Cover Crop Productivity in Contrasting Growing Conditions and Influence on the Subsequent Crop

In arable systems, cover crops provide multiple ecosystem services involved in soil protection and fertility. They can efficiently compete against weeds, control erosion or recycle nutrients. The supply of these services is however largely dependent on cover crop growth as most of the services are related to biomass production. The choice of a cover crop adapted to the growing conditions is thus essential. Growing mixtures instead of sole crops is expected to be a way to overcome variable growing conditions and to insure high biomass production.Different field trials have been conducted from 2013 to 2016 in Nyon, Switzerland to assess cover crop biomass production and stability, and their influence on the following crop. Indian mustard, field pea, black oat and phacelia were sown as sole crops and in mixtures with different diversity levels (2, 3 and 4 species). A mixture of 11 species (50% of legumes and 50% of other species) was also tested. Biomass production was assessed about three months after seeding, just before the seeding of the next main crop, in two 0.5 m × 0.5 m quadrats. For each cover crop, a risk of failure, e.g. the probability of producing less than 3 t/ha (minimal biomass allowing to provide the services expected from cover crops), was estimated. Weed pressure was appraised by weed biomass in quadrats. The yield of the following main crop, here winter wheat, was determined after harvesting with a combine harvester, at wheat maturity, in summer. Sole crops showed very contrasting performance according to the growing conditions. Pea was the most productive in low yielding conditions with 2 t/ha while other sole crops produced only 0.5 t/ha. Pea was barely more productive in high yielding conditions, reaching only 3 t/ha when cover crop average was 6 t/ha. By contrast, mustard and oat showed high production potential in these conditions, exceeding 7 t/ha. Pea should thus be favoured when the growing conditions are clearly identified as limiting (low N availability), while oat or mustard should be chosen in favourable conditions. However, in general, conditions are hardly predictable. Our results showed that mixtures should be preferred as they were adapted to a wider range of environments than sole crops, performing well regardless of the conditions and resulting in a lower risk of failure than sole crops. The 11-specie mixture revealed that generally 4 to 5 species are sufficient to insure a good performance regardless of the conditions. Regarding cover crop effect on the following crop, we evidenced the importance of high biomass production for efficient weed control and positive influence on crop yield in no till treatments.Our results showed that cover crop mixtures rather than sole crops should be chosen as they insure high biomass production and thus a good supply of ecosystem services. In addition, cover crop cultivation, even for a short period, proved to be paramount to the maintenance of grain yield and soil fertility on the long term, especially in reduced tillage systems

Cover Crops to Secure Low Herbicide Weed Control Strategies in Maize Grown with Reduced Tillage

As a key-element of conservation agriculture, the occasional or systematic suppression of full-inversion ploughing implies an adaptation of the cropping system. To assess the ability of cover crops to control weeds in a subsequent maize crop grown with reduced tillage, three annual experiments were implemented at the research station of Agroscope Changins, Nyon, Switzerland. Ten non-wintering cover crop (CC) species were sown in mid-summer and compared to a bare soil treatment in strip-plot experiments including different weeding strategies according to integrated weed management rules. In case of a predictable impasse for weed control, an alternative management option was chosen 1) at the end of winter: total herbicide application instead of no herbicide application, 2) at the beginning of May before maize sowing: minimum soil tillage instead of no tillage. The ability of cover crop species to control weed was evaluated at the stage 2-4 leaves of maize. The shoot dry matter yield of maize was measured at harvest at the end of August. At the beginning of November, mean CC dry shoot biomass varied between 1.2 and 11.1 t DM ha-1 depending on experimental year and CC species. On average over the three years, Asteraceae (Helianthusannuus and Guizotiaabyssinica) showed the highest shoot dry matter among the tested species (> 6.0 t DM ha-1). Legume species (Pisumsativum arvense, Trifolium alexandrinum and Vicia sativa) and Brassicaceae species (Brassicacampestrisoleifera and Raphanussativuslongipinnatus) presented the lowest 3-year mean shoot biomass (≤4.0 t DM ha-1) At the end of winter, the three legume species and Avenastrigosa showed the highest plant residue soil cover and Brassicaceae species the lowest one. CC residue soil cover at the end of winter was only slightly positively correlated with CC autumn shoot biomass. In three out of eight cases, the chosen weeding strategy was very efficient in terms of weed control at the stage 2-4 leaves of maize. In the remaining five cases, the weeding strategy did not succeed in preventing weed infestation at the beginning of maize development. A mean weed cover higher than 15% was observed when no total herbicide and/or no tillage was applied before maize sowing. In three out of these five cases, a significant CC effect on weed cover could be observed. CC species able to produce high amounts of biomass in autumn appeared to be useful in terms of weed control. The most efficient CC species varied from year to year: G. abyssinica in 2011, H. annuus in 2012 and A. strigosa in 2014. CC effect on maize yield was significant in a single case, but the effect of CC species tended to be positive compared to the control treatment without CC. Despite only partial efficacy, the use of cover crops is recommended for limiting weed incidence in cropping systems aimed at reducing soil tillage and herbicide use

