Soil Water Content Profiles Research Articles

Yield advantage and water saving in maize/pea intercrop

Intercropping is a well-established strategy for maximization of yield from limited land, but mixed results have been obtained as to its performance in terms of water use efficiency. Here, two maize/pea intercrop layouts were studied in comparison to sole maize and sole pea with and without plastic cover on maize to reduce evaporation. Growth patterns over time and yield were determined. Profiles of soil water content over depth and across rows in the intercrop were measured at three times to quantify water extraction and its spatial and temporal distribution. Several indices were calculated to characterize the efficiency of land and water use of intercrops as compared with sole crops of maize and pea. Land equivalent ratio ranged from 1.18 to 1.47, indicating that intercropping was an effective strategy for maximizing land use efficiency. Water equivalent ratio, WER, defined to characterize the use efficiency of the water resource in intercropping, in analogy with LER, ranged from 0.87 to 1.16, and ΔWU, the relative departure of actual water use in intercropping from expected use, ranged from −13.7% to 19.8%, indicating variability in the effect of intercropping on water use efficiency. Plastic film in maize increased yield and water use efficiency, but did not significantly affect LER or WER, indicating that intercropping advantage was not affected by plastic film mulch, and the advantages of film mulch were conserved under intercropping. A cropping system of 4 rows maize with 4 rows peas, with 30cm between maize rows and 20cm between pea rows, was superior in yield and water use efficiency to a system with 2 rows maize and 4 rows of pea with 40cm between maize rows and 20cm between pea rows. It is concluded that intercropping of maize and pea enhances land use efficiency compared to growing them as sole crops. Film mulch saves water in sole crops as well as intercrops.

Can weighing lysimeter ET represent surrounding field ET well enough to test flux station measurements of daily and sub-daily ET?

Weighing lysimeters and neutron probes (NP) are both used to determine the change in soil water storage needed to solve for evapotranspiration (ET) using the soil water balance equation. We compared irrigated cotton ET determined using two large (3×3×2.4-m deep) weighing lysimeters and eight NP soil water profiles located outside the lysimeters in cotton fields during the BEAREX08 field campaign (see [16] Evett et al., 2012). The objectives were to (i) determine if lysimeter-based ET fluxes were representative of those from the fields, designated NE and SE, in which the lysimeters were centered, and (ii) investigate different methods of computing the soil water balance using NP data. Field fluxes were determined from the soil water balance using neutron probe measurements of change in profile water content storage. Fluxes of ET from the SE lysimeter were representative of those from the field throughout the season and can be used with reasonable certainty for comparisons of ET fluxes and energy balance closure derived from Bowen ratio (BR) and eddy covariance (EC) measurements whose footprints lay in the SE field. Comparisons of ET fluxes from EC and BR systems to those from the NE lysimeter should consider that NE lysimeter fluxes were up to 18% larger than those from the NE field during the period of rapid vegetative growth. This was due to plants on the lysimeter having greater height and width than those in the field. Nevertheless, the data from this and companion studies documents substantial underestimation of crop ET by EC stations under the conditions of BEAREX08. Comparison of zero flux plane (ZFP) and simple soil water balance methods of calculating ET from NP data showed them to be equivalent in this study; and for the ZFP method, the depth of the control volume should be determined by the depth at which the hydraulic gradient reverses, not by the depth of calculated minimum flux. If supported by a sufficiently dense and widespread network of deep soil water balance based estimates of ET in the surrounding patch and by ancillary measurements of crop stand and growth within the lysimeter and in the surrounding patch, a weighing lysimeter can provide accurate ET ground truth for comparisons with ET estimated using flux stations or ET calculated using satellite imagery. It must be emphasized that the water balance measurements must include soil profile water content measurements to well below (e.g., 0.5 to 1m below) the root zone in order to close the water balance.

