Why is a plant residue C:N ratio of < 25:1 ideal for microbes? (three reasons)
Nitrogen is not limiting Microbes have C:N ratios of ~8:1 Residues are generally easier to decompose
What is the best combination of residues if the goal is to increase SOM?
Oat (C:N 70) and hairy vetch (C:N 11)
What are SOM inputs? 4 of them
Different types of plant tissue (lignin, cellulose) Different types of plant root exudates (carbohydrates, amino acid) different animal input (manure, urine, chitin) different microbial, plant, and animal cellular components (proteins, lipids, DNA)
Where does SOM come from?
What is the ideal microbial diet C:N ratio?
How fast is decomposition of C:N ratio is > 24:1?
Much slower than if it was <24:1
What materials have a faster decomposition rate? (5 of them)
Green matter= leaves vegetation Legume cover crop Young cereal, brassica Poultry manure Manure slurries
What materials have a slower decomposition rate? (4 of them)
Brown matter - stems, roots Mature cereals (rye, wheat, oats) Solid manure plus C (dairy bedded with straw) Mature compost
Why would you want low C:N ratios?
fast turnover short term N promote predation and further N release
Why would you want high C:N ratios? (3)
feed slow growing, more efficient microbes more diverse microbial community food web can help with pathogen and pest suppression
What is the benefit of cover crops when it comes to building SOM?