Specific interactions leading to transgressive overyielding in cover crop mixtures

Growing mixtures of species instead of sole crops is expected to increase the ecosystem services provided by cover crops. This study aimed at understanding the interactions between species and investigating how they affect the performance of the mixture. Four species were combined in six bispecific mixtures in a field experiment. The performance of each species when grown in a mixture was compared to its performance as a sole crop at different sowing densities, to characterise the influence of intra- and interspecific competition for each species. Intra- and interspecific competition coefficients were quantified using a response surface design and the hyperbolic yield-density equation. Interactions between the four species ranged from facilitation to competition. Most of the mixtures exhibited transgressive overyielding. Without nitrogen (N) fertilisation, high complementarity between species allowed to achieve the highest biomass. With N fertilisation, high dominance of one mixture component should be avoided to achieve good performance. A revised approach in the use of the land equivalent ratio for the evaluation of cover crop mixtures is also proposed in this study. It allows to better identify transgressive overyielding in mixtures and to better characterise the effect of one species on the other within the mixture

Auswirkungen des letzten Nutzungstermins von Weiden im Herbst auf den Ertrag im darauf folgenden Frühling

The consequences of a late closing date in autumn on pasture performance in spring are mostly unknown under Mid-European climatic conditions. An experiment on two sites in the Swiss lowlands showed that a delay of the closing date from early October to late November reduced spring yield by 50% (238-821 kg DM/ha) in early April and 18% (556-986 kg DM/ha) in Mai. This reduction of spring yield was particularly high (up to 75%) if the residual herbage mass before winter was below 300-500 kg DM/ha. On the other hand residual herbage mass above this threshold did not increase spring yield considerably. Thus, the utilisation of pasture in late autumn is recommended, if conditions are favourable and if grazing does not reduce the residual herbage mass below 300-500 kg DM/ha, corresponding to a herbage height of 5-6 cm (plate pasture meter)

In situ TEM study of reduction and reoxidation of NiO/ceramic composites

Nickel/ceramic solid oxide fuel cell anodes exhibit a dimensional instability when experiencing a reduction-oxidation cycle. As fuel is supplied on the anode side, the as-sintered nickel oxide phase (NiO) reduces to metallic Ni and then remains in this state during operation. Yet, several factors may lead to an accidental reoxidation of the Ni, which may rupture parts of the cell, hence degrading its performance. The mechanisms behind the dimensional instability of Ni/yttria-stabilised zirconia (YSZ) anodes are investigated here through an innovative environmental transmission electron microscopy assessment. NiO particles and NiO/YSZ composites are reduced and reoxidised in the microscope in a few mbar of hydrogen and oxygen, respectively, up to 500-850 °C. Images, diffraction patterns, electron energy-loss spectra and energy-filtered micrographs are acquired, usually at constant temperature intervals during the reactions, to capture in situ the nanostructure, crystallography and chemistry. The reaction kinetics are retrieved from both the changes in shapes of the Ni L23 edges in energy-loss spectra and from energy-filtered images (with nm-resolution), analysed to provide quantitative data and correlated to the structure. Complementary data include post-exposure microscopy, in situ X-ray diffraction and density functional theory computations. While the surface nucleation of Ni domains, their growth and impingement control the reduction of NiO particles, the results reveal a modification of the mechanisms in the presence of yttria-stabilised zirconia, with the transfer of oxygen from NiO to the oxygen vacancies of the YSZ ceramic now triggering the reaction. Intragranular voids form in both cases as oxygen is removed. The final Ni structure at high temperature is then observed to coarsen as it minimises its surface energy, with the percolation of the Ni phase influenced by the symmetry of its grain boundaries. The reoxidation of Ni is controlled mainly by the outward diffusion of Ni ions through the grain boundaries of the growing NiO film. While some NiO inward growth occurs through the formation of oxide film cracks, the Ni2+ outward diffusion process remains unbalanced and voids form in the NiO phase. These internal voids are responsible for the dimensional instability of the composite along with Ni coarsening at high temperature. Several parameters for improved performance and redox tolerance are then identified based on these results

