In a newly published study, researchers dug into how fertilizing with manure affects soil quality, compared with inorganic fertilizer.
In the summer of 2015, they collected soil samples at a variety of depths using a push probe auger. Then they analyzed the samples.
- Manure helped keep soil pH—a measure of acidity or alkalinity—in a healthy range for crops. Inorganic fertilizer made the soil more acidic.
- Manure increased soil organic carbon for all the measured soil depths compared to inorganic fertilizer and control treatments. More carbon means better soil structure.
- Manure significantly increased total nitrogen compared to fertilizer treatments. Nitrogen is key to plant growth.
- Manure increased water-stable aggregates. These are groups of soil particles that stick to each other. Increased water-stable aggregates help soil resist water erosion. Inorganic fertilizer application decreased these aggregates.
- Manure increased soil electrical conductivity at all soil depths in comparison to inorganic fertilizer and control treatments. Higher soil electrical conductivity means higher salt levels in the soil.
Ozlu and his team concluded that long-term annual application of manure improved most soil quality properties compared to inorganic fertilizer. “Increased electrical conductivity is one of the few negative impacts of manure,” Ozlu said.