Search

Introduction: Cover crop services depend on biomass production and species composition of the cover crop stand. In this study, we investigated the interactions in shoot biomass of dual cover crop mixtures and their competitiveness to suppress weeds before winter under different growing conditions. Methods: A field experiment was performed on sandy loam soil in Triesdorf, Germany, for two consecutive years. The cover crop species white mustard (Sinapis alba L.), oil radish (Raphanus sativus var. oleiformis L.), phacelia (Phacelia tanacetifolia J.), Egyptian clover (Trifolium alexandrinum L.), common vetch (Vicia sativa L.), field pea (Pisumsativum L.), and field bean (Vicia faba L.) were grown in pure stands or dual mixtures. Cover crops were sown in August, and shoot biomass was harvested at the end of the vegetation period. Cover crop shoot biomass was dried, and the share of each species and the sown test weed (Brassica napus L.) were determined. Results: The share of shoot biomass of a cover crop species in dual-species mixtures was closely related to its shoot biomass in its pure stand. In both years, mustard and phacelia showed similar interactions in shoot biomass production when growing with a second species. Regarding competitiveness against weeds, cruciferous species outperformed other cover crop species and could suppress weeds even if they were mixed with a less competitive partner. Weed suppression of mixtures with phacelia depended on the second component in the mixture and was more effective in a dry season. Legume species, especially Egyptian clover and common vetch could not suppress weeds in a pure stand. Discussion: Our results show that species with high weed suppression potential as single stands retain this ability in dual cover crop mixtures, regardless of the suppression potential of the second species that completes the mixture. [ABSTRACT FROM AUTHOR]

Soil structure is sensitive to intensive soil management. It can be ameliorated by a reduction in soil cultivation and stimulation of plant and microbial mediators for aggregate formation, latter a prerequisite and measure for soil quality. Cover crops (CC) are part of an integrated approach to stabilize or improve soil quality. Thereby, the incorporation of diverse CC mixtures is hypothesized to increase the positive effects of CC applications. This study entailed an investigation of the legacy effect of CC on soil aggregates after three crop rotations in the second main crop (winter wheat) after the last CC treatment. Four CCs (mustard, phacelia, clover, and oat) cultivated in pure stands and a fallow treatment were compared to a mixture of the four CC species (Mix4) and a highly diverse 12 plant species mixture (Mix12) in a long-term field experiment in Germany. The organic carbon (OC) distribution within macroaggregate fractions (16–8, 8–4, 4–2, 2–1 and < 1 mm) and their aggregate stability were measured by dry and wet sieving methods, and the mean weight diameter (MWD) was calculated from water-stable aggregates. The results showed that compared to the fallow, all CCs increased the MWD between 10 and 19 % in soil under the following main crop. The average MWD increase over the fallow was slightly higher for CC mixtures (16 %) than for single CCs (12 %). Higher MWD improvement at the 20–30 cm depth also indicates additional benefits from a reduction in the cultivation depth. Structural equation modelling (SEM) suggests that single CCs were more likely to increase OC storage in small macroaggregates < 1 mm, while CC mixtures were more likely to increase OC in the largest fraction (8–16 mm). Different individual CC species or mixtures exhibited a varying involvement in the formation of different aggregate fractions. We provide evidence that litter quality, root morphology and rhizosphere input, which affect microbial mediators of aggregate formation, might be the main reasons for the observed differences between CC treatments. Cover crops are valuable multifunctional tools for sustainable soil management. Here, we showed that they contribute to structure amelioration in arable soils. Increasing the functional diversity of plant species in CC mixtures could be a strategy to further enhance the positive effects of CC in agroecosystems. [ABSTRACT FROM AUTHOR]

Phytomining comprises a promising chance to improve the supply of Ge and REEs as raw materials. Efficiency of the phytoextraction process depends on root-soil-interactions affecting the availability of the elements in the rhizosphere. Until today, data on effects of rhizosphere processes on the availability of these target elements from soils to plants are very scarce. The aim of the present study was to evaluate the variability in the accumulation of Ge and REEs in different genotypes of Phalaris arundinacea in order to identify below-ground functional root traits affecting the availability of the target compounds. In a three-year field experiment 20 genotypes of Phalaris arundinacea were cultivated on four substrates with similar element concentrations but differing organic matter contents (SOM 5.5 – 9%) and pH-values (pH 6.6 – 8). On each of the substrates each genotype was cultivated on plots (4 m2 each) with two replications. Subsequently, two genotypes with highest and lowest concentrations were selected and cultivated in a greenhouse experiment on soil and sand in order to elucidate genotypic variability in the uptake-efficiency among genotypes and mobilization of the elements in the rhizosphere. For the experimental setup we used pots filled with either 1.8 kg of quartz sand or soil (pH(H2O) = 6.2; SOM = 7.6%, Ge (total) 1.8 µg g-1; La 26.6 µg g-1, Nd 23.9 µg g-1, Gd 4. µg g-1, Er 2.5 µg g-1). Over a growth-period of four weeks all soil-grown plants received 100 ml of nutrient solutions without elements. Sand-cultured plants received 10 µmol l-1 Ge and REEs 24 h before harvest or nutrient solutions as a reference. Element concentrations in all plant samples were analyzed by ICP-MS. Considering all substrates, we found a genotypic variation in the accumulation of Ge and REEs in shoots, with average concentrations for Ge ranging from 0.03 – 0.95 µg g-1 and REEs (sums over all 16 elements) ranging from 0.02 – 5.7 µg g-1. Slightly acidic soil conditions (B2: pH 6.6.; SOM: 8%) and organic fertilizer treatment significantly increased the uptake of Ge and REEs in some genotypes, while others showed no response to changes in SOM and pH, most probably as a result of phenotypic plasticity. As a result of the greenhouse experiment we found that both, differences in the uptake efficiency of the genotypes as well as different efficiencies in the mobilization of the elements in the rhizosphere of soil-grown genotypes affects the accumulation of Ge and REEs in the shoot biomass (concentrations and amount of elements per unit area). Ongoing studies aim to identify the processes involved and cross-breed those genotypes with the highest accumulation of target compounds in order to establish a new strain of RGG most suitable for phytomining of these target compounds.These studies have been carried out in the framework of the Phalaris II project financed by the Federal Ministry of Food and Agriculture, Germany. The author is grateful to project partner DSV for supply of genotypes and laboratory assistants contributing in field work and sample preparation. [ABSTRACT FROM AUTHOR]