Inga Dirks, Juliane Streit, Catharina Meinen (2021): Above and Belowground Relative Yield Total of Clover–Ryegrass Mixtures Exceed One in Wet and Dry Years. Agriculture, 11, 206, https://doi.org/10.3390/-agriculture11030206
Grassland mixtures hold the potential for increasing biomass and productivity. In a ﬁeld experiment, monocultures and mixtures of eight white clover (Trifolium repens L.) genotypes and perennial ryegrass (Lolium perenne L.) were analyzed over three years (2015, 2016, and 2018) for their species-speciﬁc aboveground and belowground biomass. Roots were analyzed by Fourier transform infrared (FTIR) spectroscopy to identify species-speciﬁc root mass, vertical distribution, and belowground relative yield total (RYT). Aboveground biomass decreased strongly from 2015 to 2018. Aboveground and belowground RYT were always signiﬁcantly higher than one. Aboveground biomass overyielded in 2016 and 2018 compared to monocultures. Monocultures of perennial ryegrass displayed a signiﬁcantly higher proportion of roots in shallow soil layers than white clover in two of the three examined years. In mixtures, these differences in vertical root distribution between both species were not present and perennial ryegrass, and white clover occupied similar vertical niches in 2015 and 2016. Interestingly, in the dry year 2018, white clover had a higher proportion of roots in shallow soil layers than perennial ryegrass in mixtures.
Vanessa Bonke, Marius Michels, Oliver Musshoff (2021): Will farmers accept lower gross margins in exchange for sustainable cultivation methods? – First insights for mixed cropping in Germany. Sustainability, 13, 1631. https://doi.org/10.3390/su13041631
A decline in the legume cultivation has contributed to the biodiversity loss within the agricultural production across Europe. One possibility to include legumes into the production and promote sustainability is mixed cropping with legumes and nonlegumes. However, the adoption of mixed cropping is challenging for farmers and information about the profitability is scarce. If mixed cropping should become a widely established production method, it is essential to gain an understanding of famers’ evaluation of the profitability mixed cropping needs to reach. Therefore,
this article provides first empirical insights into farmers stated willingness to accept gross marginchanges compared to current production possibilities. Based on a survey with results from 134 German nonadopters conducted in 2018 we can distinguish conventional farmers with a positive, neutral and negative willingness to accept reductions in gross margins as the tradeoff for ecological benefits. Using an ordered logistic model we find that risk attitude, risk perception, the number of
measures performed for ecological focus areas, the farmer’s age and being located in the south of Germany influence their willingness to accept gross margin changes compared to currently produced cereals.
Vanessa Bonke, Oliver Musshoff (2020): Understanding German farmer’s intention to adopt mixed cropping using the theory of planned behavior. Agronomy for Sustainable Development, 40(48), 1-14. https://doi.org/10.1007/s13593-020-00653-0
The diversification of cropping systems has the potential to contribute towards a sustainable land use while preserving biodiversity. Mixed cropping is one possibility to increase biodiversity within farming systems. However, adoption of mixed cropping systems is challenging for farmers, as the agricultural sector has evolved around pure stands over the past decades and path dependencies have emerged. Yet, little is known about farmers’ motivation to adopt mixed cropping. Utilizing the theory of
planned behavior as the main framework, this paper studies the psychological factors underlying farmers’ intention to adopt mixed cropping based on an online survey with 172 German farmers. In addition, the most crucial adoption obstacles are assessed. Using partial least squares structural equation modeling, we show for the first time that attitude, perceived behavioral control, and injunctive as well as descriptive group norms explain over 52% of farmers’ intention to adopt mixed cropping. Our
results also demonstrate that perceived ecological benefits positively influence a farmer’s attitude towards mixed cropping. Missing sales opportunities for mixed yields, the uneven maturing of crops, and deficient economic benefits are ranked as the most crucial obstacles for the implementation of mixed cropping. These results, which can be relevant for other European countries as well, indicate that the introduction of a voluntary agri-environmental scheme could encourage adoption and that
considering positive effects of group norms within policy schemes could further increase adoption on a large scale.