Geostatistical filtering for improved soil water content estimation from electrical resistivity data

In order to take best advantage of the electrical resistivity data, kriging spatial component technique was applied to separate the small and large-scale structures of resistivity data. Then the spatial structures in resistivity data which are poorly correlated with soil water content are filtered out prior to integrating resistivity data into water content estimation in the soil of a 10ha area located in the Picardie region (Northern of France). The soil water content was measured until 1.2m depth in 81 sites with 0.3m increments by gravimetric method. The resistivity was exhaustively measured for three different depths: 0.5m, 1m, and 2m. The resistivity data represents a set of 5656 measurement points for each of the three depths over the 10ha study area. The methodology involves successively: (1) a principal component analysis (PCA) on the electrical measurements for the three depths of soil; (2) a geostatistical filtering of the local component and noise in the first component (PC1) of PCA which account for 90% of the variance in the electrical measurements for the three depths of soil. Results have shown that the correlation between water content of soil profile (W) and PC1 is highly improved when the local component and noise were filtered out. Finally, the influence of the smoothness of the external drift function on the quality of estimates of a target variable was empirically demonstrated. Indeed, the estimates of W were highly improved when the external drift function used in kriging is much smoother: the large scale of PC1 instead of PC1.

Data Assimilation with Soil Water Content Sensors and Pedotransfer Functions in Soil Water Flow Modeling

Soil water flow models are based on simplified assumptions about the mechanisms, processes, and parameters of water retention and flow. That causes errors in soil water flow model predictions. Data assimilation (DA) with the ensemble Kalman filter (EnKF) corrects modeling results based on measured state variables, information on uncertainty in measurement results and uncertainty in modeling results. The objectives of this work were (i) to evaluate pedotransfer functions (PTFs) as a source of data to generate an ensemble of Richards′ equation‐based models for the EnKF application to the assimilation of soil water content data and (ii) to research how effective assimilation of soil moisture sensor data can be in correcting simulated soil water content profiles in field soil. Data from a field experiment were used in which 60 two‐rod time domain reflectometry (TDR) probes were installed in a loamy soil at five depths to monitor the soil water content. The ensemble of models was developed with six PTFs for water retention and four PTFs for the saturated hydraulic conductivity (Ksat). Measurements at all five depths and at one or two depths were assimilated. Accounting for the temporal stability of water contents substantially decreased the estimated noise in data. Applicability of the Richards′ equation was confirmed by the satisfactory calibration results. In absence of calibration and data assimilation, simulations developed a strong bias caused by the overestimation of Ksat from PTFs. Assimilating measurements from a single depth of 15 cm or of 35 cm provided substantial improvements at all other observation depths. An increase in data assimilation frequency improved model performance between the assimilation times. Overall, bringing together developments in pedotransfer functions, temporal stability of soil water patterns, and soil water content sensors can create a new source of data to improve modeling results in soil hydrology and related fields.

Effects of Monovegetation Restoration Types on Soil Water Distribution and Balance on a Hillslope in Northern Loess Plateau of China

In the Loess Plateau of China, mosaic-vegetation restoration by converting cropland into fallow (to regenerate natural vegetations) and perennials performs well in soil erosion control. However, soil desiccation caused by the planted perennials threatens the sustainability of vegetation restoration. Understanding of soil water distribution and balance in monovegetation systems at hillslope scale is crucial for building a constructive mosaic-vegetation restoration pattern in the Northern Loess Plateau. The objectives in this study were to investigate effects of monovegetation restoration types on soil water distribution and balance and discuss the possible implications of the monovegetation hydrological properties for mosaic-vegetation pattern establishment at hillslope scale. In 2004, the authors chose a one-piece waste hillslope with uniform slope of 12 degrees and established four monovegetation plots subjected to shrub, grass, fallow, and cropland. Shrub, grass, and fallow are the typical vegetation restoration types, whereas cropland presents the traditional land use. Soil water content profiles, down to 400-600 cm depth, along the hillslope were measured with a neutron moisture meter from May-October in 2004, 2008, and 2009. Results showed that the rainfall infiltration depth was approximately 100 cm for shrub and grass but exceeded 300 cm for fallow and cropland. Six growth years later, shrub, grass, and fallow depleted more soil water than cropland, in the amount of 288, 313, and 62 mm, respectively. Soil water depletion in shrub and grass resulted in dried soil layers at the depth of 100-260 cm and 100-360 cm. Water balance results indicated that soil water deficit occurred in June during the rain season. The authors observed that downhill-accumulation of soil water storage, down to 400 cm depth, existed for fallow and cropland in 2004 and 2009. However, 6 growth years of shrub and grass substantially weakened such soil water downhill-accumulation tendency. This fact alone suggests that a mosaic vegetation system of planting shrub/grass downhill and setting fallow uphill would be appropriate from a standpoint of maintaining the sustainable development of vegetation restoration in the study area. Further experiments should be performed to develop the mosaic-vegetation patterns meeting the interests of both erosion control and sustainability of vegetation restoration. DOI:10.1061/(ASCE)HE.1943-5584.0000628. (C) 2013 American Society of Civil Engineers.

