Nitrogen and carbon mineralization in soils amended with biofumigant or non-biofumigant plant materials

• Plant biomass C and N mineralization in soil were assessed in laboratory trials.
• Defatted seed meals (DSMs), crop residues and green manure were compared.
• Net N mineralization was higher for DSMs than for residues and green manure.
• The presence of glucosinolates did not affect N and C mineralization.
• Soil type (loam or silty clay) did not affect N mineralization of the amendments.

Biofumigant plant materials from Brassicaceae are rich in nutrients and could represent an interesting source of organic nitrogen for crops, when used as soil amendments. In this study, we evaluated in two laboratory experiments the nitrogen and carbon mineralization in soil amended with glucosinolate-containing (Brassica carinata defatted seed meals and Brassica juncea green manure) or non-containing (carinata crop residues, and sunflower) plant materials. In the first experiment, two soils of contrasting texture (a loam and a silty clay) were amended with carinata defatted seed meals, B. juncea green manure, carinata crop residues and un-amended control. In the second experiment, a loam soil amended with carinata and sunflower defatted seed meals obtained by mechanical and solvent extraction were compared. The amount of mineralized nitrogen at the end of a 3-month incubation period was on average 56.6% of the added nitrogen in soil amended with carinata seed meals, and 39% in soil amended with B. juncea green manure, whereas nitrogen immobilization occurred in soil amended with carinata crop residues. Inorganic nitrogen release was faster in soil amended with carinata defatted seed meals. These results were related to carbon to nitrogen ratio in the plant materials. The soil type did not affect N mineralization of the amendments. No negative effect on mineralization could be attributed to the presence of glucosinolates or to the oil extraction method. Biofumigant defatted seed meals from carinata, used as soil amendments, release interesting inorganic-nitrogen amounts into soil and could therefore substitute chemical nitrogen fertilizers for crop nutrition.