The effect of plastic mulch on the fate of urea-N in rain-fed maize production in a semiarid environment as assessed by 15N-labeling

A better understanding of the fate of fertilizer nitrogen (N) is critical to design appropriate N management strategies in plastic-mulched croplands. We evaluated the effects of plastic mulch on urea-N recovery by crops and loss from soil in furrow-ridge plots, with and without maize (Zea mays L.) cropping, in a semi-arid rain-fed site in China. We applied the same rate of urea-N (281 kg ha⁻¹) to all treatments during the preparation of the furrow-ridges in 2011 and 2012 but ¹⁵N-labeled the urea in 2011 only. We used transparent film to cover all soil surfaces in the mulched treatments and seeded maize in furrows in treatments with crop. In 2011, plastic mulch increased the total N uptake in the aboveground biomass of maize by 53%, whereas it decreased the in-season labeled-N uptake by 19%, compared to non-mulched treatment. At harvest in 2011, in mulched treatments the total labeled-N remaining in the 0−170 cm soil layer was 25% greater whereas unaccounted labeled-N was 69% less, than in non-mulched treatments, regardless of whether maize was cropped. In 2012 the effect of mulch on total maize N uptake was comparable to that in 2011, but the residual soil labeled-N uptake by maize was 63% higher in mulched compared to non-mulched treatment. At harvest in 2012, plastic mulch increased total labeled-N remaining in the 0−170 cm depth in cropped soils and unaccounted labeled-N in non-cropped soils, compared with no mulch. Our results indicate that plastic mulch profoundly changes the fate of urea-N in maize production in cold and dry croplands.     

堆渣边坡生态棒护坡措施的水土保持效益

[目的]探究堆渣边坡生态棒防护措施的综合防护效果,为露天采石场裸露边坡的生态修复提供依据。[方法]利用人工降雨模拟试验,收集不同降雨强度下地表层和矿渣层的产流量、产沙量,并建立综合贡献度模型。[结果]随着坡度的增加地表层的径流总量和泥沙总量呈递增趋势,而矿渣层的径流总量和泥沙总量呈递减趋势,与径流总量相比泥沙总量变化趋势不明显;对照组与生态棒防护措施下,地表层的产流—产沙相关性均高于矿渣层;当降雨强度为30和120mm/h时,生态棒防护边坡在坡度为15°时具有较佳的防护效果,当降雨强度为60mm/h时,径流量和泥沙量受坡度变化的影响不显著。[结论]生态棒防护措施具有拦蓄坡面径流和泥沙的功能,与对照组相比可以更有效地防治坡面水土流失。     

137Cs和210Pbex双核素示踪"三北"防护林区退耕前后坡地土壤侵蚀变化

为查明"三北"防护林建设前后农耕地和退耕地土壤保持效益变化，利用137Cs和210Pbex双核素示踪技术，选择了防护林建设较为成功的张家口坝上地区（风力侵蚀区）作为典型区，研究了农耕地以及退耕地土壤137Cs和210Pbex的剖面变化规律及其示踪的土壤侵蚀变化。结果表明：1）由于耕作的混匀作用，农耕地土壤剖面中137Cs和210Pbex均呈均匀态分布；退耕地土壤剖面中137Cs和210Pbex则表现为表层（0～5cm）浓度最高、下层（5～25cm）浓度均相对较低且分布相对均匀的形态，这表明退耕后坡地土壤137Cs和210Pbex剖面形态均会发生一定变化，退耕驱动土壤137Cs和210Pbex剖面变化导致运用土壤核素估算侵蚀模型在该区域难以适用；2）基于土壤137Cs和210Pbex剖面变化规律，利用210Pbex质量平衡方程，提出了退耕地土壤210Pbex土壤侵蚀估算模型；3）利用137Cs比例模型估算退耕地土壤侵蚀速率为27.94±11.92 (t/hm2·a)，农耕地侵蚀速率为29.11±14.42 (t/hm2·a)，而利用修正后的210Pbex转换模型估算得到"三北"防护林区退耕地造林前平均侵蚀速率为82.16±14.36 (t/hm2·a)，造林后平均侵蚀速率为-41.28±33.91 (t/hm2·a)；农耕地造林前平均侵蚀速率为68.55±22.11 (t/hm2·a)，造林后平均侵蚀速率-8.52±47.32 (t/hm2·a)。这表明137Cs示踪技术主要表征了1963年以来该区坡地土壤侵蚀和沉积的平均结果，而210Pbex示踪技术则可以较好地示踪防护林建成前后的土壤侵蚀变化。此外，研究结果也表明，相比于"三北"防护林建成之前，建成之后该区农耕地和退耕地的土壤侵蚀速率均呈显著下降趋势，且均由前期的风沙侵蚀转变成了风沙沉积。     

坡地水平截流沟的设计方法与工程应用

 为解决现行水平截流沟设计方法缺乏合理性和系统性的问题,从理论分析入手,给出坡地水平截流沟的系统设计方法和具体的计算公式。用植被或树木的耗水量结合当地一定保证率下的降雨量作为主要因素确定水平沟的距离;用当地设计保证率下最大一次可能降雨量、最大降雨强度、土壤入渗速率等参数确定水平沟断面尺寸———当量宽度与深度。实际工程应用结果说明利用文中给出的方法和公式进行坡地水平截流沟的设计是可行的,与以往的经验方法相比,该方法更具合理性、可靠性,可应用于生产实践。     

基于土壤非饱和状态下对水稻田产流模型的改进及验证

水稻灌溉需水量是一个地区农田水利规划、灌溉系统规划的重要参数,也是合理开发利用水资源、水资源调度和实现地区可持续发展的重要依据。在水量平衡的基础上,对蒸散发项和渗漏项的计算方法做出改进,其中对蒸散发项的改进参考了新安江模型中二层蒸散发模型的计算方法,渗漏项的计算在实验的基础上采用半经验半理论的方法改进。最后,结合当地的...     

