地面不同垄沟形式对径流调控机制的研究

在干旱缺水、水土流失严重的黄土高原地区,地面垄沟是控制侵蚀、保持水分的有效措施。而不同垄沟形式将直接影响沟中径流量和土壤水分状况。本文设计了两种不同垄上覆盖材料和三种不同垄沟比的6组试验处理,通过2002与2003年降水季节的连续田间试验观测。结果表明:覆膜垄沟(MR)的临界产流降雨量低于不覆膜垄沟(ER),约为不覆膜垄沟(ER)的10%,两种垄沟的临界产流降雨量分别为0.4mm、4.6mm。覆膜垄沟(MR)的径流效率远高于不覆膜垄沟(ER),覆膜垄沟(MR)与土垄的平均径流效率分别在45%~70%与5%~6%之间变化。     

砂田集雨补灌对西瓜产量和土壤水分的影响

砂田在干旱半干旱地区是传统保水保墒的耕作方式,至今已有300多年的历史。对传统的砂田配合现代集雨滴灌技术种植西瓜,供试品种是西农8号,试验处理为集雨滴灌砂田(DSF),传统砂田(CSF),不覆砂的传统土田(CEF)。通过甘肃景泰十里砂河村的田间试验表明,产量比传统砂田提高近3倍。产量提高最主要的因素是在西瓜水分受到胁迫的几个关键需水期,及时实施了集雨补灌技术。从田间水分变化分析了集雨补灌砂田的增产机理。     

黄土高原旱作区马铃薯叶片和土壤水势对垄沟微集雨的响应特征

于2011年在黄土高原半干旱地区以平地不覆膜为对照,研究了不同沟垄和覆膜方式对马铃薯叶片和土壤水势水势的影响。结果表明：不同沟垄和覆膜方式在不同土层和不同生育期对土壤和叶片水势的影响差异显著。（1）土壤水势日变化趋势：0～20 cm土层,土垄处理在开花期为先下降后上升型,土垄和覆膜垄处理在块茎膨大期为先下降后上升型,覆膜垄和全膜双垄沟播处理在成熟期为先下降后上升型,其余为逐渐下降型;20～40 cm土层,各处理土壤水势呈逐渐下降趋势。（2）叶片水势日变化趋势：开花期和块茎膨大期表现为双低谷型,双低谷分别在13：00和17：00,成熟期为“V”型,即单低谷型,低谷出现在17：00。各处理变化趋势相同,但水势存在差异。土垄处理在水分关键期（开花期和块茎膨大期）叶片水势显著高于其他处理,而全膜双垄沟播处理在成熟期最高。（3）生育期土壤水势和叶片水势均表现为先减小后增大的趋势。20～40 cm土层对叶片水势影响较大,土垄处理在该土层具有较好的水分状态,蒸腾作用较强加速了水分运移速率,是导致覆膜垄和全膜双垄沟播处理水势低于土垄的主要原因。在前期降雨较少的年份,由于较小的蒸腾作用,土垄处理可以保证马铃薯承受较小的水分胁迫;在前期降雨量较多的年份,覆膜垄和全膜双垄沟播处理则可以凭借其较大的蒸腾作用发挥较大的增产效果。     

