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Multifunctional land use systems, such as agroforestry, are able to deliver several ecological services to agriculture in addition to the concurrent production of woody biomass and arable crops. For example, trees in agroforestry systems can provide shelter for wildlife and supply additional nutrients to adjacent arable fields through leaf litter inputs and fine root turnover. In addition, tree-strips have the ability to improve the groundwater quality underneath the tree-strip itself and possibly underneath adjacent fields. Unlike these commonly measured ecosystem services the microclimate conditions in temperate agroforestry systems are still a comparatively new study area (Kanzler et al. 2015, Böhm et al. 2014). This might be due to the complexity of the microclimate, which depends on various parameters such as the plant height, the planting density, and the orientation of the tree-strips. The objective of this study was to investigate the potential influence of tree-strips on microclimate using high resolution data loggers.
Blattstreumengen in Gehölzstreifen und angrenzenden Ackerbreichen innerhalb eines Agroforstsystems
(2015)
Since the 1920s, more than 80.000 ha of land have been affected by lignite opencast mining activities in the Lusatia region (Eastern Germany), resulting in the evolution of large post-mining landscapes with substrates poor in humus and nutrients. As a consequence, the current conventional crop production on these post-mining areas is restricted. Against this background, the increasing demand for woody biomass for bioenergy, and thus the cultivation of fast growing trees for woody biomass production, could represent a promising option to enhance the productivity of land reclaimed from mining. Accordingly, considerable research has been carried out over the last two decades on reclamation technology, in addition to attempts to improve the soil quality through the use of different fast growing tree species in the Lusatia lignite region. Through such studies, it has been shown that it is possible to cultivate a sustainable supply of bioenergy wood through the use of black locust (Robinia pseudoacacia L.) trees, even under the unfavourable growth conditions of the marginal post mining areas. Since this knowledge is mainly based on studies of monocultural plantations (SRC), in 2007 a short rotation alley cropping system (SRACS) was established in the reclaimed lignite mining site “Welzow-Süd” with the purpose of obtaining fresh insight. The present paper evaluates the positive impacts of agroforestry land-use in terms of soil fertility, agricultural crop production, and soil protection against wind erosion based on the results of several years of examination made in this degraded area.
The cultivation of fast growing trees on agricultural sites is an area undergoing a growth in interest due to the rising demand for woody biomass as a source of bioenergy. Short rotation alley cropping systems (SRACS) represent a promising possibility to combine annual crops for food, fodder or bioenergy with woody plants for biomass production, doing so through an integration of hedgerows of fast growing trees into conventional agricultural sites. Against such developments, the question has arisen as to what extent hedgerows in SRACS can act as an effective windbreak despite their management-related low height of only a few meters. On the basis of multiannual recorded wind velocity data in high resolution at two sites in Germany, it could be shown that the wind speed on crop alleys was reduced significantly by such hedgerows. At the central point of 24 m wide crop alleys, the wind speed decreased on an annual average basis by more than 50 % when compared to the wind speeds of open field. The overall amount of reduction was strongly dependent on the location within the crop alleys, the height of trees, the distance between two hedgerows, and their orientation. In reflection upon these results, it was concluded that the establishment of SRACS could lead to enhanced soil protection against wind erosion and thus to ecological and economic benefits for agricultural sites.
Due to its ability to grow on marginal sites black locust (Robinia pseudoacacia L.) has been widely planted as a short rotation coppice (SRC) system that produce a renewable biomass feedstock in several post-mining areas of East Germany. However, as most of these sites are still in an initial stage of reclamation with low humus and nutrient contents, phosphorous can play a significant role as a plant limiting factor, because legumes require more P than other plants for their development. In April 2011, two experiments were conducted to evaluate the influence of higher rates and different applications of phosphorus fertiliser on the nutrition, survival, and biomass production of two different-aged black locust SRC plantations on the post lignite-mining site “Welzow-Süd”, situated in NE Germany. Treatments were applied as triple superphosphate (30, 60 and 120 kg P ha-1) and PK fertiliser (60 kg P ha-1) through broadcasting or banding on recently harvested or planted trees, respectively. Soil, leaf and woody biomass data were analysed utilising the Mann-Whitney U test and the Spearman correlation coefficient (rS). Following two growing seasons, it was observed that the total dry weight yields of the black locust seedlings were increased strongly by up to 8 times when compared to the control group, particularly when TSP was applied through banding. P fertilisation, however, did not affect the biomass yield of six-year-old black locust trees, but P concentration in leaves among treatments of both sites was still significantly increased and sufficient from a quantity upwards of 60 kg P ha-1. Taken together, a comparably moderate amount of P fertiliser (60 kg ha-1) had a strong impact on P uptake and growth performance in the examined black locust seedlings, which reveals a high potential to improve the current fertilisation practices for SRC black locust plantations grown on our research site.
A leaf net photosynthesis model is presented driven by light and modulated by temperature and air humidity. From this the seasonal variation of CO2 uptake and release could be modelled to estimate the annual carbon fluxes of sun and shade leaves. In fully expanded leaves light is the major factor determining daily carbon balances, and highest observed daily carbon gains in sun leaves amounted to 748.9 mmol CO2 m-2 day-1 in poplar and to 536.3 mmol CO2 m-2 day-1 in black locust, while the annual carbon gains amounted to 46,824 mol CO2 m-2 in black locust and 66,803 mol CO2 m-2 in hybrid poplar. Results obtained via gas exchange measurements and from the leaf model clearly indicate a potentially better growth performance of the poplar compared to black locust on the investigated site. The presented photosynthesis model provides a good and realistic estimation for seasonal carbon balances on the leaf level for both species.