Effects of conservation tillage practices on winter wheat water-use efficiency and crop yield on the Loess Plateau,China

In the semi-humid to arid loess plateau areas of North China, water is the limiting factor for rain-fed crop yields. Conservation tillage has been proposed to improve soil and water conservation in these areas. From 1999 to 2005, we conducted a field experiment on winter wheat (Triticum aestivum L.) to investigate the effects of conservation tillage on soil water conservation, crop yield, and water-use efficiency. The field experiment was conducted using reduced tillage (RT), no tillage with mulching (NT), subsoil tillage with mulching (ST), and conventional tillage (CT). NT and ST improved water conversation, with the average soil water storage in 0–200 cm soil depth over the six years increased 25.24 mm at the end of summer fallow periods, whereas RT soil water storage decreased 12 mm, compared to CT. At wheat planting times, the available soil water on NT and ST plots was significantly higher than those using CT and RT. The winter wheat yields were also significantly affected by the tillage methods. The average winter wheat yields over 6 years on NT or ST plots were significantly higher than that in CT or RT plots. CT and RT yields did not vary significantly between them. In each study year, NT and ST water-use efficiency (WUE) was higher than that of CT and RT. In the dry growing seasons of 1999–2000, 2004–2005 and the low-rainfall fallow season of 2002, the WUE of NT and ST was significantly higher than that of CT and RT, but did not vary significantly in the other years. For all years, CT and RT showed no WUE advantage. In relation to CT, the economic benefit of RT, NT, and ST increased 62, 1754, and 1467 yuan ha⁻¹, respectively, and the output/input ratio of conservation tillage was higher than that of CT. The overall results showed that NT and ST are the optimum tillage systems for increasing water storage and wheat yields, enhancing WUE and saving energy on the Loess Plateau.     

Distribution of soil water-stable aggrega-tes and organic carbon content affectedby tillage systems: a meta analysis

A better understanding of soil carbon( C) distribution within aggregate fractions is essential to evaluating the potential of no-till for sustaining productivity and protecting the environment. A metaanalysis on 744 comparisons from 34 studies was conducted to determine the effects of three different tillage treatments( conventional mouldbould ploughing tillage( CT),reduced tillage( RT) and no tillage( NT)) on water-stable aggregate size distribution,soil C concentration in aggregate fractions.The meta-analysis indicates that compared with CT treatment, NT/RT significantly( P 0. 05)increases macro-aggregate above 20 cm by 20. 9%-82. 2%( 2. 00 mm) and 5. 9%-19. 1%( 0. 25-2.00 mm),whereas NT/RT significantly reduces micro-aggregate and silt clay fractions above 20 cm.NT/RT significantly( P 0. 05) increases the SOC in macro-aggregate( 0. 25 mm) and microaggregate( 0. 25 mm) size classes above 20 cm soil depth compared with CT. The results suggest that soil sampling depth should be considered to evaluate the influence of tillage systems on the distribution of soil aggregate,and the content of aggregate-associated C content.     

Modeling the soil water balance based on time-dependent hydraulic conductivity under different tillage practices

A simulation model with time-dependent hydraulic conductivity parameters was used to predict the effects of three different tillage practices: conventional tillage (CT), no-tillage (NT) and subsoiling tillage (ST) on the components of the soil water balance during the summer maize growing season. The predictive capability of the model was improved, particularly for the subsoiling tillage case. The simulation results show that temporal changes in soil hydraulic conductivity induced by different tillage practices can affect percolation, water storage, transpiration and evaporation. Differences in the simulated components of the water balance were found to be small between CT and NT practices, but larger in the ST case. Compared with the conventional and no-tillage methods, subsoiling promotes infiltration and deep percolation, thereby favoring a possible recharge of the groundwater. Actual evaporation is always lower in the subsoiled plots, whatever the hydrological year. Transpiration is similar for the three treatments, suggesting no significant differences in water availability, except in wet years where it is higher in subsoiled soils.     

