REGINA – With low commodity prices and high input costs, one of the first places a farmer might consider cutting costs is fertilizer.
However, Stu Brandt, an agronomist at the Agriculture Canada research farm at Scott, Sask., said this might not be the place to start.
At the recent Saskatchewan Soil Conservation Association conference in Regina, Brandt said optimizing plant nutrition depends on several factors, not the least of which are fertility in the soil, the capacity of that soil to supply nutrients and supplementation by fertilizer nutrients.
Read Also
VIDEO: Green Lightning and Nytro Ag win sustainability innovation award
Nytro Ag Corp and Green Lightning recieved an innovation award at Ag in Motion 2025 for the Green Lightning Nitrogen Machine, which converts atmospheric nitrogen into a plant-usable form.
“It’s important we maintain the right balance of macro and micronutrients. We also need to know about the uptake of nutrients by individual crops, yield potential, environmental factors that go into developing yield potential and in particular, moisture conditions,” said Brandt.
Moisture is generally the limiting factor in crop production across Western Canada. But Brandt said moisture use efficiency varies across the soil zones in Saskatchewan.
The amount of water consumed before any yield is produced and the yield per unit of water are lower for the drier brown soil zones than the wetter black and grey soil zones.
If fertilizer reductions are being considered, soil moisture at seeding can be used as a guideline to make yield estimates. If moisture is below normal, a reduction may be warranted, but where moisture is above normal, yield is more likely to be reduced by nutrient deficiencies than by moisture.
Brandt said other inputs have to be taken into consideration, as well. There is little point in making dramatic cuts to fertilizer when other inputs are at levels that support much higher yield.
In one study, at low fertilizer rates, canola yields increased as seeding rates increased from 2.5 pounds per acre to five lb. per acre, but there was no further increase at 7.5 lb. Under moderate and high fertility levels, there was a response to the high seeding rates.
Similarly, at the low seed rate, yield increased when fertility moved from low to mid levels, but not mid to high. The highest yield was obtained with the combination of the high seed and the high fertilizer rate. The optimum level of one input was determined by the level of another input.
Net returns favoured mid to high fertilizer rates combined with mid to high seed rates. High rates of one input along with low rates of the other tended to provide lower income. With the low seeding rate, net income became more variable as fertilizer rates were increased.
“Why would we consider cutting back on fertilizers? Lack of water is a big factor, low grain prices and high fertilizer prices are all factors that enter into the economic side of fertilizer application rates,” Brandt said.
Limited cash flow is an issue. Brandt said farmers may not have enough money to spend on all the inputs they feel are necessary to optimize crop production. They need to make the most of the limited dollars available.
“Generally we target the nutrient we spend the most money on – nitrogen. It’s important to understand how crops respond to nitrogen and that we grow them in a moisture-limited environment.”
Under wet conditions, a lot of nitrogen is needed to optimize yield. But as moisture lessens, so does the amount of nitrogen required to bring up yield. Under drought conditions, the supply coming from the soil is more than adequate to meet crop requirements.
Brandt said the nitrogen rate needed for maximum yield is always higher than the rate needed for maximum economic return. When grain prices are low, the optimal amount of nitrogen is consistently lower than when grain prices are higher. However, grain prices tend to have a much smaller impact on the optimal level of nitrogen than does moisture stress. This means moisture conditions have a greater impact on optimum nitrogen rates than commodity prices.
Brandt said wheat and canola show similar responses. A 40 percent decrease in canola price only reduced the optimum nitrogen rate by about 15 percent, while a 40 percent reduction in available moisture reduced the optimum rate by about 40 percent.
A 50 percent increase in the cost of fertilizer only resulted in about a 10 to 15 percent reduction in the optimal nitrogen rate for canola, suggesting that prices have a smaller effect than available moisture. But the combination of low canola prices and high nitrogen cost could reduce the optimal rate by 25 to 30 percent.
Conservation tillage, nitrogen-fixing crops and past fertilizer use are being used by western Canadian farmers to improve their soil quality. The question remains whether these practices can reduce fertilizer requirements in the future.
“There are indications that fertilizer nitrogen requirements may be reduced by putting nitrogen-fixing pulses in the rotation, not only in the year we grow the nitrogen-fixing crop but in subsequent years. And after a number of cycles through these rotations, the amount we can rely on may be 10 to 20 lb. per acre, and maybe substantially larger,” Brandt said.
“There are indications that direct seeding and other conservation tillage practices build the capacity of the soil to supply nitrogen, protect the soil against nutrient losses associated with erosion and those practices should begin to show themselves in a reduction of fertilizer nitrogen requirements.”
Previous fertilizer use can have a big impact on requirements over time.
“We often associate phosphorus with an early response in the growing season, but it also has other impacts on yields. We need to understand how we balance phosphorus with nitrogen,” he said.
“At a moderate application of nitrogen, say 55 lb. per acre, you might not see much of a response to a low phosphorus rate. As we go to a higher nitrogen application rate, the response becomes larger and it may be economic to go to relatively high rates of phosphorus. Certainly, if we’re targeting high yields with one nutrient, we need to ensure we’re supplying adequate amounts of other nutrients to achieve the optimum yield.”
On long-term studies at Scott, under a fallow-wheat-wheat rotation, Brandt said phosphorus removal was fairly substantial in the early years. Part was not fertilized at all and part was fertilized since about 1930.
“Phosphorus removal was reduced somewhat when fertilizer was added on the summerfallow phase. From 1957 to 1983, applying 15 lb. per acre on the fallow phase, the rates of removal increased, because herbicide use and improved crop varieties boosted grain yields substantially,” he said.
“In 1994, we started applying 25 lb. on fallow and since that time we’ve reversed that trend. We’re actually building a supply of phosphorus in that soil. The message here is if you’ve been doing a good job of replacing the nutrients that you have been removing over time, and have built up a small surplus, it may be appropriate to start drawing that surplus down during difficult economic times.”
Brandt said one common question is whether farmers can reduce fertilizer use and become more efficient.
“We’ve looked at reduced input systems at Scott for a number of years and I’m pretty pessimistic that we can achieve a great deal in terms of efficiency by cutting back on nutrient use,” he said.
“If we look at a global scale, in North America, nitrogen application rates exceed removal rates by about 25 percent. But in Saskatchewan, our nitrogen removal tends to exceed replacement by about 17 percent. So I don’t see where we have a huge potential to cut our nitrogen application rates and not pay for it. And with phosphorus, crop removal exceeds … replacement by about 27 percent.
“The fact of the matter is when we first broke this land, there was an abundance of these nutrients. Had we not removed them, they would have created some serious environmental problems for us. But we’re now reaching the point where we need to balance removal with replacement.”
Brandt concluded that any benefit from fertilizer cuts should be viewed as a short-term benefit.
