As water scarcity becomes of greater concern in arid and semi-arid regions due to altered weather patterns, greater and more accurate knowledge regarding evapotranspiration of crops produced in these areas is of increased significance to better manage limited water resources. This study aimed at determining the actual evapotranspiration (ETa) and crop coefficients (Ka) in California date palms. The residual of energy balance method using a combination of surface renewal and eddy covariance techniques was applied to measure ETa in six commercial mature date palm orchards (8–22 years old) over one year. The experimental orchards represent various soil types and conditions, irrigation management practices, canopy characteristics, and the most common date cultivars in the region. The results demonstrated considerable variability in date palm consumptive water use, both spatially and temporally. The cumulative ETa (CETa) across the six sites ranged from 1299 to 1501 mm with a mean daily ETa of 7.2 mm day−1 in June–July and 1.0 mm day−1 in December at the site with the highest crop water consumption. The mean monthly Ka values varied between 0.63 (December) and 0.90 (June) in the non-salt-affected, sandy loam soil date palms with an average density of 120 plants ha−1 and an average canopy cover and tree height of more than 80% and 11.0 m, respectively. However, the values ranged from 0.62 to 0.75 in a silty clay loam saline-sodic date palm orchard with 55% canopy cover, density of 148 plants ha−1, and 7.3 m tree height. Inverse relationships were derived between the CETa and soil salinity (ECe) in the crop root zone; and between the mean annual Ka and ECe. This information addresses the immediate needs of date growers for irrigation management in the region and enables them to more efficiently utilize water and to achieve full economic gains in a sustainable manner, especially as water resources become less available or more expensive.
Abstract Changes in climate patterns are dramatically influencing some agricultural areas. Arid, semi‐arid and coastal agricultural areas are especially vulnerable to climate change impacts on soil salinity. Inventorying and monitoring climate change impacts on salinity are crucial to evaluate the extent of the problem, to recognize trends and to formulate irrigation and crop management strategies that will maintain the agricultural productivity of these areas. Over the past three decades, Corwin and colleagues at the U.S. Salinity Laboratory (USSL) have developed proximal sensor and remote imagery methodologies for assessing soil salinity at multiple scales. The objective of this paper is to evaluate the impact climate change has had on selected agricultural areas experiencing weather pattern changes, with a focus on the use of proximal and satellite sensors to assess salinity development. Evidence presented in case studies for Californiaʼs San Joaquin Valley (SJV) and Minnesotaʼs Red River Valley (RRV) demonstrates the utility of these sensor approaches in assessing soil salinity changes due to changes in weather patterns. Agricultural areas are discussed where changes in weather patterns have increased root‐zone soil salinity, particularly in areas with shallow water tables (SJV and RRV), coastal areas with seawater intrusion (e.g., Bangladesh and the Gaza Strip) and water‐scarce areas potentially relying on degraded groundwater as an irrigation source (SJV and Murray‐Darling River Basin). Trends in salinization due to climate change indicate that the infrastructure and protocols to monitor soil salinity from field to regional to national to global scales are needed. Highlights Climate change will have a negative impact on agriculture, particularly in arid regions. Proximal/remote sensors are useful to assess climate change impact on soil salinity across scales. Salt‐water intrusion, shallow water tables and degraded water reuse will increase soil salinity. Infrastructure and protocols to monitor soil salinity across multiple scales are needed.
Modeling and monitoring vadose zone processes across multiple scales is a fundamental component of many environmental and natural resource issues including nonpoint source (NPS) pollution, watershed management, and nutrient management, to mention just a few. In this special section in Vadose Zone Journal we present a collection of papers reflecting current trends in modeling and monitoring vadose zone processes from field to landscape scales. The objectives of this introductory paper are to set the stage for the special issue by providing background information, by showing the interrelationship of the papers, and by identifying the significant contribution(s) of each paper. The spectrum of topics covered includes (i) issues of scale, (ii) spatial analysis of model error, (iii) modeling of NPS pollutants and hillslope stability, (iv) the use of estimation and conditioning tools such as upscaling, pedotransfer functions, and generalized likelihood uncertainty estimation, (v) data assimilation in conjunction with flow modeling and passive microwave remote sensing to estimate moisture distribution, (vi) effective hydraulic parameters across spatial scales, (vii) spatiotemporal stability of soil properties (e.g., Cl − , B, and NO 3 –N transport; salinity; and soil physical and hydraulic properties), and (viii) nested sampling to determine spatial patterns. A commonality among the papers, whether for modeling or monitoring vadose zone processes, is the question of how to address complex issues of spatial and/or temporal variability at the scale of interest. Future research will likely involve inverse modeling, the use of multiple sensors to monitor at various scales, and continued applications of pedotransfer functions, upscaling and downscaling, and hierarchy of scales.
Noninvasive electromagnetic (EM) induction techniques are used for salinity monitoring of agricultural lands and contaminant detection in soils and shallow aquifers. This study has four objectives. The first objective is to summarize an earlier linear model of the response of the EM38 ground conductivity meter and to discuss a more accurate nonlinear response model. The second objective is to verify experimentally whether the linear and nonlinear models derived for homogeneous media are valid in heterogeneous soil profiles. The third objective is to present an inverse procedure that combines the nonlinear model with Tikhonov regularization. The fourth objective is the experimental verification of inverse procedures with the linear and nonlinear models for inversion of soil conductivity profiles using aboveground electromagnetic induction measurements on fourteen saline Californian soil profiles. The linear and nonlinear models derived for homogeneous media are indeed valid in heterogeneous soil profiles. However, since the errors of the linear model are approximately double those of the nonlinear model, the latter is the preferred one. A small difference was found in the errors of the inverse procedures between the linear and nonlinear models. In this study, the inverse procedures with the linear model and with the nonlinear model produce equally good solutions at EM38 measurements below 100 mS m−1, while at higher electrical conductivities the inverse procedure with the nonlinear model appears to yield slightly better results. The inverse procedure with the linear model is preferred for all conductivities since it needs considerably less computer resources.
SUITABLE inventories of soil salinity do not exist in the United States, nor are there monitoring programs to track the salinity status of soils. National or state programs to protect soils against salinity are likewise nonexistent.
Proper operation of a viable, permanent irrigated agriculture, which also uses water efficiently, requires periodic information on soil salinity. Only with this information can the effectiveness of irrigation project operation be assessed with respect to salt balance and water use efficiency.
The need for monitoring will likely increase. Less water will be available for leaching as the competition increases for water now used in irrigation. In addition, restrictions are expected to be placed on the discharge of salt from irrigation projects. With less leaching, there will be a corresponding increase in soil salinity.
Monitoring soil salinity is complicated by salinity's spatial variability. Numerous samples are needed to characterize an area. Monitoring is also complicated by salinity's dynamic nature, due to the influence of management practices, water table depth, soil permeability, consumptive water use, rainfall, and salinity of the perched groundwater. When the need for repeated measurements is multiplied by the extensive requirements of a single sampling period, the expenditures of time and …
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