基于不变矩和神经网络的泵机组轴心轨迹自动识别

基于泵机组故障信号处理的需要,介绍了不变矩原理,同时对神经网络建模,包括其样本获取进行了详细讨论;由于泵机组的多种故障与表征其运行状态的轴心轨迹形状有关,根据不变矩的平移、伸缩和旋转不变性特征,对实时检测的轴心摆度信号进行不变矩处理,利用BP型神经网络对其进行模式识别,进而判断出轴心轨迹的形状．为了弥补泵机组用于神经网络训练样本的不足,采用数值模拟与现场测试相结合的方法,将获取的所有样本进行求不变矩处理,并连同样本对应的实际形状作为神经网络的训练样本．网络训练完成后,将其输出结果与轴心轨迹图形进行比较验证．以山西大禹渡泵站水泵机组故障检测及诊断为例,在样本中选取其中的10组数据,比较的结果表明神经网络自动识别的结果准确．该方法为泵机组轴心轨迹自动识别和实现泵机组故障诊断智能化提供了依据．     

两种化学改良剂对盐渍化土壤作用机制及对棉花生长的影响

通过对膜下滴灌棉田施加旱地龙和禾康两种土壤改良剂,研究两种不同化学改良剂对改良盐碱地的应用效果及对棉花生长与产量的影响,为盐碱地改良提供理论依据.结果表明:在滴灌棉田施用旱地龙和禾康后,土体含盐量呈下降趋势,脱盐率分别为30.3%和17.7%,而对照区脱盐率仅为10.4%;借助钠吸附比概念对土壤阳离子组成进行分析,旱地...     

节水防污型农田水利系统构建及其效果分析

不合理的农田水肥管理是造成农业面源污染的主要原因之一。为了探寻灌区水稻节水、增产和减污相统一的措施,提出运用由田间、草沟、塘堰湿地和骨干沟"四道防线"组成的系统净化农田排水,并在广西桂林市青狮潭灌区及广西灌溉试验中心站开展了系统的试验研究。通过站内不同水肥处理下对田间节水、水稻增产、氮磷流失减少指标的分析,优选水稻田间最优水肥管理模式,即采用间歇灌溉模式、施氮肥总量不变、适当减少氮肥基肥增加追肥用量;在站外根据现有的水系分布构建"四道防线"系统,分析了各道防线对农田排水的净化效果以及提高净化效果的主要措施。由"四道防线"构成的节水防污型农田水利系统对农田氮磷排放具有良好的净化效果,实现了减少农田面源污染和修复农田水环境的目的。     

Depth-specific distribution and importance of nitrite-dependent anaerobic ammonium and methane-oxidising bacteria in an urban wetland

Anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) are two recently discovered processes in the nitrogen cycle that are catalysed by anammox bacteria and n-damo bacteria, respectively. Here, the depth-specific distribution and importance of anammox bacteria and n-damo bacteria were studied in an urban wetland, Xixi Wetland, Zhejiang Province (China). Anammox bacteria related to Candidatus Brocadia, Candidatus Kuenenia and Candidatus Anammoxoglobus, and n-damo bacteria related to “Candidatus Methylomirabilis oxyfera” were present in the collected soil samples. The abundance of anammox bacteria (2.6–8.6 × 10⁶ copies g⁻¹ dry soil) in the shallow soils (0–10 cm and 20–30 cm) was higher than that (2.5–9.8 × 10⁵ copies g⁻¹ dry soil) in the deep soils, whereas the abundance of n-damo bacteria (0.6–1.3 × 10⁷ copies g⁻¹ dry soil) in the deep soils (50–60 cm and 90–100 cm) was higher than that (3.4–4.5 × 10⁶ copies g⁻¹ dry soil) in the shallow soils. Anammox activity was detected at all depths, and higher potential rates (12.1–21.4 nmol N₂ g⁻¹ dry soil d⁻¹) were observed at depths of 0–10 cm and 20–30 cm compared with the rates (3.5–8.7 nmol N₂ g⁻¹ dry soil d⁻¹) measured at depths of 50–60 and 90–100 cm. In contrast, n-damo was mainly occurred at depths of 50–60 cm and 90–100 cm with potential rates of 0.7–5.0 nmol CO₂ g⁻¹ dry soil d⁻¹. This study suggested the niche segregation of the anammox bacteria and n-damo bacteria in wetland soils, with anammox bacteria being active primarily in deep soils and n-damo bacteria being active primarily in shallow soils.     

半立方抛物线形明渠共轭水深的迭代算法

【目的】寻求半立方抛物线形明渠共轭水深的迭代计算方法。【方法】根据半立方抛物线形明渠断面的几何形态及棱柱体水平明渠水跃方程,推求得到半立方抛物线形明渠共轭水深的迭代计算公式,并从理论上证明其收敛性;通过对工程中不同流量Q与不同断面形状参数p多种组合情况下的共轭水深进行计算和趋势线拟合,建立计算共轭水深迭代初值的直接计算式。【结果】推导出半立方抛物线形渠道断面的水跃方程,并进而得到跃前水深、跃后水深的迭代计算公式,运用迭代初值直接计算式求出迭代初值,将该值代入共轭水深迭代计算公式,经过几步迭代便可收敛得到精度很高的共轭水深值。【结论】推求的半立方抛物线形明渠共轭水深迭代计算公式物理概念明确、计算简捷、精度高、适用范围广,可以满足工程实践要求。