Robust and cost-effective system for measuring and logging of data on soil water content and soil temperature profile

The paper describes the system for measuring and logging of data on soil water content and soil temperature profile. The system was tested in a field and shows great potential for performing continuous measurements. It has several benefits including ease of manufacture, low cost, reliable performance and the ability to download the data without specialized software.

Design and Field Tests of an Access-Tube Soil Water Sensor

Accurate soil profile water content monitoring at multiple depths has heretofore been possible only using the neutron probe (NP) but with great effort and at infrequent time intervals. Despite the existence of several frequency domain electromagnetic (EM) sensor systems for profile water content measurements, accuracy and spatial representativeness has been precluded by fundamental problems related to soil conductivity and structure effects on the volume explored by the EM field of these sensors, which causes nonrealistic spatial variation in reported profile water contents. Time domain reflectometry (TDR) methods have the distinct advantage of employing a moving EM field that must pass through and be affected by both the drier and wetter soil structures in which the TDR electrodes are embedded. This article describes a profiling water content system based on TDR. The design, laboratory calibration, and field testing is detailed. The sensor system provides unattended, real-time, data acquisition. And, it can be installed without disturbing the soil around the access tube on the outside of which the TDR electrodes are embedded. The correlation coefficient between neutron probe and TDR measured soil water content was 0.94 with a slope of 1.40 and an intercept of -0.08 m3m-3. Bias between TDR and NP readings (TDR-NP) was positive at all depths below 10 cm, ranging from 0.021 and 0.096 m3 m-3. Uncertainty in data of ~0.012 m3 m-3 for soil water, and uncertainty in bulk electrical conductivity of 0.030 S m-1 (both partly due to unreliable mechanical electrical connections) shows that improvements must be made before such a system is acceptable for widespread use.

The influence of stoniness and canopy properties on soil water content distribution: simulation of water movement in forest stony soil

Mountainous forest soils usually contain a large number of rock fragments (particle diameter >2 mm), which influence soil properties. Data characterizing hydraulic properties of these soils usually describe only the fine soil fraction (particle diameter <2 mm) properties. To quantitatively describe soil water movement in stony soils, it is necessary to evaluate effective hydrophysical characteristics, involving the influence of stones, that is, the effective hydraulic conductivity and retention capacity should be known. Properties of evaporating surface (plant canopy) also play important role in formation of soil water movement and retention. This work presents results of the study of rock fragments (stoniness) effect on soil water content profiles and soil water dynamics during the season. Stony and homogeneous soil behavior is compared. The effect of different canopies (spruce forest, low vegetation) and bare soil in both types of soils on soil water dynamics is also studied. Stones as a part of soil are decreasing its water capacity and hydraulic conductivity as well. This is expressing in the decrease of stony soil water content retention capacity. High interception capacity of trees, followed by the low undercanopy precipitation, leads to the decreased soil water content of the upper soil layer. Combination of stony soil and dense forest canopy led to the low undercanopy precipitation, to relatively low infiltration totals into soil, and to decreased outflow.

Investigation of Factors Controlling the Regional-Scale Distribution of Dried Soil Layers Under Forestland on the Loess Plateau, China

