Dirk Freese

Ecological benefits provided by alley cropping systems for production of woody biomass in the temperate region: a review

In temperate Europe alley cropping systems which integrate strips of short rotation coppices into conventional agricultural fields (ACS) are receiving increasing attention. These systems can be used for crops and woody biomass production at the same time, enabling farmers to diversify the provision of market goods. Adding trees into the agricultural land creates various additional benefits for the farmer and society, also known as ecosystem services. However, tree-crop interactions in the temperate region have not been adequately substantiated which is identified as a drawback to the practical implementation of such systems. In order to bridge this gap, the current paper aims to present a comprehensive overview of selected ecosystem services provided by agroforestry with focus on ACS in the temperate region. The literature indicates that compared with conventional agriculture ACS have the potential to increase carbon sequestration, improve soil fertility and generally optimize the utilization of resources. Furthermore, due to their structural flexibility, ACS may help to regulate water quality, enhance biodiversity, and increase the overall productivity. ACS are shown as suitable land use systems especially for marginal sites. Based on the available data collected, we conclude that ACS are advantageous compared to conventional agriculture in many aspects, and therefore suggest that they should be implemented at a larger scale in temperate regions.

Carbon Sequestration in European Agroforestry Systems

Agroforestry systems (AFS) are recommended for Europe through the European Rural Development Council regulation 1698/2005, in recognition of their role in reducing carbon (C) emissions and promoting C sequestration which would help to fulfil the Kyoto Protocol requirements. These systems have been found to be a good tool to reduce fire risk and C release in southern European countries. The implementation of AFS could also reduce C release to atmosphere because of the value given to non-timber products, thereby reducing chances for clear cutting of trees. Furthermore, the tree component in AFS will add C into the soil through litterfall and root decomposition, which takes place at deeper soil layers than under agronomic crops or pasture. Tree management practices such as regulating tree density and planting arrangement will influence the C sequestered in the system. Compared with the tree components, the understory components of AFS have less impact on the total C sequestration. The higher inputs of residues generated by the trees in AFS than in tree-less systems may cause high soil C sequestration potential, but soil C increase depends on the incorporation and mineralization of C in the soil, which are affected by understory crop management practices.

Decomposition and nutrient release of leguminous plants in coffee agroforestry systems

SUMMARY Leguminous plants used as green manure are an important nutrient source for coffee plantations, especially for soils with low nutrient levels. Field experiments were conducted in the Zona da Mata of Minas Gerais State, Brazil to evaluate the decomposition and nutrient release rates of four leguminous species used as green manures (Arachis pintoi, Calopogonium mucunoides, Stizolobium aterrimum and Stylosanthes guianensis) in a coffee agroforestry system under two different climate conditions. The initial N contents in plant residues varied from 25.7 to 37.0 g kg -1 and P from 2.4 to 3.0 g kg -1 . The lignin/N, lignin/polyphenol and (lignin+polyphenol)/N ratios were low in all residues studied. Mass loss rates were highest in the first 15 days, when 25 % of the residues were decomposed. From 15 to 30 days, the decomposition rate decreased on both farms. On the farm in Pedra Dourada (PD), the decomposition constant k increased in the order C. mucunoides < S. aterrimum < S. guianensis < A. pintoi. On the farm in Araponga (ARA), there was no difference in the decomposition rate among leguminous plants. The N release rates varied from 0.0036 to 0.0096 d -1 . Around 32 % of the total N content in the plant material was released in the first 15 days. In ARA, the N concentration in the S. aterrimum residues was always significantly higher than in the other residues. At the end of 360 days, the N released was 78 % in ARA and 89 % in PD of the initial content. Phosphorus was the most rapidly released nutrient (k values from 0.0165 to 0.0394 d -1 ). Residue decomposition and nutrient release did not correlate with initial residue chemistry and biochemistry, but differences in climatic conditions between the two study sites modified the decomposition rate constants.

Organic Matter Dynamics in Reclaimed Lignite Mine Soils under Robinia pseudoacacia L. Plantations of Different Ages in Germany

In temperate regions, cultivation of Robinia pseudoacacia L. has recently received considerable attention because it is a fast-growing species for biomass and bioenergy production, while acting as a potential carbon (C) sink to counterbalance carbon dioxide (CO2) emissions and an alternative to agricultural crops on marginal sites. The objective of our work was to compare total organic carbon (TOC), total nitrogen (TN), and organic C fractions in postlignite mining soils under different development stages of R. pseudoacacia. Soil samples from three different depths (0–3, 3–10 and 10–30 cm) were taken in plantations 2, 3, 4, and 14 years old (R2, R3, R4, and R14, respectively). The TOC and TN contents increased with increasing tree age in all layers (P < 0.01). In the top 30 cm, TOC and TN stocks ranged from 11.7 to 59.8 Mg C ha−1 and from 0.30 to 2.61 Mg N ha−1 at R2 and R14, respectively. The rate of C sequestration was calculated to be 4.0 Mg C ha−1 year−1. Microbial biomass C and N were strongly correlated to TOC (r2 = 0.96 – 0.81; P < 0.001) and TN contents (r2 = 0.92 – 0.91; P < 0.001). The light fraction C (CLF) accounted for 15–30% and the heavy fraction C for 70% of TOC in all layers. In the 0- to 3-cm layer, CLF increased by 0.5 g kg−1 year−1. The results indicate that plantations of R. pseudoacacia are an attractive alternative to increase soil C contents in reclaimed lignite mining soils. In the short term, microbial biomass C and light fraction C are sensitive and provide an appropriate measure to assess soil C changes caused by cultivation of R. pseudoacacia.