Monitoring and modelling the three-dimensional flow of water under drip irrigation

The interpretation of soil water dynamics under drip irrigation systems is relevant for crop production as well as on water use and management. In this study a three-dimensional representation of the flow of water under drip irrigation is presented. The work includes analysis of the water balance at point scale as well as area-average, exploring uncertainties in water balance estimations depending on the number of locations sampled. The water flow was monitored by detailed profile water content measurements before irrigation, after irrigation and 24 h later with a dense array of soil moisture access tubes radially distributed around selected drippers. The objective was to develop a methodology that could be used on selected occasions to obtain ‘snap shots’ of the detailed three-dimensional patterns of soil moisture. Such patterns are likely to be very complex, as spatial variability will be induced for a number of reasons, such as strong horizontal gradients in soil moisture, variations between individual sources in the amount of water applied and spatial variability is soil hydraulic properties. Results are compared with a widely used numerical model, Hydrus-2D. The observed dynamic of the water content distribution is in good agreement with model simulations, although some discrepancies concerning the horizontal distribution of the irrigation bulb are noted due to soil heterogeneity.     

Developing a reliable strategy to infer the effective soil hydraulic properties from field evaporation experiments for agro-hydrological models

The Richards equation has been widely used for simulating soil water movement. However, the take-up of agro-hydrological models using the basic theory of soil water flow for optimizing irrigation, fertilizer and pesticide practices is still low. This is partly due to the difficulties in obtaining accurate values for soil hydraulic properties at a field scale. Here, we use an inverse technique to deduce the effective soil hydraulic properties, based on measuring the changes in the distribution of soil water with depth in a fallow field over a long period, subject to natural rainfall and evaporation using a robust micro Genetic Algorithm. A new optimized function was constructed from the soil water contents at different depths, and the soil water at field capacity. The deduced soil water retention curve was approximately parallel but higher than that derived from published pedo-tranfer functions for a given soil pressure head. The water contents calculated from the deduced soil hydraulic properties were in good agreement with the measured values. The reliability of the deduced soil hydraulic properties was tested in reproducing data measured from an independent experiment on the same soil cropped with leek. The calculation of root water uptake took account for both soil water potential and root density distribution. Results show that the predictions of soil water contents at various depths agree fairly well with the measurements, indicating that the inverse analysis is an effective and reliable approach to estimate soil hydraulic properties, and thus permits the simulation of soil water dynamics in both cropped and fallow soils in the field accurately.     

Modelling of Soil Water Dynamics in an Irrigated Corn Field using Direct and Pedotransfer Functions for Hydraulic Properties

A simulation study of the soil waterdynamics in a corn field was carried out inan area of Northern Greece during the 1996growing period. The soil water dynamicswere evaluated using a one-dimensionalmodel based on the Galerkin finite elementmethod. The simulations were carried out ontwo plots in the field which differed as tothe amount and timing of nitrogenfertilizer application. The irrigationwater was applied to the field ininadequate quantities, which resulted inlow water availability. Two procedures forobtaining soil hydraulic properties weretested with regard to the application inthe simulations. The pedotransfer functionsdeveloped by Vereecken et al. (1989,1990) were used to determine the parametersof the soil hydraulic functions, which werethen used in the model to simulate the soilwater dynamics. The simulated results werecompared with available measurements ofwater content at different depths in thesoil during the growing period. Thequalitative and quantitative procedures formodel evaluation showed that there was goodagreement between the simulated and themeasured values of water content atdifferent depths of soil. Results show thatsimulations based on pedotransfer functionspredict the water content reasonably wellcompared to results with the directedestimated hydraulic functions.     

土壤盐分对春小麦水盐动态及光合特性的影响

为了解土壤含盐量对滴灌春小麦土壤水盐运动以及其光合生理指标的影响,并为滴灌春小麦在盐碱地种植提供理论依据和技术支撑,通过桶栽试验,研究了土壤含盐量分别为0.15%(CK),0.80%,1.10%,1.40%,1.70%,2.00%,2.30%,2.60%条件下,春小麦土壤水盐运动规律以及其光合特性变化状态.结果表明,在春小麦整个生育期内,土壤含水率总体变化呈现递减趋势;随着土层深度的增加,土壤水分和盐分质量分数均表现出增加的趋势,土壤含盐量越高其平均含水率越高;各处理0~40 cm土层盐分质量分数在小麦生育期末与播种时相比均有不同程度的下降,处于脱盐状态;土壤盐分初始质量分数为0.15%,0.80%以及1.10%的春小麦叶片水分利用效率最高,同时也具有较高的净光合速率.     

