Browsing by Subject "soil moisture"

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  • Islam, Md. Safiqul (Helsingfors universitet, 2016)
    Mulching, as a cultivation technique, has been adopted since the early twentieth century in agriculture for improving various aspects of crop production. However, the use of mulching was boosted by the introduction of plastic mulch, which has been reported as a harmful substance to the farm environment. Therefore, the need for an environmentally benign mulch material is obvious. The present study investigated the effects of paper and biodegradable plastic mulches on the cucumber yield, soil temperature and moisture content (at 10 cm depth), and the control of weed growth in an agricultural field located at the University of Helsinki in Southern Finland. The degradability of mulches was also investigated. The null hypothesis was that all the mulches would have a similar effect on the abovementioned aspects. Four paper mulches, i.e., BP, KB, CK, and OB, accompanied by biodegradable mulch (BIO) and a bare soil (BG) treatment were under investigation. Each of these treatments had 4 replicates, and a randomized complete block design (RCBD) was adopted. Sensors were installed at 10 cm depth in each study plot to measure the soil temperature and moisture content. In addition, the experimental plots were watered by drip irrigation. All the attained data were analyzed using SPSS statistical software. The results of the study revealed noteworthy positive effects (P<0.05) of mulch application on cucumber yields together with soil temperature, early fruiting, and weed growth regulation compared to the un-mulched bare ground, exclusive of soil moisture content. The daytime soil temperature (DST) was higher than at night (NST), indicating a positive association of the mulch effect with plant growth and crop earliness. However, no suggestive improvement in soil moisture was found through mulch application during the study period. Edge degradation was only found for paper mulches during the study period, suggesting their environment friendliness. The CK and KB papers were the most effective and most environmentally positive mulch materials, and could be a suitable choice for Finnish vegetable growers. The findings of this study could assist paper manufacturers in improving the qualities of mulch papers regarding vegetable production. Future research aims at assessing the effects of mulches on the physiology of plants studied under mulched techniques together with the development of cheaper and more environmentally benign mulch materials.
  • Haapala, Tapani; Palonen, Pauliina; Korpela, Antti; Ahokas, Jukka (2014)
  • Nystuen, Kristin O.; Sundsdal, Kristine; Opedal, Øystein H.; Holien, Håkon; Strimbeck, G. Richard; Graae, Bente J. (2019)
    Abstract Questions How do mat thickness, physical structure and allelopathic properties of terricolous mat-forming lichens affect recruitment of vascular plants in dwarf-shrub and lichen heath vegetation?. Location The mountains of Dovrefjell, central Norway. Methods In autumn, seeds of ten vascular plant species were collected and sown in a common garden experiment with mats of six lichen species and bare-soil controls as experimental treatments. We recorded growing season soil temperature and moisture, and seedling recruitment and growth after one year. The effect of lichen secondary compounds on germination was tested in a growth chamber experiment and compared to the lichen-plant interactions detected under field conditions. Results The lichen mats buffered extreme soil temperatures and soil drying in dry weather, with soils below the thickest mats (Cladonia stellaris and C. rangiferina) experiencing the lowest temperature fluctuations. Seedling recruitment and seedling growth in the field and seed germination in the lab were species-specific. Seedling recruitment rates were overall higher within lichen mats than on bare soil, but the c. 6.5 cm thick mats of C. stellaris reduced recruitment of many species. The lab experiment suggested no overall strong effect of lichen allelopathy on seed germination, and effects on seed germination were only moderately correlated with the lichen-plant interactions observed for seedling recruitment in the field. Conclusions In harsh environments like alpine dwarf-shrub and lichen heaths, the presence of lichens and the resulting amelioration of the microclimate seems more important for vascular plant recruitment than are allelopathic effects often reported in lab experiments. We might therefore expect most terricolous lichens, depending on the plant species in focus, to facilitate rather than hamper the early stages of plant recruitment into lichen-dominated arctic-alpine heath vegetation. This article is protected by copyright. All rights reserved.