Oleksandra Kuchma, Dennis Janz, Ludger Leinemann, Andrea Polle, Konstantin Krutovsky, Oliver Gailing (2020): Hybrid and Environmental Effects on Gene
Expression in Poplar Clones in Pure and Mixed with Black Locust Stands. Forests, 11, 1075; doi:10.3390/f11101075
Mixed cropping might be seen as an alternative to monocultures by better protecting biodiversity and improving ecosystem services and resources. In the presented study, we tested the
genetic and ecological effects of pure and mixed propagation of different poplar hybrids planted together with black locust trees. Poplar (Populus) hybrids are widely used for bioenergy in monoculture systems due to their rapid and high biomass production. Black locust (Robinia pseudoacacia L.) is a species with the ability to fix nitrogen and seen as a promising candidate for mixed cultivation. Eight different poplar hybrids and black locust trees from three provenances planted in two study sites with different environmental conditions were tested in varying combinations in pure and mixed stands to observe effects of the different hybrids and genotypes, site conditions and the mixed growing on the performance of poplar and its gene expression. Transcriptome analyses of leaves from four poplar clones selected according to their divergent growth performance were conducted to study differential gene expression that can be an important indicator of differences in growing conditions and success. Differences in gene expression were most pronounced among hybrids and different genotypes of the same hybrid, followed by the study site influence, and were least pronounced between mixed and pure stands. The genotypes of the same hybrid were clearly separated from each other. Clear separation between the study sites for all clones was also observed. Only a few genes were differently expressed in pure vs. mixed stand comparisons for each clone, but there were no common genes that were differently expressed in pure vs. mixed stands in all clones. In total, 199 genes showed differential expression between the study sites regardless of poplar clone or type of stands. The analysis suggested that plant genotypes and environmental conditions were more important at the early stage of stand development than pure or mixed cultivation.
Jessica Rebola-Lichtenberg, Juliane Streit, Peter Schall, Christian Ammer, Dominik Seidel (2020): From facilitation to competition: the effect of black locust
(Robinia pseudoacacia L.) on the growth performance of four poplar‑hybrids (Populus spp.) in mixed short rotation coppice. New Forests.https://doi.org/10.1007/s11056-020-09813-2
Short rotation coppices play an important role in providing biomass for energetic use. Mixing fast-growing tree species in short rotation coppices may show complementarity effects
and increased yield. The aim of this study was to analyze the effect of species interaction in mixed short rotation coppices with fast-growing Populus spp.-hybrids and the N-fixing
Robinia pseudoacacia. Four different Populus-hybrids (AF2, Fritzi Pauley, Hybride 275 and Max 1), planted alternately in pure and mixed stands with R. pseudoacacia were
used for the analysis. Height and root collar diameter were measured once a year, over a period of four years (2014–2017). Additionally, in the third year, aboveground competition
was surveyed with a terrestrial laser scanner and root biomass was analyzed to assess belowground competition. Soil nitrogen was also determined in order to verify enrichment
properties of mixtures compared to pure stands. Populus-hybrids’ stem volume showed no significant differences between stand types in the first year after planting. In the second
and third year, however, two Populus-hybrids (AF2 and Max 1) had a higher stem volume increment of up to 3.8 times than stem volume increment in pure stands. This may
be related to the fact that soil nitrogen was 39% higher in the mixtures than in pure stands. However, in the 4th year after stand establishment, R. pseudoacacia’s crowns were so massive
and broad, that this species was far more competitive than the Populus-hybrids. With the exception of P. ‘Fritzi Pauley’, which showed no significant differences between stand
types, growth rates reversed for the other three Populus-hybrids. AF2, Max 1 and Hybride 275 showed up to 75% lower stem volume increment in mixtures compared to pure stands.