保护性耕作下土壤水分变化特征模拟研究

为了对陇中黄土高原沟壑区不同保护性耕作措施下的土壤含水率进行差异性分析,利用长期定位试验,设置春小麦/豌豆、豌豆/春小麦轮作序列下传统耕作、免耕、传统耕作秸秆覆盖和免耕覆盖4种耕作措施,以当地月平均气温、月降水量、月平均辐射量、月平均蒸发量、月作物耗水量作为输入,以0~200 cm土层土壤含水率作为输出,建立基于长短期记忆(Long short-term memory,LSTM)神经网络的土壤含水率预测模型,并对模型的有效性进行评估,然后利用该模型模拟4种耕作措施下0~200 cm土层土壤含水率的动态变化过程。结果表明,基于LSTM神经网络建立的土壤含水率模型对陇中黄土高原沟壑区保护性耕作下土壤含水率预测具有较好的适用性,其模拟值与实测值的平均均方根误差为2.29%、平均相对误差为6.79%、平均决定系数为0.82。豌豆/春小麦轮作序列中4种耕作措施下的土壤含水率比春小麦/豌豆轮作序列的土壤含水率增加1.49%、1.61%、1.69%和1.76%,4种耕作措施下0~200 cm土层的土壤含水率由大到小依次为:免耕覆盖、免耕、传统耕作秸秆覆盖、传统耕作,免耕覆盖下的土壤含水率分别比免耕、传统耕作秸秆覆盖和传统耕作增加1.27%、1.75%和2.81%。免耕覆盖对0~30 cm土层土壤含水率的影响最为显著,其土壤含水率分别比免耕、传统耕作秸秆覆盖和传统耕作平均增加1.60%、2.63%和4.18%。4种耕作措施下的土壤含水率随季节发生变化,免耕覆盖下的土壤含水率整体高于其他3种耕作措施,且在作物生长前期的蓄水保墒效果更加显著。研究区豌豆/春小麦轮作序列中4种耕作措施的土壤含水率相对较高,而不同耕作措施下免耕覆盖更有利于提高该地区农田土壤水分,为陇中黄土高原沟壑区最适宜的耕作方式。     

Cautionary notes on the use of pedotransfer functions for estimating soil hydraulic properties

The performance of published pedotransfer functions was evaluated in terms of predicted soil water content, pressure heads, and drainage fluxes for a layered profile. The pedotransfer functions developed by Vereecken et al. (1989), Vereecken et al. (1990) were used to determine parameters of the soil hydraulic functions θ(h) and K(h) which were then used as input to SWATRER, a transient one-dimensional finite difference soil water model with root uptake capability. The SWATRER model was used to simulate the hydraulic response of a multi-layered soil profile under natural climatic boundary conditions for a period of one year. The simulations were repeated by replacing the indirectly estimated water retention characteristic by (1) local-scale, and (2) field-scale mean observed θ(h) relationships. Soil moisture contents and pressure heads simulated at different depths in the soil profile were compared to measured values using these three different sets of hydraulic functions. Drainage fluxes at one meter below ground surface have also been simulated using the same three sets of hydraulic functions. Results show that simulations based on indirectly estimated moisture retention characteristics (obtained from pedotransfer functions) overpredict the observed moisture contents throughout the whole soil profile, but predict the pressure heads at shallow depths reasonably good. The results also show that the predicted drainage fluxes based on estimated retention functions are about four times as high compared to the drainage fluxes simulated using measured retention curves.     

Comparison between mechanistic and functional models for estimating soil water balance: deterministic and stochastic approaches