Comparative hydrological behaviour of two small catchments in semi-arid Zimbabwe

This paper describes and compares the hydrological responses of runoff, soil moisture and groundwater levels to rainfall events for two small semi-arid catchments over a 2-year period. Romwe received 1430 and 756 mm of rainfall in the 19999/00 and 2000/01 season, respectively. Mutangi received 756 and 615 mm of rainfall in the same years. Romwe generated 520 and 102 mm of runoff in the 19999/00 and 2000/01 seasons, respectively, while Mutangi generated 82 and 69 mm of runoff in the same years. The runoff response of the catchments was dominated by a relatively quick response to rainfall and with little or no significant contribution from regional groundwater or ‘old water’ sources. Total soil moisture storage to a depth of 120 cm was higher at Romwe than Mutangi for the entire study period reflecting the differences in the soil types. The groundwater level was closer to the surface and responded more quickly to rainfall at Romwe compared to Mutangi where water levels were between 12 and 16 m below the surface. There was a significant relationship between profile soil moisture and water table level at Romwe and none was observed at all in Mutangi. Significant (p<0.05) monthly rainfall runoff relationships were observed at both Romwe and Mutangi. At Romwe and Mutangi 91% and 76% of the runoff variation was accounted for by rainfall in the 1999/00 season, respectively. The rainfall–runoff relationship were different at Romwe for the two seasons, it was higher in the 1999/00 season than the 2000/01 season when 91% and 49% of the runoff variation was due to rainfall, respectively. The relationships were almost similar at Mutangi during the two seasons.     

Water table control on rill initiation and implications for erosional response

On sloping sandy agricultural soil sites near Toronto, Canada, summer storms adequate to generate runoff occur frequently, but rill development occurs mainly in spring when snowmelt or rainfall-induced runoff occurs above frozen subsoil. This suggests that on low and moderate slopes on these soils rill initiation is controlled primarily by hydraulic impedance close to the surface, rather than critical hydraulic conditions in runoff. Laboratory flume experiments were carried out on 10 m slopes at 1.5°, 5° and 9° with loamy sand/clay composite soil sample to test this hypothesis. Runoff with hydraulic conditions adequate for rill initiation occurred rapidly in most tests, but on 1.5° and 5° slopes little knickpoint scour or sediment transport occurred before water table development. This coincided with reduced surface soil strength, knickpoint scour and marked increase in sediment discharge, particularly on 5° slopes where increase was 20- to 30-fold. Further increase in sediment discharge occurred when water tables reached the surface. On 9° slopes runoff occurred more quickly, with higher hydraulic values. Significant rill incision and sediment discharge occurred well before water table development, and ultimately reached much higher values than on lower slopes. Results show that soil erodibility can change dramatically over short time periods during storms due to soil moisture conditions, and that the presence of a hydraulic impedance close to the surface which causes a perched water table to develop can strongly influence rill incision and sediment transport. The influence is unlikely to be marked on soils which are very erodible regardless of moisture conditions, or on extremely resistant soils. It will also be limited on very gentle or steep sites, but can be a significant factor in rill development on intermediate slopes.     

基于SCS-CN模型的半干旱黄土高原区秸秆炭覆盖集雨垄径流预测

垄沟集雨种植是缓解我国半干旱黄土高原区干旱、水土流失和土壤侵蚀的主要雨养农业技术。小流域水文模拟通常采用径流曲线数(Soil conservation service curve number,SCS-CN)模型。在标准SCS-CN模型中,由于径流曲线数CN值取值未考虑土壤水分动态变化,导致径流预测产生不合理的突变。以甘肃省定西市垄沟微型生物炭集雨垄为研究对象,根据实测降雨-径流数据,采用修正曲线数(Modified curve number,MoCN)法改进标准SCS-CN模型。结果表明:(1)随集雨垄垄宽增加(垄坡减小),标准SCS-CN模型和MoCN模型的CN值增加,随生物炭覆盖量增加,标准SCS-CN模型和MoCN模型的CN值减小;(2)MoCN模型的CN值高于标准SCS-CN模型;(3)MoCN模型的纳什效率系数(Nash-sutcliffe coefficient)较标准SCS-CN模型提高40%~275%,相关系数(Correlation coefficient)较标准SCS-CN模型提高1%~20%。修正曲线数MoCN模型能有效提高模型模拟精度,可为我国半干旱黄土高原区垄沟集雨种植系统地表径流预测及水土保持提供参考。     

Influence of canopy and topographic position on soil moisture response to rainfall in a hilly catchment of Three Gorges Reservoir Area,China

