Todd Skaggs

United States Department of Agriculture | USDA · Agricultural Research Service (ARS)

Citrus is affected by many diseases, and hence, the movement of citrus propagative materials is highly regulated in the USA. Currently used regulatory pathogen detection methods include biological and laboratory-based technologies, which are time-consuming, expensive, and have many limitations. There is an urgent need to develop alternate, rapid, e...

Climate change is intensifying the hydrologic cycle and altering ecosystem function, including water flux to the atmosphere through evapotranspiration (ET). ET is made up of evaporation (E) via non‐stomatal surfaces, and transpiration (T) through plant stomata which are impacted by global changes in different ways. E and T are difficult to measure...

RNA-binding proteins (RBPs) are key players in regulating cell fate and essential developmental processes. Systematic profiling of the RNA-binding proteome (RBPome) is thus indispensable for researchers aiming to understand the mechanisms of post-transcriptional gene regulation. RBPome identification methods developed in humans, mice, and bacteria...

Water shortages in the Western United States will continue to be one of the foremost American agricultural challenges in the coming years. As agriculture is the largest consumer of water in the western US, improvements in irrigation scheduling and modeling are needed to maximize production under limited water. Various satellite-based remote sensing...

RNA-binding proteins (RBPs) play critical roles in posttranscriptional gene regulation. Current methods of systematically profiling RBPs in plants have been predominantly limited to proteins interacting with polyadenylated (poly(A)) RNAs. We developed a method called plant phase extraction (PPE), which yielded a highly comprehensive RNA-binding pro...

Efficient irrigation is critical for managing scarce water resources where precipitation is minimal. Field-scale irrigation is largely unaccounted for in landscape evapotranspiration models, primarily due to the unavailability of data and the lack of water balance components in energy balance-based evapotranspiration models. To overcome these chall...

Monitoring and mapping soil salinity are valuable for irrigation management and reclamation of salt-affected agricultural soils in arid and semi-arid regions. Proximal measurements of apparent soil electrical conductivity (ECa) can help characterize soil salinity spatial distributions. However, ECa is not solely a function of salinity. ECa is stron...

RNA-binding proteins (RBPs) are versatile effectors in posttranscriptional gene regulation. Systematic profiling of RBPs in plants has been limited to proteins interacting with polyadenylated (poly(A)) RNAs due to the lack of an efficient method of isolating RBPs associated with non-poly(A) RNAs. Here we reported the establishment and application o...

The almond crop has high economic importance on a global scale, but its sensitivity to salinity stress can cause severe yield losses. Salt-tolerant rootstocks are vital for crop economic feasibility under saline conditions. Two commercial rootstocks submitted to salinity, and evaluated through different parameters, had contrasting results with the...

Quantifying soil structure has been a long‐standing challenge in soil physics. Among the proposed indices and parameters, slope at the inflection point of soil water retention curve has been widely used. In this short communication, we provide theoretical insights and show that under full saturation conditions, the pore‐throat radius at the inflect...

California is increasingly experiencing drought conditions that restrict irrigation deliveries to perennial nut crops such as almonds and pistachios. During drought, poorer quality groundwater is often used to maintain these crops, but this use often results in secondary salinization that requires skilled management. Process-based models can help i...

Soil salinity increases when growers are forced to use higher salinity irrigation waters due to water shortages. It is necessary to estimate the impact of irrigation water on soil properties and conditions for crop growth to manage the effects of salinity on perennial crops. Therefore, in this study, we monitored root zone salinity in five almond a...

The almond crop has high economic importance on a global scale but its sensitivity to salinity stress can cause severe yield losses. Salt-tolerant rootstocks are vital for crop economic feasibility under saline conditions. Two commercial rootstocks submitted to salinity, and evaluated through different parameters, had contrasting results with the s...

Approximately 1 billion ha of the global land surface is currently salt-affected, representing about 7% of the earth’s land surface. Whereas most of it results from natural geochemical processes, an estimated 30% of irrigated lands globally are salt-affected through secondary human-induced salinization. Application of lower quality, alternative irr...

Despite the high sensitivity of Flux Variance Similarity (FVS) partitioning to leaf‐level water use efficiency (WUE), relatively little work has been done comparing WUE algorithms. We evaluated four intercellular CO2 concentration parameterizations (constant_ppm, constant_ratio, and linear and square root functions of vapor pressure deficit) and on...

Although the eddy covariance (EC) technique provides direct and continuous measurements of evapo-transpiration (ET), separate measurement of evaporation (E) and transpiration (T) at the ecosystem level is not possible. For partitioning ET into E and T, high frequency (10 Hz) time series EC observations collected from Apr 2016 to May 2018 over a rai...