The effects of drought on plants have been extensively documented in water-limited systems. However, its effects on soil are seldom considered because of the lack of comparative data on profile soil water content (SWC). A dried soil layer (DSL) within the soil profile is a typical indication of soil drought caused by climate change and/or ill-advised human practices. The regional spatial variability, dominant factors, and predictive models of DSL under forestland were explored in the present study. SWC at 0–600 cm of 125 pre-selected sites across the entire Loess Plateau was measured, and then two evaluation indices of DSL (the thickness of DSL, DSLT; SWC within the DSL, DSL–SWC) were calculated. The corresponding soil, topography, plant, and meteorology factors (a total of 28 variables) for each site were also measured. Most of the forestlands across the Plateau had DSL formation within the soil profile (102 of 125 study sites). The DSL levels were considered to be serious, with DSLT generally exceeding 300 cm with a mean DSL–SWC of only 7.9% (field capacity (FC) = 18.1%). DSLT and DSL–SWC indicated a moderate and strong spatial dependence with ranges of 69 and 513 km, respectively. Thicker DSLs were mainly distributed in the center of the Plateau, whereas thinner DSLs were observed in the southern and southeastern parts. In contrast, DSL–SWC distributions demonstrated an obvious decreasing trend from the southeast to the northwest. Dominant factors affecting DSLT under forestlands were FC, bulk density, slope gradient, slope aspect, and capillary water content; while dominant factors for DSL–SWC were FC, aridity, sand content, altitude, vegetation coverage, and evaporation. Moreover, predictive models developed by multiple regressions were relatively accurate when predicting DSLs, especially DSL–SWC. Understanding these associations with DSLs formation in forestland is helpful for efficient water resource management, silviculture, and eco-environment restoration on the Loess Plateau and in other water-limited regions around the world.

Scaling to generalize a single solution of Richards' equation for soil water redistribution

Using scaling methods, a single solution of Richards' equation (RE) will suffice for numerous specific cases of water flow in unsaturated soils. In this study, a new method is developed to scale RE for the soil water redistribution process. Two similarity conditions are required: similarity in the shape of the soil water content profiles as well as of the water flux density curves. An advantage of this method is that it is not restricted to a specific soil hydraulic model - hence, all such models can be applied to RE. To evaluate the proposed method, various soil textures and initial conditions were considered. After the RE was solved numerically using the HYDRUS-1D model, the solutions were scaled. The scaled soil water content profiles were nearly invariant for medium- and fine-textured soils when the soil profile was not deeply wetted. The textural range of the soils in which the similarity conditions are held decreases as the initial conditions deal with a deeply wetted profile. Thus, the scaling performance was poor in such a condition. This limitation was more pronounced in the coarse-textured soils. Based on the scaling method, a procedure is suggested by which the solution of RE for a specific case can be used to approximate solutions for many other cases. Such a procedure reduces complicated numerical calculations and provides additional opportunities for solving the highly nonlinear RE as in the case of unsaturated water flow in soils.

Analyzing relationships among water uptake patterns, rootlet biomass distribution and soil water content profile in a subalpine shrubland using water isotopes

Stable isotopic characteristics of plant water represent an integrated response of root systems to water sources with different isotopic signatures. Analysis of these signatures can help to identify many ecological processes involved in the uptake, transport and utilization of different water sources. In August 2003, we collected soil water samples throughout the soil profile from a subalpine shrub ecosystem in Wolong Nature Reserve, West China, along with stem water samples from the two dominant shrub species, Quercus aquifolioides and Salix luctuosa. Stable isotope contents of the different water samples were determined in conjunction with rootlet biomass distribution of each species and soil water content throughout the soil profile. Results indicated that these subalpine non-phreatophytic shrubs utilized soil water primarily from the top 30 cm of the soil profile. Water uptake patterns were significantly positively correlated with rootlet biomass distribution as well as the soil water content profile. Hence, the two shrubs could play an important role in keeping rainwater from entering river channels quickly, thereby reducing risk of flooding.

Time-variable soil hydraulic properties in near-surface soil water simulations for different tillage methods

Abstract Simulating near-surface soil water dynamics is challenging since this soil compartment is temporally highly dynamic as response to climate and crop growth. For accurate simulations the soil hydraulic properties have to be properly known. Although there is evidence that these properties are subject to temporal changes, they are set constant over time in most simulations studies. The objective of this study was to improve near-surface soil water simulations by accounting for time-variable hydraulic properties. Repeated tension infiltrometer measurements over two consecutive seasons were used to inversely estimate the hydraulic properties of a silt loam soil under different tillage – conventional (CT), reduced (RT), and no-tillage (NT). Simulated water dynamics with constant and time-variable hydraulic parameters were compared to observed data in terms of the soil water content and water storage in the near-surface soil profile (0–30 cm). The measurements indicate a considerable temporal variability in the saturated hydraulic conductivity, the field-saturated water content and the parameter α of the van Genuchten/Mualem model. Temporal variability was largest for CT and RT, whereas under NT, replicates of measured water contents and hydraulic properties showed a considerable large spatial variability. Simulations with time-constant hydraulic parameters led to underestimations of soil water dynamics in winter and early spring and overestimations during late spring and summer. The use of time-variable hydraulic parameters significantly improved simulation performance for all treatments, resulting in average relative errors below 13%. Since simulation results agreed with observed water dynamics in two seasons, the applicability of inversely estimated hydraulic properties for soil water simulations is demonstrated. Thus, simulations that address applied questions in agricultural water management may be improved by using time-variable hydraulic parameters. The simulated water balance indicated that RT and NT result in better water storage than CT and therefore may increase water efficiency under water-limited climatic conditions.

