Irrigation management to optimize controlled drainage in a semi-arid area

On the west side of the San Joaquin Valley, California, groundwater tables have risen after several decades of irrigation. A regional semi-permeable layer at 100 m depth (Corcoran Clay) combined with over-irrigation and leaching is the major cause of the groundwater rise. Subsurface drain systems were installed from the 60¿s to the 80¿s to remove excess water and maintain an aerated root zone. However, drainage water resulting from these subsurface systems contained trace elements like selenium, which were determined at toxic levels to fish and waterfowl. To maintain healthy levels of salt and selenium in the San Joaquin River, the natural drain out of the San Joaquin Valley, outflow of drainage water from farms was severely restricted or completely eliminated. Several on-farm management methods are being investigated to maintain agricultural production without off-farm drainage. One method is drainage water reuse through blending with irrigation water. Another method is to reuse drainage water consecutively, where drainage water from one field is used as irrigation water for another field. Progressively more salt tolerant crops need to be grown in such a system along the reuse path, and salts can eventually be harvested using solar evaporators. A method described in this paper aims to reduce the volume of drainage water during the growing season by increasing shallow groundwater use by crops before it is drained from the field. Five years of crops were grown on two weighing lysimeters using drip irrigation. Two years of cotton were grown under high frequency drip irrigation (applications up to 10 times a day), followed by two years of safflower (early season crop) and one year of alfalfa (perennial) under low frequency drip irrigation (twice a week). One lysimeter maintained a shallow groundwater table at 1.0-m below soil surface, while the other lysimeter was freely drained at the bottom (3.0-m below soil surface). High frequency irrigation requires more irrigation water over a season than low frequency irrigation in the presence of shallow groundwater, since low frequency irrigation induces more shallow groundwater use by crops. Groundwater use for cotton was measured as 8% of total seasonal crop water use, while measurements under safflower showed that 25% of seasonal crop water use came from groundwater. Measurements under alfalfa, in its first year of establishment, showed 15% of seasonal crop water use coming from the groundwater. To maintain a sustainable system, leaching of salts need to occur. Leaching under the proposed irrigation/drainage management system would occur in the early growing season with winter precipitation, pre-plant irrigation and the first irrigation of the growing season, when the water table can be maintained at shallower depths through restriction of the outflow of the subsurface drainage system (groundwater control)

Irrigation management to optimize controlled drainage in a semi-arid area

On the west side of the San Joaquin Valley, California, groundwater tables have risen after several decades of irrigation. A regional semi-permeable layer at 100 m depth (Corcoran Clay) combined with over-irrigation and leaching is the major cause of the groundwater rise. Subsurface drain systems were installed from the 60¿s to the 80¿s to remove excess water and maintain an aerated root zone. However, drainage water resulting from these subsurface systems contained trace elements like selenium, which were determined at toxic levels to fish and waterfowl. To maintain healthy levels of salt and selenium in the San Joaquin River, the natural drain out of the San Joaquin Valley, outflow of drainage water from farms was severely restricted or completely eliminated. Several on-farm management methods are being investigated to maintain agricultural production without off-farm drainage. One method is drainage water reuse through blending with irrigation water. Another method is to reuse drainage water consecutively, where drainage water from one field is used as irrigation water for another field. Progressively more salt tolerant crops need to be grown in such a system along the reuse path, and salts can eventually be harvested using solar evaporators. A method described in this paper aims to reduce the volume of drainage water during the growing season by increasing shallow groundwater use by crops before it is drained from the field. Five years of crops were grown on two weighing lysimeters using drip irrigation. Two years of cotton were grown under high frequency drip irrigation (applications up to 10 times a day), followed by two years of safflower (early season crop) and one year of alfalfa (perennial) under low frequency drip irrigation (twice a week). One lysimeter maintained a shallow groundwater table at 1.0-m below soil surface, while the other lysimeter was freely drained at the bottom (3.0-m below soil surface). High frequency irrigation requires more irrigation water over a season than low frequency irrigation in the presence of shallow groundwater, since low frequency irrigation induces more shallow groundwater use by crops. Groundwater use for cotton was measured as 8% of total seasonal crop water use, while measurements under safflower showed that 25% of seasonal crop water use came from groundwater. Measurements under alfalfa, in its first year of establishment, showed 15% of seasonal crop water use coming from the groundwater. To maintain a sustainable system, leaching of salts need to occur. Leaching under the proposed irrigation/drainage management system would occur in the early growing season with winter precipitation, pre-plant irrigation and the first irrigation of the growing season, when the water table can be maintained at shallower depths through restriction of the outflow of the subsurface drainage system (groundwater control)

Changes in spatial and temporal variability of SAR affected by shallow groundwater management of an irrigated field, California

