Pre-planting weather data determines how much spring nitrogen to apply

Pre-growing season information can be used to guide farmers to adjust their fertilizer application, according to Ziyi Li, doctoral researcher in the Department of Natural Resources and Environmental Sciences (NRES) at Illinois and lead author on the new study published in Field Crops Research.

Soil nitrogen reduced through leaching

Wetter pre-growing seasons reduce soil nitrogen through leaching, Li’s study shows. With no added fertilizer in spring, a pre-season uptick in precipitation led to yield reductions between 5 and 14%. But with spring fertilizer applied at about 150 lb nitrogen per acre, the 2018 average rate in Illinois, heavy pre-season precipitation still dropped yield by 1-3%.

“In our analysis, we found applying more fertilizer can mitigate and even eliminate the yield loss induced by excess pre-growing-season precipitation. Based on our model, if an Illinois farmer applies 150 lb of nitrogen per acre, the 1-3% yield loss can be prevented by adding about 16 lb more nitrogen,” Li says.

Reduced soil microbial activity

In colder-than-normal pre-growing seasons, soil inorganic nitrogen – and end-of-season yield – declined due to reduced soil microbial activity and enhanced leaching. But in this case, adding extra fertilizer in spring may not do much.

“The effects of cold pre-growing season temperatures on yield cannot be eliminated by adding additional fertilizer,” Li says. “That’s because the temperature not only affects the nitrogen content in soil, but also seems to limit early growth in ways that affect yield potential, even if weather returns to normal later.”