Black locust (Robinia pseudoacacia L.) ecophysiological and morphological adaptations to drought and their consequence on biomass production and water-use efficiency

BackgroundSuccessful plantation efforts growing Robinia pseudoacacia L. (black locust) in the drier regions of Hungary and East Germany (Brandenburg), have demonstrated the potential of black locust as an alternative tree species for short-rotation biomass energy plantations.MethodsThe response of black locust to water limitation was investigated in a lysimeter experiment. Plants were grown under three different soil moisture regimes, with values set at 35%, 70%, and 100% of the soil water availability, namely WA35, WA70, and WA100. Their morphological adaptation and productivity response to water constraint were assessed together with their water-use efficiency. Furthermore, the ecophysiological adaptation at the leaf level was assessed in terms of net photosynthesis and leaf transpiration.ResultsDuring the growing season, plants in the WA35, WA70, and WA100 treatments transpired 239, 386, and 589 litres of water respectively. The plants subjected to the WA35 and WA70 treatments developed smaller leaves compared with the plants subjected to the WA100 treatment (66% and 36% respectively), which contributed to the total leaf area reduction from 8.03 m2 (WA100) to 3.25 m2 (WA35). The total above-ground biomass produced in the WA35 (646 g) and WA70 (675 g) treatments reached only 46% and 48% of the biomass yield obtained in the WA100 (1415 g). The water-use efficiency across all treatments was 2.31 g L−1. At vapour pressure deficit (VPD) values <1.4 kPa trees growing under the WA35 soil moisture regime showed a stomatal down-regulation of transpiration to 5.3 mmol m−2 s−1, whereas the trees growing under the WA100 regime did not regulate their stomatal conductance and transpiration was 11.7 mmol m−2 s−1, even at VPD values >2 kPa.ConclusionsBlack locust plants can adapt to prolonged drought conditions by reducing water loss through both reduced transpiration and leaf size. However, under well-watered conditions it does not regulate its transpiration, and therefore it cannot be considered a water-saving tree species.

Effects of Drought Frequency on Growth Performance and Transpiration of Young Black Locust (Robinia pseudoacacia L.)

Black locust (Robinia pseudoacacia L.) is a drought-tolerant fast growing tree, which could be an alternative to the more common tree species used in short-rotation coppice on marginal land. The plasticity of black locust in the form of ecophysiological and morphological adaptations to drought is an important precondition for its successful growth in such areas. However, adaptation to drought stress is detrimental to primary production. Furthermore, the soil water availability condition of the initial stage of development may have an impact on the tree resilience. We aimed to investigate the effect of drought stress applied during the resprouting on the drought tolerance of the plant, by examining the black locust growth patterns. We exposed young trees in lysimeters to different cycles of drought. The drought memory affected the plant growth performance and its drought tolerance: the plants resprouting under drought conditions were more drought tolerant than the well-watered ones. Black locust tolerates drastic soil water availability variations without altering its water use efficiency (2.57 g L−1), evaluated under drought stress. Due to its constant water use efficiency and the high phenotypic plasticity, black locust could become an important species to be cultivated on marginal land.

Agroforestry for Mine-Land Reclamation in Germany: Capitalizing on Carbon Sequestration and Bioenergy Production

Surface mining operations generate significant and large-scale landscape disturbances. As a consequence, effective reclamation management is required to ensure the establishment of a sustainably productive, ecologically valuable, and economically attractive post-mining landscape. In the post-surface-mining landscape of Lower Lusatia (northeast Germany), a new land-use option during reclamation is the establishment of alley cropping systems (ACSs) producing food and woody biomass for obtaining bioenergy. The established multi-row tree strips are typically managed as short rotation coppices (SRC), for which black locust (Robinia pseudoacacia L.) is the most frequently used tree species. The alley cropping systems are promising land-use systems for mine-site reclamation because they provide a multitude of ecological and economic benefits; furthermore, within these plantations, significant amounts of carbon (C) can be accumulated in the biomass and the soil. The results of field studies on C sequestration in R. pseudoacacia stands on reclaimed mine sites within the Lusatian region indicate an average shoot dry matter (DM) production of R. pseudoacacia between 3 and 10 Mg DM ha−1 year−1 depending on the plantation age and rotation period. The DM yields for foliage biomass ranged between 12 and 32 % of the shoot biomass for 2- and 4-year-old trees. Estimates of the C storage within the soil are up to 7 Mg C ha−1 year−1 within 0–60 cm depth. In summary, the results support the hypothesis that ACS of R. pseudoacacia may be in many respects a beneficial land-use system for marginal, post-mining landscapes, with a significant C sequestration potential above- and belowground.