Rainfall provides essential water resource for vegetation growth and acts as driving force for hydrologic process, bedrock weathering and nutrient cycle in the steep hilly catchment. But the effects of rainfall features, vegetation types, topography, and also their interactions on soil water movement and soil moisture dynamics are inadequately quantified. During the coupled wet and dry periods of the year 2018 to 2019, time-series soil moisture was monitored with 5-min interval resolution in a hilly catchment of the Three Gorges Reservoir Area in China. Three hillslopes covered with evergreen forest(EG), secondary deciduous forest mixed with shrubs(SDFS) and deforested pasture(DP) were selected, and two monitoring sites with five detected depths were established at upslope and downslope position, respectively. Several parameters expressing soil moisture response to rainfall event were evaluated, including wetting depth, cumulative rainfall amount and lag time before initial response, maximum increase of soil water storage, and transform ratio of rainwater to soil water. The results indicated that rainfall amount is the dominant rainfall variable controlling soil moisture response to rainfall event. No soil moisture response occurred when rainfall amounts was 8 mm, and all the deepest monitoring sensors detected soil moisture increase when total rainfall amounts was 30 mm. In the wet period, the cumulative rainfall amount to trigger surface soil moisture response in EG-up site was significantly higher than in other five sites. However, no significant difference in cumulative rainfall amount to trigger soil moisture response was observed among all study sites in dry period. Vegetation canopy interception reduced the transform ratio of rainwater to soil water, with a higher reduction in vegetation growth period than in other period. Also, interception of vegetation canopy resulted in a largeraccumulated rainfall amount and a longer lag time for initiating soil moisture response to rainfall. Generally, average cumulative rainfall amount for initiating soil moisture response during dry period of all sites(3.5–5.6 mm) were less than during wet period(5.7–19.7 mm). Forests captured more infiltration water compared with deforested pasture, showing the larger increments of both soil water storage for the whole soil profile and volumetric soil water content at 10 cm depth on two forest slopes. Topography dominated soil subsurface flow, proven by the evidences that less rainfall amount and less time was needed to trigger soil moisture response and also larger accumulated soil water storage increment in downslope site than in corresponding upslope site during heavy rainfall events.     

Effect of nitrogen amendments on microbial biomass, above-ground biomass and nematode population in the Negev Desert soil

Nitrogen amendments (0, 25, 50 and 100 kg NH₄NO₃/ha) were used to study the responses of primary production, microbial biomass and nematode population in desert soil. The study was conducted in the Israeli Negev Desert, a region characterized by low and randomly distributed rainfall. Over a 1-year study period, nitrogen amendments resulted in a significant (p<0·01) increase in soil microbial biomass. Soil microbial biomass also increased concomitantly with the increase in soil organic matter. The number of free-living nematodes in the soil increased with the increase in soil moisture, ranging from 43,000 individuals per square metre at the end of the summer to 351,000 individuals per square metre during the rainy season. No significant correlation was found between the nitrogen treatments and the nematode population, whereas a significant positive correlation was found between the nitrogen amendments and the above-ground biomass (r²=0·94, p<0·03). The nitrate proportion of the total soluble nitrogen in the soil also increased with the increase in soil moisture. This study provides baseline data for nitrogen amendments on soil microbial status, as well as insights into the importance of nitrogen in fertility in arid environments.     