We assume that, in spite of the initially observed facilitation between the species, the competition exerted by R. pseudoacacia started dominating after 4 years and began to surpass
the benefits of facilitation.
Sara Heshmati, Bettina Tonn, Johannes Isselstein (2020): White clover population effects on the productivity and yield stability of mixtures with perennial ryegrass and chicory. Field Crops Research. https://doi.org/10.1016/j.fcr.2020.107802
Due to complementary resource use of the components, grass-clover mixtures are usually higher yielding compared to unfertilized pure grass stands. The number and identity of species in a mixture are known as important factors for the mixture’s productivity. How intraspecific variability of component species affects the productivity of mixtures has received less attention. We established an experiment to investigate how and to what extent different populations of white clover (Trifolium repens L.) affect mixture performance. Eight novel populations of white clover and one variety of perennial ryegrass (Lolium perenne L.) and chicory (Cichorium intybus L.) were grown as monocultures and in two- and three-species mixtures at two sites differing in soil fertility. Aboveground herbage was cut twice in the establishing year and four times in each of the three following years. The accumulated dry matter yield was calculated as the sum of the four annual dry matter yields. There was no significant interaction between white clover population and crop stand (i.e., white clover monoculture or mixtures with partner species) on dry matter yield accumulated over four years; the white clover population that performed well in monoculture also did so in mixtures. At both sites, the binary mixtures of white clover and chicory produced significantly higher dry matter yields than the white clover monocultures and other mixtures. Inclusion of chicory in mixtures significantly increased the stability of yield production as well. Site conditions strongly affected the performance of the forage species mixtures. We found that the benefit of mixtures over monocultures was more related to the identity of species in mixture than to the white clover population.
Jessica Rebola-Lichtenberg, Peter Schall, Peter Annighöfer, Christian Ammer, Ludger Leinemann, Andrea Polle, Dejuan Euring (2019): Mortality of Different Populus Genotypes in Recently Established Mixed Short Rotation Coppice with Robinia pseudoacacia L. Forests, 10, 410; https://doi.org/10.3390/f10050410
Short rotation coppices play an increasing role in providing wooden biomass for energy. Mixing fast-growing tree species in short rotation coppices may result in complementary effects and
increased yield. The aim of this study was to analyze the effect on mortality of eight different poplar genotypes (Populus sp.) in mixed short rotation coppices with three different provenances of the N-fixing tree species black locust (Robinia pseudoacacia L.). Pure and mixed stands were established at two sites of contrasting fertility. Survival of poplar was assessed for each tree two times a year, for a period of three years. In the first two years, high variation in mortality was observed between the genotypes, but no significant differences between pure and mixed stands were identified. However, three years after planting, higher mortality rates were observed in the mixtures across all poplar genotypes in comparison to pure stands. The expected advantage on growth of combining an N-fixing tree with an N-demanding tree species, such as poplar, was overshadowed by the Robinia’s dominance and competitiveness.
Juliane Streit, Catharina Meinen & Rolf Rauber (2019): Intercropping effects on root distribution of eight novel winter faba bean genotypes mixed with winter wheat. Field Crops Res. 235, 1-10. https://doi.org/10.1016/j.fcr.2019.02.014
The spatial root distribution of plant species is generally altered by intra- and interspecific competition. The assessment of species specific root distribution in intercrops was limited so far because of the difficulties to identify roots on a species level. We investigated horizontal and vertical root distribution of eight winter faba bean genotypes (Vicia faba L.) and one winter wheat cultivar (Triticum aestivum L.) grown in sole stands and in 50/50 substitutive row intercrops.
Root samples were taken within and between rows with a root auger down to 60 cm soil depth in May 2015 and May 2016 at a field site in central Germany. We used Fourier transform infrared (FTIR) spectroscopy for root species identification. Vertical root distribution was described by the equation y=1 - βd according to Gale and Grigal (1987).