Storm water infiltration in a monitored green roof for hydrologic restoration

The objectives of this study are to provide detailed information about green roof performance in the Mediterranean climate (retained volume, peak flow reduction, runoff delay) and to identify a suitable modelling approach for describing the associated hydrologic response. Data collected during a 13-month monitoring campaign and a seasonal monitoring campaign (September-December 2008) at the green roof experimental site of the University of Genova (Italy) are presented together with results obtained in quantifying the green roof hydrologic performance. In order to examine the green roof hydrologic response, the SWMS_2D model, that solves the Richards' equation for two-dimensional saturated-unsaturated water flow, has been implemented. Modelling results confirm the suitability of the SWMS_2D model to properly describe the hydrologic response of the green roofs. The model adequately reproduces the hydrographs; furthermore, the predicted soil water content profile generally matches the observed values along a vertical profile where measurements are available.

Infiltration and drainage processes in multi-layered coarse soils

Huang, M., Barbour, S. L., Elshorbagy, A., Zettl, J. D. and Si, B. C. 2011. Infiltration and drainage processes in multi-layered coarse soils. Can. J. Soil Sci. 91: 169–183. Infiltration and drainage processes in multi-layered soils are complicated by contrasting hydraulic properties. The objective of this study was to evaluate the performances of the hysteretic and non-hysteretic models to simulate the infiltration and drainage processes from three different natural soil profiles containing as many as 20 texturally different layers. Hydraulic properties were estimated from soil textures using pedotransfer functions and were calibrated and validated using measured water contents during infiltration and drainage phases, respectively. The results supported the use of the Arya-Paris pedotransfer function to estimate the wetting curve when contact angles are incorporated. The unique Kozeny-Carmen equation parameter was evaluated by optimizing the estimated saturated hydraulic conductivity. The calibrated numerical model (Hydrus-1D) accurately simulated soil water content profiles and water volumes during the infiltration and drainage phases. The mean error of prediction (MEP) between the measured and estimated soil water contents varied from –0.030 to 0.010 cm3 cm−3, and the standard deviation of prediction (SDP) from 0.003 to 0.057 cm3 cm−3. The simulation was improved for more heterogeneous soil profiles when hysteresis was taken into account. The measured and simulated results indicated that the soil profile with vertical heterogeneity in soil texture can store more water than the similar textured vertically homogeneous soils under drained conditions.

In situ separation of root hydraulic redistribution of soil water from liquid and vapor transport

Nocturnal increases in water potential (ψ) and water content (θ) in the upper soil profile are often attributed to root water efflux, a process termed hydraulic redistribution (HR). However, unsaturated liquid or vapor flux of water between soil layers independent of roots also contributes to the daily recovery in θ (Δθ), confounding efforts to determine the actual magnitude of HR. We estimated liquid (J(l)) and vapor (J(v)) soil water fluxes and their impacts on quantifying HR in a seasonally dry ponderosa pine (Pinus ponderosa) forest by applying existing datasets of ψ, θ and temperature (T) to soil water transport equations. As soil drying progressed, unsaturated hydraulic conductivity declined rapidly such that J (l) was irrelevant (<2E-05 mm h(-1) at 0-60 cm depths) to total water flux by early August. Vapor flux was estimated to be the highest in upper soil (0-15 cm), driven by large T fluctuations, and confounded the role of HR, if any, in nocturnal θ dynamics. Within the 15-35 cm layer, J(v) contributed up to 40% of hourly increases in nocturnal soil moisture. While both HR and net soil water flux between adjacent layers contribute to θ in the 15-65 cm soil layer, HR was the dominant process and accounted for at least 80% of the daily recovery in θ. The absolute magnitude of HR is not easily quantified, yet total diurnal fluctuations in upper soil water content can be quantified and modeled, and remain highly applicable for establishing the magnitude and temporal dynamics of total ecosystem water flux.

