Content of organic carbon and total nitrogen inStagnic Albeluvisols depending on fertilization

Abstract

The content of soil organic carbon (SOC) and total nitrogen (N_tot) was studied in a long-term field experiment with a three-field crop rotation (potato – spring wheat – spring barley) set up on arable sandy loam Stagnic Albeluvisol at Eerika, Tartu, Estonia. The studied factors were: (A) organic fertilizers with three treatments: (i) without organic fertilizer, (ii) farmyard manure (60 t ha^?1) used in every third year, and (iii) different organic (alternative) fertilizers (beet leaves + straw; pure beet leaves; slurry + straw; cereal straw) and (B) mineral nitrogen fertilizer with the rates: N-0; N-40; N-80; N-120 and N-160 kg ha^?1. The study years were 1993, 1996 and 1999. The average content of SOC (1.03%) was significantly influenced by the use of organic fertilizers. Only N_tot (mean value 0.110%) was influenced also by fertilization with mineral nitrogen. The C/N ratio (mean value 9.5) reflected changes in the content of SOC and N_tot     

Measurement of soil water and nutrients by its electrical properties

Abstract

An instrument for measurement of soil dielectric constant ε _r , electrical conductivity EC _a, and soil temperature was tested on soils under potato crop to investigate contents of soil volumetric water θ and nutrients for eventual use in a field crop model.

To approximate the dependence of θ on ε _r , a logarithmic equation was chosen. Satisfactory results were obtained on stone-free areas, with the mean relative variance between θ-values determined by dielectric constant and converted from a gravimetric method remaining within the limits of measuring error. However, variances were higher for stony soils, with ε _r -values at the same θ being considerably higher. To reconcile data from stony and stone-free soils, a formula was composed.

Salinity, calculated by a semi-empirical model based on Hilhorst's theory using measured values of EC _a, ε _r , and soil temperature, correlated well with contents of K and Mg in the soil. A lower correlation resulted for P, and was practically absent for Ca. Inequality of these regression equations at different measuring sites demonstrates the necessity of considering soil pH when assessing plant nutrients in the soil.     

Small-scale plant species richness and evenness in semi-natural grasslands respond differently to habitat fragmentation

The study explores whether small-scale species diversity, species evenness and species richness in semi-natural grassland communities are similarly associated with present management regime and/or present and historical landscape context (percentage of different land-cover types in the surroundings). Species diversity, evenness and richness were recorded within 441 50 × 50 cm grassland plots in 4.5 × 4.5 km agricultural landscape on Öland, Sweden. Recent and historical land-cover maps (years 2004, 1959, 1938, 1835, and 1800) were used to characterize the present and past landscape context of the sampled vegetation plots. Partial regression and simultaneous autoregressive models were used to explore the relationships between species diversity measures (Shannon diversity, richness and evenness) and different explanatory variables while accounting for spatial autocorrelation in the data. The results indicated that species richness was relatively sensitive to grassland isolation, while the response of species evenness to isolation was characterized by a degree of inertia. Because the richness and evenness components of species diversity may respond differently to habitat fragmentation, we suggest that monitoring projects and empirical studies that focus on changes in biodiversity in semi-natural grasslands should include the assessment of species evenness - as a complement to the assessment of species richness. In addition, our results indicated that the development and persistence of a species-rich and even grassland vegetation was favoured in areas that have historically (in the 19th century) been surrounded by grasslands. Information on landscape history should, whenever possible, be incorporated into the planning of strategies for grassland conservation.     

