Qualitative and quantitative response of soil organic carbon to 40 years of crop residue incorporation under contrasting nitrogen fertilisation regimes

Abstract

Abstract.Crop residue incorporation (RI) is recommended to increase soil organic carbon (SOC) stocks. However, the positive effect on SOC is often reported to be relatively low and alternative use of crop residues, e.g. as a bioenergy source, may be more climate smart. In this context, it is important to understand: (i) the response of SOC stocks to long-term crop residue incorporation; and (ii) the qualitative SOC change, in order to judge the sustainability of this measure. We investigated the effect of 40 years of RI combined with five different nitrogen (N) fertilisation levels on SOC stocks and five SOC fractions differing in turnover times on a clay loam soil in Padua, Italy. The average increase in SOC stock in the 0-30 cm soil layer was 3.1 Mg ha -1 or 6.8%, with no difference between N fertilisation rates. Retention coefficients of residues did not exceed 4% and decreased significantly with increasing N rate (R 2 = 0.49). The effect of RI was higher after 20 years (4.6 Mg ha -1 ) than after 40 years, indicating that a new equilibrium has been reached and no further gains in SOC can be expected. Most (92%) of the total SOC was stored in the silt and clay fraction and 93% of the accumulated carbon was also found in this fraction, showing the importance of fine mineral particles for SOC storage, stabilisation and sequestration in arable soils. No change was detected in more labile fractions, indicating complete turnover of the annual residue-derived C in these fractions under a warm humid climate and in a highly base-saturated soil. The applied fractionation was thus useful to elucidate drivers and mechanisms of SOC formation and stabilisation. We conclude that residue incorporation is not a significant management practice affecting soil C storage in warm temperate climatic regions.

Soil carbon dynamics in wheat plots established on grassland in 1911 as influenced by nitrogen and phosphorus fertilizers

“…Nitrogen fertilization, with or without P application, significantly increased SOC concentration (Table 1), in agreement with other findings (Smith et al 2015;Poeplau et al 2017). Applying P fertilizer had no consistent influence on SOC concentration.…”

Assessing the Climate Regulation Potential of Agricultural Soils Using a Decision Support Tool Adapted to Stakeholders' Needs and Possibilities

“…Another treatment that has been the subject of multiple LTEs is the effect of mineral N fertilizer on C sequestration. Although generally no effect is observed (e.g., Nardi et al, 2004;Triberti et al, 2008;Poeplau et al, 2017), some authors report a small increase in SOC stocks after mineral N fertilization (Dersch and Böhm, 2001;Ladha et al, 2011). However, a potential increase in SOC stocks can be offset by the greenhouse gases produced during the manufacturing of mineral N fertilizer (Gao et al, 2018).…”

Assessment of crop growth, soil properties and crop yield in an upland acidic soil with inorganic fertilizer blended with organic amendments in summer rice cropping seasons

“…As the addition of organic materials to soil channels the accumulation of extra carbon (Bharali et al 2017;Baruah and Baruah 2015;Kirkby et al 2013), SOC was found enhanced under T3, T5 and T6, i.e., under the inorganic fertilizer blended with organic materials. The increased SOC helps microbes to provide nutrients to plants by keeping carbon and nitrogen balanced in soil, otherwise microbes would decompose existing organic carbon of the soil (Fontaine et al 2004;Murphy et al 2015;Poeplau et al 2017). The SOC was found increased under inorganic T2 also, which might be due to the fact that the application of urea assimilated carbon by improving leaf, shoot and root biomasses of rice plants (Liu et al 2017;Ge et al 2016;Zhu et al 2018).…”