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961.
Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH4–N and NO3–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grassland→shrubland→secondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land‐use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20‐ to 40‐cm layer was significantly lower compared with the topsoil (0–20 cm) across all land‐use types. TN, soil organic matter (SOM) and NH4–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.  相似文献   
962.
Delayed flower bud formation was recorded when a single spray of 200 ppm ethephon was applied to rooted chrysanthemum cuttings three days after planting in long days. The cuttings were of three American garden cvs and an autumn-flowering cv known to bud readily in long days. The technique might be useful for propagators and growers of chrysanthemums to delay bud formation on stock plants and on rooted cuttings.  相似文献   
963.
Swine manure and wood shavings used as a drying bed were removed from a High-Rise? hog facility following two production cycles. The manure was composted in aerated pilot-scale vessels for four weeks or a mechanically turned windrow for ten weeks. Total dry matter losses during the pilot-scale studies were 30 and 32.5 % for continuously and intermittently aerated systems, respectively. Compost from both systems was stable with emission rates of 0.07-0.11 mgCO2 h?1 gvs?1. Moisture, O2, CO2 and NH3 use/losses during the process as well as chemical properties of the initial and composted manure are presented. Incorporation of the compost at a 5% amendment rate (v/v) into a standard pine bark container medium significantly (P = 0.05) increased growth of two woody plant species. Higher amendment rates were toxic to some plants due to high initial NH4+ concentrations in the medium. The compost significantly (P=0.05) increased growth and suppressed Pythium root rot of poinsettia when incorporated at 10% (v/v) into a standard sphagnum peat mix. The compost can be utilized as a value-added disease-suppressive product in the ornamentals industry.  相似文献   
964.
To gain more insight into the hydrological behaviour of coarse-textured soils, the physical properties of artificially created soil mixtures with different texture were determined. The mixtures were prepared according to the specifications of the United States Golf Association (USGA) for constructing putting greens. In addition, the effect of 10 vol.% organic matter addition was studied. The soil moisture retention and hydraulic conductivity relationships of the different mixtures were determined and their hydrological behaviour was studied using the numerical model SoWaM. Both texture and organic matter addition substantially affected the hydraulic properties. Hydraulic conductivity significantly increased with increasing coarseness while moisture retention decreased. On the other hand, organic matter addition reduced saturated hydraulic conductivity by a factor of 10 to 100 and distinctly increased moisture retention capacity. The amounts of total available water were increased by the addition of organic matter between 144% (slightly coarse texture) and 434% (very coarse texture). Results indicate that the mixtures can contain only 2–16% plant available water and therefore need frequent irrigation to maintain plant growth. Addition of organic matter seems a good solution to reduce the irrigation water requirements but it increases the risk of ponding or runoff because of large reductions in the saturated hydraulic conductivity sometimes to below the rate of 3.6 m/day recommended by the USGA.  相似文献   
965.
966.
Im Statischen Düngungsversuch Bad Lauchstädt werden nach Erweiterung der Versuchsfrage seit 1978 die Prüffaktoren: Stalldung (2 Stufen), Corg‐Gehalt im Boden (6 Stufen) und Mineral‐N‐Mengen (5 Stufen) in der Fruchtfolge Kartoffeln, Winterweizen, Zuckerrüben, Sommergerste geprüft. Nur bei Sommergerste konnte eine Ertragswirkung des Stalldungs im Vergleich zu ausschließlicher Mineraldüngung nachgewiesen werden. Die jährlichen Veränderungen der Corg‐ und Nt‐Gehalte im Boden betrugen bei jeweils extremen Änderungen des Düngungsregimes bis zu 0, 012% Corg bzw. 0,0013% Nt.  相似文献   
967.
