1,720,961 research outputs found
Spatial distribution of tree and grassland fine roots in an alley cropping system
No full textAlley cropping systems are known as more sustainable land use alternatives compared to monoculture cropland. In addition to the improvement of above-ground structures and creation of biotopes relevant to nature conservation, the improvement of resource development through various root systems plays a major role. We studied the interaction of the root systems in an alley cropping system combining permanent grassland and willows and at a reference grassland site. The system was established 12 years prior to our study on a site with a shallow groundwater table at 130 cm depth. We measured carbon stocks in the topsoil and determined the share of root-bound carbon relative to the total carbon pool and extracted soil cores up to a depth of 150 cm along a distance gradient to the trees and at a reference grassland site with no tree influence. The maximal rooting depth of the grassland roots increased with increasing distance to the tree lines and total root biomass was higher than under the grassland reference up to a distance of 2.5 m from the tree line. Tree roots extended up to a distance of 5.5 m from the trees and we could distinguish zones of tree root dominance very close to the trees, zones of grassland root dominance at distances ≥
8.5 m and an interaction zone in between those two extremes. We conclude that alley cropping increases belowground biomass as compared to grassland and has therefore a higher potential to store carbon in the subsoil.Open-Access-Publikationsfonds 202
Adjusting nitrogen fertilization to spatial variations in growth conditions in silvopastoral systems for improved nitrogen use efficiency
No full textAbstract Grass swards in silvopastoral systems have a lower herbage production near trees than open grassland. This is related to a lower nitrogen (N) uptake in an area close to the tree lines. The N use efficiency for the whole field can then be improved when N input is spatially adjusted and the overall amount reduced. We performed a 2-year field experiment to gain insights into this idea for making savings on N inputs by studying the response of the grass sward to fertilizer N input in relation to the distance from trees. We hypothesized an interaction between N input rate and position to the tree line on grassland herbage production and N uptake and, accordingly, N use efficiency. The field trial was carried out in a silvopastoral system in Germany consisting of the factors year (2019 and 2020), position (2.5, 6.5 and 24.5 m distances to tree line), annual N application rate (0, 15 and 30 g N m −2 ) and harvest date (four harvests per year). We found significant interactions between position × N rate for all target variables, and usually also in interactions with the harvest date or year. The N application close to trees at a distance < 6.5 m had in most cases no significant influence on herbage production but significantly increased herbage production by up to 35% at positions further away. Omitting the N fertilization in a corridor of 6.5 m near the trees would contribute directly to the saving of fertilizer N without a negative trade-off in herbage production.Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Georg-August-Universität Göttingen 50110000338
Tree lines influence soil temperatures, sward growth dynamics and litter decomposition in permanent grassland
No full textFunder:
http://dx.doi.org/10.13039/501100010571
BMBF Berli
High and dry: Barley (Hordeum vulgare) yield benefits from tree presence in a temperate alley cropping system during a drought year
No full textAbstract Alley cropping systems (ACS) are promoted as sustainable, resilient and multifunctional land-use systems. However, concerns about yield reductions persist and whether these are driven by microclimate alterations or below-ground competition for water remains unclear. In this study, we measured wind speed, air temperature, and global radiation at seven positions within a 48 m wide crop alley of a short rotation ACS in Germany with summer barley ( Hordeum vulgare ) and poplar ( Populus nigra × P. maximowiczii and P. trichocarpa Torrey & A. Gray ) and on a treeless reference field (OF) during a particularly dry and warm year. Additionally, gravimetric soil water content and crop yield were assessed with high spatial resolution. Our results show that tree strips influenced all measured parameters. Global radiation and air temperature patterns varied dynamically with shading, while night-time air temperatures were unexpectedly highest on the OF. Wind speeds were reduced by up to 98% near tree strips and 81% further away. Soil water content displayed a U-shaped pattern, with higher values near tree strips, a rare observation in ACS. Crop yields in the ACS were twice as high as in the OF, despite being lower near tree strips. Yields were strongly correlated with global radiation but not with air temperature, wind speed, or soil water content. These findings provide preliminary evidence that tree presence in ACS can, under certain conditions, contribute to increased crop yields. The results suggest that ACS provide potential benefits for sustainable land-use, but further multi-year and multi-site studies are needed to validate the observed yield patterns across different environments and years, particularly under varying climatic conditions. Further research should also explore the indirect effects of microclimate modifications on soil water dynamics, including evapotranspiration.German Federal Ministry of Education and ResearchBrandenburgische Technische Universität Cottbus - Senftenberg http://dx.doi.org/10.13039/50110002202
