森林土壤酚类物质的消解规律

采用室内模拟培养的研究方法,对4种森林生态系统(天然更新常绿阔叶林、一代杉木老龄林、二代杉木萌芽天然更新林、二代杉木人工林)土壤酚类物质含量的动态变化规律进行研究.结果表明,在常温或冷藏状态下,各系统土壤总酚、复合态酚和水溶性酚含量基本上呈现明显降低的趋势,各系统土壤总酚、复合态酚和水溶性酚的总消解率分别为64.91%-91.21%、58.13%-83.24%和65.27%-83.78%.在冷藏状态下,土壤总酚的消解率比在常温状态的土壤低,说明低温抑制了土壤总酚的消解作用,而对土壤复合态酚和水溶性酚的消解率影响不明显.不同森林生态系统的土壤总酚和复合态酚的消解率均存在显著差异,不同森林生态系统土壤水溶性酚的消解率差异不显著.初始酚类物质含量高的土壤系统,其消解率也较高,表明如果没有外来的酚类物质继续加入,土壤中各种酚类物质的消解率较高.由此推测,在野外自然条件下,酚类物质在土壤中发生严重积累并造成林木中毒的可能性较小.     

高钾用量和根区施肥可提升皖南不同质地土壤烟叶钾含量

钾是烟叶的品质元素之一,提升烟叶钾含量一直是我国烟草行业关注的重点之一。本文选取安徽烤烟主产区皖南宣城市砂土与黏土两类典型土壤,以云烟97为试验材料,研究田间条件下不同高钾用量水平与施肥方式对烟叶钾含量的影响。研究结果表明,在耕层土壤全层混施方式下,随着施钾量增加(0、300、600、900、1 200、1 800、2400mg/kg,以纯K计),两种质地土壤烟叶钾含量均显著上升,呈先快速增加而后缓慢增加的趋势。在钾肥用量低于1 200 mg/kg时,每增加钾肥用量100 mg/kg,砂土和黏土烟叶不同部位钾含量分别平均增加2.4 g/kg和1.0 g/kg。更高钾肥用量可使砂土烟叶钾平均含量提升到44.0 g/kg,黏土则只能提升到26.2 g/kg。两类土壤钾肥效果差异极大的原因与土壤固钾能力有关,土壤速效钾含量与烟叶钾含量呈线性相关,而黏土钾肥固定率平均为71%,远高于砂土的25%,这是两种质地土壤钾肥肥效差异的根本原因。在常规同等钾肥用量条件下(K2O25kg/667m2),氮磷钾根区集中施用较常规条施显著促进了烟叶对钾的吸收,提升了烟叶钾含量,而且砂土的效果要好于黏土,其原因也与根区施肥可显著提升烟叶根区土壤速效钾含量有关。以上结果表明,选择固钾能力弱的土壤,提高钾肥用量并改进施肥方法可以有效提升皖南烟叶钾的含量。     

Optimal Management Practices for Nitrogen Application in Corn Cultivated During Summer and Fall in the Tropics

Optimal management practices for nitrogen (N) fertilization is well defined for corn (Zea mays) cultivated during summer (“summer” corn), but not for corn cultivated during the fall (“fall” corn) in the tropics. Two experiments were carried out to evaluate N rates (50, 100, 200, and 300 kg N ha^?1), N application timing (pre-planting – PP, V2–V3, and V5–V6) and N split application, once (at PP, V3, and V6), two (at V3+ V6) and three times (at PP+ V3+ V6) in corn cultivated during summer (2014/2015) and fall (2015/2016). Data on corn grain yield (CGY), weight of 1000-grains, leaf N content and values of soil-plant analyses development (SPAD) were collected and analyzed using univariate, multivariate (principal component analysis, PCA) and regression analysis. Results showed that corn growth was affected by N rates and splitting. Corn cultivated during summer presented higher CGY and weight-1000 g than corn cultivated during the fall. The highest yields were obtained with higher N rates on “summer” corn (125 kg N ha^?1) than “fall” corn (50 kg N ha^?1). Split N-application at vegetative growth stages, V3+ V6, or PP+ V2+ V6, provided higher yields for “summer” corn, while only PP application was a reliable period of N fertilization for “fall” corn. The finding is that corn cultivated during the fall presented a lower response to N and no obvious advantages to split N fertilization when compared to corn cultivated during summer. These optimal management practices for N fertilization in corn production in the tropics depend on soil water availability.     