Die n-versorgung der getreidepflanzen im iosdv?-?tartu?-?pflanzenanalysen und n-bestimmung im boden

Der Internationale Organische Stickstoffdauerdüngungversuch (IOSDV) Tartu wurde 1989 mit den N-Stufen: 0-40-80-120-160 kg N/ha und den verschiedenen organischen Düngungsstufen: 400 dt/ha Rübenblatt, 40 dt/ha Stroh und 600 dt/ha Stallmist auf einer Fahlerde angelegt. Es wurden NH₄- und NO₃- N im Humushorizont des Bodens untersucht und der N-Gehalt im Aufwuchs von Sommerweizen und Sommergerste. Die mineralische und die mineralische-organische Düngung beeinflussten die Bestockung und Blüte der Getreidepflanzen. Die Getreidepflanzen waren während dieser Zeit ausreichend mit Stickstoff versorgt. Die gemessenen Werte stimmten mit den Angaben zur optimalen N-Versorgung in der Literatur überein (<citeref rid="b1">Bergmann, 1986</citeref>). Die N-Gehalte im Korn korrelierten positiv mit den Erträgen. Die N_min-Werte im Boden zeigten erwartungsgemäß im Herbst eine bessere Korrelation zum Ertrag von Sommergerste als die im Frühjahr gemessenen N_min-Werte. Sie wurden stärker durch den mineralisch gedüngten Stickstoff als durch die Nachwirkung der organischen Düngung beeinflusst. Die Ertrag von Sommerweizen war mehr durch die Witterungsbedingungen während der Vegetationszeit beeiflusst. The aim of the international organic-nitrogen long-term experiment (Internationaler organischer Stickstoffdauerdüngungsversuch (IOSDV), initiated in 1989) is to compare the effects of different forms of mineral nitrogen fertilizer (0-40-80-120-160 kg N/ha) with different organic amendments (beet leaves, 400 dt/ha; straw, 40 dt/ha; and FYM, 600 dt/ha) on loamy Podzoluvisol (FAO). The ion-exchangeable NH₄-nitrogen and NO₃-nitrogen content in humus layer and N-content in shoots of different stages of spring barley and spring wheat were studied. Mineral and organic fertilization influenced N-uptake at anthesis and tillering stage. Cereal plants had a sufficient supply of nitrogen at this time. Measured data are well in accordance with published results (Bergmann, 1986). Results of optimal N-content of shoots at different stages correlated positively and significantly with grain yields. N_min content in the humus layer in autumn was correlated better as in spring with grain yields of spring barley. In the vegetation period, N_min content correlates better with treatment with mineral nitrogen fertilizer than with use of organic amendments. In addition, yield of spring wheat is significantly correlated with weather conditions.     

Effect of different management on biochemical properties of organic matter in Fragi-Stagnic Albeluvisols

Abstract

This study was conducted to measure the concentrations of N_total, N-NH₄ ⁺, N-NO₃ ^?, total organic carbon, dissolved organic carbon, and indole-3-acetic acid (IAA) and also activity of nitrate reductase as well as activity of urease from Fragi-Stagnic Albeluvisols' organic matter in a field experiment (crop rotation: potato – spring wheat – spring barley). Samples were obtained from long-term field studies at Eerika near Tartu, Estonia, and from the forest Tiksoja. The experimental plots were under different regimes of organic and mineral fertilizers. The concentrations of N_total, indole-3-acetic acid, activity of urease and C/N ratios were generally the highest in the forest soil Tiksoja. Application of organic and mineral fertilizers increased the activity of both enzymes as well as the concentrations of indole-3-acetic acid in soils. The various fertilizer regimes influenced biochemical factors in soils as well as crop yields. The increase of crop yields was associated with the activity of both enzymes and the content of indole-3-acetic acid in soils.     

