Fractionation and Characterization of soil organic carbon during transition to organic farming

Fractionation and Characterization of soil organic carbon during transition to organic farming, Abdelrahman, H. M. , Bari, Italy, (2012) copy at

Thesis Type:

PhD Thesis


The transition from conventional to organic farming is the most difficult period facingorganic growers. Total soil organic carbon (SOC) might not be a suitable tool to track the changes in organically based soil fertility within a 2- to 3-year transition period. Labile fractions that are important for nutrient cycling and supply are likely to be controlled by management to a much greater extent than is total soil organic matter (SOM).!Isolation and characterization of labile fractions are likely to better show the effects of management on SOM and better provide more information on fertility status. Two field experiments were established in 2009 in the south of Italy, at Foggia and Metaponto, to study the changes in SOM pools during the transition to organic farming. Experiments were a cereal/leguminous crop rotation under treatments of amendments (compost and fertilizers) permitted in organic farming performed in triplicate replication. Soils were sampled at the beginning of the project and after each crop harvest in 2010 and 2011. A sequential fractionation procedure was used to separate different SOM-fractions: light fraction (LF), two size classes of particulate organic matter (POM), mobile humic acid (MHA) fraction and Ca-bound humic acid (CaHA) fraction. Isolated fractions were quantified and analyzed for their contents of C and N. Soil, LF, POM and MHA were characterized for their contents of seven carbohydrates and amino compounds, namely 19 amino acids (AAs) and two amino sugars. Masses of the fractions increased during the 2-year course with noticeable increases in the LF and POM. Compost application contributed to significantly greater quantities of LF, POM and MHA than did fertilizer application. Carbohydrate contents, over the 2-year scale, decreased in LF while it increased noticeably in POM and slightly in the MHA fraction. Amino compounds constituted up to 30% of total soil N with a major contribution of the humified fractions, MHA and CaHA. The obtained results recommend inclusion of leguminous crops in crop rotation and application of compost for building up soil fertility during the transition to organic farming. The introduced fractionation procedure is recommended for studying SOM in short-term studies.