陇中黄土高原丘陵沟壑区不同植被恢复模式下次降雨产流产沙特征

基于甘肃省清水县汤峪河径流小区2015—2017年的观测数据,研究不同植被恢复模式条件下坡面次降雨入渗、产流产沙特征。结果表明：不同植被恢复模式条件下的土壤入渗量与降雨强度呈二次函数关系,存在入渗量达到最大值的临界降雨强度。入渗速率与降雨历时可以用幂函数关系表达,符合考斯恰可夫入渗模型。不同植被恢复模式条件下的产流率在0.003 3~0.003 6 mm·min^-1之间,相对裸地的减流率为54%~58%。产流率与降雨强度之间呈二次函数关系（R²>0.88）,产流率的主要影响因素是降雨强度。径流含沙量平均值乔灌混合区（3.13 g·L^-1）>灌木林（2.95 g·L^-1）>乔木林（2.79 g·L^-1）>草地（2.58 g·L^-1）,径流含沙量与降雨强度呈线性递增函数关系。裸地的产沙量显著高于各植被小区（P<0.05）,是各植被小区的43~57倍,各植被小区的减沙率在93%~94%之间,减沙效益高于其减流效益。各植被坡面土壤流失量与降雨侵蚀力呈线性递增函数关系;产流率与侵蚀产沙率之间呈极显著正相关关系（P<0.01）,二者间可采用二次函数关系表达。本研究成果可为黄土高原丘陵沟壑区水土保持优化配置提供理论依据。     

沙地降雨入渗水分动态

应用土壤水动力学基本原理，结合先进仪器的使用，从动力学角度，以能态观点定量研究沙地水分入渗动态。通过野外现场观测，分析不同深度含水率和吸力随时间变化过程，研究沙地降雨入渗水分传递过程，探讨入渗条件下沙地水分运动的动力学机制和特征。     

Slope runoff study in situ using rainfall simulator in mountainous area of North China

Simulated rainfall is a valid tool to examine the runoff generation on the slope.13 simulated rainfall experiments with different rainfall intensities and durations are completed in a 5 m ×10 m experimental plot in mountainous area of North China.Simultaneously,rainfall,surface runoff,soil-layer flow,mantel-layer flow and soil moisture are monitored respectively.From the results,it is found that the hydrographs in all layers have the characteristics of rapid rise and fall.The recessions of surface flow and soil-layer flow are much faster than that of mantel-layer flow.Surface flow,the main contributor,makes up more than 60% of the total runoff in the study area.It even exceeds 90% in the cases of high intensity rainfall events.Runoff coefficient(ratio of total runoff to rainfall amount) is mainly influenced by rainfall amount,rainfall intensity and antecedent soil moisture,and the relationship can be well expressed by a multiple linear regression function α = 0.002P + 0.182i + 4.88Wa-0.821.The relation between the rainfall intensity and the lag time of three flows(surface runoff,soil-layer flow and mantel-layer flow) is shown to be exponential.Then,the result also shows that the recession constant is 0.75 for surface runoff,is 0.94 for soil-layer and mantel-layer flow in this area.In this study area,the dominant infiltration excess runoff is simulated by Horton model.About 0.10 mm/min percolation is observed under the condition of different rainfall intensities,therefore the value is regarded as the steady infiltration rate of the study area.     

Initiation conditions for debris flows generated by runoff at Chalk Cliffs, central Colorado

We have monitored initiation conditions for six debris flows between May 2004 and July 2006 in a 0.3 km² drainage basin at Chalk Cliffs; a band of hydrothermally-altered quartz monzonite in central Colorado. Debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14° to 45°. The availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes. Rainfall exceeding I = 6.61(D)^− 0.77, where I is rainfall intensity (mm/h), and D is duration (h), was required for the initiation of debris flows in the drainage basin. The approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0.15 m³/s. Colluvium in the basin was unsaturated immediately prior to (antecedent) and during debris flows. Antecedent, volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4–9%, and 4–7%, respectively. During debris flows, peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10–20%, and 4–12%, respectively. Channel sediment at a depth of 45 cm was unsaturated before and during debris flows; antecedent moisture ranged from 20–22%, and peak moisture ranged from 24–38%. Although we have no measurements from shallow rill or channel sediment, we infer that it was unsaturated before debris flows, and saturated by surface-water runoff during debris flows.Our results allow us to make the following general statements with regard to debris flows generated by runoff in semi-arid to arid mountainous regions: 1) high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff, 2) locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows, and 3) rainfall and simulated surface-water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment.     

