Roots under the load of heavy machinery in spruce trees

The effects of the passage of forwarders on soil and damage to spruce root systems along an experimental trail were studied. The site was characterized by medium-textured soil of the pseudogley type under favorable moisture conditions. Due to the passages, the soil was compacted down to a depth of 20 cm, soil porosity was decreased by 5% (volume) and soil aeration was decreased by more than 5%. Substantially higher values of mechanical soil resistance occurred (estimated by penetrometric measurements) in a soil pit situated in a rut after passages. Pressure measured by sensors placed at a depth of 10 cm below the soil surface reached values ranging from 0.09 to 0.11 MPa in plots uncovered with slash and 0.03–0.07 MPa in plots covered with slash after two to four passages, and 0.06–0.07 after six to ten passages. Soil surface deformations occurred in the upper soil layers through tire impression. This resulted in the origin of ruts, whose depth and width was dependent on the type of tires, their load, surface conditions, type and texture of soil, soil moisture and number of passages. Pressure in the soil layers imposed by the tire of a given type, inflation and load changed in relation to depth, ground cover, soil properties and reinforcing components on the soil surface. Sap flow in coarse roots actually treated by a moving heavy load clearly and immediately responded with a sharp increase followed by a similar decrease (peak flow) after several minutes. On average, the flow rate decreased by about 8% after the first treatment compared to the untreated state, and remained the same after passing the peak during the second pass when the maximum load was applied. However, this decrease amounted to about 40%, when compared to the “relative zero flow” after root severing. This indicates serious local damage to the conducting system. Even when loading directly damaged rather small fractions of the total root systems, it opened tree tissues to subsequent fungal infection, whose impact could be very serious in future years. Flow in stem sections oriented in the opposite direction to the trail and the flow in stem sections and root buttresses oriented toward the trail (but where roots were not actually growing below the trail or grew deeper in the soil), neither responded to the treatment or responded insignificantly. Sap flow responded only in surface roots below trails, occurring down to a depth of about 10 cm below the original soil (litter) surface. This occurred only when a significant part of the roots (with the total projected area of treated root branches more then 500 cm²) were under the tires. This indicates the protective ability of soils and also, a possible method of artificial root protection.     

Recognition of the invasive species Robinia pseudacacia from combined remote sensing and GIS sources

Monitoring the spread of invasive species is crucial for nature conservation; however regularity can only be assured if cost-effectiveness can be achieved. We aimed at testing low-cost remote sensing sources and simple methodology for recognising the invasive species Robinia pseudacacia and thus founding a monitoring scheme. A study area with mixed wooded stands containing R. pseudacacia has been selected for this purpose in NE Slovenia. Four different sources (Landsat ETM and airborne orthophotos from summer and spring) were tested together with a filtering for forested areas. Filtering was based either on Landsat information or on a forest polygon layer as alternatives. Generalised linear models were constructed in a training window within the study area to establish a statistical rule of recognition for the species based on spectral information. Models were tested both within and outside the training window for accuracy. As means of accuracy assessment both the well-established AUC and the specially adapted Jaccard index have been applied.The best and most reliable recognition was achieved by using the spring orthophoto, in which the species was captured in flower, combined with a GIS filtering by a forest vector layer. The superiority of this combination was especially striking when tested over the full study area. The Jaccard index appeared to be more sensitive in discrimination between models. Thus we conclude that even spectrally less detailed data sources may provide a basis for successful monitoring if the phenology of the target species is also considered.     

Winter wheat fertilizing using nitrogen–sulphur fertilizer

Precise field experiments were established on two sites with winter wheat under different soil-climatic conditions in the Czech Republic. Four treatments were fertilized with same dose of nitrogen (200 kg N ha^?1) and increasing dose of sulphur (0, 10, 20 and 40 kg S ha^?1) using nitrogen–sulphur (N–S) fertilizer with calcium sulphate form. Soil and plant aboveground biomass samples were taken in the stages of development BBCH 26–28; 30–32; 37–39; 49–51. The winter wheat grain yield ranged between 7.20 and 10.86 t ha^?1 and had an increasing trend with increasing sulphur dose. Although the differences were usually not statistically significant, there were found increasing tendencies of bioavailable sulphur content in soil with increasing S split doses. Soil S content decreased with time probably due to plant uptake. Sulphur dose did not influence the S content in plant aboveground biomass. The total S contents in grain after harvest ranged between 0.09% and 0.14% and were not significantly influenced with the fertilizing treatment. The same statement is valid for the S content in straw, which ranged between 0.03% and 0.11%. Both, S content in winter wheat seeds and straw were strongly influenced by the site conditions.     

Curing kinetics study of melamine–urea–formaldehyde resin/liquefied wood

The objective of this research was to investigate the effect of liquefied wood (LW) on the cure kinetics and network properties of melamine–urea–formaldehyde (MUF) resins by differential scanning calorimetry. The MUF/LW compounds exhibited two distinct cross-linking processes. It can be assumed that there did not appear to be a coreaction of the MUF with the LW. The overall apparent activation energies (E _a) of the curing reactions were calculated using the Kissinger equation. An nth-order kinetic model was used to describe the cross-linking of MUF/LW compounds, of various compositions, cured at different heating rates. The E _a values for the cross-linking process of the MUF/LW compounds predominantly tended to be approximately 80 and 71 kJ mol^?1 for MUF and LW, respectively. The apparent reaction orders of the MUF cross-linking process of the MUF/LW compounds were in the range 1–2, whereas the n values of the LW were approximately unity or less, which hints to there being a more complex mechanism of this process.     