The partitioning of water vapor and carbon dioxide (CO2) exchange between vegetation and the atmosphere remains a current research priority. A technique that has been proposed to simultaneously partition these fluxes, based on the correlation between their high-frequency concentration time series, has been the subject of recent empirical evaluation...

Evaporation (E) and transpiration (T) respond differently to ongoing changes in climate, atmospheric composition, and land use. It is difficult to partition ecosystem-scale evapotranspiration (ET) measurements into E and T, which makes it difficult to validate satellite data and land surface models. Here, we review current progress in partitioning...

Evaporation (E) and transpiration (T) respond differently to ongoing changes in climate, atmospheric composition, and land use. Our ability to partition evapotranspiration (ET) into E and T is limited at the ecosystem scale, which renders the validation of satellite data and land surface models incomplete. Here, we review current progress in partit...

https://sciencetrends.com/mapping-soil-salinity-from-space-keeping-an-eye-on-degradation-of-the-worlds-farmland/

Management zones (MZs) are used in precision agriculture to diversify agronomic management across a field. According to current common practices, MZs are often spatially static: they are developed once and used thereafter. However, the soil–plant relationship often varies over time and space, decreasing the efficiency of static MZ designs. Therefor...

The saturated hydraulic conductivity of soil, Ks, is a critical parameter in hydrological models that remains notoriously difficult to predict. In this study, we test the capability of a model based on percolation theory and critical path analysis to estimate Ks measured on 95 undisturbed soil cores collected from contrasting soil types. One parame...

Testing soil salinity assessment methodologies over different regions is important for future continental and global scale applications. A novel regional-scale soil salinity modeling approach using plant-performance metrics was proposed by Zhang et al. (2015) for farmland in the Yellow River Delta, China, a region with a humid continental/subtropic...

Core Ideas Partitioned evaporation and transpiration is important for validating vadose zone models. New partitioning approaches overcome spatiotemporal limitations of previous methods. Some techniques can be applied to existing data to increase E and T observations. Intercomparisons of approaches at a variety of field sites are needed to better as...

Cover: Scudiero et al. used satellite imagery to model root-zone soil salinity in the western San Joaquin Valley. They found 30% of mapped farmland to be strongly or extremely saline. In the map section shown on the cover, soil salinity ranges from non-saline (dark green) to extremely saline (red). Image credit: USDA-ARS and University of Californ...

Though more costly than petroleum-based fuels and a minor component of overall military fuel sources, biofuels are nonetheless strategically valuable to the military because of intentional reliance on multiple, reliable, secure fuel sources. Significant reduction in oilseed biofuel cost occurs when grown on marginally productive saline-sodic soils...

Soil salinity is a major threat to sustainable agriculture, especially in arid and semi-arid regions. Updated and accurate inventories of salinity in agronomically and environmentally relevant ranges (i.e., <20 dS/m, when salinity is measured as electrical conductivity of the saturation extract, ECe) are essential for producers and decision-makers...

Salinity-affected farmlands are common in arid and semi-arid regions. To assure long-term sustainability of farming practices in these areas, soil salinity (ECe) should be routinely mapped and monitored. Salinity can be measured through soil sampling directed by geospatial measurements of apparent soil electrical conductivity (ECa). We present a mo...

Soil salinity negatively impacts the productivity and profitability of western San Joaquin Valley (WSJV) farmland. Many factors, including drought, climate change, reduced water allocations, and land-use changes could worsen salinity conditions there, and in other agricultural lands in the state. Mapping soil salinity at regional and state levels i...

Upscaling and/or estimating saturated hydraulic conductivity Ksat at the core scale from microscopic/macroscopic soil characteristics has been actively under investigation in the hydrology and soil physics communities for several decades. Numerous models have been developed based on different approaches, such as the bundle of capillary tubes model,...

Monitoring soil salinity (ECe) is important for planning and implementing agronomic and irrigation practices. Salinity can be measured through soil sampling directed by geospatial measurements of apparent soil electrical conductivity (ECa). Using data from a long-term (1999-2012) monitoring study at a 32.4-ha saline field located in California, USA...

Soil salinity is recognized worldwide as a major threat to agriculture, particularly in arid and semi-arid regions. Producers and decision makers need updated and accurate maps of salinity in agronomically and environmentally relevant ranges (i.e., <20dSm−1, when salinity is measured as electrical conductivity of the saturation extract, ECe). State...