Immediate and subsequent effects of drying and rewetting on microbial biomass in a paddy soil

Many surface soils in Japan may experience more frequent and intense drying–rewetting (DRW) events due to future climate changes. Such DRW events negatively and positively affect microbial biomass carbon (MBC) through microbial stress and substrate supply mechanisms, respectively. To assess the MBC immediately after DRW and during the incubation with repeated DRW cycles, two laboratory experiments were conducted for a paddy soil. In the first experiment, we exposed the soil to different drying treatments and examined the MBC and hourly respiration rates immediately after the rewetting to evaluate the microbial stress. In the second experiment, we compared microbial growth rates during the incubation of the partially sterilized soil with a continuously moist condition and repeated DRW cycles to evaluate the contribution of the substrate supply from non-biomass soil organic C on MBC. First, all drying treatments caused a reduction in MBC immediately after the rewetting, and higher drying intensities induced higher reduction rates in MBC. A reduction of more than 20% in MBC induced the C-saturated conditions for surviving microbes because sufficient concentrations of labile substrate C were released from the dead MBC. Second, repeated DRW cycles caused increases in the microbial growth rates because substrate C was supplied from non-biomass organic C. In conclusion, MBC decreased immediately after DRW due to microbial stress, whereas MBC increased during repeated DRW cycles due to substrate C supplied from non-biomass organic C.     

Effects of rice husk biochar on selected soil properties and nitrate leaching in loamy sand and clay soil

Biochar is a product of pyrolysis of biomass in the absence of oxygen and has a high potential to sequester carbon into more stable soil organic carbon (OC). Despite the large number of studies on biochar and soil properties, few studies have investigated the effects of biochar in contrasting soils. The current research was conducted to evaluate the effects of different biochar levels (0 (as control), 1% and 3%) on several soil physiochemical properties and nitrate leaching in two soil types (loamy sand and clay) under greenhouse conditions and wet-dry cycles. The experiment was performed using a randomized design with three levels of biochar produced from rice husks at 500 °C in three replications. Cation exchange capacity increased significantly, by 20% and 30% in 1% and 3% biochar-amended loamy sand soil, respectively, and increases were 9% and 19% in 1% and 3% biochar-amended clay soil, respectively. Loamy sand soil did not show improvement in aggregate indices, including mean weight diameter, geometric mean diameter, water stable aggregates and fractal dimension, which was contrary to the results for the clay soil. Rice husk biochar application at the both rates decreased nitrate leaching in the clay soil more than in the loamy sand. Our study highlights the importance of soil type in determining the value of biochar as a soil amendment to improve soil properties, particularly soil aggregation and reduced nitrate leaching. The benefits of the biochar in the clay soil were greater than in the loamy sand soil.     

Carbon dioxide sequestration capability of an unmanaged old-growth broadleaf deciduous forest in a Strict Nature Reserve

The seasonal trend of plant carbon dioxide (CO₂) sequestration is related to the photosynthetic activity, which in turn changes in response to environmental conditions. Great interest has turned to the CO₂ sequestration (CS) potential of temperate forests which play an important role in global carbon (C) cycle contributing to the lowering of atmospheric CO₂ concentration. In such context, the CS of an unmanaged old broad-leaf deciduous forest developing inside a Strict Nature Reserve, and its variations during the year were analyzed considering the monthly variations of leaf area index (LAI) and net photosynthetic rates (N_P). Overall, the total yearly CS of the forest was 141 Mg CO₂ ha^?1 year^?1 with the highest CS value monitored in June (405 Mg CO₂ month^?1) due to the highest LAI (5.0 ± 0.8 m² m^?2) and a high N_P in all the broadleaf species. The first CS decline was observed in August due to the more stressful climatic conditions that constrained N_P rates. Overall, the total CS of the forest reflects the good ecological health of the ecosystem due to its conservative management.     