Relationships between available soil water and indicators of plant water status of sweet sorghum to be applied in irrigation scheduling

Optimal crop production depends greatly on available soil water, and it is therefore important to know when and how much to irrigate in order to attain agronomic potential. In this work, plant indicators are used to assess water stress. These are compared with available soil water to find the critical point for irrigation scheduling of sweet sorghum. The experimental trial was carried out in Bečej, in the Vojvodina region, on a sweet sorghum crop, grown in moderate climatic conditions on a well-drained, deep chernozemolic meadow soil. Plant indicators tested were predawn and midday leaf water potential and crop and air temperature difference. All the methods were sensitive to water deficit in plants, but not all can be used for irrigation scheduling. The predawn leaf water potential was the most reliable parameter among those tested due to its relative independence from weather conditions and a valid indicator of plant water status. This was not the case with canopy-air temperature difference. The predawn leaf water potential corelation with available soil water indicates that the threshold value for irrigation scheduling of sweet sorghum is when the former has decreased to –0.45 MPa. This corresponds to a soil water depletion to about 10% of available water in the active root zone. The canopy-air temperature difference was sufficiently sensitive to indicate the onset of mild plant water stress, although it showed a certain threshold value when water shortage appeared, which occurred when the air and canopy temperature were the same. Received: 9 April 1996     

RFLP analysis of Hypericum perforatum L. somaclones and their progenies

Three adjacent EcoRI fragments of the rDNA unit from Lycopersicon esculentum, eleven anonymous genomic and two anonymous cDNA clones from Brassica napus and three restriction endonucleases: BamHI, EcoRI and EcoRV were used for RFLP analysis of the genome of Hypericum perforatum L. A polymorphic band identified with EcoRI and two rDNA probes in five somaclones originated from the same genotype was detected in all progenies of two somaclones indicating the inheritance of the molecular changes. rDNA unit heterogeneity represented by two types of RFLP pattern revealed among somaclones and seed-derived control plants using EcoRV and two rDNA probes may indicate an alloploid origin of Hypericum perforatum. The occurrence of the identical RFLP patterns in some R₀ somaclones and seed-derived plants and their progenies may be related to the apomictic mode of reproduction which is assumed to be prevalent in Hypericum perforatum. The differences in RFLP patterns of progenies when compared with the maternal plants (1 out of 10 progenies of one control plant and 1 out of 8 progenies of one somaclone) may indicate that some progenies have originated through sexual recombination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sulphur isotope characteristics of two north Bohemian forest catchments

Sulphate concentrations and ³⁴S ratios were monitored in bulk precipitation, spruce throughfall, and soil water (depth of 30 and 90 cm) at ervená jáma (CER) and Naetín (NAC), two severely polluted sites in the Czech Republic, between December 1992 and September 1994. Throughfall [SO₄ ^2–], up to 80 mg L^–1 in winter and as low as 7 mg L^–1 in summer, was higher than [SO₄ ^2–] in bulk precipitation (annual average 6 mg L^–1). There was a distinct seasonaity in S isotope abundances, with lower ³⁴S_BULK in summer (+4 per mil CER, + 6 per mil NAC) and lower ³⁴S_TF in winter (+3 per mil CER, +4 per mil NAC). Wintertime ³⁴S_BULK was around +8 per mil at CER and +10 per mil at NAC, summertime ³⁴S_TF was close to +7 per mil at both sites. For only a 1- month period in spring, bulk precipitation S became isotopically lighter than throughfall S. Bulk precipitation data from CER were in good agreement with those from the nearby monitoring station Lesná (LES), typically differing by less than 10 mg L^–1 and 2 per mil in [SO₄ ^2–] and ³⁴S, respectively. Suction lysimeters (soil depth of 30 and 90 cm) yielded higher sulphate concentrations and lower ³⁴S ratios compared to both bulk and throughfall precipitation. Little seasonality was observed in [SO₄ ^2–] at 30 cm (around 40 mg L^–1); at 90 cm [SO₄ ^2–] was higher in winter (70 mg L^–1) than in summer (45 mg L^–1). ³⁴S at 90 cm was <+5 per=" mil=" in=" 1993=" and=" up=" to=" +7.5=" in=" 1994,=" lower=" in=" the=" first=" year=" and=" higher=" in=" the=" second=" year=" compared=" to=" the=" depth=" of=" 30=" cm.=" sulphur=" fluxes=" at=" cer=" and=" nac=" are=" characterized=" by=" distinct=" isotope=" compositions=" and=" can=" therefore=" be=" used=" to=" trace=" s=" pathways=" and=" transformations=" in=" the=" forest=">     

Comparison of postharvest practices used for cereal straw decomposition in a clay loam soil

During 2008–2011 model field experiments were carried out at the Joni?k?lis Experimental Station of Lithuanian Research Centre for Agriculture and Forestry on a clay loam Endocalcaric Endogleyic Cambisol. The study was aimed to establish the comparison of various postharvest practices (mineral nitrogen fertilizer alone or together with a bioactivator Penergetic k, livestock slurry, red clover biomass, and straw incorporation in the soil by a stubble cultivator at a 10 cm depth) on the acceleration of the initial (nine-month period) decomposition of winter wheat straw. During this period straw mass decomposition intensity (DIM) was 20.7–29.1%, carbon (C) concentration decreased by 6.5– 22.8%, while an increase occurred in nitrogen (N) 1.1–2.2 times. The highest straw decomposition rate was recorded when after straw incorporation autumn was warm and humid. That year straw mass C to N ratio (C/N) was 38–46. Under less favourable autumn conditions, the highest decomposition of straw was achieved having applied mineral N (with and without Penergetic) and livestock slurry and having incorporated the straw in the soil (C/N = 40–55). A slower decomposition rate was observed for the straw spread on the soil surface with mineral N addition or on undersown red clover.