Cover crops as a tool to reduce reliance on intensive tillage and nitrogen fertilization in conventional arable cropping systems
Introduction
The intensification of arable production has made a substantial contribution to increased world food production over the last 50 years (Tilman et al., 2002). However, current agricultural practices have also given rise to environmental concerns regarding decreased biodiversity, reduced water quality, and degraded soil quality (Stoate et al., 2001). Although the use of mineral fertilizers and pesticides has led to a considerable increase in productivity, arguably the main ecosystem service provided by agriculture, this has been at the cost of other regulating and supporting services provided by agro-ecosystems (Power, 2010). The internal regulation of nutrient cycles, the natural control of pests and diseases, and the abundance and diversity of soil organisms are often downregulated in intensively managed fields. As a result, high agricultural productivity becomes dependent on anthropogenic-synthetic inputs and is no longer sustainable in the long-term (Geiger et al., 2010; Tsiafouli et al., 2015).
Ideally, a sustainable system will maintain the right balance between external inputs and ecosystem service delivery, thus providing high productivity based on optimized internal regulatory processes and resilience of the system (Bender et al., 2016). This goal could be achieved by including agricultural practices that promote regulating and supporting ecosystem services and preserving soil quality, also called ecological engineering.
One example of this is conservation agriculture (CA), which principles include reduced tillage, improved crop rotation, and permanent soil coverage (Teasdale et al., 2007; Hobbs et al., 2008; Doltra and Olesen, 2013). Although CA contributes to soil conservation, reduced consumption of fossil fuels, a reduced work load, and is widely propagated in the America’s and Australia, adoption rates in Europe are still very low (Derpsch et al., 2010; Kertész and Madarász, 2014; Casagrande et al., 2016). The main reasons why CA is not widely adopted in Europe include the often more complex crop rotations (e.g. presence of ley), problems related to weed control, and delayed spring nutrient mineralization.
Another option to improve the sustainability of agricultural production is the use of cover crops. Cover crops are grown between two main crops and are a crucial element of CA systems to reach an appropriate soil coverage during fallow period as well as maintain productivity (Hartwig and Ammon, 2002; Pittelkow et al., 2015; Marcillo and Miguez, 2017). Cover crops provide a range of ecosystem services, as they have been shown to protect soil against erosion, reduce the risk of surface and ground water pollution, improve soil structure, and promote soil biota (Dabney et al., 2001; Kohl et al., 2014; Schipanski et al., 2014; Blanco-Canqui et al., 2015). Moreover, cover crops play an important role in the management of nitrogen (N) within arable cropping systems, either by preventing leaching losses (non-legume species) (De Notaris et al., 2018; Thapa et al., 2018) or by providing additional N input through biological fixation (legume species) (Thorup-Kristensen et al., 2003; Couëdel et al., 2018). Cereal-based systems, particularly maize, benefit greatly from additional N input by legume cover crops, as shown by several studies (Miguez and Bollero, 2005; Gabriel and Quemada, 2011; Liebman et al., 2012; Tosti et al., 2012; Komainda et al., 2017).
All these benefits have been extensively described as well as the importance of direct cover crop management, e.g. sowing and termination date or termination techniques (Thorup-Kristensen and Dresboll, 2010; Alonso-Ayuso et al., 2014; Radicetti et al., 2016; Osipitan et al., 2019). Cover crops have also been shown to be important when conservation tillage is applied or to reduce N applications. However, few studies have investigated to which extent cover crop based agro-ecosystem services are influenced by the combination of these management practices or, more generally, perform within defined cropping systems. (Wittwer et al., 2017). Both tillage and fertilization greatly influence soil properties and processes, such as organic matter mineralization (Balesdent et al., 1990; Kandeler et al., 1999) and weed abundance, which in turn influence crop nutrition and productivity (Shelton et al., 2017). For example, it is still unclear if and to which extent cover crops can reduce the reliance on fertilizers under different tillage intensities without impairing crop yield. Moreover, earlier studies reported that legume cover crops can fix more than 100 kg N ha−1 year−1, but it is still difficult to predict how much of this N can be effectively used by the following crop (Thorup-Kristensen et al., 2003; Büchi et al., 2015). Additionally, cover crops could suppress weeds and thus have the potential to reduce tillage and herbicide use, especially if cover crops can be easily managed before the main crop is planted (Dorn et al., 2015). Thus, it is increasingly important to gain a clearer understanding of the interactions between cover cropping and other field management practices, such as tillage intensity or fertilization in an effort to optimize cover crop effects on productivity and profitability, and thereby achieve a wider adoption of this practice by farmers as a mean of ecological intensification (Roesch-McNally et al., 2017).