Radiometric pooled faecal culture for the detection of Mycobacterium avium subsp paratuberculosis in low-shedder cattle

OBJECTIVE: To identify the optimum pooling rate for pooled faecal culture (PFC) as a diagnostic tool in bovine Johne's disease control, for detection of cattle shedding low concentrations of Mycobacterium avium subsp paratuberculosis (Map). METHOD: Thirteen target animals were selected by delayed growth of Map from initial individual radiometric faecal cultures (first growth index at 5 weeks or later). A procedure based on radiometric culture and IS900 polymerase chain reaction and restriction endonuclease analysis confirmation was then used for PFC. RESULTS: Eight samples (stored for up to 17 months at -80 degrees C) yielded Map on subsequent culture, either from undiluted faeces or those mixed with normal cattle faeces at dilution rates from 1 in 5 to 1 in 50. From a regression equation, culture-positive animals were considered to be shedding relatively low levels of Map (< 6 x 10(4)/g of faeces). Pooling dilutions of more than 1 in 5 reduced PFC sensitivity. A minimum incubation period of 10 weeks at a dilution of 1 in 5 is recommended to detect such infected cattle. This pooling rate in radiometric culture is probably capable of detecting cattle shedding < or = 5 x 10(3) Map organisms/g of faeces, representing an estimated inoculum per culture vial of fewer than 20 viable organisms. CONCLUSION: Map was detected in more than 50% of the stored faecal samples from cattle shedding low concentrations of the organism. A pooling rate of 5 samples per pool is required to reliably detect infected low-shedder cattle using PFC based on radiometric culture.     

A biomechanical analysis of industrial forest plantation workers in East Kalimantan

The objectives of this study are to clarify physiological work loads and physical loads acting on the lumbar region of workers and to propose a safe work environment in tropical forestry operations. The research was conducted in the industrial forest plantations of East Kalimantan, Indonesia, in 1996. In this study, heart rates and the physical lumbar burden of industrial forest plantation workers were measured for three types of work, that is, weeding, planting and path clearing. In addition, the load moment at the L₅/S₁ and the disc compression force were calculated using low-back biomechanical models. As a result, compression forces at the L₅/S₁ disc during weeding, planting and path clearing were estimated and found to be below the Action Limit (AL) by National Institute for Occupational Safety and Health (NIOSH). However, it was also found that some work posture types during path clearing by chain saw were sometimes above the AL. A part of this paper was orally presented at the 108th Annual Meeting of the Japanese Forestry Society (1997).     

An empirical model for estimating nitrate leaching as affected by crop type and the long-term N fertilizer rate

Abstract. An empirical model was developed for prediction of annual average nitrate leaching as affected by the long-term rate of N fertilization and crop type. The effect of N fertilization was estimated from annual values of nitrate leaching obtained from two Danish investigations of drainage from pipe drains with four rates of N fertilization on a loamy sand and sandy clay loam from 1973-89. The effect of crop at normal N fertilization was estimated from 147 observations of annual nitrate leaching obtained from field measurements. The nitrate leaching model consists of a relative N fertilization submodel and an absolute submodel for specific combinations of crop, soil and drainage at the normal rate of N fertilization. The relative submodel is Y/Y _lN= exp[0.7l(N/ N₁– I)], where Y is the nitrate leaching (kg N/ha per year) at fertilization rate N , and Y _IN and N₁ are the corresponding values at the normal rate of N fertilization. The relative submodel is valid for cereals, root crops and grass leys fertilized with mineral fertilizer at N/N ₁ < 1.5, and on the prerequisite that the fertilization rate N has been constant for some years. To illustrate the use of the relative leaching submodel, estimated values of Y _IN corrected to mean annual drainage for 1970 to 1990 in Denmark for spring cereals and grass on sandy and loamy soils are given as input to the relative leaching submodel. The model can be used for sandy to loamy soils to estimate the mean nitrate leaching over a number of years.     

Assessment of nitrogen mineralization potential and availability from neem seed residue in a savanna soil

 Nitrogen (N) mineralization and availability from neem seed residue after oil extraction was studied in a laboratory incubation and greenhouse cropping. Several decomposition models were tested for estimating potentially mineralizable N and mineralization rates from the residue. Net N mineralization was best described by a Gompertz function and a mixed-order rate model with R ²=0.996 for each and residual mean square error (RMSE)=8.3 for the Gompertz function and 8.8 for the mixed-order rate model. A consecutive reaction model also fitted the data closely (R ²=0.983; RMSE=16.6) and is preferable to a Gompertz function or a mixed-order rate model because of its mechanistic basis. Potentially mineralizable N estimated by the decomposition models ranged from 335 to 489 mg N kg^–1 representing between 32% and 43% of total N applied. Actual cumulative N mineralized in a 98-day incubation period was 339 mg N kg^–1 soil. Bio-available N from neem residue and inorganic N (urea) with maize as a test crop in a greenhouse cropping gave similar biomass yield and N uptake, suggesting rapid N mineralization from neem residue to meet plant nutrition. Received: 15 July 1998