Spatial distribution of surface conditions and runoff generation in small arid watersheds, Zin Valley Badlands, Israel

High rill density may be regarded as indicative of frequent and integrated runoff along a drainage network. However, field observations of soil development and rill geometry in small, first-order catchments (0.1 to 1 ha) of the Zin Valley Badlands, northern Negev, Israel, suggest a pattern of partial area contribution and frequent flow discontinuities along hillslopes and channels. Changing soil properties, associated with an increase of slope angle and slope length, appear to be responsible for high infiltration on the slopes, leading to nonuniform runoff generation within small drainage basins. Runoff observation, sprinkling tests, and soil analysis along ridges and sideslopes were carried out to test this hypothesis. The results confirmed that infiltration capacity on the sideslopes is significantly higher than on the ridges. Under current rainfall conditions, only extreme rainfall intensities are sufficient to generate runoff along entire slopes. The discontinuous nature of most runoff events causes erosion on ridges and deposition on slopes, which enhances soil development on the valley sideslopes, creating a positive feedback on infiltration rate and depth. This demonstrates that the links between within-storm rainfall conditions and spatial distribution of soil characteristics have to be incorporated into our understanding of landscape development in badlands.     

青海湖湖东沙地不同沙丘降雨入渗研究

降雨入渗对干旱、半干旱区土壤水分的影响很大,降雨量、降雨强度、土壤前期含水量等要素都会影响水分的入渗过程。本文通过监测青海湖湖东沙地3种类型沙丘的土壤水分和降雨情况,对区内降雨特征以及不同要素对沙丘水分入渗的影响进行了分析。结果表明：降雨量只有达到某一临界值才发生下渗,流动沙丘、固定沙丘、经治理（人工植被+麦草方格沙障）的流动沙丘发生下渗的临界降雨量分别为5.6 mm、1.6 mm、0.2 mm。水分累积入渗量随降雨量增大而增加,降雨量相同的情况下,入渗量大小表现为经治理的流动沙丘>固定沙丘>流动沙丘。当降雨量和土壤前期含水量相近时,入渗量随降雨强度的增大而增加,尤其在小降雨事件下,降雨强度是影响入渗的关键因素,大降雨事件下降雨量则成为影响入渗的决定因素。降雨量和降雨强度相近的情况下,入渗量与土壤前期含水量呈负相关关系。随着降雨量增大,入渗水分全部消耗所需要的时间逐渐增加,尤其当降雨量大于10 mm时,入渗水分消耗所需时间将随着降雨量的增大迅速增加。     

典型黄土坡面土壤侵蚀特征及径流流速空间变化试验研究

为了明确土壤性质对坡面侵蚀方式作用机制的影响,本研究采用室内模拟降雨试验,选取黄土高原典型暴雨强度,在不同坡度条件下,对两种黄土的坡面侵蚀方式、形态特征、产流产沙过程及其相应径流流速的变化规律进行了研究。结果表明,绥德土径流量明显高于安塞土,10º、15º和20º时前者的平均径流量分别比后者高出51.1%、55.5%和63.0%,且前者更易形成细沟,使得其平均含沙量和平均产沙率分别是后者的1.14~3.59倍和2.50~8.48倍。在片蚀阶段,与绥德土相比,安塞土的含沙量较高,后者的平均含沙量是前者的1.24~1.73倍,但两种土壤的含沙量和产沙规律相同,均表现为先快速增加到最大值,然后逐渐降低到相对稳定状态,该现象证明片蚀的初期阶段主要受控于径流输沙能力,后期受径流的剥蚀能力控制。在细沟侵蚀阶段,绥德土细沟发育以沟头溯源侵蚀为主,崩塌作用频繁,该侵蚀形式不仅控制着细沟形态的总体特征,也导致含沙量和产沙率均急剧增加,该阶段平均含沙量是相应片蚀阶段的3.25~4.34倍。细沟沟口下方坡面存在明显的泥沙沉积带,表明细沟集中水流的搬运能力远高于坡面漫流,细沟侵蚀主要受径流输沙能力控制。两种土壤的径流流速均表现为坡面下部高于坡面上部,径流稳定后高于径流稳定前,总体来看,绥德土和安塞土上坡和径流稳定后的平均流速分别是下坡和径流稳定前的1.4倍、1.25倍和1.75倍、1.29倍,此外细沟侵蚀或侵蚀强度与微地貌形态之间的互馈作用对径流流速也有较大影响。     

