USDA researchers compared three manured fields with three neighboring fields using synthetic fertilizer.
Six North Dakota fields
The study, published on 12 October 2026, examined six fields in Towner County, North Dakota. Three had a history of swine-manure application; three neighboring fields used synthetic fertilizer only. Researchers sampled the upper 15 centimetres of soil in 2022 and compared yield records from 2013 through 2022.
Phosphorus and zinc differed
Soybean and spring-wheat yields were similar between the two groups of fields. The manured fields had more available phosphorus and zinc in the sampled soil. The researchers found no consistent difference in the measured soil carbon, nitrogen and salt indicators; aggregate responses varied with soil texture.