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BTU
In a five-year old alley cropping system in Brandenburg, Germany, the extension of the root system of black locust (Robinia pseudoacacia L.) trees into the neighbouring agricultural field alleys was investigated. Along transects between the hedgerows and the middle of the neighbouring field alleys, samples were collected at distances of 1.30, 4.3 and 49.3 m to the hedgerow border and for the soil depths 0-15, 15-30, 30-45 and 45-60 cm by using an auger with a diameter of 8 cm. Roots were separated from the soil by means of washing and sieving. The root samples were then sorted and analysed for root length densities and dry masses. The results indicate a logarithmic decrease of root length densities and root masses of black locust with increasing distance to the trees, although, the number of positive samples was too small to conduct a substantiated statistical analysis. In result, the authors assume that the tree roots did not extend into the agricultural alley for the considered soil depths substantially, but, nevertheless, suggest a modified sampling method or/and the investigation of older tree stands for future studies.
Depth gradient of soil C, N and S contents in an alley cropping system for biomass production
(2017)
In a six-year-old alley cropping system with fast growing trees for biomass production (ACS), the depth distribution of soil contents of carbon (C), nitrogen (N) and sulphur (S) under the trees (poplar) and under the neighbouring agricultural field was investigated. The measured soil contents were usual for agricultural sites and showed a significant decrease with increasing soil depth under the trees. These results might indicate that the introduction of trees into agricultural areas leads to an alteration of the soil distribution pattern of C, N, S from a pattern typical for agricultural soils (more or less constant values at least within the ploughing horizon from 0-30 cm) to a pattern more typical for forest ecosystems (comparatively higher values in the topsoil, lower values in the deeper soil). However, for more reliable results measurements should be repeated and preferably older stands should be investigated.
In the temperate zone short rotation coppice systems for the production of woody biomass (SRC) have gained great interest as they offer a pathway to both sustainable bioenergy production and the potential sequestration of CO₂ within the biomass and the soil. This study used the carbon model SHORTCAR to assess the carbon cycle of a poplar (Populus suaveolens Fisch. x Populus trichocarpa Torr. et Gray cv. Androscoggin) and a black locust (Robinia pseudoacacia L.) SRC. The model was calibrated using data from established SRC plantations on reclaimed mine sites in northeast Germany and validated through the determination of uncertainty ranges of selected model parameters and a sensitivity analysis. In addition to a ‘reference scenario’, representing the actual site conditions, 7 hypothetical scenarios, which varied in climate conditions, rotation intervals, runtimes, and initial soil organic carbon (SOC) stocks, were defined
for each species. Estimates of carbon accumulation within the biomass, the litter layer, and the soil were compared to field data and previously published results. The model was sensitive to annual stem growth and initial soil organic carbon stocks. In the reference scenario net biome production for SRC on reclaimed sites in Lusatia, Germany amounted to 64.5 Mg C ha⁻¹ for R. pseudoacacia and 8.9 Mg C ha⁻¹ for poplar, over a period of 36 years. These results suggest a considerable potential of SRC for carbon sequestration at least on marginal sites.
Alley cropping system is an agroforestry practice in which arable crops are cultivated between tree hedgerows. For more than 15 ye ars we have been doing research in agroforestry which has been carried out on different experimental sites in the field covering about 250 acres of alley cropping, more areas with short rotation coppice, and other tree-based field experiments located close to C ottbus / Germany. The presence of woody species in the alley cropping production system has been shown to contribute significantly to carbon sequestration, nutrient cycling, improved water availability for crops, stimulation of higher soil faunal activities, soil erosion control, soil fertility improvement and sustained levels of crop production.
Alley cropping systems have also come into focus for reclamation of post-mining areas where the initial content of soil organic matter (SOM) is generally close to zero and soil fertility is very low. The increase of SOM in reclamation areas depends on amount of biomass production and return to soil, and mechanisms of C protection. Production of Robinia pseudoacacia L. under alley cropping system has received considerable interest in these areas as an alternative to agricultural crops and an additional wood source, while acting as a potential C sink to counterbalance greenhouse gases emissions. The woody biomass accumulation of R. pseudoacacia reached 29.8 t drymass ha-1 after 6 years of establishment on reclaimed mine sites in northeastern Germany. Due to its high potential of litterfall production and N2 fixation, R. pseudoacacia contributed to improve soil physical, chemical and biological properties though increasing SOM, converting spoils into productive and sustainable soils. For this reason, in the temperate zone, agroforestry systems attract more and more public attention as they offer a promising and comprising way for adapting agricultural production to climate change and providing comprehensive ecosystem services. A comprehensive assessment of the ecosystem services in agroforestry systems in temperate regions should consider the potential to produce biomass and food, the evaluation of the carbon and nutrient budgets, the assessment of the potential impact of agroforestry on biodiversity at landscape scale and finally the exploration of the sustainability functions and socio-economic cross-cutting issues. These key parameters are relevant to policy by providing current and reliable information on the interactions between land management, ecosystem services and society.