威连滩冲沟砂黄土的风蚀与降雨侵蚀模拟实验

 通过风洞与模拟降雨实验，研究了风力与降雨对青海省贵南县威连滩冲沟砂黄土的复合侵蚀作用。实验得出：①风蚀后的降雨使砂黄土表面在风干过程中形成了一层较为坚硬的结壳，增大了土壤的抗蚀性，降低了第二次风洞实验后期的风蚀率;②土壤水分与人为扰动是影响土壤风蚀的两个重要因素。当土壤水分较小时，风蚀率受人为扰动影响巨大;当土壤水分较大时，人为扰动对土壤风蚀的影响较小;③在持续降雨的实验条件下，砂黄土的产流、产沙量随着雨强的变化而改变。这种变化与表土的侵蚀率、可蚀性物质的多少、土壤水分以及土壤的入渗率等都有很大的关系。     

Biodegradation of municipal refuse and chicken manure in a winter-wheat ecosystem in Saudi Arabia

Addition and incorporation of organic fertilizers is known to improve the properties of agricultural soils. Therefore, during 22 weeks of field incubation we studied the biodegradation (measured by static absorption of CO₂) of two organic manures viz. municipal refuse and chicken manure incorporated into sandy soils, under sprinker irrigation, at the rates of 0, 16·5, 33·0, 49·5 and 66·0, and 0, 4·1, 8·25, 16·5, and 33·0 tonnes/ha, respectively.The results obtained indicated that the cumulative amount of CO₂ respired was linearly correlated with the rate of organic material applied (p < 0.001). Statistical analysis of the data obtained showed that both the intercept (rate of decomposition) and the slope (rate of reaction with time) increased with increasing rate of application of organic manure. The magnitude of increment was highest at the application rates of 33·0 and 8·25 tonnes/ha for municipal refuse and chicken manure, respectively. The rate of increment, generally, declined thereafter thus indicating that these two rates are the optimum levels of incorporation of the appropriate organic manures under the conditions of this study.The maximum organic-carbon mineralized, accounting for 10·5 and approximately 50%, was obtained at the optimum rates for municipal refuse and chicken manure, respectively. Both simple and multiple regression equations describing the relationship between soil temperature and soil-moisture content each separately and in combination, as independent variables, and the cumulative rate of CO₂ production were computed. A substantially strong relationship with soil temperature but inconsistent and contradicting results with soil moisture were obtained. Inclusion of soil temperature and moisture in a single model as an independent variable in relation to cumulative CO₂ as a dependent variable improved the soil moisture-CO₂ production relationship.     

Relations between interrill erosion processes and sediment particle size distribution in a semiarid Mediterranean area of SE of Spain