Horizontal root distribution did not differ between bean and wheat and between sole stands and intercrops averaged across the eight bean genotypes: Bean and wheat root biomass was on average 65% lower between rows than within rows in sole stands and in intercrops. Both species proliferated into the soil space between the rows and into the intercropping partner’s row to a similar extent. Bean developed 36% of its root biomass in 0–10 cm soil depth, while wheat had 51%. Bean and wheat had shallower roots within their own row in intercrops (βbean=0.933; βwheat=0.858) compared to their own row in sole stands (βbean=0.945; βwheat=0.902). In the intercrops both species occupied deeper soil layers within their partner’s row (βbean=0.947; βwheat=0.960) compared to their own row (βbean=0.933; βwheat=0.858). This change in vertical root distribution was more pronounced for wheat than for bean. Bean genotypes grown in sole stands did not differ in their horizontal and vertical root distribution. However, there were significant differences between bean genotypes within wheat rows in the intercrops: bean genotype Vf6 had the largest horizontal spread but the most shallow root growth within the wheat row, while Vf5 showed the lowest horizontal spread and the highest root fractions in deep soil layers within the wheat row. The alteration of the vertical root distribution of both species in intercrops, compared to the sole crops, could lead to a better resource utilization and an intercrop advantage.
Juliane Streit, Catharina Meinen, William Nelson, Daniel Siebrecht-Schöll, Rolf Rauber (2019): Above- and belowground biomass in a mixed cropping system with eight novel winter faba bean genotypes and winter wheat using FTIR spectroscopy for root species discrimination. Plant Soil, https://doi.org/10.1007/s11104-018-03904-y
Legume-cereal mixtures are often characterized by higher biomass and grain yields compared to their sole crop equivalents due to complementary resource use. Little is known about the contribution of the root system to this overyielding potential and the related cultivar differences. This study investigated pure stands and mixtures of eight winter faba bean (Vicia faba L.) genotypes and one winter wheat cultivar (Triticum aestivum L., cv. Genius) with regard to their intra- and interspecific variation of shoot and root biomass and overyielding potential at full flowering of the bean. Shoot biomass of 1 m2 was harvested and roots were sampled with a root auger down to 0.6 m soil depth in two sampling years. Fourier transform infrared (FTIR) spectroscopy was successfully used to determine species specific root biomasses in mixtures. Statistics were performed using linear mixed effects models. Mixtures of winter faba bean and winter wheat overyielded more below- than aboveground. Bean genotypes grown in mixtures with wheat differed significantly in their root biomass, root:shoot ratio and overyielding potential but not in their shoot biomass. Genotype differences in root biomass and overyielding indicate breeding potential of winter faba bean cultivars for mixed cropping.
Edith Rapholo, Jude J. O. Odhiambo, William C. D. Nelson, Reimund P. Rötter, Kingsley Ayisi, Marian Koch,Munir P. Hoffmann (2019): Maize–lablab intercropping is promising in supporting the sustainable intensification of smallholder cropping systems under high climate risk in southern Africa. Experimental Agriculture, 1–14, doi:10.1017/S0014479719000206
Identifying options for the sustainable intensification of cropping systems in southern Africa under prevailing high climate risk is needed. With this in mind, we tested an intercropping system that combined the staple crop maize with lablab, a local but underutilised legume. Grain and biomass productivity was determined for four variants (i) sole maize (sole-maize), (ii) sole lablab (sole-lablab), (iii) maize/lablab with both crops sown simultaneously (intercropped-SP) and (iv) maize/lablab with lablab sown 28 days after the maize crop (intercropped-DP). Soil water and weather data were monitored and evaluated. The trial was conducted for two seasons (2015/2016 and 2016/2017) at two sites in the Limpopo Province, South Africa:
Univen (847 mm rainfall, 29.2 °C maximum and 18.9 °C minimum temperature average for the cropping season over the years 2008–2017) and Syferkuil (491 mm rainfall, with 27.0 °C maximum and 14.8 °C minimum temperature). Analysis revealed three key results: The treatment with intercropped-SP had significantly lower maize yields (2320 kg ha−1) compared with maize in intercropped-DP (2865 kg ha−1) or sole-maize (2623 kg ha−1). As expected, maize yields in the El Ni˜no affected in season 2015/2016 were on average 1688 kg ha−1 lower than in 2016/2017. Maize yields were significantly lower (957 kg ha−1) at Univen, the warmer site with higher rainfall, than at Syferkuil. In 2015/2016, maximum temperature at Univen exceeded 40 °C around anthesis. Furthermore, soil water was close to the estimated permanent wilting point (PWP) for most of the cropping season, which indicates possible water limitations. In
Syferkuil, the soil water was maintained well above PWP. Lablab yields were low, around 500 ha−1, but stable as they were not affected by treatment across season and site. Overall, the study demonstrated that intercropped-DP appears to use available soil water more efficiently than sole maize. Intercropped-DP could therefore be considered as an option for sustainable intensification under high climate risk and resource-limited conditions for smallholders in southern Africa.
