气候因素对水稻单产影响的实证分析—基于湖北农户层面的分层模型

温度、降水及高温热害等气候条件与水稻生产息息相关。论文基于2003—2011年湖北农户层面的2 610个样本数据及气象数据,在考察湖北地区水稻生长期高温热害时空变化特征的基础上,建立了水稻单产及其影响因素的分层模型,重点探讨了温度、降水、极端高温等气候因素对湖北水稻单产的影响,并检验了温度、降水对水稻单产的非线性影响。研究发现,湖北省高温热害呈现明显的时空变化特征。2003—2011年湖北省高温热害呈先降后增的变化趋势,伴随“V”型波动。空间上,高温热害在鄂中和鄂东地区比较严重,鄂西地区和江汉平原则相对更轻。另一方面,气候因素对水稻单产的影响存在明显差异。温度对水稻单产具有显著的促进作用,且两者间存在显著的倒“U”关系,降水对水稻单产的影响并不显著,而高温热害对水稻单产具有显著的负向影响。另外,机械、劳动等要素投入与农田水利等基础设施建设能够显著提高水稻单产。因此,加强对湖北省气象因素的预警及预报,改善农田水利设施、优化播种期、选择适宜品种等方式对于提高水稻单产具有重要意义。     

太湖地区典型轮作与休耕方式对稻田水稻季N2O和CH4排放量的影响

轮作休耕是实现"藏粮于地、藏粮于技"的重要途径之一,目前在太湖稻田区域主要推广紫云英(Astragalus sinicus L.)-水稻(Oryza sativa L.)、油菜(Brassica napus L.)-水稻和休耕-水稻典型轮作与休耕方式。在太湖地区典型稻田水稻生长季设置了6个处理:(1)紫云英-水稻轮作,不施N肥处理,MRN0;(2)紫云英-水稻轮作,当地常规施肥量(300 kg·hm^-2,以纯氮计,下同),MRN300;(3)油菜-水稻轮作,不施N肥处理,RRN0;(4)油菜-水稻轮作,当地常规施肥量(300 kg·hm^-2),RRN300;(5)休耕-水稻轮作,不施N肥处理,FRN0;(6)休耕-水稻轮作,当地常规施肥量(300 kg·hm^-2),FRN300。通过田间试验,研究了不同轮作与休耕方式对水稻产量、氮肥利用率及稻田温室气体CH₄和N₂O排放的影响,从而为综合评价轮作休耕方式提供科学依据。田间试验结果显示,与不施氮肥处理相比,在不同轮作休耕方式下施氮300 kg·hm^-2,可增加53.7%—60.0%的水稻产量,以MRN300处理水稻产量最高,与RRN300和FRN300处理相比,水稻产量分别提高了1.6%和6.0%。在不施氮水平下,MRN0、RRN0和FRN0各轮作处理间N₂O排放通量和累积排放量均值差异不显著(P>0.05)。而在施氮300 kg·hm^-2下,紫云英-水稻轮作可降低N₂O排放通量和累积排放量,与RRN300和FRN300处理相比,N₂O排放通量分别降低了36.0%(P<0.05)和2.1%(P>0.05)。在同一施氮水平下,紫云英-水稻轮作CH₄排放通量和累积排放量最小,与RRN300和FRN300处理相比,MRN300处理CH₄排放通量分别降低了1.1%和6.7%,CH₄和N₂O的全球增温潜势(GWP)分别降低了3.3%和6.5%,单位水稻产量温室气体排放强度(GHGI)分别降低了4.6%和11.6%。综上,紫云英-水稻轮作对提高水稻产量,降低温室气体排放效果最好。     