Erosion and sediment characteristics were measured using simulated rainfall on two cultivated soils of contrasting lithology (Quaternary calcareous colluvium and Tertiary marls) in a semiarid Mediterranean area of SE Spain. Two rainfall intensities, high (56.0±2.4 mm h⁻¹) and medium (31.4±1.4 mm h⁻¹), were used in order to know the mechanisms involved in each selected condition. For each simulated event, runoff and sediment were sampled at 1-min intervals on a 1-m wide by 2-m long erosion plot. The erosion rate was calculated as the total amount of soil lost divided by the time period of the test. The duration of the test was that needed to reach steady state runoff, an average time of 24.5 min for Quaternary calcareous colluvium and 17.7 min for Tertiary marls. The size distribution of the transported sediment in the field (effective size distribution) was compared with equivalent measurements of the same samples after chemical and mechanical dispersion (ultimate size distribution) to investigate the detachment and transport mechanisms involved in sediment mobilisation. The results showed that the soil type determined the hydrological response, regardless of the rainfall intensity. The erosional response was, however, determined by the rainfall and soil surface characteristics.In Quaternary calcareous colluvial soils, the predominant erosion process depended on the rainfall intensity, with a prevailing detachment-limited condition in high-intensity events and prevailing transport-limited conditions in those events of medium intensity. These differences in the main erosion processes were reflected in the size of the transported material and in the change in sediment size within the storm. Thus, a time-dependent size distribution of the eroded material (decreasing coarse fractions and increasing fine fractions with runoff time) was observed for high-intensity events. In medium-intensity events, on the other hand, the time-independent size distribution of the eroded material indicated transport-limited erosion.Due to the rapid surface crusting on the Tertiary marl soil, no differences in the main erosion processes or in the sediment size distribution occurred for the different rainfall intensities tested. The erosion of marl soils was determined mainly by the limited quantity of available sediment.The effective size of material was a more sensitive parameter than the ultimate size of the sediment to study the way in which the sediment was transported.     

北京地区农田氮素养分随地表径流流失机理

田间模拟降雨径流试验研究了北京地区农田暴雨径流氮素流失与雨强、作物覆盖、施肥因子的关系，以及侵蚀泥沙的粒径分布特征和对氮的富集作用。结果表明：（1）降雨强度越大，地表径流模数和侵蚀模数增大，氮素流失越多；作物覆盖有效地减少地表水土和颗粒态氮流失；（2）颗粒态氮浓度占径流全氮浓度的88.9%(施尿素）和98％以上（未施氮肥），是农田径流氮损失的主要形态；（3）施用化学氮肥增大了农田径流溶解态氮浓度，化学氮肥容易通过地表径流流失；（4）侵蚀泥沙的团聚体组成和原来土壤有很大差异，粒径＜0.25mm的团聚体，尤其是含氮量较高的＜0.045mm团聚体的富集是侵蚀泥沙富集氮的主要原因。减少地表径流和土壤侵蚀，降低表土速效氮含量是减少农田地表径流氮养分流失的关键。     

Differential responses of hillslope and channel elements to rainfall events in a semi-arid area

The degree of hydrological connectivity of hillslope elements in a semi-arid climate was studied at the season and event timescales. Field data were obtained in Rambla Honda, a Medalus project field site situated in SE Spain, on micaschist bedrock and with 300 mm annual rainfall. The season timescale was assessed using correlation analysis between soil moisture and topographic indices. The event timescale was studied by a quasi-continuous monitoring of rainfall, soil moisture, runoff and piezometric levels. Results show that widespread transfers of water along the hillslope are unusual because potential conditions for producing overland flow or throughflow are spatially discontinuous and extremely short-lived. During extreme events, runoff coefficients may be locally high (ca. 40% on slope lengths of 10 m), but decrease dramatically at the hillslope scale (<10% on slope lengths of 50 m). Two mechanisms of overland flow generation have been identified: infiltration excess, and local subsurface saturation from upper layers. The former occurs during the initial stages of the event while the latter, which is quantitatively more important, takes place later and requires a certain time structure of rainfall intensities that allow saturation of the topsoil and the subsequent production of runoff. Hillslopes and alluvial fans function as runoff sources and sinks respectively. Permanent aquifers are lacking in Rambla Honda. Variable proportions of hillslope areas may contribute to flash floods in the main channel, but their contribution to the formation of saturated layers within the sediment fill is very limited.