Alternative arable cropping systems: A key to increase soil organic carbon storage? Results from a 16 year field experiment
Introduction
Soil is one of the major components of the biosphere, delivering various essential ecosystems services. It constitutes the main terrestrial carbon sink, containing 1500 Gt of carbon across one meter depth (Batjes, 1996). Farming practices impact this compartment through modification of carbon inputs coming from crop residues or organic fertilizers and indirectly by affecting soil organic carbon (SOC) turnover through soil disturbance. Optimized farming practices with high organic inputs, permanent plant cover and reduced soil tillage can play an essential role in soil carbon sequestration, defined by difference with a reference cropping system (e.g. Luo et al., 2010a), and thus in mitigating climate changes (West and Post, 2002, Freibauer et al., 2004, Powlson et al., 2011). Combining these practices can generate alternative cropping systems differing from the dominant paradigm of conventional systems as they share similar inspirations such as sustainable development of agriculture with the improvement ofenvironmental performance (Beus and Dunlap, 1990).
During the last twenty years, alternative cropping systems have been tested including some which may be less profitable for farmers (Eltun et al., 2002). Conservation, organic and integrated agriculture are examples of alternative systems with expected environmental benefits, including a greater soil organic carbon sequestration, depending on the implemented practices. Conservation agriculture is characterized by the suppression of soil tillage, more diversified crop successions and permanent plant cover. No-tillage systems are often included in this category (Corsi et al., 2012), although they often do not fulfill the last two criteria. Another alternative cropping system is organic agriculture which aims at minimizing its impact on soil, water and air quality. Systemic prevention of weeds, pests and diseases, combined with nutrient self-sufficiency is the core of sustainable organic production (Lammerts van Bueren et al., 2002) since external inputs should be limited (Watson et al., 2002). In such a farming system, crop production is mainly based on organic fertilizers (i.e. manure, compost), green manures and frequent tillage most often essential to control weeds. Low input system, also known as integrated system, combines some practices applied in organic or conservation systems, as it promotes natural regulation in the farming system in order to limit the use of external inputs and sustain farm income (Eltiti, 1992). Overall, reduced intensity in soil tillage, reduced and better adjusted fertilization, increased frequency of cover crops and weaker use of pesticides are the main features that distinguish alternative from conventional system.
Existing reviews on SOC storage in alternative vs conventional systems report contradictory results. They can arise from the difficulty of fulfilling all methodological requirements such as measurements of the initial state, measurements of C concentration and bulk density at a sufficient depth (at least 030 cm in order to include variation of the ploughing depth in the time) in order to calculate SOC stocks at equivalent soil mass between different dates. Higher SOC stocks were recorded in some studies dealing with cropping systems similar to conservation agriculture in which ploughing was stopped and the number of crops increased in the rotation for a same duration (West and Post, 2002, Calegari et al., 2008). However, recent meta-analyses selecting studies conducted with an adequate methodology revealed that SOC sequestration potential in no-till systems had been over-estimated (Luo et al., 2010a, Virto et al., 2011). Concerning organic cropping systems, several studies agreed on their ability to store more SOC than conventional ones (Mondelaers et al., 2009, Leifeld and Fuhrer, 2010, Gomiero et al., 2011, Gattinger et al., 2012, Tuomisto et al., 2012). These authors mainly attributed the extra C storage to a greater application of livestock manure in the organic systems. However, Leifeld et al. (2013) indicated that the proportion of conventional and organic systems in the meta-analysis of Gattinger et al. (2012) was unbalanced in terms of systems with external carbon inputs (27% and 92% respectively), leading to a misinterpretation. Since organic fertilizer (including manure) addition rate is a major driver of SOC sequestration, its uneven distribution makes the comparison between organic and conventional systems difficult and hampers the identification of possible other drivers, such as crop rotation and nature of carbon inputs (Leifeld et al., 2009). Finally, the number of experiments comparing conventional and alternative arable systems without livestock manure is scarce.