Soil salinity undermines global agriculture by reducing crop yield and impairing soil quality. Irrigation management can help control salinity levels within the soil root-zone. To best manage water and soil resources, accurate regional-scale inventories of soil salinity are needed. The past decade has seen several successful applications of soil sa...

Irrigation in California’s Central Valley (USA) has decreased significantly due to water shortages resulting from the current drought, which began in 2010. In particular, fallow fields in the west side of the San Joaquin Valley (WSJV), which is the southwest portion of the Central Valley, increased from around 12% in the years before the drought (2...

Rock permeability has been actively investigated over the past several decades by the geosciences community. However, its accurate estimation still presents significant technical challenges, particularly in spatially complex rocks. In this short communication, we apply critical path analysis (CPA) to estimate permeability in porous rocks from measu...

Near-ground geophysical soil sensors provide valuable information for precision agriculture applications. Indeed, their readings can be used as proxy for many soil parameters. On-the-go soil sensor surveys are, typically, carried out intensively (e.g., every 2 m) over many parallel transects. Two types of soil sensors measurements are considered in...

Soil salinization is a major natural hazard to worldwide agriculture. We present a remote imagery approach that maps salinity within a range (i.e., salinities less than 20 dS m-1, when measured as the electrical conductivity of the soil saturation extract), accuracy, and resolution most relevant to agriculture. A case study is presented for the wes...

Water for irrigation is a major limitation to agricultural production in arid zones of the world. Irrigating with low leaching fractions in arid zones leads to soil salinization, thereby causing reduction in crop yield. Throughout his career, John Letey made unprecedented strides towards efficient agricultural water use to manage soil salinity, cul...

Soil salinization is widely recognized to be a major threat to worldwide agriculture. Despite decades of research in soil mapping, no reliable and up-to-date salinity maps are available for large geographical regions, especially for the salinity ranges that are most relevant to agricultural productivity (i.e., salinities less than 20 dS m-1, when m...

Irrigation is a widely used water management practice that is often poorly parameterized in land surface and climate models. Previous studies have addressed this issue via use of irrigation area, applied water inventory data, or soil moisture content. These approaches have a variety of drawbacks including data latency, accurately prescribing irriga...

A significant portion of present-day soil and Earth science research is computational, involving complex data analysis pipelines, advanced mathematical and statistical models, and sophisticated computer codes. Opportunities for scientific progress are greatly diminished if reproducing and building on published research is difficult or impossible du...

Irrigation is a widely used water management practice that is often poorly parameterized in land surface and climate models. Previous studies have addressed this issue via use of irrigation area, applied water inventory data, or soil moisture content. These approaches have a variety of drawbacks including data latency, accurately prescribing irriga...

Due to the diminishing availability of good quality water for irrigation, it is increasingly important that irrigation and salinity management tools be able to target submaximal crop yields and support the use of marginal quality waters. In this work, we present a steady-state irrigated systems modeling framework that accounts for reduced plant wat...

Given a time-series of potential evapotranspiration and rainfall data, there are at least two approaches for estimating vertical percolation rates. One approach involves solving Richards' equation (RE) with a plant uptake model. An alternative approach involves applying a simple soil moisture accounting procedure (SMAP) based on a set of conceptual...

Despite decades of research in soil mapping, characterizing the spatial variability of soil salinity across broad regions remains a crucial challenge. This work explores the potential benefits of employing reflectance data from the six spectral bands (blue, 450-520 nm; green, 520-600 nm; red, 630-690 nm; near-infrared, 770-900 nm; infrared-1; 1550-...

Despite decades of research in soil mapping, characterizing the spatial variability of soil salinity across large regions remains a crucial challenge. This work explores the potential use of Landsat 7 (L7) satellite reflectance data (30 × 30 m resolution) to facilitate salinity mapping. Reflectance data spanning a seven-year period (2007-2013) were...

One strategy for maintaining irrigated agricultural productivity in the face of diminishing resource availability is to make greater use of marginal quality waters and lands. A key to sustaining systems using degraded irrigation waters is salinity management. Advanced simulation models and decision support tools can aid in the design and management...

This chapter provides an overview of alternative approaches for modeling water flow and contaminant transport problems in soils and groundwater. Special focus is on flow and transport processes in the variably saturated vadose zone between the soil surface and the groundwater table. The governing flow and transport equations are discussed for both...

Contaminant transport processes in streams, rivers, and other surface water bodies can be analyzed or predict-ed using the advection-dispersion equation and related transport models. In part 1 of this two-part series we presented a large number of one-and multi-dimensional analytical solutions of the standard equilibrium advection-dispersion equa-t...

