Conduciveness of different soilless growing media to <Emphasis Type="Italic">Pythium</Emphasis> root and crown rot of cucumber under near-commercial conditions

Substrates made from rockwool, coir dust, pumice and perlite were compared for conduciveness to Pythium root and crown rot in cucumber under near-commercial conditions. Rockwool slabs of 7 cm height were more conducive to the Pythium disease than coir dust slabs, pumice or perlite under these conditions. Temperature, oxygen concentration and water content were determined in the substrates to explain differences in conduciveness between the inorganic substrates rockwool, pumice and perlite by differences in the physical conditions. Temperature and oxygen concentration could not explain the differences but the higher disease level on rockwool was associated with a much higher water content of this substrate as compared to coir dust, pumice and perlite. Increasing the height of the substrate from 7 to 14 cm greatly decreased the percentage of diseased plants due to the Pythium disease on rockwool but had no effect on the level of disease on perlite when the substrate had been infested 4 cm below the planting hole. This difference in response in substrate height between rockwool and perlite could be explained by a much larger decrease in water content with substrate height in the rockwool than in the perlite substrate. Temperature in the substrates were above 30 °C for more than 6 h on sunny days in June and reached maximum values of 35 °C or more. These temperatures are highly favourable for the pathogen P. aphanidermatum but will have adverse effects on most biocontrol strains.     

铜绿假单胞菌菌剂载体的筛选

为将铜绿假单胞菌应用于重金属污染环境的生物修复,以硅藻土(1~3 mm)、硅藻土(3~6 mm)、活性炭和轻石为材料,通过测定不同材料的吸水率、菌体吸附与释放作用及制备菌剂的活菌数,筛选出适宜的菌剂载体.结果表明,在设定的载体浓度下(0~20 g·L-1),不同载体的菌体去除率随浓度提高而增大,Q值在4.90%~49.60%之间;载体负载量随浓度提高而减小,L值在923.33~82.83 mg·g-1之间;硅藻土、活性炭的Q值在30 min达到最大.硅藻土(1~3 mm)、硅藻土(3~6mm)、活性炭和轻石的吸水率依次为60.3%、43.3%、23.4%和33.1%;以上4种载体制备的菌剂(菌剂A、B、C和D)的活菌释放率依次为27.4%、28.8%、19.7%和37.1%.室温保存30 d后,菌剂A活菌数为6.25×108CFU·g-1,减少了78.4%,菌剂B活菌数为1.12×1010CFU·g-1,是初始值的5.38倍,菌剂C的活菌数为2.95×108CFU·g-1,减少了73.9%,菌剂D的活菌数为3.61×109CFU·g-1,增殖了127.0%.可见,载体浓度及吸附时间显著影响其对菌体的吸附作用,3~6 mm硅藻土的负载量适中,菌体存活率高,活菌释放率高,可作为铜绿假单胞菌的菌剂载体.     

An Improved Procedure for Determining Magnesium Fertilizer Dissolution in Field Soils

Abstract

The sequential extraction procedure currently used to measure magnesium (Mg) fertilizer dissolution in soils consists of removing dissolved Mg (step 1), and partially dissolved Mg (step 2), followed by an 18‐h extraction with 2 M HCl at room temperature to determine undissolved Mg (step 3). This procedure is satisfactory for soluble and moderately soluble Mg fertilizers but is not an accurate procedure for slightly soluble fertilizers, such as serpentine. When step 3 is replaced by a digestion procedure using 2 M HCl for 4 h at 90–95°C (improved step 3), the total serpentine Mg recovery (dissolved and undissolved Mg) from soil samples, either immediately after serpentine was added to soil or after a 21‐day incubation with moist soil, was about 100% compared to 40–50% by the original procedure. The improved procedure also increased the recovery of serpentine Mg applied to field soils. Therefore, this study recommends that the third step of the sequential extraction procedure be replaced by a 4 h digestion using 2 M HCl (90–95°C).     