酸雨对生菜的光合、抗氧化系统和产量的影响研究

目前国内外有关酸雨对植物生长危害的影响研究多集中在森林植物和粮食作物,而酸雨对叶菜类蔬菜生长的相关研究较少。酸雨的频发可能会影响蔬菜的生长,进而降低蔬菜产量。为探究酸雨对叶菜类蔬菜生理和产量的影响,选取生菜(Lactuca sativa L.var.ramosa Hort.)作为试验材料,采用野外原位研究方法,探究模拟酸雨(pH梯度为3.0、4.0、5.0)和自然降水(CK)对生菜光合、抗氧化系统和产量的影响。结果表明,pH 4.0和5.0酸雨对生菜光合系统影响不显著,pH 3.0酸雨对生菜光合系统影响显著;在整个试验期内,pH 3.0酸雨显著降低生菜净光合作用8.4%—17.0%。pH 3.0、4.0和5.0酸雨均显著提高生菜超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量,表明酸雨会激活生菜抗氧化系统,同时会对生菜叶片膜系统造成损伤;在第20天后,pH 3.0酸雨下生菜过氧化氢酶(CAT)活性显著下降13.8%%—35.2%。pH 5.0酸雨对生菜产量影响不显著;pH 4.0和3.0酸雨显著降低生菜地上部产量,分别降低14.6%和16.7%。pH 3.0酸雨使生菜地下部产量显著降低19.0%。综上可见,模拟酸雨对生菜的光合系统、抗氧化酶系统和产量均产生显著影响,且酸雨对生菜的影响阈值在pH 4—5之间,pH 4.0以下的酸雨明显降低生菜产量,但酸雨强度为pH 5.0时已存在生菜减产的风险,研究结果可为生菜栽培的相关农户以及决策部门提供参考。     

花果期持续受渍对油菜生长、产量与含油量的影响

油菜是江汉平原广泛栽培的越冬作物，在春季雨水较多时常遭遇持续受渍胁迫，对产量有明显影响。为了探索春季油菜田的排水管理，取得较高产量，通过测坑试验和小区试验，初步研究了花果斯持续受渍对油菜生长，产量和含油量的影响。结果表明：油菜花果期持续受渍，主要是通过单株的有效角果数，千粒重等因素影响产量；随着持续受渍时间的延长，各受渍处理的单株有效角果数减少，千粒重降低，产量下降，与对照相比，较短时间（比如2天）持续受渍对油菜生长发育，产量形成以及籽粒含油量影响不大，但较长时期持续受渍会对油菜的这些方面产生不良影响，此类水分胁迫是生产上重点防治的对象。因此，在考虑地下水位动脉及其作用时间对油菜影响的排渍指标研究中，应主要从持续受渍程度对产量的影响方面建立关系，确定适宜的新型排渍指标。     

PREDICTIVE ASSESSMENT OF SEVERITY OF AGRICULTURAL DROUGHTS BASED ON AGRO-CLIMATIC FACTORS1

ABSTRACT: Past historical evidence indicates that droughts have had great impacts on human life. Drought (or scarcity of water) is assessed based on two key factors, namely, the estimated water demand, and the expected water supply. The formulation of these key factors for a region largely depends on the agro-climatic and economic conditions. Consideration of one such key factor is the relationship between the crop yield and water deficit in the assessment and prediction of agricultural droughts. The varying nature of this relationship from crop to crop adds to the complexity of agricultural drought analysis. To overcome this difficulty in analyzing agricultural droughts of a region, it is adequate to consider and place emphasis on a single crop (i.e., an index crop) grown homogeneously over the major area of the region. From one year to another year, the pattern of water requirement during the growing season of an index crop is rather stationary, and the water supply in arid and semi-arid area is mainly from seasonal random precipitation. In a region, grain yield of the index crop and, in turn, assessment of the severity of drought can reasonably be predicted as a function of the time of crop sowing and the distribution of rainfall, provided that temporal and spatial effects of other contributing factors (crop variety, soil fertility status, crop disease, pest control, cultivation practices etc.) on grain yield are considered to be uniformly distributed (i.e., stable). A predictive method of assessing agricultural droughts in an arid area of western India is presented. The major crop (Pearl Millet) of this region is grown from. July through September. The formulation of the proposed predictive method inherently implies that the grain yield of the main crop is a reliable indicator of agricultural drought. In the development of this predictive relationship (i.e., a regression type model) a number of potential yet simple variables affecting the grain yield in the region were investigated. The soil moisture index, although generally considered significant compared to the simple variables, has been found to account for insignificant variation in the grain yield. Results of our investigations suggest that it would be advisable to exclude the soil moisture index variable from the model. The proposed regression model can be used in the prediction of grain yield of the main crop several months ahead of crop harvesting operations and, in turn, the assessment of agricultural drought severity as mild, moderate, or severe. Such an assessment is expected to be helpful to planners for arranging appropriate measures to effectively combat agricultural drought situations.     

