C:N ratio

Common C:N ratios

%C %N

Blood meal 43 13

Legume Hay (dry) 40 2-2.5

Fresh cow manure 12-20 0.6-1.0

Oat straw 48 0.5

Wood chips 25-50 0.1

C: N ratio

• Total N includes organic N, ammonium N And nitrate N. C:N ratio can be estimated by multiplying the 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 by

Kjeldahl 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