Influence of different forage grasses on nitrate capture and leaching loss from a pumice soil

Nitrogen (N) uptake and loss in leachate from a pulse of ¹⁵N-labelled synthetic cow urine applied to a pumice soil were compared in a glasshouse lysimeter experiment among the grass species, Agrostis capillaris , Dactylis glomerata , Phalaris aquatica , Lolium multiflorum , L . perenne and a L . multiflorum/A. capillaris mixture. In addition, four L. perenne treatments investigated the effect of infection by Neotyphodium lolii strains. Leachate volumes and leachate nitrate concentrations were measured. At final harvest 24 weeks after sowing, dry matter (DM) mass of shoots and roots, plant N and ¹⁵N contents, soil residual mineral N, and root diameters and lengths were measured. Endophyte had no effect on plant or nitrate variables. Lysimeters planted with L . perenne (pooled endophyte treatments) leached 48 mg of NO₃-N compared with <3 mg N for the other grasses. Recovery of ¹⁵N was highest in A. capillaris (0·99), followed by D. glomerata and P. aquatica (0·89), the L . multiflorum / A. capillaris mixture (0·87), L . multiflorum (0·60) and L . perenne (0·44). Low ¹⁵N recoveries and high leaching losses from L . perenne were associated with low plant and root masses of DM and low rooting depth. High aerial mass of DM, root systems extending below 20 cm and high root masses of DM in lysimeters with A. capillaris , P. aquatica and D. glomerata contributed to a high rate of nitrate interception by these species and low leachate losses. The L . multifloru m/ A. capillaris mixture was intermediate between the two species for most of the variables measured.     

Soil testing of horticultural substrates (i) Evaluation of 1: 1.5 water extract for nitrogen

Abstract

The 1: 1.5 water extraction of horticultural substrates for N was evaluated using N uptake as the criterion. Three crops, tomato (1 trial), chrysanthemum (2 trials) and verbena (2 trials) were grown in a number of substrates including peat, peat + pumice, bark, peat + sawdust + sand and JIP. The number of N application rates varied from 7 in the tomato trial to 20, 22 or 25 in the chrysanthemum and verbena trials. The relationship between soil test value and N uptake was quadratic rather than linear, and was very good, especially for the chrysanthemum and verbena trials (R² nearly always greater than 0.9). The relationship varied among the substrates depending on whether N was retained (e.g. bark) resulting in overestimation of N uptake, or on whether N was released (e.g. JIP) resulting in underestimation.     

Rapid X‐ray spectrographic determination of major element homogeneity in Mazama pumice

Abstract

Permanent powder mounts were prepared for X‐ray spectrographic analysis by molding bakelite powder at 24,000 psi and heating to 110C. Spraying with clear acrylic resin maintains surface permanency for non‐clayey samples. Standard curves for Si, Al, Fe, K, Ca, and Ti prepared with USGS and NBS rock powders were used to determine that two distinct textural layers of Mazama pumice had similar major element contents. Ground pumiceous lapilli from the weathered AC horizon (20–30 cm depth) had 4% less Ca, 4% less Si, 8% less K, 9% more Ti, 12% more Al, and 16% more Fe than unweathered pumice in the C1 and C2 horizons.     

橡胶浮石混凝土的抗冻性能及微观结构

为探究冻融循环条件下橡胶浮石混凝土宏观性能和孔隙结构的变化规律,进行冻融循环、单轴压缩试验,通过扫描电子显微镜(SEM)以及核磁共振(NMR)技术对橡胶浮石混凝土抗冻性进行分析,同时建立其抗冻性预测模型.结果表明:加入0.12~0.18 mm的橡胶可有效降低冻融条件下浮石混凝土表面的剥蚀、内部的损伤以及力学性能的衰减,冻融200次时,加入0.15 mm橡胶的浮石混凝土质量损失率最小,为-0.14%,相对动弹性模量最大,为67.36%;冻融循环作用下橡胶浮石混凝土内部孔隙会发生劣化,小孔隙逐渐向大孔隙演变,无害孔和少害孔向有害孔和多害孔演变,加入0.12~0.18 mm的橡胶可有效抑制孔隙的劣化,使混凝土内部结构更为密实;通过橡胶浮石混凝土抗冻性预测模型可得到,加入0.15 mm橡胶的浮石混凝土抗冻周期最长,较普通浮石混凝土抗冻周期延长12.76%.     