The Effect of Closing Date and Type of Utilisation in Autumn on Grass Yield in Spring

Due to the low cost of grazed grass, most dairy farmers extend the grazing period in autumn. However, delaying the closing date may reduce the grass yield in the following spring (Roche et al., 1996; O’Donovan et al., 2002). The objective of this experiment, conducted in the Swiss lowlands, was to quantify the effects of closing date and type of utilisation in autumn on grass yield in the following spring

Effect of species identity and diversity on biomass production and its stability in cover crop mixtures

Thanks to positive interactions between species, growing mixtures of cover crops allows improving the ecosystem services provided by cover crop cultivation. In this study, the influence of species diversity but also of species identity and mixture composition on cover crop biomass production and its stability in diverse growing conditions was studied. Several field experiments (varying soil type, preceding crop, soil tillage, sowing density, nitrogen fertilization and spatial replication) were set up in Switzerland during the period 2013−2016. In these experiments the performance of cover crop species grown as sole crops was compared to that of multispecific mixtures. Part of these experiments followed a simplex design in which four cover crop species were combined together with different proportions, producing a total of 25 mixtures of varied diversity. The other experiments compared sole crop and mixture biomass production in standard randomised block or split plot experiments. Globally, mixtures tended to produce slightly more biomass than the sole crops, with an average between 2 t/ ha and 3.2 t/ha for sole crops and of about 3.5 t/ha for mixtures. Overyielding as well as transgressive overyielding were observed, in 81% and 37% of the cases on average, respectively. However no effect of the level of species diversity within mixtures could be found. Biomass production of cover crops was highly influenced by their growing conditions and by the identity of the species involved, especially for sole crops and bispecific mixtures. The analyses of the simplex experiments allowed to show that species interactions played an important role in biomass production in 7 out of 15 growing conditions, even for a short growing period of about three months. Most of the cover crop mixtures with the highest biomass production had a rather low diversity, i.e. about two species on average, but the identity of the species involved in these mixtures depended on the growing conditions. Our results do not show a strong diversity effect on the biomass production of cover crop mixtures cultivated for a short growing period, but a stronger effect of species identity and of the growing conditions. Mixtures with low diversity generally outcompete more diverse mixtures, but more diverse mixtures offer an insurance effect given the unpredictability of growing conditions during cover crop cultivation

Correlation of fluorescence microscopy, electron microscopy, and NanoSIMS stable isotope imaging on a single tissue section.

Correlative light and electron microscopy allows localization of specific molecules at the ultrastructural level in biological tissue but does not provide information about metabolic turnover or the distribution of labile molecules, such as micronutrients. We present a method to directly correlate (immuno)fluorescent microscopy, (immuno)TEM imaging and NanoSIMS isotopic mapping of the same tissue section, with nanometer-scale spatial precision. The process involves chemical fixation of the tissue, cryo sectioning, thawing, and air-drying under a thin film of polyvinyl alcohol. It permits to effectively retain labile compounds and strongly increases NanoSIMS sensitivity for 13C-enrichment. The method is illustrated here with correlated distribution maps of a carbonic anhydrase enzyme isotype, β-tubulin proteins, and 13C- and 15N-labeled labile micronutrients (and their anabolic derivates) within the tissue of a reef-building symbiotic coral. This broadly applicable workflow expands the wealth of information that can be obtained from multi-modal, sub-cellular observation of biological tissue