Comparison of Noah simulations with eddy covariance and soil water measurements at a winter wheat stand

Weather and climate simulations are critically dependent on an accurate representation of land surface exchange processes. The present study tests the performance of the Noah land surface model (LSM) for energy partitioning and soil water dynamics on a winter wheat stand in southwest Germany. The model was parameterized field-specifically, i.e., data on leaf area index, green vegetation fraction, albedo, and soil texture were derived from measurements, and tested against a set of eddy covariance (EC) and soil water data collected in the 2009 season. With respect to energy partitioning, the field-specific parameterization performed fairly well during the main vegetation period. During ripening, starting in mid-July until harvest on 6 August, however, the sensible heat flux was distinctly underestimated. In August, the bias increased to −105.5 W m −2. As a consequence, evapotranspiration was overestimated during this period. After introducing a time-variable minimum stomatal resistance ( R c,min), the model performed much better. The model also delivered acceptable results during crop maturing. The Noah LSM was unable to simulate the observed soil water dynamics. While the measured soil water content profiles showed a distinct gradient with depth, the Noah LSM tended to deplete the soil profile uniformly. Our study shows that for cereal-dominated croplands phenology and crop development play a crucial role in energy partitioning, especially during the ripening stage. Disregarding the dynamics of the physiological properties of the crops in the Noah LSM leads to significant bias in energy partitioning. Finally, we critically discuss the current approach to correct measured EC flux data for the energy residual based on the Bowen ratio with regard to LSM calibration and performance.

Equations for Drainage Component of the Field Water Balance

Accurate estimates of the drainage component of the field water balance are needed to achieve improved management of drainage in irrigated crop production systems and obtain improved estimates of evapotranspiration (ET) from soil water measurements. Estimating drainage for numerous soil and field conditions necessitates the use of simple, yet accurate, drainage equations containing easily measured parameters. The Wilcox drainage model is a relatively simple mathematical equation with a high degree of accuracy and applicability to field conditions. Our objectives were to develop Wilcox-type drainage rate equations for three coarse-textured soils of the west-central Great Plains and assemble previously determined, but fragmented, Wilcox-type drainage equations and supporting information for three medium-textured soils of the region. Drainage plots for collection of data for development of Wilcox-type drainage equations were established on two coarse-textured soil profiles in 2008 near Garden City, Kansas. Total water content of the soil profiles was measured over time during ~48-day drainage events. Total water was plotted against drainage time on log-log scales, and the linear regression equation relating the two variables was determined. These linear equations of profile water (log10) vs. drainage time (log10) were used to develop Wilcox-type drainage equations in which drainage rate (dW/dT in mm/day) is expressed as a function of soil profile water content (in mm). Drainage rate equations in this article can be used to estimate the drainage component of the field water balance for improved irrigation water management and more accurate estimates of ET from soil water measurements.

Modeling of Full and Limited Irrigation Scenarios for Corn in a Semiarid Environment