Nelson, W.C.D, M.P. Hoffmann, V. Vadez, R.P. Roetter, A.M. Whitbread (2018): Testing pearl millet and cowpea intercropping systems under high temperatures. Field Crops Research 217 150–166. https://doi.org/10.1016/j.fcr.2017.12.014
With the potential threat of more frequent climate extremes putting semi-arid crop production in jeopardy, there is a need to establish more climate resilient cropping practices. Intercropping is often practiced by farmers in semi-arid regions and is perceived as a risk reducing practice. However, there is little knowledge of how and to what extent it can be a viable option under future conditions. As testing a complex adaptation strategy in controlled environments is difficult, conducting field experiments in the dry season offers opportunities to test cropping systems under extreme but real-world conditions. Consequently, a field trial was run in semi-arid India over a two-year period (2015 and 2016) in the dry and hot (summer) season. These trials were set up as a splitsplit- plot experiment with four replicates to assess the performance of simultaneously sown sole versus intercropped stands of pearl millet and cowpea, with two densities (30 cm and 60 cm spacing between rows - both with 10 cm spacing within rows), and three water treatments (severe stress, partial stress, and well-watered) applied with drip irrigation. Results showed that intercropping pearl millet led to a significantly lower total grain yield in comparison to the sole equivalent. Pearl millet’s highest yields were 1350 kg ha−1 when intercropped and 2970 kg ha−1 when grown as a sole crop; for cowpea, 990 kg ha−1 when intercropped, and 1150 kg ha−1 as a sole crop. Interestingly, even when maximum daily temperatures reached up to 42.2 °C (on Julian day 112 in 2016), well-watered, pearl millet produced reasonable yields. Cowpea yields were often lower than 1000 kg ha−1. Only under the highest irrigation treatment (well-watered) sole cropped, low density were yields of 1150 and 1110 kg ha−1 achieved in 2015 and 2016, respectively. We conclude that successful intercropping systems must be highly specific to conditions and demands. More research would be needed to identify suitable cowpea genotypes and planting densities that could allow for higher intercropped pearl millet yields.
Corsa Lok Ching Liu, Oleksandra Kuchma, Konstantin V. Krutovsky (2018): Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future. Global Ecology and Conservation 15 e00419
Plantation forests are increasing rapidly in the world in order to alleviate deforestation and degradation of natural forests, along with providing various goods and services. While monoculture plantations have been the dominant type of plantation in practice and wellrecorded in research, in the face of intensifying climate change and resource scarcity, there is a growing interest in mixed-species plantations. Agroforestry systems are also catching the attention of foresters, smallholders and landowners. However, there are relatively limited number of studies on successful species mixtures. This paper first reviews the progression of monocultures and mixed-species, followed by the comparisons of advantages, disadvantages and effects on the surrounding natural ecosystems between these two types of plantations. The paper further investigates combinations of species with complementary traits for efficient use of limiting resources associated with improvement in growth development and production of tree species, as well as examining some other challenges in mixed-species. In addition, it is helpful to select and combine tree/crop species in mixtures based on complementary traits that maximise positive and minimise negative interactions and using the advance molecular technologies for genetic analysis. With careful design and proper management, mixed-species plantations with two, three or four species can be more productive and have more advantages in biodiversity, economy and forest health over monocultures. Many researchers are still working on different projects to explore the potential benefits and to promote the applications of mixed-species plantations and agroforestry.