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 groundwater consumption by crops, thus reducing drainage that needs disposal. This approach is not without potential pitfalls; upward movement of groundwater in response to crop water uptake may increase salt and sodium concentrations in the root zone. The purposes for this study were: to observe changes in the spatial and temporal distributions of SAR (sodium adsorption ratio) and salt in a field managed to minimize drainage discharge; to determine if in situ drainage reduction strategy affects SAR distribution in the soil profile; and to identify soil or management factors that can help explain field wide variability. We measured SAR, soil salinity (EC1:1) and soil texture over 3 years in a 60-ha irrigated field on the west side of the San Joaquin Valley, California. At the time we started our measurements, the field was beginning to be managed according to a shallow groundwater/drainage reduction strategy. Soil salinity and SAR were found to be highly correlated in the field. The observed spatial and temporal variability in SAR was largely a product of soil textural variations within the field and their associated variations in apparent leaching fraction. During the 3-year study period, the percentage of the field in which the lower profile (90-180cm) depth averaged SAR was above 10, increased from 20 to 40%. Since salinity was increasing concomitantly with SAR, and because the soil contained gypsum, sodium hazard was not expected to become a limiting factor for long term shallow groundwater management by drain control. It is anticipated that the technology will be viable for future seasons.Drainage control Shallow groundwater management Sodium

Design of a User-Friendly Automated Multistep Outflow Apparatus

The multistep outflow (MSO) test is a widely used laboratory method for direct measurement of the soil moisture retention curve, θ(h), or indirect estimation of θ(h) and the unsaturated hydraulic conductivity curve, K(h). Manual MSO testing is time consuming and while automated systems have been described in the literature, many require significant effort to fabricate and operate, or have not been described in sufficient detail to allow rapid setup and implementation by others. In this work, a user-friendly, easily assembled, automated multistep outflow (AMSO) test apparatus was designed and built using National Instruments (Austin, TX) hardware and LabVIEW software. Control codes were written to support four testing regimes. The first option allows the pressure steps to be set manually while continuously measuring the water level in the burette. Three fully automated options are also available in which pressure steps are changed automatically after (i) a user-specified time period has elapsed, (ii) water level changes in the burette are negligible, or (iii) tensiometer measurements of the soil-water pressure head in the sample become constant for a specified period of time. To verify performance, five soil samples were subjected to a manual hanging column test and then retested using the automated system. Good correspondence between soil moisture values at the applied pressure steps with manual and AMSO tests was observed (RMSE values \u3c 0.0125 m3 m−3). Two samples were also drained and rewetted with the new system to show its utility for studying hysteresis

Parametrização do método do perfil instantâneo para a determinação da condutividade hidráulica do solo em experimentos com evaporação Parameterization of the instantaneous profile method to determine soil hydraulic conductivity in evaporation experiments

A condutividade hidráulica do solo é uma propriedade cuja quantificação é essencial para qualquer estudo que envolva o movimento da água no solo. Os métodos para sua determinação baseados na drenagem interna, como o do perfil instantâneo - MPI, são os mais empregados, restringindo-se à determinação da condutividade hidráulica entre a condição de solo saturado e a umidade na capacidade de campo. Com a finalidade de obter a condutividade hidráulica para menores valores de umidade, propôs-se um método de emprego do MPI com evaporação, apresentando-se o procedimento para a determinação do plano de fluxo zero e estimativa da densidade de fluxo. Demonstrou-se a aplicação do método, obtendo-se resultados de condutividade hidráulica para a camada superficial de um perfil monitorado a partir de um experimento de campo realizado durante um período de 12 dias. A profundidade máxima do plano de fluxo zero estimado foi de aproximadamente 0,50 m. A faixa de umidade obtida variou de 0,25 a 0,21 m³ m-3, valores complementares aos obtidos em experimentos sem evaporação no mesmo local. Os resultados indicaram a viabilidade do método, útil especialmente para se estender à faixa de umidade obtida na camada superficial de tais experimentos.<br>Soil hydraulic conductivity is an essential property and its quantification is essential for any study that involves soil water movement. Methods of determination based on internal drainage, such as the instantaneous profile method (IPM) are among the most commonly used, but their determination is restricted to the soil water range between saturation and field capacity. In order to obtain hydraulic conductivity for lower water contents, we propose an IPM that takes into account evaporation as well as a calculation routines to determine the zero flux depth and to estimate flux densities. The application of the method is demonstrated by obtaining results for hydraulic conductivity of the surface layer of a monitored profile in a 12 -day field experiment. The estimated maximum zero flux depth was about 0.50 m. Soil water content varied from 0.25 to 0.21 m³ m-3, complementing the range obtained in experiments without evaporation at the same site. Results confirm the applicability of the method, which is especially useful to extend the range of soil water contents in the surface layer obtained in this kind of experiment

Selected research opportunities in soil physics Oportunidades selecionadas de pesquisa em física do solo

Selected research opportunities are discussed in order to guide soil science research, with emphasis on soil physics, with the aim of improving agricultural productivity and environmental quality.<br>Oportunidades selecionadas de pesquisa são discutidas para orientar a pesquisa em ciência do solo,com ênfase na física do solo, com o objetivo de melhorar a produtividade agrícola e a qualidade do ambiente