In many models used to simulate soil-water relationships, representations of the transport mechanisms in the soil-plant-atmosphere continuum, range from mechanistic to functional. The objective of this paper is to compare two functional models, FAO (Doorenbos and Pruitt, 1977) and Ritchie (1985)models, with a mechanistic model (Maraux and Lafolie, 1998) to simulate the soil water balance of maize and sorghum grown in sequence in Nicaragua. In the FAO model, the soil is described as a single reservoir which is characterized by its amount of water varying on a daily time scale, depending on the rain, drainage, and actual evapotranspiration. In the Ritchie model, the soil is regarded as a multilayered soil profile. The maximum evapotranspiration is divided between soil evaporation and plant transpiration, and drainage occurs if the amount of water arriving in the last layer corresponds to a water content greater than the field capacity. The mechanistic model is based on the Richards' equation. Comparison of the three models was first made according to a deterministic approach with parameters coming from the same database. We then considered a stochastic approach for which 800 hydraulic characteristics of the soil were generated, according to the spatial variability observed at the field scale and to the scaling theory applied to similar porous media. A distribution of the stochastic parameters used in the three models was thus derived. Results showed that the order of magnitude of the evapotranspiration was similar for the three models (902, 874, 842 mm cumulative evapotranspiration for a 203 day period for the MM, Ritchie, and FAO models, respectively). Adding a capillary rise mechanism in the functional models improved moderately the soil-water balance. Evapotranspiration and drainage showed moderate sensitivity to spatial variability in soil hydraulic properties (coefficients of variation less than 1.6%), whereas final water storage (after 203 days) showed a greater sensitivity (coefficients of variation from 7.9–15.7%, depending on the model).     

Effect of temporal variability in soil hydraulic properties on simulated water transfer under high-frequency drip irrigation

The effect of changes in the hydraulic properties of a loamy topsoil on water transfer under daily drip irrigation was studied over a cropping cycle. Soil water contents were measured continuously with neutron probes and capacitance sensors placed in access tubes (EnviroSMART) and were compared to predications made by the Hydrus-2D model. Three different sets of hydraulic parameters measured before and after irrigation started, were used.Our results demonstrated that, based on the assumptions used in this study, the accuracy of the Hydrus predictions is good. Graphical and statistical comparisons of simulated and measured soil water contents and consequently the total water storage revealed a similar trend throughout the monitoring period for the all three different sets of parameters. The soil hydraulic properties determined after irrigation started were found to be much more representative of the majority of the irrigation season, as confirmed by the accuracy of the simulation results with high values of the index of agreement and with values of RMSE similar in magnitude to the error associated with field measurements (0.020 cm³ cm⁻³). The highest RMSE values (about 0.04 cm³ cm⁻³) were found when the model used input soil parameters measured before irrigation started.Generally, changes in topsoil hydraulic properties over time had no significant effect on soil moisture distribution in our agro-pedo-climatic context. One possible explanation is that daily water application was conducted at the same time as maximal root water uptake. This meant the soil did not need to store total daily crop water requirements and consequently that the water redistribution phase represented a very short stage in the irrigation cycle. It is probable that irrigating in the daytime when crop evapotranspiration is highest could prevent the effects of a temporal change and other problems connected with the soil. Moreover, water will be always available for the crop. Further experiments are needed to justify the results and to study the effects of low frequency drip irrigation on soil hydraulic characterization and consequently on soil water transfer in order to improve irrigation scheduling practices.     

利用电容式传感器连续监测土壤硝态氮质量分数的试验研究

通过室内和田间试验,研究土壤硝态氮质量分数与电容式传感器监测的土壤电导率、含水率和温度的定量关系。在室内以NH4NO3分析纯为溶质,进行了溶液质量浓度0～10g/L的7次土柱试验;在2009年和2010年春玉米生育期内监测了不同滴灌水量条件下土壤电导率、含水率和温度动态变化。结果表明,土壤电导率能较好的反映土壤硝态氮质量分数的变化;土壤硝态氮质量分数与电导率、含水率和温度之间的关系可用二次多项式描述,且3个土壤参数对土壤硝态氮质量分数的影响均达到了极显著水平(P≤0.01);由于回归模型的拟合精度受土壤初始养分盐分质量分数及空间变异等因素的影响,为获得较高的预测精度,应进行田间标定。     