Sandra Granzow, Kristin Kaiser, Bernd Wemheuer, Birgit Pfeiffer, Rolf Daniel, Stefan Vidal and Franziska Wemheuer (2017): The Effects of Cropping Regimes on Fungal and Bacterial Communities of Wheat and Faba Bean in a Greenhouse Pot Experiment Differ between Plant Species and Compartment. Front. Microbiol. 8:902. doi: 10.3389/fmicb.2017.00902
Many bacteria and fungi in the plant rhizosphere and endosphere are beneficial to plant nutrient acquisition, health, and growth. Although playing essential roles in ecosystem functioning, our knowledge about the effects of multiple cropping regimes on the plant microbiome and their interactions is still limited. Here, we designed a pot experiment simulating different cropping regimes. For this purpose, wheat and faba bean plants were grown under controlled greenhouse conditions in monocultures and in two intercropping regimes: row and mixed intercropping. Bacterial and fungal communities in bulk and rhizosphere soils as well as in the roots and aerial plant parts were analyzed using large-scale metabarcoding. We detected differences in microbial richness and diversity between the cropping regimes. Generally, observed effects were attributed to differences between mixed and row intercropping or mixed intercropping and monoculture. Bacterial and fungal diversity were significantly higher in bulk soil samples of wheat and faba bean grown in mixed compared to row intercropping. Moreover, microbial communities varied between crop species and plant compartments resulting in different responses of these communities toward cropping regimes. Leaf endophytes were not affected by cropping regime but bacterial and fungal community structures in bulk and rhizosphere soil as well as fungal community structures in roots. We further recorded highly complex changes in microbial interactions. The number of negative inter-domain correlations between fungi and bacteria decreased in bulk and rhizosphere soil in intercropping regimes compared to monocultures due to beneficial effects. In addition, we observed plant species-dependent differences indicating that intra- and interspecific competition between plants had different effects on the plant species and thus on their associated microbial communities. To our knowledge, this is the first study investigating microbial communities in different plant compartments with respect to multiple cropping regimes Granzow et al. Cropping Regimes and Microbial Communities using large-scale metabarcoding. Although a simple design simulating different cropping regimes was used, obtained results contribute to the understanding how cropping regimes affect bacterial and fungal communities and their interactions in different plant compartments. Nonetheless, we need field experiments to properly quantify observed effects in natural ecosystems.
Dominic Lemken, Mandy Knigge, Stephan Meyerding and Achim Spiller (2017): The Value of Environmental and Health Claims on New Legume Products: A Non-Hypothetical Online Auction. Sustainability 2017, 9, 1340; doi:10.3390/su9081340
Legumes are valued in agricultural systems, as they can contribute to a more sustainable land use. However, their economic value is low. Despite health and environmental benefits, marketers struggle to communicate the worth of legumes to consumers. We evaluate the worth of health and, in particular, environmental claims that would spread consumers’ awareness of ecological advantages.Utilizing a large consumer sample, we execute binding online auctions. Comparing claim-treated and untreated subjects (between design), we model the price premium that potential customers are willing to pay (WTP) for having pasta in a legume instead of a wheat version. We find that claims may increase the WTP, however, a mix of environmental and health claims is superior to individual claims. Effect sizes suggest that the mix of claims increases the WTP by roughly 35% (20 cents). The link of WTP and food attitudes, such as concern for health in eating habits or social reservations towards legumes, varies depending on whether the green-pea or chickpea pasta was evaluated. A critical perception of legumes’ association with flatulence reduces the WTP. Developing the online auction may enable researchers to increase the external validity of consumer samples. We discuss implications for researchers and marketers.
