Changes in labile fractions of soil organic matter during the conversion to organic farming

Authors: ABDELRAHMAN, HAMADA - Cairo University; COCOZZA, CLAUDIO - University Of Bari; Olk, Daniel - Dan; VENTRELLA, DOMENICO - Italian Agricultural Research Council; MONTEMURRO, FRANCESCO - Italian Agricultural Research Council; MIANO, TEODORO - University Of Bari

Submitted to: Journal of Soil Science and Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2020
Publication Date: 2/8/2020
Citation: Abdelrahman, H.M., Cocozza, C.C., Olk, D.C., Ventrella, D., Montemurro, F., Miano, T. 2020. Changes in labile fractions of soil organic matter during the conversion to organic farming. Journal of Soil Science and Plant Nutrition. https://doi.org/10.1007/s42729-020-00189-y.
DOI: https://doi.org/10.1007/s42729-020-00189-y

Interpretive Summary: Carbon in the soil plays important roles in soil performance. Measuring soil carbon can help identify practices of land management that help carbon accumulate in soil. However, some carbon lasts in the soil for many years, while other carbon cycles in soil over weeks to months, depending on composition and location in the soil. Therefore young soil carbon should be distinguished from old soil carbon when studying how recent land management affects carbon accumulation. Several methods have been proposed for separating soil carbon into younger and older fractions, and researchers typically take one of two approaches. Here we studied fractions from both of the two major approaches. We found that both types of fractions showed carbon accumulation when a crop field is being converted into organic farming through large additions of organic fertilizers. These findings support further joint use of these three fractions to study the effects of land management on young fractions of soil carbon. These results will benefit researchers who study the effects of land management on young fractions of soil carbon or who study the types of carbon found in soil.

Technical Abstract: Organic farming is an alternative farming system for resolving environmental consequences of conventional agriculture. The objective of this study was to investigate the changes in labile soil organic matter (SOM) fractions during the conversion from conventional to organic farming. Two field experiments converted from conventional to organic farming during 2009–2011 were used at Foggia (FG) and Metaponto (MT) in the south of Italy. Soils were cultivated with lentil and wheat in rotation and treated with compost or fertilizer in three replicates. A sequential fractionation scheme was used to separate the light fraction (LF), particulate organic matter (POM) and the mobile humic acid (MHA) fraction. Isolated fractions were quantified and analyzed for C and N. Although soil organic carbon (SOC) responded to the fertilization treatments, the labile fractions were more responsive as shown by the significant increases in fractional contents for all three fractions and especially the larger proportional increases in LF and POM. The MHA represented 15% of SOC at both sites. The LF represented only 5–6% of total SOC, but it was the most responsive fraction to changes in land management. Compost application contributed to significantly greater quantities of LF, POM and MHA than did the fertilizer application. The integration of SOM physical fractions with humified chemical fractions has proven useful to depict short-term C cycling in field conditions and during the transition to organic farming, as revealed by the relative response of these fractions to experimental conditions.