Population growth in urbanizing areas such as the Front Range of Colorado has led to increased pressure to transfer water from agriculture to municipalities. In some cases, farmers may remain agriculturally productive while practicing limited or deficit irrigation, where substantial yields may be obtained with reduced water applications during non-water-sensitive growth stages, and crop evapotranspiration (ET) savings could then be leased by municipalities or other entities as desired. Site-specific crop simulation models have the potential to accurately predict yield and ET trends resulting from differences in irrigation management. The objective of this study was to statistically determine the ability of the CERES-Maize model to accurately differentiate between full and limited irrigation treatments in northeastern Colorado in terms of evapotranspiration (ET), crop growth, yield, water use efficiency (WUE), and irrigation use efficiency (IUE). Field experiments with corn were performed near Fort Collins, Colorado, from 2006 to 2008, where four replicates each of full (100% of ET requirement for an entire season) and limited (100% of ET during reproductive stage only) irrigation treatments were evaluated. Observations of soil profile water content, leaf area index, leaf number, and grain yield were used to calibrate (2007) and evaluate (2006 and 2008) the model. Additionally, ET and water use efficiency (WUE) were calculated from a field water balance and compared to model estimates. Over the three years evaluated, CERES-Maize agreed with observed trends in anthesis date, seasonal cumulative ET (Nash-Sutcliffe efficiency ENS = 0.966 for full irrigation and 0.835 for limited irrigation), leaf number in 2007 (ENS = 0.949 for full irrigation and 0.900 for limited irrigation), leaf area index in 2008 (ENS = 0.896 for full irrigation and 0.666 for limited irrigation), and yield (relative error RE = 4.1% for full irrigation and -3.4% for limited irrigation). Simulation of late-season leaf area index in limited irrigation was underestimated, indicating model overestimation of water stress. Simulated cumulative ET trends were similar to observed values, although CERES-Maize showed some tendency to underpredict for full irrigation (RE = -7.2% over all years) and overpredict for limited irrigation (RE = 12.7% over all years). Limited irrigation observations showed a significant increase in WUE over full irrigation in two of the three years; however, the model was unable to replicate these results due to underestimation of ET differences between treatments. While CERES-Maize generally agreed with observed trends for full and limited irrigation scenarios, simulation results show that the model could benefit from a more robust water stress algorithm that can accurately reproduce plant responses such as those observed in this study.

Temporal variability of soil water content under different surface conditions in the semiarid region of the Pernambuco state

Rainfall in the semiarid region of Pernambuco is characterized by irregular distribution in time and space, which significantly hinders the rainfed agriculture in the region. This work aims to evaluate the temporal profile of soil moisture in the semiarid region of the Pernambuco State (Brazil) and the effect of different soil surface conditions on soil water content variation and the yield of rainfed beans. To monitor soil water content, five plots 4.5 m wide by 11 m long were installed in a Yellow Argisol (Ultisol). The following treatments were adopted in the experimental plots: natural vegetation, bean intercropped with cactus, beans planted down the slope, beans planted along contour lines with mulch and rock barriers, and bare soil. In each plot, eight PVC access tubes were installed for monitoring the soil water content profile at depths of 0.20 and 0.40 m using a neutron probe device. The surface condition significantly influenced the soil water content variation, both in the dry and rainy seasons. The use of mulch, associated with rock barriers, provided higher soil water content levels than the other treatments and increased the rainfed beans production.

Simulating landscape catena effects in no-till dryland agroecosystems using GPFARM

This study evaluated the site-specific applicability and efficacy of the GPFARM decision support system (DSS) based on underlying simulation model performance for dry mass grain yield, crop residue, total soil profile water content, and total soil profile residual NO 3–N across a landscape catena for dryland no-till experimental locations in eastern Colorado. Relative error of simulated mean, normalized objective function (root mean square error divided by the observed mean), and index of agreement evaluation statistics were calculated to compare modeled results to observed data. A one-way, fixed-effect ANOVA was also performed to determine differences among experimental locations and summit, sideslope, and toeslope landscape positions. GPFARM simulations matched observed data trends, with the model correctly distinguishing variations between the summit and toeslope landscape positions. In addition, experimental observations and GPFARM simulations both indicated that the toeslope landscape position was the most productive for grain yield and also exhibited higher amounts of crop residue, total soil profile water content, and total soil residual NO 3–N. The GPFARM crop model performed adequately but was inconsistent in simulating winter wheat, corn, and sorghum dry mass grain yield. GPFARM performance in simulating crop residue was poorer than for crop grain yield. GPFARM predicted mean total soil profile water content was generally within ±20% of the observed mean across locations and landscape positions, with the model somewhat biased towards overpredicting total soil profile water content at the summit and sideslope landscape positions. Total soil profile residual NO 3–N was underpredicted by GPFARM across all locations and landscape positions by an average of 30%. Although GPFARM appears to have reasonably simulated long-term output responses across a landscape catena for the eastern Colorado experimental locations (especially given the simplifying assumptions in many of the GPFARM simulation components and the inherent variability present at the experimental plot level), different interpretations of GPFARM performance can be made depending on the evaluation statistic of interest. Furthermore, the model cannot fully account for water and chemical movement across the landscape catena; simulation results suggest that addition of a spatially-distributed routing component should offer improvements in GPFARM prediction accuracy across a catena where surface runoff or lateral subsurface flow is occurring.