Epsilon Archive for Student Projects

Abstract

Increasing the organic matter content in soil improves the soil productivity, its abil-ity to hold water, deliver nutrients and it protects against erosion. It is also a way to sequester carbon (C) as a strategy to mitigate climate change. Straw incorporation is a widespread management practice that can be used for this purpose. However, straw can also be used for other purposes such as feed or bioenergy. The effect of straw incorporation on soil organic carbon (SOC) varies between studies and we need to improve our understanding of the effect of straw incorporation on C dynam-ics in order to use the resource in the best possible way. This study investigates the effect of straw incorporation on SOC stocks as well as C fractions under different nitrogen (N) fertilization levels. By studying different C fractions, and not only the bulk soil, more detailed knowledge is obtained about the C dynamics. For this study, soil samples were taken in 2006 from a long-term field trial in a clay soil in Italy. The results showed that straw incorporation significantly increased the SOC stock with 3.15 Mg ha-1 in the bulk soil. The effect of straw incorporation did de-crease over the years in comparison with earlier results from the long-term experi-ment. The earlier observed effect of N on SOC was no longer present in the bulk soil. After 40 years of treatment, 3.3% of the total C input was retained in the soil. Two fractions were significantly affected by the straw incorporation, the non-resistant C associated with clay and silt particles (SC-rSOC) and the dissolved or-ganic carbon. No significant effect due to residue treatment was found in the other fractions and N fertilization had no significant effect in any of the fractions. The C fraction varying most was the particulate organic matter followed by the fraction of C attached to sand particles and stable aggregates. The resistant fraction did not change with straw incorporation and seems to be insensitive to the treatments in a decadal perspective. Most C was stored in the SC-rSOC fraction and this was also the fraction that showed the highest significant increase after straw incorporation. Since this is believed to be one of the most stable fractions, straw incorporation might lead to a long-term C sequestration even though the absolute amount C se-questered was small.