Comparison of type and depth of lysimeter for measuring the leaching losses of nitrogen under urine patches

Abstract. A study of the leaching losses of nitrate under urine patches in irrigated and non-irrigated dairy pastures in the South East of South Australia was undertaken with repacked and monolith lysimeters 1 m deep, and with monolith lysimeters 150, 300 and 450 mm deep. The aim was to quantify differences in measurements of drainage and nitrogen fluxes for these different lysimeters. Drainage of water and N flux were found to vary significantly between types and depths of lysimeters. Drainage volumes in repacked lysimeters were 78% and 33% more than in monolith lysimeters in irrigated and non-irrigated paddocks, and N fluxes were 5 and 3 times higher in repacked lysimeters respectively. The results indicate that lysimeter estimates of recharge rates and N fluxes to water tables are best determined by leaching studies which are longer term, and use deep monolith lysimeters. Shorter term studies and the use of shallow or repacked lysimeters have potential to distort conclusions.     

USING TISSUE ANALYSIS AS A TOOL TO PREDICT BAHIAGRASS PHOSPHORUS FERTILIZATION REQUIREMENT

Tissue analysis in combination with soil testing has been recently incorporated in the fertilization recommendations for bahiagrass in Florida; however, limited research is available to validate the proposed critical tissue phosphorus (P) level. A greenhouse experiment was conducted to identify the critical minimum tissue P concentration below which bahiagrass dry matter (DM) yield is impacted. Treatments consisted of three nitrogen (N) rates (0, 50, and 100 kg N ha^?1), four P rates (0, 20, 40, 60 kg P₂O₅ ha^?1) and two clipping intervals (28 and 56 d). Bahiagrass yields and tissue P increased in response to P application. Phosphorus uptake showed a quadratic response to P rates when N was applied. Phosphorus recovery increased linearly as P rate increased. Root mass responded to P, even at the smallest (20 kg ha^?1) rate. Data indicated that tissue P concentration of 1.3 (±0.2) g kg^?1 can be used as an indicator of bahiagrass P deficiency.     

仿驯鹿足底形貌胎面单元对轮胎防滑性能影响分析

轮胎胎面单元形貌结构对冬季轮胎防滑性能提升至关重要。为提高轮胎防滑性能,基于驯鹿足部特征,运用工程仿生技术,设计了有棱纹和无棱纹仿生防滑胎面单元。采用冰面附着试验和有限元数值模拟,与同尺寸常规人字形胎面单元比较,对仿生防滑胎面单元的防滑性能进行了分析。在试验低压状态下(压强≤0.02MPa)通过冰面与3种胎面单元的附着试验,结果表明在相同的速度、温度和压力条件下无棱纹仿生胎面单元摩擦系数最高,是人字形胎面单元的1.04～1.26倍。通过有限元数值分析,在低压0.02 MPa作用下,有棱纹仿生胎面单元、无棱纹仿生胎面单元和人字形胎面单元下的冰表面温度相对于初始温度分别升高了0.21、0.66和0.54℃,无棱纹仿生胎面单元温度升高最大,表明在低压条件下,无棱纹仿生胎面单元防滑性能最好。在高压状态(压强=2 MPa),有限元分析发现有棱纹仿生胎面单元、无棱纹仿生胎面单元和人字形胎面单元下的冰表面温度相对于初始温度分别升高了7.76、4.07和3.39℃,有棱纹仿生胎面单元升高温度最大,表明在高压状态下,有棱纹仿生胎面单元防滑性能最好。无棱纹仿生胎面单元和有棱纹仿生胎面单元分别在低压和高压状态下具有优良的防滑特性。该研究可为轮胎胎面单元的冰面防滑设计提供参考。     

Current and Future Outlook of Dredged and Sewage Sludge Materials in Agriculture and Environment (3 pp)

-  In the late 1960’s there was an increasing realization in the U.S.A. and other parts of the world, especially in Europe of the potential problems associated with the disposal of spoil and sewage sludge materials. While insufficient information was available to determine potential adverse effects of disposal on land, many people including those in the scientific community had articulated their objections on the use of these materials in agriculture because data do not provide adequate environmental protection information. In many cases, site-specific geochemical and biological factors are typically excluded from the decision process (Wenning and Woltering 2001). Because of continued studies and far-reaching research during the last 40 years on the environmental effects of dredged and sludge materials, the scientific community and regulatory agencies in the U.S.A. are now in a much better position to appraise the environmental and possible agricultural impacts connected with the disposal of dredged and sludge materials by diverse disposal methods.     

气候情景下典型开垦与退耕区耕地动态变化的定量模拟

全球气候变化是当前关注的热点问题,研究气候情景下中国典型开垦与退耕区耕地动态变化对保障中国粮食安全具有重要意义.该研究以东北地区作为典型区,基于设计的土地利用规划情景和RCPs (representative concentration pathways)气候情景,采用土地利用变化动态(DLS,dynamics of land system)模型模拟了在规划情景和RCPs气候情景下开垦与退耕区2010～2030年耕地的空间分布格局,分析不同耕地类型未来的变化趋势.研究结果表明:规划情景下水田呈持续减少的态势,而旱田在2000～2010年有小幅增长的态势,而后出现大面积减少;AIM(Asia-Pacific integrated model)气候模式情景下旱田增长趋势也较明显,水田则保持小幅减少的态势;MESSAGE(Model for energy supply strategy alternatives and their general environmental impact)气候模式情景下,耕地面积呈减少的态势.从不同用地类型之间的转移分析得出,该区域开垦与退耕相逆的现象在未来情景下仍会延续,但是发生的频率却随时间的推移逐渐降低.该研究为开垦与退耕区应对气候变化,合理进行农业规划和耕地保护提供参考.     