Alley cropping tree lines alter temperature and light quantity and influence daily growth rates of grassland
No full textTree lines do not reduce grassland productivity and herbage quality in alley cropping under drought
No full textPerceptual Influence of Elementary Three-Dimensional Geometry: 1) Object-ness
No full textCommonly complex cognitive concepts cannot consistently be connected to simple features of the world. Geometrical shape parameters and (e.g. edge features, compactness, color) may play a role for defining individual objects, but might be too variable to allow for concept formation. Earlier works had suggested that the formation of object concepts is strongly influenced by the division of our world along convex to concave surface transitions. In this first paper in a sequence of two we address this issue using abstract 3D geometrical structures (polycubes). In a first experiment, we let our subjects manipulate and compare polycubes with different compactness and different concavity/convexity asking which of them they would perceive as an object. Both parameters (compactness and concavity/convexity) are not correlated in these stimuli. Nonetheless, we find that subjects with clear prevalence choose compact and convex ones. We continue to ask how strongly this influences the way we construct objects. Thus, in a second experiment we let humans combine polycubes to form an object. Also here we find that they prefer compact and convex configurations. This suggests that this simple geometric feature may underlie our cognitive understanding of object-ness not only with respect to perception but also by influencing how we build our world
Perceptual Influence of Elementary Three-Dimensional Geometry: 2) Fundamental object parts
No full textObjects usually consist of parts and the question arises whether there are perceptual features which allow breaking down an object into its fundamental parts without any additional (e.g. functional) information. As in the first paper of this sequence, we focus on the division of our world along convex to concave surface transitions. Here we are using machine vision to produce convex segments from 3D-scenes. We assume that a fundamental part is one, which we can easily name while at the same time there is no natural subdivision possible into smaller parts. Hence in this experiment we presented the computer vision generated segments to our participants and asked whether they can identify and name them. Additionally we control against segmentation reliability and we find a clear trend that reliable convex segments have a high degree of name-ability. In addition, we observed that using other image-segmentation methods will not yield nameable entities. This indicates that convex-concave surface transition may indeed form the basis for dividing objects into meaningful entities. It appears that other or further subdivisions do not carry such a strong semantical link to our everyday language as there are no names for them
Growth responses of grass swards to tree-mediated temporal and spatial dynamics of light and temperature in a silvopastoral system
Full text linkAgroforestry can increase the resilience of agriculture to the predicted changes in climate. Alley cropping systems are a form of agroforestry where tree lines are integrated into the agricultural area in regular distances. Combined with grassland, they increase the climate change mitigation potential by increasing carbon storage. Additionally, tree lines have a positive effect on microclimate parameters with lower potential evapotranspiration rates close to the trees due to reductions in wind speed and air temperature. The present thesis includes four studies on the interactions between trees and grassland in two willow (Salix spp.) × grassland alley cropping systems. In the first study, we quantified the tree-mediated change in microclimate parameters and photosynthetically active radiation available to the grass sward and linked them to changes in daily growth rates. In the second study, we determined the lateral extent of the tree root system as well as the vertical distribution of below-ground biomass of trees and grassland at different distances to the tree line. The third study focused on the interactions between grassland and trees under moderate and extreme drought. In the fourth study, we measured the effect of the tree lines on growth and decomposition processes. The first study was conducted in an
alley cropping system with narrow spacing (9 m) of the tree lines oriented Northwest–Southeast while the other studies were conducted in an alley cropping system with wide spacing (50 m) and tree lines oriented North–South.