Biomass, Carbon and Nitrogen Distribution in Living Woody Plant Parts of Robinia pseudoacacia L. Growing on Reclamation Sites in the Mining Region of Lower Lusatia (Northeast Germany)

In the lignite mining region of Lower Lusatia (NE-Germany), Robinia pseudoacacia L. is an increasingly popular tree for the biomass production with short rotation coppices (SRCs) on reclamation sites. In order to evaluate biomass production, C and N allocation patterns in R. pseudoacacia stands between shoot, stump, coarse, and fine roots samples were collected from seedlings and three adjacent plantations and plants that were one, two and twelve years old. Results indicated that the summarized average dry matter production (DM) of the woody plant parts increased with plant age up to 7.45 t DM ha−1 yr−1 with a corresponding shoot increment of up to 4.77 t DM ha−1 yr−1 in the twelve-year-old stands. The shoot to root ratio changed from 0.2 for the one-year-old trees to 2.0 in the twelve-year-old plantation, whereby an average amount of 3.4 t C ha−1 yr−1 and 0.1 t N ha−1 yr−1 was annually bound in the living woody plant parts over the period of twelve years. Summing up, the results suggest a high potential for C and N storage of R. pseudoacacia what is also beneficial for land reclamation due to positive implications on soil humus and general site fertility.

Soil Respiratory Indicators Including Carbon Isotope Characteristics in Response to Copper

The human impact on soil functions with reference to environmental pollution and climatic changes have received great attention during the last decades. A widespread and integral environmental indicator is the soil microbial respiration and can be estimated either on the basis of carbon dioxide evolution or of oxygen uptake. In accordance with many previous studies, we found that soil respiration decreased in the presence of heavy metals such as Cu. The Cu spiking of an acid and unpolluted, organic-rich pine forest soil at approximately the limits for sewage sludge (100 to 200 μ g Cu g −1 soil) led to high concentrations of up to 0.35 μ g Cu per ml in the soil solution and reduced carbon dioxide evolution by 27% and the oxygen uptake by 18% during basal respiration. Thus, the respiratory quotient (RQ) which is defined as the carbon dioxide evolution related to oxygen uptake was reduced with increasing Cu levels. The Cu effect was also detected after the addition of glucose as a readily available substrate. In the soil investigated, the carbon isotope characteristic of the 13 C-CO 2 evolved did not give any indication of specific carbon use and fractionation processes during basal metabolism as indicated by enrichment or depletion of 13 C values. However, carbon isotope characteristic of the 13 C-CO 2 evolved showed that glucose addition stimulated mineralization of the soil organic matter (SOM) which derived from either increased biomass turnover or simulated dead SOM degradation and is defined as priming effect. The results showed that (1) the evaluation of heavy metal effect on soil respiratory indicators and the transformation of active SOM are method-dependent and (2) under aerobic conditions, soil microbial communities consumed relatively more oxygen in the presence of Cu than in its absence in this acid, unpolluted and organic rich soil under pine forest.

Transpiration and biomass production of the bioenergy crop Giant Knotweed Igniscum under various supplies of water and nutrients

Abstract Soil water availability, nutrient supply and climatic conditions are key factors for plant production. For a sustainable integration of bioenergy plants into agricultural systems, detailed studies on their water uses and growth performances are needed. The new bioenergy plant Igniscum Candy is a cultivar of the Sakhalin Knotweed (Fallopia sachalinensis), which is characterized by a high annual biomass production. For the determination of transpiration-yield relations at the whole plant level we used wicked lysimeters at multiple irrigation levels associated with the soil water availability (25, 35, 70, 100%) and nitrogen fertilization (0, 50, 100, 150 kg N ha-1). Leaf transpiration and net photosynthesis were determined with a portable minicuvette system. The maximum mean transpiration rate was 10.6 mmol m-2 s-1 for well-watered plants, while the mean net photosynthesis was 9.1 μmol m-2 s-1. The cumulative transpiration of the plants during the growing seasons varied between 49 l (drought stressed) and 141 l (well-watered) per plant. The calculated transpiration coefficient for Fallopia over all of the treatments applied was 485.6 l kg-1. The transpiration-yield relation of Igniscum is comparable to rye and barley. Its growth performance making Fallopia a potentially good second generation bioenergy crop.