As the crop comes off some farmers are already thinking about next spring — specifically about getting a jump on things by fertilizing this fall.
There are lots of compelling reasons to follow this strategy. Fertilizer prices tend to be lower this time of year, and spreading the workload out lets them get the crop in faster next spring, just to name two.
It can be done but the trick is to keep this fall’s application in the ground so it shows up in next fall’s harvest instead of heading downstream in the spring run-off.
“That’s where you often resort to quoting the four Rs,” said John Heard of Manitoba Agriculture. “There is no single right answer and those four Rs provide quite a bit of flexibility to tailor a good answer to the individual farmer.”
The four Rs are a reference to the Right source, the Right rate, the Right time and the Right place. Each of these will differ depending on the weather and soil type so the Rs are a set of guidelines for individual farmers based on the quirks of their land. It’s a matter of matching formulation and application to local environment. The first rule of fall application is keep it cool and keep it dry.
“You can start by delaying that application until the latest possible time so the nitrogen doesn’t convert to the nitrate form and by banding it instead of broadcasting,” suggests University of Manitoba soil scientist Don Flaten. “Farmers may consider using enhanced efficiency products like ESN (environmentally smart nitrogen) or nitrogen that has stabilizers incorporated within it.”
In the cool fall soil the microbes slow down to ready themselves for winter and as the temperature drops so also does their metabolism. Since they’re not hungry they don’t go to work on nitrifying the fertilizer into a more water-soluble form. It’s one way of keeping the nitrogen where you put it.
“We also have some technological advancements that allow us to combat those losses,” Heard said. “One is called nitrapyrin. With anhydrous ammonia it’s called N-Serve or when applied to urea it’s called eNtrench and it inhibits the bacteria that converts ammonium to nitrate. So we can choose to use Mother Nature and low temperatures or we can also use a chemical inhibition.”
So keep the nitrogen cool, keep it dry and keep it away from soil bacteria as best you can. With phosphorus, keep it dry and keep it away from the soil surface.
“We know from studies in Manitoba that 80 per cent of the phosphorus that gets into the water gets there with the snowmelt,” Heard said. “The snowmelt really only contacts the frozen surface before the spring thaw so if we can minimize the phosphorus levels at the surface, that’s going to be beneficial.”
A fall application of phosphorus should be banded and below the surface and this keeps it in place during the spring melt. Heard says this is what the majority of farmers is doing because it’s not only environmentally responsible, it’s economical as well. This covers Right source and Right time. Another thing to consider is Right place and this deals with the soil type and how these soils respond to water.
“A really sandy soil is susceptible to leaching losses so if fall nitrogen converts to nitrate it can be washed down below the root zone through leaching,” Flaten said. “If you have a heavy clay soil, leaching isn’t a risk, it’s water standing at the surface. This can result in a lack of oxygen and when the micro-organisms don’t have access to oxygen, they’ll use nitrate as a substitute and convert plant-available nitrogen into nitrogen gas that’s lost to the atmosphere.”
“The standing water is the one that is giving agriculture a bit of a black eye over nitrous oxide,” Heard said. “That’s when it’s converted to nitrous oxide and that’s the greenhouse gas that’s 300 times worse than carbon dioxide. That’s the one that has worldwide attention right now.”
So there are no easy answers that apply to every acre of every farm — but taking the four Rs into account and applying them to the field conditions go a long way to making a fall application practical and economical.
“As long as you’re willing to follow the rules, putting fertilizer where it’s safe and banded into the soil below the surface,” Heard said. “It prevents any surface run-off because it’s not exposed at the surface.”