SNOWPACK CHANGES RESULTING FROM TIMBER HARVEST INTERCEPTION,REDISTRIBUTION, AND EVAPORATION1

ABSTRACT: Three processes were examined as causing snowpack changes in forest clearings. Two of the three contribute to increases and one counteracts by reducing snowpack. The two that increase snowpack are redistribution and decreased loss to interception. Snow evaporation from a clearing counteracts snowpack increases. Research has indicated that as vegetation density increases, so too does the loss to interception. As snow in the canopy reaches the limit that the canopy can hold (the threshold amount) evaporation increases. Aerodynamics of the forest canopy were studied as well. As timber is cut, wind patterns are disturbed, creating disruptions in the wind velocity gradient depositing snow in openings. This redistribution leads to an increased snow water equivalent and augments runoff. Snow evaporation was shown to increase proportionally with opening size. Evaporation offsets the water yield gains derived from forest cut. It was found that this offset is inclusive to the measurements of water yield changes in experimental forests. An optimal size of harvest block may be five tree heights in width as suggested by numerous studies.     

不同生境下瘤胃菌丛菌体密度与VFA的关系

在温度，搅动强度和Ｃ／Ｎ经３个生态因素发生梯度变化的情况下，本文在人工瘤胃装置内对瘤胃菌从９５０２３－１进行了连续发酵试验，逐日测定瘤肋细菌数量和ＶＦＡ产量的变化，对两者之间的关系进行了相关和回归分析。     

When is overfishing underfishing?

The term overfishing is being used with increasing frequency to designate an undesirable level of fisheries exploitation. All too often, however, the term is taken as being self-evident. This article demonstrates that many definitions of overfishing are possible, depending essentially on what objective is being pursued for the fishery. Various possible biological and economic objectives are considered, both in a static and dynamic model of the fishery. Consideration is given to the best utilization of the fish stock from the viewpoint of the individual fishermen as well as that of society. It is shown that overfishing by one definition may be underfishing by another, and it is concluded therefore that anyone using the term overfishing ought, as a matter of course, to define it.     

EFFECTS OF A NORTH CENTRAL WASHINGTON WILDFIRE ON RUNOFF AND SEDIMENT PRODUCTION1

ABSTRACT: Runoff was measured from a 564-ha catchment located on the Entiat Experimental Forest for nine years before a severe wild-fire in 1970 destroyed the mixed conifer vegetation. Runoff records from the Chelan River (2 393 km²) were used as control data for determining changes in water yield during the seven years following the fire. The first post-fire year was a period of transition in which the soil profile retained more water than in previous years and measured runoff was 8.9 cm greater than the predicted value based on pre-fire conditions. Runoff from the burned catchment during subsequent years was much greater than measured values before the fire. Measured minus predicted runoff, based on the pre-fire calibration equation, varied from 10.7 cm during the dry year of 1977 to 47.2 cm during the abnormally wet year of 1972. Flow duration curves indicated that runoff at each percent value after the fire was at least double the comparable pre-fire value. Sediment production increased dramatically after the fire because of increased flow rates, increased overland flow caused by reduced infiltration capacity, and mass soil movement. Sediment yield is beginning to decrease as stream channels become stabilized and vegetation on upper slopes improves infiltration capacity.     

DELIVERY OF SUSPENDED SEDIMENT AND POLLUTANTS FROM NONPOINT SOURCES DURING OVERLAND FLOW1

ABSTRACT: Delivery of sediment and particulate pollutants from diffuse sources is shown to be related to the loss of sediment carrying energy of runoff during the overland flow phase. The loss is caused by the termination of rainfall and by reduction of flow energy during the recession phase of the overland flow hydrograph. It has been demonstrated both by theoretical analyses and experimental measurements that the saturated sediment concentration in overland flow is a function of rainfall erosivity and the runoff flow rate. The hypotheses were verified by field measurements from a small homogeneous watershed.