Growth of advance regeneration of Norway spruce after clear-cutting

We developed a basal area growth model for recovery of advance growth of Norway spruce trees after clear-cutting. Stem diameter growth at ground level and needle-mass characteristics were measured on permanent sample plots in Estonia. Both tree ring analysis (destructive sampling on one sample plot) and yearly repeated measurement data (two plots) were used to quantify advance growth. Basal area growth of small trees was estimated by multiple regression analysis. Previous-year basal area of the tree and basal area growth explained tree performance the next year. Tree needle-mass variables characterizing the acclimation status of the tree were included in the model as explanatory factors. Needle samples (one shoot from the upper third of each tree crown) were collected each year after the growth period from all sample trees. Needle masses of shoots from consecutive years were correlated and this variable was used as a predictor in the simulation model. Accelerating growth was observed in trees that exceeded the growth threshold in the year after release: the greater the needle mass per shoot, the greater the acceleration in growth. Competition among advance regeneration trees was included in the model: small trees under taller neighbors exhibited reduced growth. We found that trees released from a long period of heavy shade can survive, but the time needed for acclimation and resumption of competitive growth rates is considerably longer than for trees released from light shade. Such trees can be used for forest regeneration, but competition control (particularly reducing the proportion of fast-growing hardwoods) is required.     

Wildfire promotes broadleaves and species mixture in boreal forest

Postfire tree species compositions are predicted to be the same prior to fire according to the direct regeneration hypothesis (DRH). We studied 94 upland boreal forest stands between 5 and 18 years after fire in Ontario, Canada. Postfire species-specific regeneration density was positively related to prefire stand basal area for Pinus banksiana, Populus spp., Betula papyrifera and Picea mariana, but not for Picea glauca and Abies balsamea. In addition, seedling density of Populus spp., B. papyrifera, P. mariana, P. glauca and A. balsamea were positively affected by build up index and, except Populus spp., their density increased with age of burn. To facilitate testing the DRH, we introduced a term called compositional difference (CD) that is the difference in a species relative percentage between the postfire and prefire stand. The testable null hypothesis is CD = 0 for a given species. CD was not different from 0 for P. banksiana, was 19.8% for Populus spp., 10.4% for B. papyrifera, −17.9% for P. mariana, −14.6% for P. glauca, and −14.9% for A. balsamea, indicating fire increases broadleaves at the expenses of mid- and late-successional coniferous species. Compositional increases of Populus spp. and B. papyrifera in postfire stands occurred mostly where these species were a minor component prior to fire. In conclusion, the DRH was supported by the specific positive relationships between postfire regeneration densities and prefire basal area for P. banksiana, Populus spp., B. papyrifera and P. mariana. However, if the DRH is used for predicting postfire composition, P. banksiana is the only species that had the same composition between postfire and prefire stands. Nevertheless, CD for P. banksiana was negatively related to its prefire composition. Similarly, CD for other species was negatively related to their prefire compositions with varying effects of build up index and age of burn. Our results suggest, if fire occurrences increase with global change, the boreal landscape will be more dominated by hardwoods and mixtures of conifers and hardwoods.     

Regeneration in windthrow areas in hemiboreal forests: the influence of microsite on the height growths of different tree species

Natural regeneration of windthrow areas is an important issue when planning forestry measures after forest disturbances. Seedling recruitment was investigated in storm-damaged hemiboreal mixed forests in eastern Estonia. The establishment and growth of seedlings from natural regeneration was registered for tree species in soil pits and in mounds of uprooted trees in stands that were either heavily or moderately damaged. Seedling growth is expected to be better in large but shallow soil pits created by uprooted Norway spruce [Picea abies (L.) Karst.] and poorer in small but deep pits created by the hardwoods in the area, silver birch (Betula pendula Roth.) and European aspen (Populus tremula L.). The most abundant regenerating species was birch. Pits hosted larger seedling numbers than mounds, due to soil instability in mounds. Rowan (Sorbus aucuparia L.) showed significantly faster growth than the other seedling species. Norway spruce pits were preferred to pits of other species by both birch and spruce seedlings. Black alder [Alnus glutinosa (L.) J. Gaertn.] did not show a preference for pits of a certain species of uprooted tree. Both spruce and rowan preferred hardwood mounds over spruce mounds. Storm severity also affected species composition: birch predominantly occurred on pits and mounds in heavily disturbed areas, while spruce was more abundant in the moderately damaged areas. The effects of advance regeneration and surrounding stands on seedling microsite preferences should be considered in future research and subsequent management recommendations.