农膜残留对土壤水动力参数及土壤结构的影响

随着地膜的大规模连续使用,农膜残留随之剧增,从而破坏了原有土壤结构,改变了土壤水分入渗及持水性能,严重阻碍了土壤水分和溶质运移。饱和导水率和土壤水分特征曲线是表征水分入渗性能及进行水分和溶质运移的重要参数,为了定量化和可视化残膜对水力特性及土壤结构的影响规律,通过设置5个残膜量处理(0、5、100、200、400 kg/hm2),利用室内试验研究了不同残膜量对水分入渗及土壤持水性能的影响,并基于CT扫描技术分析残膜对土壤结构的影响效应。结果显示:随着残膜量增加,饱和导水率呈显著指数下降趋势(p0.05),当残膜量达到200 kg/hm2时,饱和导水率仅为无膜处理的12%。在高吸力阶段(100 k Pa),残膜量增加土壤反而越易脱水,持水性能反而变差,即特征曲线左移;基于van Genuchten模型和Gardner模型对不同残膜量处理的吸力和土壤含水率进行拟合,精度均较高,模型中经验参数随残膜量增加均呈明显规律变化。当残膜量增加后,二值化后的CT图像显示片状黑斑面积明显增加,并与残膜量呈比例关系,其中400 kg/hm2处理黑斑面积是无膜处理的19倍。     

Effects of tillage and fallow period management on soil physical behaviour and maize development

Effects of two tillage treatments and two fallow period managements under continuous maize cropping on soil temperature, soil water dynamics and maize development were evaluated over a 4-year period (2005–2008). Tillage treatments were conventional tillage with mouldboard ploughing and conservation tillage with disk harrowing. The fallow period managements were bare soil or soil sown with a cover crop after maize harvest. For each year, topsoil temperature (0–20 cm-depth) was lower under conservation tillage systems at sowing, from 0.8 to 2.8 °C. This difference persisted several weeks after sowing, and disappeared afterwards. Under conservation tillage, higher soil water content was generally measured at sowing and during the growing season strong fluctuations were observed at 40 cm-depth. Under conventional tillage, soil water content varied mainly in the tilled layer (20 cm-depth). Tillage and fallow period management affected water flow rate at 40 cm-depth. During the maize growing season, the lowest drainage volumes were measured in 2006 and 2008 under conservation tillage in cover cropped plots. No effect of fallow period management on maize development and yield was observed but significantly higher yields were measured under conservation tillage in 2005 and 2007. From this 4-year experiment under continuous maize cropping, using cover crop and reducing tillage intensity enhanced water use efficiency while maintaining or increasing maize yields.     

Yield and soil system changes from conservation tillage in dryland farming: A case study from North Eastern Tanzania

Yield levels in smallholder farming systems in semi-arid sub-Saharan Africa are generally low. Water shortage in the root zone during critical crop development stages is a fundamental constraining factor. While there is ample evidence to show that conservation tillage can promote soil health, it has recently been suggested that the main benefit in semi-arid farming systems may in fact be an in situ water harvesting effect. In this paper we present the result from an on-farm conservation tillage experiment (combining ripping with mulch and manure application) that was carried out in North Eastern Tanzania from 2005 to 2008. Special attention was given to the effects of the tested treatment on the capacity of the soil to retain moisture. The tested conservation treatment only had a clear yield increasing effect during one of the six experimental seasons (maize grain yields increased by 41%, and biomass by 65%), and this was a season that received exceptional amounts of rainfall (549 mm). While the other seasons provided mixed results, there seemed to be an increasing yield gap between the conservation tillage treatment and the control towards the end of the experiment, and cumulatively the yield increased with 17%. Regarding soil system changes, small but significant effects on chemical and microbiological properties, but not on physical properties, were observed. This raises questions about the suggested water harvesting effect and its potential to contribute to stabilized yield levels under semi-arid conditions. We conclude that, at least in a shorter time perspective, the tested type of conservation tillage seems to boost productivity during already good seasons, rather than stabilize harvests during poor rainfall seasons. Highlighting the challenges involved in upgrading these farming systems, we discuss the potential contribution of conservation tillage towards improved water availability in the crop root zone in a longer term perspective.     