Dominic Lemken, Achim Spiller, Marie von Meyer-Höfer (2017): The Case of Legume-Cereal Crop Mixtures in Modern Agriculture and the Transtheoretical Model of Gradual Adoption. Ecological Economics 137 (2017) 20–28
Mixed cropping (MC), the growing of two or more coexisting crops in one field, specifically the mix of cereal and grain legumes, can contribute to a more sustainable agricultural land use. Despite a variety of ecological benefits and promising grain productivity, applications are scarce among farmers in developed countries. In consideration of MC's potential this study interviews farm managers to profile characteristics of adopters. The transtheoretical model (TTM) is applied to capture adoption and adoption tendencies. The results point to a significant positive role of land owned vs. leased, adoption of reduced tillage and adoption intensity of legumes in general. The perception of technical barriers and the perception of MC's usefulness are also major drivers that proponents need to address. In general, the TTM provides a gradual measure of farmer's willingness to adopt, leading to more variance than binary classifications,which makes TTM especially useful to adoption research of marginalized ecological practices.
Mehmet Senbayram, Christian Wenthe, Annika Lingner, Johannes Isselstein, Horst Steinmann,
Cengiz Kaya and Sarah Köbke (2016): Legume-based mixed intercropping systems may lower agricultural born N2O emissions. Energy, Sustainability and Society (2016) 6:2 DOI 10.1186/s13705-015-0067-3
Background: The area used for bioenergy crops (annual row crops (e.g., wheat, maize), herbaceous perennial grasses, and short-rotation woody crops (e.g., poplar)) is increasing because the substitution of fossil fuels by bioenergy is promoted as an option to reduce greenhouse gas (GHG) emissions. However, biomass used for bioenergy production is not per se environmentally benign, since bioenergy crop production is associated with negative side effects such as GHG emissions from soil (dominated by N2O). N2O emissions vary greatly in space and time; thus, direct comparison of soil N2O fluxes from various agro-ecosystems is certainly crucial for the assessment of the GHG reduction potential from energy crops.
Methods: Therefore, our study aimed to evaluate the two different agro-ecosystems (cropland and agro-forestry) cultivated in central Germany for their environmental impact. In a 1-year field experiment, we compared N2O fluxes from cropland (non-fertilized wheat, N-fertilized wheat, non-fertilized faba bean, and wheat mixed intercropping with faba bean) and agro-forestry (non-fertilized poplar, N-fertilized poplar, non-fertilized Robinia, and poplar mixed intercropping with Robinia) as a randomized split-block design.
Results: Rainfall at the field site was slightly over average during the period from 1 April to 1 July in 2014 (201 mm rain) and considerably below average during the same period in 2015 (100 mm rain). Cumulative mean N2O fluxes were up to five fold higher in agro-forestry than in arable crop treatments during 2014 growing period. We hypothesized that the difference in N2O emissions when comparing arable land and agro-forestry was mainly due to the limited water and nutrient uptake of plantations during the first year. Among the arable crops (wheat, N-fertilized wheat, wheat mixed intercropped with bean, and bean), seasonal and annual N2O emissions were highest in soils when faba bean was grown as a mono-crop. On the other hand, cumulative mean N2O fluxes were 31 % lower (p < 0.05) when faba bean mixed with wheat than in soils planted with N-fertilized wheat.
Conclusions: The latter clearly suggests that using legume crops as intercrop or mixed crop in wheat may significantly mitigate fertilizer-derived N2O fluxes and may be an effective proxy for increasing GHG emission savings for energy crops.