Before finalizing your nutrient plans for 2019, carefully consider the impact this past year’s high-yielding crops had on nutrient levels in fields, especially phosphorus (P) and potassium (K) levels.
“When guys have 200-bu. corn and 70-bu. soybeans, they’re taking about 130 lb. of phosphorus and 152 lb. of potash/potassium from the soil [in a two-year rotation],” says Bob Perry, general manager, Perry Agricultural Laboratory, based in Bowling Green, Mo.
Crops need potassium early in the season for root development, and again as the plant grows to promote healthy stalks, stems and flower production. Potassium is vital to growth as well, and a deficiency can result in stunted growth, defoliation and weakened response to weather changes.
Perry recommends having at least 50 lb. of phosphate per acre (25 ppm) and 300 lb. of potassium per acre (150 ppm) available each season.
“Before farmers apply nutrients each crop season, they need to take soil tests and past yields into consideration,” says Sally Flis, director of agronomy at The Fertilizer Institute. “If they haven’t tested in a while they should; it helps determine if there are certain fields or areas of fields they need to focus on more.”
Farmers should soil test fields at least every other year, according to Ken Sechler, senior agronomist with Southern States Cooperative. Over time the information can help farmers establish a good nutrient baseline.
“With higher yields crops remove more nutrients, so you’ll want to monitor fields year-over-year more closely,” says David Hardy, North Carolina Department of Agriculture and Consumer Service soil scientist. Be sure to pay attention to soil type, and monitor its potential for leaching, he recommends.
Tom Bruulsema, International Plant Nutrition Institute vice president, Americas and research, adds phosphorus needs are best determined by evaluating soil tests against the phosphorus balance in the field. “If your soil test is too high, a deficit is appropriate,” he says.
Hardy recommends farmers check on their crops throughout the season by pulling plant tissue samples, which give a snapshot of how a crop is using nutrients and how the fertility program is working.
“I’ve gotten to where I rely a lot on tissue samples—it gives me an idea of what’s going on,” says Curtis Furr, North Carolina corn, soybean and cotton farmer. He plants wheat immediately following corn and says it’s important to double-check the crop has what it needs because corn often pulls most of the nutrients before wheat is planted.
Pulling tissue samples is easy, Furr says. Walk the field and pull 20 samples from 20 different plants scattered throughout. Send in the samples for analysis and wait for the results. “It’s not very expensive either—a $10 sample could save you thousands.”
Each bushel pulled out of the field means nutrients are depleted from the soil, and if nutrients are not replenished you cap the crop’s yield potential based on what genetics and management could produce.
“The maximum corn yield is more than 500 bu. per acre, so we have the genetics to achieve that—the rest is how we manage,” Perry says. Wallets might be tight right now, but you could lose more money in yield loss if you don’t cater to the crop and the soil’s nutrient requirements.
4 Steps to Better Results
Here are a four steps nutrient specialists Ken Sechler and Tom Bruulsema say will improve your nutrient programs:
- Soil test on a consistent basis.
- Calculate the form and individual nutrient balances.
- Understand the role placement plays in nutrient uptake.
- Consider using a private lab for evaluation; compare how the results stack up to Extension tests.