Starved Soil Kills Yield Potential

truck in field
You’re always pushing for better yields, and all the pieces finally fell together in 2016. Record or near-record yields across the country not only topped off grain bins but also depleted soil nutrients. As you plan for your 2017 crop, it’s important to replenish soil nutrients so yield isn’t held back from reaching its potential.

In 2016, the national corn yield beat previous records by about 4 bu. at 175.3 bu. per acre and soybeans yielded a record 52.5 bu. per acre. At the national average yield, a 
500-acre corn farmer pulled 39.44 tons of nitrogen, 16.22 tons of phosphorus and 11.83 tons of potassium out of the soil—not including leeching or other nutrient losses.

“The availability of nutrients changes during the year due to biological, chemical and physical properties,” says Leslie Glover, USDA soil scientist. “Using the same nutrient program [year over year] is like going to the doctor and getting the exact same medication without getting any examination to determine the current state.”

North Carolina corn, soybean and cotton farmer Curtis Furr is taking the high yields into account for his next crop. In 2016, he saw a 20% increase in corn yields and a 25% increase in soybean yields. 
“With that extra 20 bu. of corn, I’ll need to put something on [double crop] wheat possibly,” he says.

Carefully consider the impact big yielding crops has on phosphorus and potassium levels in fields.

While nitrogen might typically be the first nutrient you think about when it comes to high yields, it’s important to consider other nutrient needs as well.

“When guys have 200-bu. corn and 70-bu. beans they’re taking about 130 lb. of phosphorus and 152 lb. of potash/potassium out of the soil [in that two year rotation],” says Bob Perry, general manager, Perry Agricultural Laboratory, a soil testing lab in Bowling Green, Mo. “A lot of folks are just putting on 
100-lb./100-lb.—all of a sudden they’re behind.”

Crops need phosphorus in full form early for root development and as the plant grows to promote healthy stalks, stems and flower production. Potassium plays a vital role in plant growth as well, and deficiency can result in stunted growth, defoliation and weakened response to weather changes such as drought.

“When we have poor fertility we’re much more susceptible to any deviation in weather,” Perry says. “Going through any stress is harder when you don’t have the fertility you need.”

Perry recommends soil to have at least 50 lb. of phosphate per acre (25 ppm) and 300 lb. of potassium per acre (150 ppm) each season. 

Be mindful of the three keys to determining soil and crop nutrient needs: soil tests, tissue tests and yield history.

“Before farmers apply nutrients each crop season, they need to take soil tests and past yields into consideration,” explains 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.”

Use soil tests and tissue tests as the road maps to good fertility. In addition, keep yield goals in mind as they affect nutrient levels needed for the crop. Take a look at the chart on the right to see how much nitrogen, phosphorus and potassium it takes on average to grow 1 bu. of corn.

“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. Pay attention to soil type and monitor its potential for leaching, he adds.

In addition to keeping soil tests up-to-date, Hardy recommends farmers check on their crops throughout the season by pulling plant tissue samples. Tissue tests give a snapshot of how a crop is using nutrients and how the fertility program is working.

“I’ve gotten where I rely a whole lot on tissue samples—it gives me an idea of what’s going on,” Furr says. He plants wheat immediately following corn and says it’s important to double check the crop has what it needs because the corn often pulls much 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.”

Simply relying on what’s been done in the past might not suffice this year.

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 over 500 bu. per acre so we have the genetics to achieve that—the rest is how we manage,” Perry says. Wallets might be tight, but you could lose more money in yield loss if you don’t cater to the crop and soil’s nutrient requirements.

Soil type and organic matter play a significant role in whether or not your farm has a nutrient deficiency. It’s important to understand your soil type, know what your yield took out of the soil, what your yield goals are for 2017 and what nutrients you need to apply to restore the soil and be prepared for a productive season.

“If you’re not collecting yield and soil data you need to start,” Flis says. “Keep records and learn to use them to plan into the future.”

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