The current interest in soil health issues has expanded our thinking and spawned much research and new farm-scale work with many new-to-us plant species. Cover crops are planted in the non-commercial season to add diversity to the mix and juice up the soil organisms that go along with the different plants. In wet years, cover crops also use up some of our excess moisture.
Green manure is used in a season where the land is given a ‘rest’ from removal of forage or seed. Green manure crops often include a legume to add to the nitrogen supply for subsequent crops.
But all of the above is predicated on moisture being in plentiful or even excess supply. From 2005 to recent years that has been the case even in the dry Brown and Dark Brown soil zones — alias Palliser Triangle.
Green manure on the Prairies
When my Grandfather broke the soft sweet clay at Milden, Sask., in 1906 he accessed centuries of soil nutrient accumulation by prairie grasses. Put in some seed, stand back and watch 40- to 50-bushel wheat crops grow, as long as it rained enough. No inputs required.
It made the Brits mad. They had long since sucked the juice out of their land and had to manure heavily to get a crop. They saw the Canadian Prairies as unfair competition.
In 1920 the Soil Science Department was formed at the University of Saskatchewan. The first Department head was a soil microbiologist. Dr. Hansen said we were embarking on a soil mining process and must have legumes in the rotation to sustain our soils. Even by 1920 the drop in soil organic matter and nitrogen was evident.
In those days, legumes meant a perennial crop like alfalfa. Using forage crops in rotation was widely recommended but little practiced because it did not work. The alfalfa sucked the soil completely dry and lowered any water table that might be near. Annual crop failure on alfalfa/grass breaking was common.
Lessons from the garden
When I purchased my Dundurn farmstead in 1994 it had a very nice sheltered garden patch of about half an acre. It had been let go for many years so I cleaned it up around 1996 with cultivation, etc., and established the now outdated half and half system. Half was row cropped as garden and half was summerfallowed the old fashioned way.
Soil fertility maintenance was using all of the lawn clippings, leaves etc., from our Saskatoon home and any neighbours that wanted to get rid of grass. That has been spread on the summerfallow half and worked in. The system produced bountiful yields of garden crops — big juicy tomatoes are the star of the show.
All of this bounty comes with almost no fertilizer except for a dab under the tomatoes at time of transplant and a shot of nitrogen and sulphur to corn when it is about a foot tall.
When the real wet cycle came on gangbusters in 2010 with 20 inches of rain, things changed. The water table rise was such that, at one point, the water table was at two feet. The old mantra of “save water” had to be changed to “use up the extra water.” That was accomplished by planting green manure crops in the summerfallow half of the garden. Soil improvement was soon evident by the arrival of a few earthworms.
For the dry year of 2017 (there were 4.5 inches of rain from April 1 to July 31), some watering was done and the end result was fine.
In 2017 barley was broadcast planted and cultivated/harrowed on April 20 for the 2018 crop area. A good stand established, and as it came near heading it was mowed down and regrew. It was mowed two or three times and finally cultivated out. The object of planting the barley was to use up the extra water and improve the soil. It did that in spades and even used up some of the water I should have saved for the 2018 crop.
Oops. It was soon evident that there was a near surface dry layer. Germination was slow, and despite watering efforts it was not possible to rescue the corn. I gave up and let Mother Nature take its course. Most puny corn plants did produce some seed. The far end of the row is a lower elevation that did not have the dry layer and gave us lots of corn.
On May 12 of 2018 I seeded wheat and peas in the 2019 garden spot. As soon as I realized what was happening I immediately mowed it out and then cultivated. Any plant brave enough to emerge is dealt with before it can suck up any precious moisture.
The lesson is that cover crops and green manure are a good soil building exercise in moist climates (i.e. Black and Thick Black soils of the Canadian Prairies. But, in the Brown and Dark Brown soil zones (the Palliser Triangle) it will not work except in especially wet cycles like we have enjoyed for the past many years.
The statement of Dr Hansen in 1920 about legume crops in rotation was correct. It has come to pass with the development of the pulse crops lentils and peas, particularly lentils. Lentils suck lightly on the soil moisture and are often harvested in late July or early August, leaving lots of calendar to catch rains to store water for next year. They also leave some nitrogen behind for the following cereal or oilseed.
My garden food production exercise is back to the old way until Mother Nature plays her next card. More detailed soil moisture probing will dictate practice. I rather think there will also be some rethinking of cover crops in drier areas.