Here, we studied a long term experiment (16-yr) including four purely arable cropping systems without manure fertilization. Our objectives were to: i) compare SOC stocks in these systems; ii) predict the dynamics of SOC stocks with a simulation model and iii) understand the drivers of C storage with the help of modelling. The evolution of SOC stocks between 1998 and 2014 was simulated using the simple AMG model (Saffih-Hdadi and Mary, 2008). We tested two hypotheses: i) SOC stocks can evolve differently due to variations in carbon inputs between cropping systems and ii) the mineralization rate of SOC is unaffected by the type of cropping system.
Section snippets
Site and soil characteristics
The study was conducted at the long-term experimental site of La Cage, Versailles, France (48°48⿲N, 2°08⿲E) established in 1998 by INRA. Before 1998, the whole site was conducted under a conventional management. The purpose of the experiment is to evaluate the agronomic, economic and environmental performances of three alternative systems compared to a conventional cropping system which is representative of arable farming in Northern France. During the studied period (19982014), the mean
Crop yields and residues
Mean wheat yields decreased in the following order: CON > LI > CA > ORG (Table 2). They varied between 9.7 t ha1 yr1 and 5.4 t ha1 yr1 and were strongly related to the mineral N fertilizer rate (R2 = 0.80, p < 0.05). Pea yields were similar for CON and LI (4.3 t ha1 yr1 on average) and smaller in CA and ORG (3.1 t ha1 yr1 on average). Rapeseed yields were 4.5 and 3.8 t ha1 yr1 for CON and LI respectively and much smaller in ORG with 0.8 t ha1 yr1 (due to pest attacks) hence this crop was stopped after
Discussion
The La Cage experiment is characterized by alternative cropping systems with specific crop rotations (i.e. with cover or catch crops), no use of livestock manure or other exogenous organic fertilizer and a mineral fertilization in CON, LI and CA. We compare our results here with other studies on similar farming practices and for soil measurements made at least over 030 cm depth.
Conclusion
We quantified SOC stocks and their temporal dynamics over 16 years in the long-term experiment of La Cage (northern France) comparing conventional and alternative cropping systems. The SOC stocks did not change throughout time in conventional (CON) and low-input (LI) systems, slightly increased in the organic (ORG) system and increased markedly in the top soil layer (010 cm) of the conservation agriculture (CA) system. The amount and nature of C inputs, particularly the additional belowground
Acknowledgements
The study was supported by a PhD scholarship from the French Ministry of Agriculture. The Seine-Normandie Water Agency is acknowledged for providing funding by the ENBIO project. La Cage experiment is coordinated by INRA Versailles (France). We gratefully acknowledge P. Saulas, D. Le Floch and C. Montagnier for managing the experiment, J.P. Pétraud, F. Mahu and E. Venet for their technical assistance in soil sampling, C. Dominiarczyk and A. Teixeira for processing samples and O. Delfosse for
References (80)
- et al.
Major contribution of roots to soil carbon storage inferred from maize cultivated soils
Soil Biol. Biochem.
(1996) - et al.
Evaluation of the soil crop model STICS over 8 years against the on farmdatabase of Bruyeres catchment
Eur. J. Agron.
(2008) - et al.
Soil profile carbon and nutrient stocks under long-term conventional and organic crop and alfalfa-crop rotations and re-established grassland
Agric. Ecosyst. Environ.
(2012) - et al.
Soil organic carbon and C-13 abundance as related to tillage, crop residue, and nitrogen fertilization under continuous corn management in Minnesota
Soil Tillage Res.
(2000) - et al.
Combined role of no-tillage and cropping systems in soil carbon stocks and stabilization
Soil Tillage Res.
(2013) - et al.
Effects of catch crops, no till and reduced nitrogen fertilization on nitrogen leaching and balance in three long-term experiments
Agric. Ecosyst. Environ.
(2010) - et al.
Soil C and N stocks as affected by cropping systems and nitrogen fertilisation in a southern Brazil acrisol managed under no-tillage for 17 years
Soil Tillage Res.
(2005) - et al.
Long-term effect of contrasted tillage and crop management on soil carbon dynamics during 41 years
Agric. Ecosyst. Environ.
(2014) - et al.
A comparison of environmental, soil fertility, yield, and economical effects in six cropping systems based on an 8-year experiment in Norway
Agric. Ecosyst. Environ.
(2002) - et al.
Carbon sequestration in the agricultural soils of Europe
Geoderma
(2004)