This is the second instalment of a series of letters from Gary Martens, who is an instructor in plant science with the University of Manitoba. His ‘nano’ experimental farm is located near Kleefield, Man.
First I will lay out the principles by which I planned the crop rotation. These principles are derived from a long-term understanding of disease and of residue management.
Eric Brende in his book Better Off says, “A principle is not the prisoner of the particular. It is transportable. As a matter of fact, being able to transport a principle to a new particular is the skill of the wise.”
Each farm will have its own set of goals which will influence the crop rotation as will the soil’s capabilities and the climate limitations in an area. Each farm’s crop rotation will be unique to the farm, but the principles behind the crop rotation will be universal.
It has been my contention for a while that a dynamic, agronomically based crop rotation will be as profitable as one based on the market prices of crops and that the agronomically based crop rotation will improve soil health, is less risky, more stable, and produces less migraine headaches from stressful marketplace decision-making.
A principle that is recognized by most farmers in most places in the world is that the same crop should not be grown repeatedly on the same field. Restricting our discussion to annual crops for a minute, broadleaf crops are usually alternated with grass crops.
Many of our broadleaf crops are susceptible to the same diseases. For example, sclerotinia impacts canola, soybeans, edible beans, peas, sunflowers, potatoes and more. On the grass side, fusarium head blight affects wheat, oats, barley, rye, corn, canaryseed and more.
Based on the above principle of managing disease, my crop rotation for the field with peas/canola in 2013 (planted on May 13) had fall rye in 2012, flax in 2011 and oats in 2010 and hay before that. The field with wheat and oats underseeded with red clover in 2013 (planted May 14) had hemp in 2012 and was a hayfield of alfalfa, grass and dandelions for many years previously.
Let’s go back to Gliessman’s steps or levels to attaining better profitability I referred to in the article that published May 23. Level 1 was increasing input efficiency and Level 2 was input substitution.
Since the major dollar cost and energy cost in growing an annual crop is nitrogen fertilizer it makes sense to think about ways of reducing that cost. In an attempt to grow our own nitrogen Martin Entz has implemented a green manure crop every third year in the annual crop rotation. That is, annual grass, annual broadleaf, green manure, annual grass, annual broadleaf, green manure and so on. A green manure of peas and oats for example will produce approximately 80 pounds of nitrogen per acre for the following crop, but it costs a whole year of production to produce that 80 pounds.
Under these conditions, it costs approximately $1 per pound to grow your own nitrogen. This is twice as much as you can buy it for, so for the average farmer this is not an economically feasible method of providing nitrogen.
Grazed green manure
Harun Cicek made a profound discovery at the Ian N. Morrison research farm in Carman when the green manure was grazed. Eighty per cent of the nutrients that livestock graze are returned to the field as urine, high in ammonia nitrogen and feces, high in phosphorus.
Not only are all these nutrients returned to the green manure field, the nutrient availability is enhanced for the following crop. Whereas plowing in a green manure of peas and oats will produce 80 pounds of nitrogen per acre, the same peas and oats green manure that is grazed will produce 120 pounds of nitrogen per acre for the following crop.
One hundred and twenty pounds of nitrogen per acre is completely adequate to grow almost any annual crop. Grazing the green manure drops the cost of nitrogen to $0.67 which is getting close to the cost of buying nitrogen, especially if you include the costs of delivering it to the field and the time required to haul and fill the airseeder.
I intend to implement the grazed green manure principle in the future. Now I still have enough perennial hay and pasture coming out of production to provide adequate nutrients for my annual crops.
We were fortunate enough to finish planting our crops just before the beautiful, gentle rain started on May 18 in Kleefeld. Now comes the joy of scouting our fields, watching for the eager sprouts reaching for the sun. Our first scouting activities will be to count the plant populations and make notes for next year’s seeder calibration.