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The importance of short rotation forests and agroforestry systems for woody biomass production for bioenergy will increase in Central Europe within the next decades. In this context, black locust (Robinia pseudoacacia) has a high growth potential especially at marginal, drought-susceptible sites such as occur in Brandenburg State (Eastern Germany). As a pioneer tree species black locust grows under a wide range of site conditions. The native range of black locust in Northern America is classified by a humid to sub-humid climate with a mean annual precipitation of 1020 to 1830 mm. In Central and Eastern Europe, this species is cultivated in a more continental climate with an annual precipitation often below 600 mm. Therefore, black locust is known to be relatively drought tolerant compared to other temperate, deciduous tree species. Because of its N2-fixation ability black locust plays generally an important role for the improvement of soil fertility. This effect is of particular interest at marginal sites in the post-mining landscapes.
In order to estimate the N2-fixation potential of black locust at marginal sites leaf samples were taken from black locust trees in short rotation plantations planted between 1995 and 2007 in post-mining sites south of Cottbus (Brandenburg, NE Germany). The variation of the natural 15N abundance was measured to evaluate the biological nitrogen fixation. The nitrogen derived from the atmosphere can be calculated using a two-pool model from the quotient of the natural 15N abundances of the N2-fixing plant and the plant available soil N. Because representatively determining the plant available soil N is difficult, a non-N2-fixing reference plant growing at the same site with a similar root system and temporal N uptake pattern to the N2-fixing plant is often used. In our case we used red oak (Quercus rubra) as a reference.
The average nitrogen content in the leaves of black locust ranged from 3.1% (C/N 14.8) in 15 years old trees to 3.4% (C/N 14.4) in 3 year-old trees, respectively. A higher content of nitrogen was found in leaves of re-sprouted trees with 4.3% (C/N 11.5). The estimated percentage of nitrogen derived from the atmosphere (% NdfA) in black locust was 63% – 83% compared to 56% in seabuckthorn (Hippophaë rhamnoides) and 79% in common broom (Genista scuparia). The annual leaf biomass production of black locust varied between 1325 (2 years old trees) and 2576 kg/ha a (4 years old trees). The estimated leaf nitrogen fixed by Robinia was approx. 30.5 - 59.2 kg/ha a.
From the results, we can conclude that the biological nitrogen fixation by Robina is an important factor for the nitrogen balance of short-rotation plantations on nutrient poor-soils.
Als Pionierbaumart besiedelt die Robinie (Robinia pseudoacacia) schnell offene Flächen und gilt im Vergleich zu anderen mitteleuropäischen Baumarten als relativ gut angepasst an trockene Standorte mit lockeren Böden. Sie gehört zu den wenigen Baumarten Mitteleuropas, die zur biologischen Stickstoff-Fixierung (BNF) befähigt sind. In dieser Studie soll der jährliche Eintrag von Stickstoff (N) aus der biologischen N-Fixierung der Robinie in Kurzumtriebsplantagen und Agroforstsystemen abgeschätzt werden.
Alley cropping systems (ACS) are agroforestry practices in which perennial trees or shrubs are grown in wide rows and arable crops are cultivated in the alleys between the tree rows. Recently, ACS which integrate stripes of short rotation coppices into conventional agricultural sites have gained interest in Germany. These systems can be used for simultaneous production of crops and woody biomass which enables farmers to diversify the provision of market goods. Adding trees into the agricultural landscape creates additional benefits for the farmer and society also known as ecosystem services. An ecosystem service provided by land use systems is carbon sequestration. The literature indicates that ACS are able to store more carbon compared to agriculture and their implementation may lead to greater benefits for the environment and society. Moreover, carbon sequestration in ACS could be included in carbon trading schemes and farmers rewarded additionally for the provision of this ecosystem service. However, methods are required which are easy to use and provide reliable information regarding change in carbon sequestration with change of the land use practice. In this context, our aim was to develop a methodology to assess carbon sequestration benefit provided by ACS in Germany. Therefore, the change of carbon in both soil and biomass had to be considered. To predict the change in soil carbon our methodology combined the 2006 IPCC Guidelines for National Greenhouse Gas Inventories and the soil organic carbon balance recommended by the Association of German Agricultural Investigation and Research Centers (VDLUFA). To reflect the change in biomass carbon average annual yields were adopted. The results showed that ACS established on agricultural sites can increase the carbon stored because in the new soil-plant system carbon content is higher compared to agriculture. ACS have been recommended as suitable land use systems for marginal sites, such as post-mining areas. In such areas soil carbon usually increases at a faster initial rate compared to agricultural land which means that these areas could provide high level of carbon sequestration service in the short term. The approach will be broadened to include assessment of other ecosystem services provided by ACS in Germany which would increase the possibility to adequately compensate farmers for the supply of environmental benefits.
Alley cropping systems which integrate strips of short rotation coppices into conventional agricultural sites (ACS) have recently gained increasing interest in Germany. These ACS can be used for the simultaneous production of crops and woody biomass which enables farmers to diversify the provision of market goods. Integrating trees into the agricultural landscape can create additional benefits for the farmer and society also known as ecosystem services (ES). The scientific literature suggests that ACS are able to provide additional benefits as compared to conventional agriculture. Among the important ES provided by ACS are carbon sequestration, soil fertility, water quality, groundwater recharge, and biodiversity. However, assessment methods are required which are easy to use and provide reliable information regarding change in ES with change of the land use practice. In this context, our aim was to develop a methodology to assess selected ES provided by ACS in Germany. For this purpose an indicator set was selected from the literature and linked with the relevant ES previously identified. Furthermore, a model was developed to facilitate the calculation of the indicators. The results showed that ACS established at agricultural sites have higher capacity to provide ES as compared to single-crop agriculture. The capacity of ACS with 50% trees is higher than the capacity of ACS with 30% trees which suggests that the capacity of the system to provide ES increases with increased proportion of trees. The methodology seems to be a promising tool to facilitate the assessment of ES provided by the land management practices considered. In the long term this measurement approach can be broadened to include monetary evaluation of ES. This will enable rewarding farmers for providing environmental benefits therefore, accurately compensating them for the outputs supplied.