Effects of thiosulfate addition on ammonia and nitrogen removal in biofilters packed with Oyaishi (pumice tuff)

Ammonia removal is achieved partly by absorption and nitrification in biofilters, resulting in the accumulation of nitrogen and the necessity of treating the effluent water. We investigated the effects of thiosulfate addition to a biofilter containing pumice tuff for ammonia and nitrogen removal in a laboratory‐scale experiment. The addition of thiosulfate to the circulating water led to a decreased nitrate and nitrite along with an increase of sulfate. The inorganic nitrogen in the circulating water decreased by up to 44% with thiosulfate addition compared to without thiosulfate. Batch experiments revealed that denitrification activity decreased exponentially along with increases in dissolved oxygen; however, approximately 30% of denitrification activity was maintained at dissolved oxygen concentration of 3.3 mg/L. Metabarcoding of 16S rRNA genes indicated that the genus Thiobacillus had a relative abundance of 0.002%–0.016% of total bacteria in the biofilter packing material. The circulating water pH was decreased below 5 with sulfur oxidation, and ammonium was accumulated without pH control resulting in a decrease in the relative abundance of the family Nitrosomonadaceae. Its relative abundance increased with control of pH to near neutral, indicating that ammonia‐oxidizing activity could be maintained by adjusting pH. Thiosulfate addition could stimulate nitrogen removal by sulfur‐dependent denitrification in biofiltration systems.     

Weathered pumice influence on selected alluvial soil properties in west Nayarit, Mexico

Parent material and pumiceous alluvial soils, located in a tropical region of Mexico, were studied to supply information on soil suitability for agricultural production in the context of sustainable agriculture. In recent alluvial soils, an understanding of how soil characteristics vary with parent material and topography provides a basis for determining land utilization type, land suitability as well as land quality. The main objective of this study was to establish the relationship of soil properties to parent material in west Nayarit, Mexico. Field studies were initiated in 1993 by a request for technical assistance from the Comision Federal de Electricidad. The studied soils were derived from pumice that has been reworked and mixed with detrital material from other sources. We found that such soils have unique physical, chemical and mineralogical characteristics that are rarely found in soils derived from other parent materials. Data for two selected alluvial soil profiles are presented. These soils were developed on Holocene volcanogenic pumiceous alluvial river terraces and river floodplains, under current udic-isohyperthermic soil-climate conditions. The agronomic properties, tillage influences and fertilizer requirements of these soils have been studied extensively. To maximize their productivity and minimize deterioration, proper management must be based on an understanding of the unique physical, chemical and mineralogical properties. Results indicate that such soils have physical properties that provide a good environment for deep rooting and can supply the water necessary for vigorous plant growth. In both soils, water retention at 33 and 1500 kPa, particle surface area, calculated clay, cation exchange capacity, Al exchangeable percentage and P retention, and the occurrence of isotropic coatings on rock fragments and peds tend to increase in the presence of the large amounts of hydrolyzed pumice that are found in the 0.02–2.0 mm fraction. Scanning electron microscope–energy dispersive X-ray analyses demonstrate that the coatings dominantly consist of noncrystalline material, probably allophanic-like material as suggested by the Si/Al molar ratio of 1.0. Selective dissolution analysis reveals that these abundant noncrystalline materials consist of ferrihydrite and allophane with an atomic ratio (Al_o−Al_p)/Si_o of approximately 1.4. Both ferrihydrite and allophane have very large specific surface area and absorptive capacity that make a significant contribution to the overall properties of these soils. X-ray diffraction analysis and transmission electron microscope observation show that the major group of crystalline clay minerals in the upper section of studied soils are tubular and spheroidal halloysite. These soils were classified as Vitrandic Udifluvents according to Soil Taxonomy.