Abstract
The cultivation of perennial biomass plants on marginal soils can serve as a sustainable alternative to conventional biomass production via annual cultures on fertile soils. Sida hermaphrodita is a promising species to be cultivated in an extensive cropping system on marginal soils in combination with organic fertilization using biogas digestates. In order to enrich this cropping system with nitrogen (N) and to increase overall soil fertility of the production system, we tested the potential of intercropping with leguminous species. In a 3-year outdoor mesocosm study, we intercropped established S. hermaphrodita plants with the perennial legume species Trifolium pratense, T. repens, Melilotus albus, and Medicago sativa individually to study their effects on plant biomass yields, soil N, and above ground biomass N. As a control for intercropping, we used a commercial grass mixture without N2-fixing species as well as a no-intercropping treatment. Results indicate that intercropping in all intercropping treatments increased the total biomass yield, however, grass species competed with S. hermaphrodita for N more strongly than legumes. Legumes enriched the cropping system with fixed atmospheric nitrogen (N2) and legume facilitation effects varied between the legume species. T. pratense increased the biomass yield of S. hermaphrodita and increased the total biomass yield per mesocosm by 300%. Further, the total above ground biomass of S. hermaphrodita and T. pratense contained seven times more N compared to the mono-cropped S. hermaphrodita. T. repens also contributed highly to N facilitation. We conclude that intercropping of legumes, especially T. pratense and T. repens can stimulate the yield of S. hermaphrodita on marginal soils for sustainable plant biomass production.
Highlights
Cultivation of biomass crops on marginal soils requires careful design, establishment and maintenance of suitable cropping systems (Spiertz, 2013; Solinas et al, 2015)
Intercropping with the legumes M. sativa and M. albus did not result in changes of the S. hermaphrodita biomass, but increased significantly the total biomass yields per mesocosm by 100–200%
Intercropping of S. hermaphrodita with T. pratense and T. repens increased significantly the biomass yield of S. hermaphrodita by 8-15% compared with S. hermaphrodita mono-cropping, but T. repens delivered the least additional biomass of all intercropped species
Summary
Cultivation of biomass crops on marginal soils requires careful design, establishment and maintenance of suitable cropping systems (Spiertz, 2013; Solinas et al, 2015). Marginal soils lack the nutrient resources necessary to provide a certain minimal productivity for plant biomass production and require a more costly input than what can be recovered by the output (European Environmental Agency, 2015) Such soils may be sandy, rocky, shallow, low. Due to their long-lasting nature, roots of perennials store energy and N during dormant periods and re-sprout early in the following growing season, allowing for high nutrient use-efficiency and recycling of N over time (Millard and Grelet, 2010; Voigt et al, 2012) Such N remobilization traits would be attractive options during the selection of plant species for biomass production on marginal soils
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