Dynamic of residue decomposition and effects on labile fractions of soil organic carbon

DE SA PEREIRA, E.; GALANTINI, JA.; DUVAL, ME.

Valencia

Conferencia; Global Conference on Plant Science and Molecular Biology; 2017

Magnus Group

Cover crop (CC) residues protect the soil from erosion and their permanence on the surface is largely influenced by their biochemical constituents. Cover crops (CC) are a necessary tool for the Pampas region to avoid soil degradation after summer crops grown on a year basis, leaving the soil naked during the mild winter (Rimski-Korsakov et al. 2015). In this way, CC may influence soil organic carbon (SOC) contents by providing additional residue carbon to soil (Wang et al. 2010). Nevertheless, reported effects of CC on SOC contents are inconsistent and range from losses (Mazzoncini et al. 2011) to gains (Duval et al. 2016). In this study the dynamics of CC residues decomposition and their effects on soil labile organic carbon fractions were evaluated under controlled (incubation experiment) conditions. Three CC species (oats, Avena sativa L.; vetch, Vicia sativa L.; Persian clover, Trifolium resupinatum L.) and a no CC control (fallow) were evaluated. Shoot residues were applied on the soil surface and incubated for 362-days (with eight sampling times). Particulate organic carbon (POC), total and soluble carbohydrates (CHt and CHs, respectively) were determined in soil samples. Oats and vetch residuesdecomposed faster than clover, where k valueswere1.3, 1.4 and 1.9 year-1, respectively. At the end of the experiment, the POC concentration was the lower in vetch (1.83 g kg-1) and clover (1.96 g kg-1) than oats (2.21 g kg-1) and fallow (3.00 g kg-1), that?s mean a loss between 45-64% of their initial values. Overall, the dynamics of residue decomposition were reflected in changes of CHt contents. The periods of greatest residue decomposition were 0 to 21 days and 130 to 201 days for vetch and oats, respectively which coincides with the greater soil CHt. Hence, this organic fraction is very sensitive to residue decomposition and can be indicators of changes in soil organic matter quality over short periods of time. Changes in soil labile carbon fractions were differentially influenced by residue quality over short periods of time. The lower POC concentrations in CC soils than in fallow soils indicated that despite extra carbon input, mineralization rate was much high in CC affecting also native organic pools. Overall, the dynamics of residue decomposition were reflected in changes of CHt contents, where the periods of greatest residue decomposition corresponded to the higher soil CHt. Hence, this organic carbon fraction is very sensitive to residue decomposition and can be indicators of changes in soil organic matter quality over short periods of time.