Beyond standard soil sampling

WHY IT’S IMPORTANT TO KNOW MORE THAN CHEMICAL COMPOSITION

odette menard is a firm believer that growers need to take a much closer look at their soil. “We need to see it more as a living creature, and not just as a physical support for growing the plant,” says the soil specialist with the Quebec Ministry of Agriculture, Food and Fisheries.

To get a true sense of the health and fertility of our soil, Menard thinks we need to go beyond standard soil sampling, which only gives us chemical nutrient levels. “The biological and physical composition of the soil are just as important to know about,” she says. “It’s like when you go to the doctor for an illness. We must be like a good doctor and investigate, and do lots and lots of different kinds of tests and find out all the information. Otherwise it’s a lucky guess about your treatment and whether any improvement will occur. We have to get away from just looking at one side of things. Standard soil tests are just an inventory of what’s there, not what is available.”

Biological and physical features of the soil greatly affect nutrient availability, Menard notes. “In good soil that is not compacted, nitrogen availability for example will be much higher for the plant than if the soil is compacted or aggregate stability is poor,” she observes. “It’s a matter of water infiltration being much lower.” Menard points to studies that show nitrogen efficiency can be as high as 75 per cent in good soils, where in compacted soils, it can be as low as 30 per cent.

“And most characteristics of soil – whether they’re chemical, biological or physical – are dynamic over time,” she adds. “The pH is a chemical characteristic that can change, for example. Some physical characteristics like basic soil type don’t change, but others, like aggregate stability are dynamic and affected by many things like compaction, erosion, active carbon, mineralized nitrogen, organic matter and biological activity.” These in turn, affect how well roots grow, vulnerability of soil to erosion, and so on.  

However, very few labs in Canada presently give information on physical or biological composition, according to Menard. “At Cornell University, they are working on setting a baseline for 12 characteristics, four chemical, four biological and four physical, that determine the health of soil, and if we could get information on even two of these for each category, that would be good,” she says. However, broader soil analysis results must also be paired with education. “If I talk to a grower and say the ph level is 4.2, he knows what I mean, but if I start talking about aggregate stability levels, he doesn’t know the numbers, what is normal, etc.,” Menard notes. She suggests we develop a system to understand the information and its application at the farm level.

taking action
Menard recommends that farmers start asking their crop advisors and agronomists about physical and biological tests for soil. “When I am on a farm, I try to dig the soil as much as I can and look at it with the farmer.”?says Menard. Her suggestion is to start by just digging a hole in one field, next to a crop row. “If it hurts your knee to dig, it’s too compacted,” she says. “Then, feel the earth, and smell it. Healthy soil smells right, but compacted, not as nice. Then, look at your crop roots – are they deep, spread out? Do this in a few fields, so you can compare. Especially dig in areas that don’t grow well. This is a good start. Then talk to your agronomist.”

Reversing and preventing compaction is a matter of taking many types of action, in Menard’s view. “The soil by itself is a group of independent particles, clay, sand, loam particles, and to have healthy soil, you need the particles to aggregate into small clumps that nutrients can attach to. This requires ‘glue,’ and microbial populations are like glue, like the cement between the bricks in the house.” She adds, “With a healthy, aggregated soil, it will be more stable and hold the nutrients and moisture. You’ll be a lot less dependent on the weather, and your soil will be less prone to compaction – and this is when you are comparing it to soil with same chemical composition.”

Using no-till helps build microbial communities, but Menard says, “No-till is only part of the solution. You should also be adding more organic matter, and using cover crops and a longer rotation. They all help feed the microbes that change the physical characteristics of the soil for the better.” “The first step to get into no-till is not to buy machinery,” she says. “That’s like saying the first step to running a marathon is to buy shoes. No, it’s to be healthy and fit and start training long before the race begins. It’s a long race in farming.” •