The first study intended to connect tree–mediated changes in microclimate parameters to daily growth rates. We hypothesized that trees affect microclimate parameters more strongly at smaller distances and that the growth of the grass sward is positively influenced by favourable microclimate with lower temperatures and higher relative humidity. The experimental factor transect position lumps distance and orientation to the tree line to measure the tree influence
in a gradient of distance and while considering the orientation relative to the tree line. We included three transect positions with distances of 0.5 m (with two orientations relative to the tree line) and 4.5 m (equidistant in the center between two tree lines). Additionally, cutting frequency with two levels (two or three annual cuts) and vegetation composition with two levels
(diverse vs. grass-clover) were included in the experimental setup arranged in a split-plot design with three repetitions per factorial combination. Air temperature and relative humidity as well as soil temperatures were monitored in each factorial combination. In addition, we measured the reduction of photosynthetically active radiation at the transect positions compared to open grassland during individual days. Daily growth rates were calculated from sward height measurements and calibration cuts (double sampling) taken every two or four weeks, respectively. We showed that the differences in annual biomass accumulation between the single transect positions aligned well with the differences in photosynthetically active radiation. The transect position with the same distance to the tree line but a higher number of sunshine hours showed higher temperatures, lower relative humidity and higher biomass accumulation under normal weather conditions. Under dry and hot weather, the positions close to the trees were favoured over the center position with 4.5 m distance to each tree line. The cutting frequency showed no consistent pattern in the interaction with year and vegetation composition. However, the diverse vegetation composition showed significantly higher biomass accumulation in the interaction with year as well as with cutting frequency. Our results show that species diversity has a positive effect on yield stability even in a series of extreme drought years. In combination with alley cropping, we conclude that the main limiting factor on grassland growth in the present alley cropping system is the amount of photosynthetically active radiation available to the grass
sward.
In the second study, we quantified root biomasses of trees and grassland up to a depth of 150 cm. We hypothesized that the tree roots extend laterally into the alley and interact with the grassland roots. Furthermore, we assumed that the fine root density of trees decreases with increasing distance. We sampled cores using a hydraulic soil corer in three repetitions in distances of 25 m, 8.5 m, 5.5 m, 4.5 m, 3.5 m, 2.5 m, 1.5 m and inside the tree line as well as in > 30 m distance on a reference grassland site. Roots were extracted in defined intervals from the core and fine root density and fine root length density were determined, using the software WinRhizo for the latter. We found a vertical displacement of tree fine root densities and fine root length densities below the zone occupied by grassland roots. Furthermore, we showed that
the maximum observed lateral extension of tree roots at this site is 5.5 m. The total belowground biomass was significantly higher up to a distance of 2.5 m close to the trees compared to the grassland reference. However, grassland root biomass was significantly reduced up to a distance of 3.5 m. We conclude that the main interaction between root systems in the present alley cropping system is niche differentiation.
The impact of drought on productivity and forage quality of permanent grassland managed in a four-cut system was determined during the first two growth periods of two experimental years. We hypothesized that under drought, the trees have a positive influence on grassland growth processes. In this study, transect positions were placed at 2 m and 6 m distance to the trees with two orientations (West-or East-facing) relative to the tree line and 25 m in the center between two tree lines. We measured biomass accumulation, crude protein and acid detergent fiber concentrations and the share of dead herbage and herbs as well as δ13C isotopic ratios at four repetitions per transect position and growth period. Our study shows that the trees do not affect biomass accumulation systematically neither under moderately dry nor extremely dry conditions. Even close to the trees (at distances ≥ 2 m), we did not detect consistently lower biomass accumulation, while forage quality of the green biomass tended to be slighly higher. Analysis of carbon isotopes showed that the stomatal conductivity is increased under extremely dry conditions close to the tree lines compared to larger distances. This result shows that the tree lines have a positive effect on the water relations of the grassland under drought.
Finally, we tested if the tree lines slow down growth and decomposition processes due to their influence on microclimate in their vicinity. We measured soil temperatures with two repetitions per factorial combination (transect position × cutting frequency) with five levels of transect position (2 m and 6 m distance with two orientations to the tree line and 25 m in the center between two tree lines) and two levels of cutting frequency (four vs. two annual cuts) during two complete years. Our study was arranged in a split-plot design with the cutting frequency assigned to the transect (main plot) and the transect position nested in the main plot. The increase of sward height was monitored every two weeks using the rising plate meter and percent soil cover was assessed visually every four weeks. Decomposition was measured with litterbags where a defined quantity of dried grassland leafy biomass is put into polyethylene bags with a defined mesh size (here 1 mm) and placed on the soil surface. The weight loss is determined after a certain time. An exponential decay function was fitted to our data and the half-life times of litter were calculated. Soil temperatures were significantly lower close to the tree lines
in both cutting frequencies but soil temperatures were slightly higher under frequent cutting. We detected a slight reduction of growth, and soil cover at the transect position with the tree line adjacent in the West. Half-life times were not affected systematically by the tree line and we observed a high variation in decomposition speeds. Our results show that even though the tree lines influence the microclimate and growth processes, they do not influence decomposition of litter to a measurable degree.
This thesis gives an impression on the complexity of the interactions between tree lines and alley crop and the influencing parameters like orientation and spacing of the tree lines that affect the impact on microclimate and competition for light.2024-06-1
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