Consequently, this study focuses on the interactions between tillage intensity, N fertilization and cover cropping in Swiss conventional arable crop production. Two replicated field experiments were conducted during the years 2012–2014 and 2013–2015 with a crop sequence of winter wheat, cover crops, and maize in Eastern Switzerland. The effect of three different cover crops (hairy vetch (Vicia villosa), oilseed radish (Raphanus sativus) and subterranean clover (Trifolium subterraneum)) were compared to fallow combined with three levels of tillage intensity coupled with weed control strategy (intensive tillage with herbicides, reduced tillage without herbicides, and no tillage with herbicides) and two levels of N fertilization.
The main aim of the study was to evaluate the extent to which the use of cover crops can decrease dependency on intensive tillage, synthetic N fertilization, and herbicides. Thus, based on the assumptions that:
- i)
cover crops help to reduce tillage intensity,
- ii)
additional N input provided by legume cover crops can partly replace the addition of synthetic N fertilizer, and
- iii)
the combination of cover cropping and reduced tillage allows a reduced use of herbicides,
we aimed to identify best combinations of the investigated management practices to sustain productivity but reduce anthropogenic inputs.
Section snippets
Study site and field experiments
Two field experiments were conducted during the years 2012–14 (Experiment I) and 2013–15 (Experiment II) at the research station Agroscope in Tänikon, Switzerland (47°28′50″ N, 8°54′25″ E, 537 m a.s.l.). The top soil of both experiments is classified as sandy loam, containing on average 21 % clay, 35 % silt and 44 % sand, with 2.1 % organic carbon content, 0.23 % total nitrogen content, and it had a pH (H2O) of 7. The long-term (1981–2010) mean annual temperature is 8.7 °C, while annual
Cover crop performance
All three cover crops established satisfactorily, with over 65 % soil cover 60 days after sowing and significantly suppressed weeds compared to the control treatment (Table 1, Supplementary Table S2). Hairy vetch produced the highest biomass, with on average over 3 t ha−1 aboveground DM biomass, followed by subterranean clover with over 1 t ha−1. Both are overwintering species in contrast to oilseed radish, which was already terminated by frost during winter and left less than 1 t ha−1 biomass
Discussion
It is known that cover crops can contribute to more sustainable cropping systems (Olesen et al., 2007; Schipanski et al., 2014; Giuliano et al., 2016). Although positive effects of cover crops on crop yield have been widely described (Tonitto et al., 2006; Marcillo and Miguez, 2017) there is still poor adoption by farmers at a larger scale (Panagos et al., 2015; Seifert et al., 2018), even if various national and regional incentives have recently initiated a positive trend and higher
Conclusions
This study demonstrates that legume cover crops can be used to partly replace fertiliser inputs without compromising yield under intensive and no tillage, and thus confirms that cover cropping has the ability to facilitate conservation agriculture and more extensive cropping practices. Compared to intensive tillage, full fertilisation and herbicide use, similar yields were obtained when either tillage intensity and/or fertilization were reduced in combination with a legume cover crop. Thus,
CRediT authorship contribution statement
Raphaël A. Wittwer: Conceptualization, Investigation, Formal analysis, Data curation, Writing - original draft, Project administration. Marcel G.A van der Heijden: Conceptualization, Writing - review & editing, Supervision, Funding acquisition.
Declaration of Competing Interest
The authors declare no conflict of interests.
Acknowledgements
We thank Werner Jossi for excellent practical support in setting up the experiment and we would like to gratefully thank Grégoire Tombez for his help to implement UAV technology and analyses for this study and for field work. This work was financed by the European Union FP7 Project n.289277: OSCAR (Optimising Subsidiary Crop Applications in Rotations) and Agroscope (Swiss Federal office of Agriculture).
References (80)
- et al.
An underground revolution: biodiversity and soil ecological engineering for agricultural sustainability
Trends Ecol. Evol. (Amst.)
(2016) - et al.
Importance of cover crops in alleviating negative effects of reduced soil tillage and promoting soil fertility in a winter wheat cropping system
Agric. Ecosyst. Environ.
(2018) - et al.
Cover crop crucifer-legume mixtures provide effective nitrate catch crop and nitrogen green manure ecosystem services
Agric. Ecosyst. Environ.
(2018) - et al.
Nitrogen leaching: a crop rotation perspective on the effect of N surplus, field management and use of catch crops
Agric. Ecosyst. Environ.
(2018) - et al.
The role of catch crops in the ecological intensification of spring cereals in organic farming under Nordic climate
Eur. J. Agron.
(2013) - et al.
Replacing bare fallow with cover crops in a maize cropping system: yield, N uptake and fertiliser fate
Eur. J. Agron.
(2011) - et al.
Persistent negative effects of pesticides on biodiversity and biological control potential on European farmland
Basic Appl. Ecol.
(2010) - et al.
Low-input cropping systems to reduce input dependency and environmental impacts in maize production: a multi-criteria assessment
Eur. J. Agron.
(2016) - et al.
Conservation agriculture in Europe
Int. Soil Water Conserv. Res.
(2014) - et al.
The value of catch crops and organic manures for spring barley in organic arable farming
Field Crops Res.
(2007)