离心机法测定土壤水分特征曲线中的收缩特性

为了探明土壤在离心力作用下的收缩规律,开展了离心机法测定土壤水分特征曲线试验.砂壤土和黏壤土分别设定3个初始容重,以离心机法测定的数据为基础,研究了离心力变化下的土壤收缩规律,并通过van Genuchten-Mualem(VG-M)模型对2种情景模式(考虑容重变化和未考虑容重变化)下所测定的土壤水分特征曲线进行拟合,并以此估算所得的土壤水力特性参数对沟灌二维水分运动特性进行了数值模拟,同时结合室内试验对比分析了参数的合理性.结果表明,离心机转速增大,土壤含水率降低,容重随之增大,当吸力为7 000 cm时,砂壤土和黏壤土的容重分别近于1.81和1.79 g/cm³;基于土壤收缩特征曲线,供试土壤收缩过程可采用三直线模型进行表征,但各收缩段的吸力范围存在差异;与未考虑容重变化所得VG-M模型中的参数值相比,考虑土壤容重变化所得的滞留含水率θ_r和进气吸力值倒数a均增大,但形状系数n均减小;以考虑土壤容重变化所得VG-M参数为基础进行沟灌二维水分运动数值模拟,其入渗水量、湿润锋运移距离(垂直和水平)与实测值的误差绝对值均值分别为5.8%,3.0%和2.6%,较未考虑容重变化时精度分别提高了39.2%,57.2%和52.9%.因此离心机法测定土壤水分特征曲线的过程中需考虑土壤容重的变化,且以此获得的参数能够较为显著地提高数值模拟精度.     

Elevation and infiltration in a level basin. I. Characterizing variability

Spatial characterization of soil physical properties could improve the estimation of surface irrigation performance. The aim of this research was to characterize the spatial and time variability of a set of irrigation-related soil properties. The small-scale experimental level-basin (729 m²) was located on an alluvial loam soil. A corn crop was established in the basin and irrigated five times during the season. A detailed survey of the soil properties (generally using a 3 × 3 m network) was performed. Classic statistical and geostatistical tools were used to characterize the variables and their interactions. Semivariograms were validated for the studied variables, except for the clay fraction, the saturated hydraulic conductivity and the infiltration parameters. The resulting geostatistical range was often in the interval of 6–10 m. For the three surveys of soil surface elevation the range was smaller, about 4 m. No correlation was found between saturated hydraulic conductivity and the other soil physical properties. Soil surface elevation showed a high correlation between surveys. After the first irrigation, the standard deviation of elevation increased from an initial 9.6 mm to 20.8 mm. The soil physical parameters were used to map the soil water management allowable depletion. In a companion paper these results are used to explain the spatial variability of corn yield and soil water recharge due to irrigation. Received: 24 February 1998     

Measurements and simulations of heat and water balance components in a clay soil cropped with winter wheat under drought stress or daily irrigation and fertilization

Soil water and temperature dynamics were measured in a field experiment with winter wheat on a clay soil. There were four treatments: Control (C), receiving natural precipitation, drought (D), protected from rain by plastic screens during the growing season, daily irrigation (I) and daily irrigation and fertilization (IF). Treatments C, D and I received the nitrogen fertilizer as a single application of solid fertilizer in spring. In IF daily dressings of nutrients were supplied in the irrigation water. All treatments received 20 g Nm^–2. An associated experiment with a newly sown grass ley (L) that was irrigated and fertilized daily (total 5.6 g Nm ^–2) was also performed. Standard meteorological variables (air temperature and humidity, wind speed, precipitation, global radiation, and relative cloudiness) and crop development data (green area index, crop height, relative root distribution in depth) above and below ground were used as driving variables within a physically based dynamic model (SOIL) for simulating water and heat fluxes. Measured soil temperature and water content from one treatment (I) were used to tune the model parameters, tentatively set from literature data. Thereafter, water and heat fluxes in the other treatments were simulated using the same parameter values but with different crop-related measurements as driving variables for each treatment. Measured soil temperature and water content in C, D, IF and L could thus be used for validation of the simulations. The theory formulated in the model could accurately explain measured treatment differences in soil water and temperature dynamics. Since the soil-related parameters were identical in all treatments, the model was shown to be applicable over a wide range of moisture conditions.     

宁夏黄灌区灌淤土水力参数研究

对宁夏黄灌区灌淤土水力参数进行了较为系统的研究.研究结果表明,原状土与扰动土饱和导水率变化范围分别为10～100 cm/d和3～50 cm/d.原状土饱和导水率随土壤剖面变化规律与扰动土一致:随着土壤深度的增加,饱和导水率呈现高低往复变化.原状土和扰动土的饱和导水率受粘粒含量、密度、孔隙度影响较大,受有机质含量影响较小...