  • Gyawali, Arun (Helsingin yliopisto, 2018)
    The balance between incoming precipitation (rainfall and snowfall) and outgoing evapotranspiration (ET), runoff and drainage to and from an ecosystem plus changes in soil moisture storage and the water equivalent of the snowpack is known as the water balance. A dominating feature of the water balance in the boreal zone is snowpack accumulation over winter and the spring snowmelt, both of which are affected by forest. In Finland, there are strong north-south gradients in the amount of precipitation, the proportion of rainfall and snowfall and temperature, and therefore latitudinal differences in the water balances components can be expected. Furthermore, the large canopy and deeper rooting of trees, together with the presence of a permanent ground vegetation cover, result in significant differences in interception, infiltration and water balance outputs of forests compared to other forms of land-use. Because of morphological and ecophysiological differences between the trees species, the water balance of Norway spruce and Scots pine dominated forests can be expected to differ. Determining the water balance of forest ecosystems across Finland would, therefore, help in assessing the hydrological ecosystem services provided by forests and form a basis for examining the effects of climate change and forest management on the water balance. This study aimed to compute the daily water balance of six Norway spruce, and three Scots pine dominated mature forest stands (plots) located throughout Finland over a 26-year study period (1990-2015). It was hypothesized that the various water balance components would systematically vary with latitude, a surrogate for climate, and differ between spruce and pine stands. The daily version of the water balance model “WATBAL” developed by Mike Starr (University of Helsinki, Dept. Forest sciences) was used for this study. The model requires daily meteorological data (precipitation, temperature, global radiation), stand parameters (canopy cover, rooting, crop coefficient), soil parameters (including infiltration coefficient, soil moisture contents at permanent wilting point, field capacity and saturation, and two soil moisture parameters for a plant available water content function). Six of the plots had soil developed in till and 3 plots had soil developed in sorted glaciofluvial deposits. Plot meteorological data for 1990-2015 was derived using spatially interpolated gridded data. If the daily air temperature was ≤0°C, any precipitation was assumed to be snowfall. The stand and soil parameters were derived from data collected from the 9 study plots by Luke (formerly Metla). The nine plots belong to the Finnish network of ICP-Forest level II plots that have been established throughout Europe. Pedotransfer functions (PTF) based on soil texture and organic matter contents were used to derive initial values for the soil hydraulic parameters. Time domain reflectometry (TDR) measured soil moisture data was available for 7 of the plots and, after carrying out careful quality control and rejection of outliers, used for calibration of modelled soil moisture and optimization of soil hydraulic parameters for those plots. Optimization was carried out using the non-linear Marquardt regression method. Goodness-of-fit for soil moisture was evaluated using correlation and R2 values from linear regression. After computing the daily water balance with the WATBAL model (using optimized soil hydraulic parameter values for the 7 plots and initial PTF values for the remaining 2 plots) the long-term mean annual and mean daily water balance components (with a 7-day moving average smoothing) were calculated. The water balances were computed for the humus layer plus 0-40 cm soil layer, which, based on literature, would have included most if not all of the roots. The dependence of the mean annual water balance components on latitude was evaluated using correlation analysis and linear regression, and the effect of tree species was tested for using the t-test on pairs of spruce-pine plots located close to each other. The raw TDR data was found to contain a considerable amount of gaps and erroneous (too high) values, often associated with the spring snowmelt. Optimization of the soil hydraulic parameters using the measured soil moisture contents calculated from the “cleaned” TDR data for the snow-free period resulted in a highly significant (p<0.001) Pearson correlation of +0.85 (R2 = 0.75) for the fit between measured and modelled soil moisture contents calculated across all 7 plots. The correlations for the individual plots were also highly significant. Based on the optimized WATBAL output, the fraction of plot mean annual precipitation as snowfall ranged from 20 to 29%. Corresponding ranges for ET, drainage and runoff were respectively 33 to 57%, 24 to 42%, and 18 to 25%. The mean annual water balance components were found to be significantly correlated to latitude, reflecting trends in precipitation and temperature. Evapotranspiration decreased with increasing latitude while maximum snow-on-ground, snowmelt and associated runoff increased with increasing latitude. Spruce mean annual ET was 9% higher than pine in one of the paired plot sets and 37% higher in the other set. For drainage, pine was 15% greater than spruce in one of the paired plot set and 74% higher in the other set of paired plots. There were no significant differences between spruce and pine plots for snowmelt and runoff. Variation around these trends were related to differences in soil hydraulic properties among the plots which, in turn, were related to differences in parent material and soil texture. The overall conclusion from this study was that the daily water balance of the forested plots could be realistically modelled using such a relatively simple water balance model as WATBAL. The importance of spatially representative and accurate soil moisture measurements for model calibration purposes was highlighted. While the importance of snowfall on the water balance increased northwards regardless of tree species, evapotranspiration was determined by both latitude and by species. Climate change can therefore be expected to have a significant impact on the water balance of Finnish forests resulting in environmentally important changes in leaching and runoff.
