Late Season Nitrogen May Improve Soybean Feed Quality

By Blake Jackson

Researchers at Kentucky State University have identified a potential solution to one of the soybean industry’s ongoing challenges - declining seed protein concentration, which can reduce the quality of soybean meal used in livestock feed.

The study, led by Deepak Khatri under the guidance of Dr. Anuj Chiluwal, examined how biochar and late-season nitrogen applications affect soybean yield and seed quality. The two-year field trial was conducted at Kentucky State University’s Harold R. Benson Research and Demonstration Farm using two soybean cultivars from different maturity groups.

Results showed that applying nitrogen fertilizer during the late stages of crop development increased seed protein levels by 1.2% to 2.8% over both growing seasons.

Researchers also found that oil concentration remained stable, meaning protein levels improved without negatively affecting oil quality.

“Declining soybean protein concentration is a major concern because it directly affects the quality of soybean meal used in animal feed,” Khatri said.

“Our research provides evidence that lower nitrogen applications during the seed-filling period can help reverse this trend.”

The research focused on nitrogen applications during the seed-filling stage, a time when soybean plants require significant nitrogen and natural soil supplies or biological nitrogen fixation may no longer meet crop demand, especially under high-yield conditions.

According to Dr. Chiluwal, earlier studies often relied on fertilizer rates that were too expensive and environmentally impractical for growers to adopt.

“Previous studies aimed at increasing soybean protein through late-season nitrogen applications relied on extremely high rates - ranging from more than 200 to 870 kilograms per hectare - making them neither economically viable nor environmentally sustainable,” Dr. Chiluwal said.

“In contrast, this study takes a different approach by testing lower nitrogen rates of 40 to 120 kilograms per hectare, applied in three split applications during the seed-filling period. The findings demonstrate that even modest nitrogen applications can improve seed protein concentration, offering a more practical and scalable solution to a significant industry challenge.”

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