The System of Rice Intensification (SRI) reportedly enhances the yields of rice (Oryza sativa L.) through synergy among several agronomic management practices. This study was conducted to investigate the effects on rice plant characteristics and yield by comparing the plants grown with different methods of cultivation – SRI vs. recommended management practices (RMP) focusing on the impact of different plant spacings. Performance of individual hills was significantly improved with wider spacing compared with closer‐spaced hills in terms of root growth and xylem exudation rates, leaf number and leaf sizes, canopy angle, tiller and panicle number, panicle length and grain number per panicle, grain filling and 1000‐grain weight and straw weight, irrespective of whether SRI or RMP was employed. Both sets of practices gave their highest grain yield with the spacing of 20 × 20 cm; however, SRI yielded 40 % more than the recommended practice. At this spacing, canopies also had the highest leaf area index (LAI) and light interception during flowering stage. The lowest yield was recorded at 30 × 30 cm spacing under both the practices, as a result of less plant population (11 m?2), despite improved hill performance. During the ripening stage, hills with wider spacing had larger root dry weight, produced greater xylem exudates, and transported these towards shoot at faster rates. These features contributed to the maintenance of higher chlorophyll levels, enhanced fluorescence and photosynthesis rates of leaves and supported more favourable yield attributes and grain yield in individual hills than in closely‐spaced plants. Moreover, these parameters further improved in SRI, apart from the enhanced percentage of effective tillers and showed substantial and positive impacts on grain yield (17 %) compared with recommended practice. In conclusion, wide spacing beyond optimum plant density, however, does not give higher grain yield on an area basis and for achieving this, a combination of improved hills with optimum plant population must be worked out for SRI.  相似文献   
968.
969.
Objectives : To describe a method of faecal smear production and to determine the sensitivity and specificity of faecal smear for detection of parasitic larvae using Baermann sedimentation as a gold standard Methods : Faecal smears were produced from samples submitted to the Royal Veterinary College Diagnostic Laboratory Service for Baermann sedimentation. An inexperienced and an experienced assessor each examined the smear for larvae for a maximum of five minutes. Results : One hundred and eighty six samples were analysed of which 28 were positive for Angiostrongylus vasorum on Baermann sedimentation. The experienced assessor had a faecal smear sensitivity of 61% and a specificity of 100%. The inexperienced assessor had a faecal smear sensitivity of 54% and a specificity of 95%. Clinical Significance : Faecal smear is an effective and cheap aid to diagnosis of canine angiostrongylosis which can be readily performed in general practice. Its use leads to a rapid detection of infection compared to other available methods. This could lead to swifter treatment of the disease and a decrease in inappropriate diagnostics. A further diagnostic method, such as Baermann sedimentation, is recommended whether the faecal smear result is positive or negative.  相似文献   
970.
After decades of searching for a practical method to estimate the N mineralization capacity of soil, there is still no consistent methodology. Indeed it is important to have practical methods to estimate soil nitrogen release for plant uptake and that should be appropriate, less time consuming, and cost effective for farmers. We fractionated soil organic matter (SOM) to assess different fractions of SOM as predictors for net N mineralization measured from repacked (disturbed) and intact (undisturbed) soil cores in 14 weeks of laboratory incubations. A soil set consisting of surface soil from 18 cereal and root‐cropped arable fields was physically fractionated into coarse and fine free particulate OM (coarse fPOM and fine fPOM), intra‐microaggregate particulate OM (iPOM) and silt and clay sized OM. The silt and clay sized OM was further chemically fractionated by oxidation with 6% NaOCl to isolate an oxidation‐resistant OM fraction, followed by extraction of mineral bound OM with 10% HF (HF‐res OM). Stepwise multiple linear regression yielded a significant relationship between the annual N mineralization (kg N/ha) from undisturbed soil and coarse fPOM N (kg N/ha), silt and clay N (kg N/ha) and its C:N ratio (R2 = 0.80; P < 0.01). The relative annual N mineralization (% of soil N) from disturbed soils was related to coarse fPOM N, HF‐res OC (% of soil organic carbon) and its C:N ratio (R2 = 0.83; P < 0.01). Physical fractions of SOM were thus found to be the most useful predictors for estimating the annual N mineralization rate of undisturbed soils. However, the bioavailability of physical fractions was changed due to the disturbance of soil. For disturbed soils, a presumed stable chemical SOM fraction was found to be a relevant predictor indicating that this fraction still contains bio‐available N. The latter prompted a revision in our reasoning behind selective oxidation and extraction as tools for characterizing soil organic N quality with respect to N availability. Nonetheless, the present study also underscores the potential of a combined physical and chemical fractionation procedure for isolating and quantifying N fractions which preferentially contribute to bulk soil N mineralization. The N content or C:N ratio of such fractions may be used to predict N mineralization in arable soils.  相似文献   
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