Analytical solutions of the advection-dispersion equation and related models are indispensable for predicting or analyzing contaminant transport processes in streams and rivers, as well as in other surface water bodies. Many useful analytical solutions originated in disciplines other than surface-water hydrology, are scattered across the literature...

Accurate prediction of pesticide volatilization is important for the protection of human and environmental health. Due to the complexity of the volatilization process, sophisticated predictive models are needed, especially for dry soil conditions. A mathematical model was developed to allow simulation of the diurnal variation of pesticide volatiliz...

Pesticide volatilization from agricultural soils is one of the main pathways in which pesticides are dispersed in the environment and affects ecosystems including human welfare. Thus, it is necessary to have accurate knowledge of the various physical and chemical mechanisms that affect volatilization rates from field soils. A verification of the in...

Advanced numerical simulation models can potentially help improve guidelines for irrigation and salinity management. Many simulation model parameters have considerable uncertainty, and ideally that uncertainty should be reflected in model predictions and recommendations. In this work, we investigate solute transport predication intervals that can b...

The advection–dispersion transport equation with first-order decay was solved analytically for multi-layered media using the classic integral transform technique (CITT). The solution procedure used an associated non-self-adjoint advection–diffusion eigenvalue problem that had the same form and coefficients as the original problem. The generalized s...

Recent studies suggest that standard guidelines for managing salinity in irrigated agriculture overestimate the leaching requirement. Transient-state, process-based model analyses offer the possibility of more efficient water and salinity management, but data are needed to evaluate the accuracy of various subcomponents of the models. In this study,...

Critical path analysis (CPA) is a method for estimating macroscopic transport coefficients of heterogeneous materials that are highly disordered at the micro-scale. Developed originally to model conduction in semiconductors, numerous researchers have noted that CPA might also have relevance to flow and transport processes in porous media. However,...

Diurnal variations in diazinon volatilization were monitored in three field experiments conducted with differing soil moisture contents. The highest flux rates in all experiments were recorded just after diazinon application, but the magnitudes of those initial rates differed according to the soil moisture content, with wetter soil producing a high...

Drip irrigation is more effective and less expensive if a large amount of soil can be wetted with each emitter without losing water or nutrients below the root zone. The distance that water spreads horizontally from a drip line and the volume of soil wetted are limiting factors that determine the spacing and number of drip lines and emitters, the f...

Spatial variability has a profound influence on a variety of landscape-scale agricultural issues including solute transport in the vadose zone, soil quality assessment, and site-specific crop management. Directed soil sampling based on geospatial measurements of apparent soil electrical conductivity (EC a) is a potential means of characterizing the...

s u m m a r y Mathematical models describing contaminant transport in heterogeneous porous media are often formu-lated as an advection–dispersion transport equation with distance-dependent transport coefficients. In this work, a general analytical solution is presented for the linear, one-dimensional advection–dispersion equation with distance-depe...

A traditional method of reclaiming salt-affected soils involves ponding water on a field and leaching salts from the soil through a subsurfacetile drainage system. Because water and salts move more slowly in areas midway between drain lines than in areas near the drains, achieving a desired level of desalinization across the entire field requires t...

In the irrigated western U.S. disposal of drainage water has become a significant economic and environmental liability. Development of irrigation water management practices that reduce drainage water volumes is essential. One strategy combines restricted drainage outflow (by plugging the drains) with deficit irrigation to maximize shallow groundwat...

Most analytical solutions available for the equations governing the advective–dispersive transport of multiple solutes undergoing sequential first-order decay reactions have been developed for infinite or semi-infinite spatial domains and steady-state boundary conditions. In this study, we present an analytical solution for a finite domain and a ti...

Methods to predict soil hydraulic properties frequently require information on the particle size distribution (PSD). The objectives of this study were to investigate various protocols for rapidly measuring PSD using the laser diffraction technique, compare the obtained PSD with those determined using the traditional hydrometer-and-sieves method (HS...

The Ejina Basin is an extremely arid subwatershed in Northwest China. The predominant natural tree species in the area, Populus euphratica, depends on groundwater for sustenance. In recent decades, groundwater overdraft and increased water diversions from the Heihe River caused water table elevations to decline, such that large areas of P. euphrati...

Sub-surface irrigation with porous clay pipe can be an efficient, water saving method of irrigation for many less developed arid and semi-arid regions. Maximizing the efficiency of clay pipe irrigation requires guidelines and criteria for system design and operation. In this study, experimental and simulated (with HYDRUS (2D/3D)) soil wetting patte...