新疆北部地区栽培草地菟丝子的发生规律及防控措施

通过分析新疆北部栽培草地菟丝子发生种类及危害规律,提出了合理的防控措施,以为该地区栽培草地菟丝子的防除提供技术支持。     

Improving the effectiveness of wood‐ash fertilization in mixed mountain pastures

Mountain pastures can be improved by the application of wood ash, but its effectiveness as a source of N, P and other elements requires improved management practices. Two application rates of wood ash (6 and 12 t ha^?1) were tested in a 4‐year trial on a low‐input fertilized pasture. Ash was complemented with mineral P, and N fixation was encouraged by sowing white clover. Wood‐ash application led to increased pasture yield (by 100%) and to increased proportions of white clover and ryegrass (60%), thus improving pasture feed value. N fixation by white clover, and possibly increased mineralization because of higher pH, may have compensated for lack of N in the wood ash. Addition of mineral fertilizer improved the supply of P, although incorporation of the wood ash into the soil may also have enhanced release of P from non‐extractable components. High amounts of compounds containing Ca and Mg contributed to the long‐term maintenance of soil reserves of these elements. Despite high inputs of K (175–350 mg kg^?1) from wood ash, annual additions of K are required to counteract depletion via plant uptake and leaching. Increased Mn availability after the treatment (up to 400 mg kg^?1) may limit repeated applications of wood ash, at least on poorly aerated soils.     

Cultivation offers effective management of subterranean clover damping‐off and root disease

Soil cultivation studies involving subterranean clover pastures were undertaken utilizing field cores from five farms and two in‐field trials. Tap and lateral root disease in cores was less (p < .001) severe and root and shoot weights greater (p < .001) following simulated cultivation. Germination and severity of root disease were both affected (p < .005) by three‐way interactions with cultivation, cultivar and field site. Cultivation in cores suppressed tap root disease for cultivars Meteora and Riverina across the five sites and Seaton Park for two sites. In‐field trials confirmed cultivation reduces root disease severity and increases germination and plant productivity. The best in‐field treatment was cultivation + fumigation that reduced (p < .05) tap and lateral root disease and increased nodulation and root and shoot weights for Riverina, Seaton Park and Woogenellup. Cultivation + fumigation also increased (p < .05) germination for Woogenellup and Seaton Park. There were negative correlations (all p < .001) between tap and lateral root disease with nodulation (R² = .85, R² = .58, respectively); tap root disease with root and shoot weight (R² = .58, R² = .854, respectively); and lateral root disease with root and shoot weight (R² = .83, R² = .64 respectively). This study highlights the close relationship between severe root disease and reduced nodulation, likely explaining much of the widespread poor nodulation in subterranean clover pastures. This study confirms that damping‐off and root disease can be mitigated by cultivation, offering producers flexibility in disease management, especially where autumn–winter feed shortages occur on a regular basis.     

Modification of the SPUR rangeland model to simulate species composition and pasture productivity in humid temperate regions

Plant, water, and soil components of the Simulation of Production and Utilization of Rangelands model (SPUR 2.4) were incorporated into the Integrated Farm System Model (IFSM 1.2) to represent the growth and competition of multiple plant species in pastures and their effects on pasture productivity and botanical composition in temperate climates. Developed for semi-arid rangelands, SPUR required major adjustment to represent temperate pastures adequately. In particular, the effects of soil moisture on root and shoot mortality and photosynthetic rates were adjusted to represent greater susceptibility of temperate plants to drought. Sensitivity analysis showed that predicted total shoot dry matter appeared most sensitive to photosynthesis and growth parameters in the spring, soil moisture parameters in the summer, and senescence parameters in autumn. Across all seasons, shoot dry matter appeared most sensitive to optimum photosynthetic temperatures, specific leaf area, start and end dates of senescence, maximum nitrogen concentration in live shoots, and a maximum shoot specific growth rate. The revised pasture model incorporated into IFSM was calibrated with 2002 field data from experimental pastures in central Pennsylvania, USA containing primarily orchardgrass (Dactylis glomerata) and white clover (Trifolium repens). Predictive accuracy of the model was then further evaluated by comparing 2003 data from the same pastures to simulated production. The integrated submodel predicted soil water content and dry matter production relatively well. It did not achieve a desired degree of accuracy in predicting the dynamics of botanical composition; however, adjustment of SPUR subroutines to allow variable maximum root:shoot ratios and competition for light and water may improve predictions. Further development and use of this integrated model can help researchers improve their understanding of temperate pasture systems, identify gaps in knowledge, and prioritize future research needs. Ultimately, the integrated model could provide more accurate assessment of the influence of management strategies on pasture productivity, animal production, and economics at the whole-farm scale.     

Tropical land use change and soil emissions of nitrogen oxides

Abstract. Increases in the emissions of globally important nitrogen (N) oxide gases have coincided with significant changes in land use in the tropics. Clearing of tropical forests and savannas for agriculture currently represents the most extensive alteration of land cover on the planet. Over the last several decades, N fertilizer use has increased globally, and in China and the developing world, use has recently surpassed that in the developed world. The potential contribution of land-use change in the tropics to the increase in N oxides is great, yet only a few studies have measured N oxide emissions after tropical land conversion. Our summary of available research shows some conversions to pastures and a few management practices, especially those using N fertilizers, increase emissions beyond those found in undisturbed ecosystems. However, not all studies show unequivocal increases in emissions. Accordingly, we call for a mechanistic understanding of the processes controlling trace gas fluxes to adequately predict under what conditions increased emissions may occur. More measurements are needed to build and test models that may improve management of N fertilizer use in tropical agricultural systems. Given the expected expansion of agriculture and increased use of N fertilizers in the tropics, increased emissions of N oxides from the tropics are likely.