  • Määttä, Tiia (Helsingin yliopisto, 2020)
    Methane (CH4) is a greenhouse gas with a great impact on global climate. In the soil, it is produced in anoxic and consumed in oxic conditions by microbes. Together with different methane transport mechanisms, methane production and consumption directly regulate the resulting soil methane flux. Boreal upland forests are generally considered to act as methane sinks due to high methane consumption. However, some studies have shown a boreal upland forest soil turning from a methane sink to a source after long-term abundant precipitation. This study aimed to examine the effects of soil moisture on CH4 flux from simulated increase in rainfall in a northern boreal upland forest soil, and how simultaneous soil temperature increase, organic litter addition and organic litter and root exclusion affect the temporal changes in flux. The study was conducted in Kenttärova forest in Kittilä, Finland in summer 2018. Split-plot design was used in the experiment with soil moisture being the main treatment variable and soil warming (T), organic litter addition (A) and organic litter and root exclusion (E) subtreatment variables. The design included two main plots: irrigation (I) and control (C), within which each subtreatment was replicated three times. In addition to the T, A and E manipulations, plots without additional manipulations (O) were included for the assessment of the effect of only soil moisture increase, and were replicated four times within both main plots. Methane flux was measured at least once a week using chamber method. Soil moisture and temperature were also continuously measured. The treatment effects were analysed using both autoregressive heterogeneous and autoregressive two-way analyses of variance, TukeyHSD method, variable correlations and Generalized Linear Models. The soil did not turn into a methane source but the results showed significant differences between the irrigation and control site, indicating a strong decreasing effect of soil moisture on soil CH4 sink in all treatment levels. All treatments had lowest uptake rates in August, possibly as a result from highest soil moisture levels. IA treatment was the most effective in producing low uptake rates possibly due to the reduction in gas diffusion. E treatments had contrasting results, IE showing increases in uptake rate by increases in soil moisture but the causes remained unsolved and the results were highly uncertain. T treatment had no effect on uptake likely due to a failure to create soil temperature differences and thus the interactions were not reliably analysed. The results suggest that the changes may have been more related to changes in methane consumption than production. Further research is needed especially for examining the combined effect of litter addition, soil moisture and soil temperature increase on methane flux with multiple temporal replications of the experiment.
  • Kemppinen, Julia; Niittynen, Pekka; Aalto, Juha; le Roux, Peter C.; Luoto, Miska (2019)
    Water is crucial for plant productivity and survival as a fundamental resource, but water conditions can also cause physiological stress and mechanical disturbance to vegetation. However, these different influences of water on vegetation patterns have not been evaluated simultaneously. Here, we demonstrate the importance of three water aspects (spatial and temporal variation of soil moisture and fluvial disturbance) for three ecologically and evolutionary distinct taxonomical groups (vascular plants, mosses, and lichens) in Fennoscandian mountain tundra. Fine‐scale plant occurrence data for 271 species were collected from 378 x 1 m2 plots sampled over broad environmental gradients (water, temperature, radiation, soil pH, cryogenic processes, and the dominant allelopathic plant species). While controlling all other key environmental variables, water in its different aspects proved to be a crucial environmental driver, acting on individual species and on community characteristics. The inclusion of the water variables significantly improved our models. In this high‐latitude system, the importance of spatial variability of water exceeds the importance of temperature for the fine‐scale distribution of species from the three taxonomical groups. We found differing responses to the three water variables between and within the taxonomical groups. Water as a resource was the most important water‐related variable in species distribution models across all taxonomical groups. Both water resource and disturbance were strongly related to vascular plant species richness, whereas for moss species richness, water resources had the highest influence. For lichen species richness, water disturbance was the most influential water‐related variable. These findings demonstrate that water variables are not only independent properties of tundra hydrology, but also that water is truly a multifaceted driver of vegetation patterns at high‐latitudes.