Record-breaking soybean yields this year have likely depleted soil nutrients that farmers will need to replace.
Why it matters: When reviewing fertility requirements for a specific field, it is usually best to look at the five-year average for that crop on that field, but in a year like this that may not be adequate.
Horst Bohner, soybean specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, said the 10-year soybean yield average for Ontario is 46 bushels per acre. This year, Bohner said he expected the average to be in the 50s.
Michelle Baker, agronomist with Millstone Crop Services in Huron County says higher yields translate to higher nutrient removal.
The International Plant Nutrition Institute nutrient removal chart shows that one bushel of soybeans harvested removes 0.84 pounds of P2O5 and 1.3 lb. of K2O per acre.
This year, with growers harvesting an extra 10 bushels in many cases, they’re removing an extra eight pounds of actual phosphorus and an extra 13 pounds of actual potassium.
“Those are big numbers and I think that is why sometimes (farmers) start to see their fertility levels slide over time. They have been fertilizing the same way, at the same rates (for many years) but are starting to achieve higher yields,” said Baker. “It’s definitely important that we keep up with that removal.”
Baker said the awareness on how much fertility soybeans take out of the ground has grown.
“There were a lot of transition years where (growers) were putting manure on and not thinking they need to meet those P and K requirements of commercial fertilizer. Now growers are more into the cash cropping scenario, and have learned that they need to be putting on adequate fertilizers to meet those needs.”
Bohner said as average yields continue to increase, most fields aren’t being fertilized to a level needed to sustain yields.
Growers should base their fertility requirements on soil-test results and gradually feed soil properly.
“The higher your yield, the more (nutrients) you will remove in the grain obviously… but how that impacts the following crop, all depends on what that soil-test value is. If that soil-test value is high, it won’t impact the following crop at all. If the value is low, then you’re driving that soil even further down,” said Bohner.
Adequate fertility requires a multi-year strategy. Farmers need to build the soil to a reasonable amount and use soil tests and crop removal rates to replenish it and maintain those levels.