C:N ratio

Common C:N ratios

%C %NBlood meal 43 13Legume Hay (dry) 40 2-2.5Fresh cow manure 12-20 0.6-1.0Oat straw 48 0.5Wood chips 25-50 0.1

C: N ratio

• Total N includes organic N, ammonium NAnd nitrate N.

C:N ratio can be estimated by multiplyingthe percent carbon of each ingredient by the number of parts by weight of that ingredient and then adding the carbon totals for ingredients.

Measuring C:N

• Nitrogen is measured byKjeldahl method (TKN)Combustion method

Measuring C:N

• The TKN method will analyze for organic N and ammonium N, but not nitrate N

• Nitrate can be recovered by modifying the TKN method

Measuring C:N

• Combustion method uses a combustion furnace such as the Leco 1000 CHN analyzer

C:N parameters

• The dividing line between immobilization and release of N is about 20:1

• >30:1 results in immobilization during the initial composting process

• 20-30:1, neither immobilization or release of mineral N

• <20:1, release of mineral N early in the decomposition process

Composting effects on C:N ratio

• Composting causes organisms to form new cell material using their stored N

• In the process carbon is burned• Organisms get rid of excess N as ammonia

C:N

• Since microbes use about 30 parts C for each part N an initial C:N ratio of 30 promotes rapid composting and would provide some N in an immediately available form in the finished compost

• Where C:N >30, there is loss of N through immobilization

Research

• UC studies show that C:N ratios of 30-35 were optimum

• Composting time increased with higher C:N ratios• If unavailable C is small, the C:N ratio can be

reduced by bacteria to 10• Composting material with a higher C:N ratio

would not be harmful to the soil,because the remaining carbon is so slowly available, N immobilization would be minimal