Researchers suggests producers could split fertilizer applications if weather is excessively wet before the growing season
Given the soaring cost of nitrogen fertilizer, farmers want to make informed decisions on application rates to maximize yields.
Researchers at the University of Illinois recently examined the role of the pre-growing seasonal weather in relation to nitrogen.
“When farmers plant corn in spring they already know what happened (with the weather) during the pre-growing season from the previous fall to the spring,” said Ziyi Li, a doctoral researcher at the university’s Department of Natural Resources and Environmental Sciences and lead author of the study.
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“We can use the pre-growing season information to guide farmers to adjust their fertilizer application.”
He said a low temperature and heavy rain during the pre-growing season may reduce the soil nitrogen content before planting through decreasing mineralization and increasing leaching loss leading ultimately to yield loss.
“Although increasing the fertilizer rate could mitigate yield loss, it may also increase the environmental loss during the growing season,” he said. “A potentially better method is to adjust the fertilizer timing by splitting a portion of the fertilizer in spring and another application during the corn’s rapid growing stage, which we call side-dress or split application.”
According to the news release, Li’s calculations found that wetter pre-growing seasons reduced soil nitrogen by leaching. With no added fertilizer in spring, a pre-growing season uptick in precipitation led to yield reductions ranging from five to 14 percent. However, with spring fertilizer applied at a rate of 150 pounds (68 kilograms) of nitrogen per acre, the 2018 average rate in the Illinois region, pre-season precipitation resulted in a yield loss of one to three percent.
“In our analysis, we found applying more fertilizer can mitigate and even eliminate the yield loss induced by excessive pre-growing season precipitation,” he said. “Based on our model, if an Illinois farmer applies 150 lb. of nitrogen per acre, the one to three percent yield loss can be prevented by adding about 16 lb. more nitrogen.”
However, while adding additional nitrogen to mitigate higher rainfall, a colder-than-normal pre-growing season cannot be protected in the same way due to the effect of reduced soil microbial activity and enhanced leaching.
Li wrote in the report that a lower temperature not only causes soil inorganic nitrogen deficiency but also reduces early growing season active root nutrient uptake and crop nitrogen demand because of cooling soil temperatures.
“The temperature not only affects the nitrogen content in the soil but also seems to limit early growth in ways that affect yield potential, even if the weather returns to normal later,” he said.
Li and his team used an advanced agro-ecosystem model known as ecosys to clarify the relationship between temperature and precipitation during the pre-growing season and soil inorganic nitrogen content leading to yield outcomes.
Kaiyu Guan, associate professor in NRES and founding director of the Agroecosystem Sustainability Center at Illinois said, “we believe the findings in this work provide some justification for the consideration of pre-growing season weather in determining the spring nitrogen fertilizer application.”
The team conducted multiple experiments by changing the pre-growing season precipitation and temperature then assessing how the changes affected soil nitrogen dynamics and crop yield.
Based on the research, Li said that they looked at how to adjust the fertilizer rate to meet yield loss in the face of extreme pre-growing season conditions. The scope of the study did not consider environment loss costs since it was focused on managing nitrogen fertilizer for productivity effectively. However, Li believes that both should be considered in tandem when providing farmers with guidance on fertilizer management.
The researchers said that the model’s results could be applied to improve nitrogen rate calculators currently in use. However, farmers who might want to fine-tune nitrogen applications could consider strip trials.
“High rates of nitrogen tend to produce dark green corn, but lower rates might do that as well,” said Emerson Nafziger, emeritus professor at the Department of Crop Sciences.
“The only way to know if you used too much nitrogen is to compare the rate you used to a lower rate in the same field. A strip in the field with a lower rate, or higher if the rate in the field is moderate, is a great way to gain confidence in lowering nitrogen rates in the future. In the unlikely event the higher rate produces enough extra yield to pay for itself, we should be able to identify the likely cause for the difference (for example, wet soils) and use that to adjust rates in the future.”
Whether farmers choose to do test stripping may depend on factors such as cost and timing.
“I believe there are some farmers conducting soil tests before planting,” said Li. “But I am not sure how many of them would choose to soil test because it increases the cost.”
The research was published in the journal Field Crops Research.
