intensive tillage and lack of organic materials returned to the soil limits the amount of food available for soil life,” he says. “An active biological component of the soil breaks down residues and other organic materials contributing to the nutrient and carbon cycles.

“Healthy soil life can help to better utilize nutrients in the soil, potentially reducing fertilizer requirements.”

When Hayes and his colleague Anne Verhallen, soil management specialist with OMAFRA, gave a presentation on soil health at this year’s Southwest Agricultural Conference, they demonstrated the impact of modern agricultural practices with a show, rather than tell, demonstration.

Using soil samples from two fields – one long-term, no-till, well-managed field, and one conventionally tilled with a poor crop rotation – they placed the soil on mesh, then poured water on the samples to emulate rain.

“The conventional soil blew apart, while the other held together better,” Hayes says, explaining that loss of organic matter and tillage have a big impact on the physical characteristics of soil.

“The result is soil which has poor aggregate stability and poor soil structure.”

Soil with poor aggregate stability breaks down into individual soil particles that are more prone to wind and water erosion. They are also prone to forming a crust on the soil, which impedes water movement into the soil and can cause crop emergence problems.

“Poor soil structure impedes water and air movement into the soil, and makes it difficult for roots to move down through the soil,” Hayes adds.

Producers can keep their soil full of life and well-structured with some key management practices, namely crop rotation, utilizing cover crops, reducing tillage and adding organic materials to the soil. The use of soil testing and good nutrient management complete the package.

Crop rotation
Long-term tillage and rotation research conducted over 20 years at the University of Guelph using data from 2009 to 2013 concluded adding winter wheat to the rotation increases corn and soybean yields by at least 10 per cent, going from 15 to 20 bushels per acre for corn and four to eight bushels per acre for soybeans. Putting red clover in the winter wheat resulted in another eight bushels per acre to corn yields.
“A corn-soybean crop rotation has the same or poorer soil health, and sometimes yields, as does a continuous corn or soybean cropping system,” Hayes says. “Adding a perennial to the rotation further improves crop yields.”

A crop rotation of three or more crops will increase soil organic matter. The greatest increase happens when perennials are included.

Cover crops
Cover crops, either seeded or volunteer, offer a number of benefits including providing nitrogen (N) for the following crop, efficient capture and recycling of nutrients, and better soil structure for a larger root system.

Cover crops also provide protection from erosion losses. For example, in the case of wind erosion, it is estimated soil blown from a field may contain 10 to 12 times more organic matter and phosphates than the heavier particles left behind.

Reducing tillage to no-till is the best practice for soil health because it can increase soil organic matter in some cases. “No-till provides a favourable environment for mycorrhizal fungi which aid the root in the uptake of phosphorus,” Hayes explains. “The maximum economic rate of N for no-till in long-term rotation plots at Ridgetown are much less than for conventional-tilled soil.”
Hayes adds that minimum tillage is a big improvement over conventional tillage as long as the number of passes and depth of tillage is kept to a minimum. “Tillage oxidizes organic matter so less disturbance reduces the loss,” he explains. “Reduced tillage will not break down aggregates and soil structure as much.”

Organic material
Adding organic material to the soil is the fastest way to increase soil organic matter. It can be in the form of manure, compost, biosolids, digestate and other sources.

Research shows that adding 75 tonnes per hectare of compost to a Brookston clay soil increased soil organic carbon from two to three per cent. “Soil organic matter is made up of about 40 per cent organic carbon,” Hayes explains. “That level of carbon was still there after five years.”

In other research and working with an Ontario farmer, Hayes added 25 tonnes per hectare of cattle manure to a field site every other year over an eight-year period in a corn-soybean rotation. Results show corn yields from four harvests increased, on average, by 10 bushels per acre.

Implementing just one of these management practices will make a difference to the soil. Using two of them will provide a greater benefit. But putting them all into play will make soil the most productive and resilient.

July 21, 2015  By Trudy Kelly Forsythe


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