Controlled Drip Irrigation Research Articles

Effect of soil water potential on methane and nitrous oxide emissions in upland soil during red pepper cultivation

Under intensive vegetable production, increased productivity is primarily considered for selecting better water management and irrigation intensity in upland soils. Soil water potential at −30 kPa (field capacity) for red pepper (Capsicum annum L.) production, which is the optimum moisture potential for plants, is recommended for Korean upland soils to maximize fruit yield; however its impact on greenhouse gas (GHG) emissions have not yet been considered. In this study, red pepper was cultivated under two soil water potentials at −30 and −50 kPa by drip irrigation control in two different textured soils (clay and sandy loams). Nitrous oxide (N2O) and methane (CH4) emissions were simultaneously investigated during the cultivation period. Results indicated N2O was the main GHG and contributed to approximate 97–9% of the total global warming potential (GWP), though the extent of its contribution varied depending on soil texture and soil moisture control with emitted CH4 being negligible throughout the investigation period. Between the treatments, soil moisture control at −50 kPa was effective in reducing the emissions of the two GHGs and also increased red pepper productivity in both clay loam and sandy loam soils. Comparing the gross GWP per unit pepper fruit yield between the treatments, maintaining soil water potential at −50 kPa by controlled irrigation led to a 50% reduction of GWP per unit pepper fruit yield. Therefore, drip irrigation control to lower soil water potential at −50 than −30 kPa is recommended to obtain high crop yield and reduce GWP per unit red pepper fruit yield for red pepper production in Korea.

Short-term soil nutrient impact in a real-time drain field soil moisture–controlled SDI wastewater disposal system

The Alabama Black Belt area is widespread of Vertisols that are generally unsuitable for conventional septic systems; nonetheless, systems of this type have been widely used in this region for decades. In order to explore alternatives for these conventional septic systems, a real-time soil moisture–controlled subsurface drip irrigation wastewater disposal system was integrated and field tested in a Houston Vertisol for 1 year. This automated disposal system effectively limited wastewater disposal during unfavorably wet drain field conditions. However, the resulting nutrient supply into the drain field was observed to be in surplus to crop growth requirements. Soil cores taken at the conclusion of the 1-year study indicated evidence of nitrate and phosphorus leaching. Available nitrates in the top 100 cm of soil showed a decreasing trend but were higher than all other parallel controls. Soil crop-available phosphorous in the soil increased below the drip line, as result that may be ascribed to soil cracking that was not properly controlled at the test site. Despite the demonstrated deficiencies, integrating timing of wastewater disposal with soil moisture conditions can supplement existing municipal or decentralized community wastewater treatment disposal systems.

Closed-loop drip irrigation control using a hybrid wireless sensor and actuator network

In this research, a closed-loop drip irrigation control hybrid wireless sensor and actuator network (HWSAN) prototype were developed and deployed in a crop field for soil property precise measurement and precision irrigation in accordance with the measured soil property. The HWSAN was composed of a wireless sensor and actuator network (WSAN) used for in-field soil property monitoring and irrigation control and a laboratory supervising system. The WSAN included ten sensor nodes, five irrigation control nodes, a central node, a gateway and a cellular modem. The laboratory supervising system was formed by a web-server. The system could automatically sample soil properties including soil moisture, electrical conductivity, and nearsurface temperature at four different depths underground and transmit field data through cellular network to the web-server. Closed-loop control was achieved through the control nodes listening uploading packets from its paired sensor nodes to control drip irrigation. Results from the quality of service (QoS) evaluation included: the data packet transmission rate was 84.76%, data accuracy rate was greater than 97% and no in-field data transmission errors.

Solubility and Leachability of Fishwaste Compost Phosphorus in Soilless Growing Media

AbstractKnowledge of solubility and leachability of fishwaste compost P is needed to effectively use fishwaste compost as a P source in soilless growing media. The fishwaste compost contained 3.6 g P kg−1 compost on a dry weight basis and had high P solubility, with 64.4% of the total P in the compost extractable by six successive extractions with 0.01 M NaCl. In the dilute salt solution, the Ca release from the compost paralleled that of P. The sequential extraction did not substantiate that Ca‐P was the predominant P form in the compost, because substantial amounts of P solubilized in 0.01 M NaCl were from the labile P (NH4Cl‐P) and potentially labile P (Fe‐ and Al‐P) pools. High solubility of the compost P resulted in elevation of P concentrations in leachates and cumulative amounts of P leached over 10 wk when the growing media containing 25% or more compost was irrigated with overhead sprinkler irrigation. Young rhododendron (Rhododendron fortunei ‘Scintillation’) did not significantly (P > 0.05) reduce P leaching from the 50% or higher compost treatments because the amount of P accumulated in the plant leaves represented 3 ± 0.9 (SD)% of P in the compost and P fertilizer combined. To reduce P leaching and minimize nonpoint P pollution, additions of P fertilizer to the soilless growing media containing the fishwaste compost should be restricted. Otherwise, the proportion of the compost in the media should be limited to 25% or less, unless it is used in conjunction with controlled drip irrigation.

The Second Las Cruces Trench Experiment: Experimental Results and Two‐Dimensional Flow Predictions

As part of a comprehensive field study designed to provide data to test stochastic and deterministic models of water flow and contaminant transport in the vadose zone, several trench experiments were performed in the semiarid region of southern New Mexico. The first trench experiment is discussed by Wierenga et al. (this issue). During the second trench experiment, a 1.2 m wide by 12 m long area on the north side of and parallel to a 26.4 m long by 4.8 m wide by 6m deep trench was irrigated with water containing tracers using a carefully controlled drip irrigation system. The irrigated area was heavily instrumented with tensiometers and neutron probe access tubes to monitor water movement, and with suction samplers to monitor solute transport. Water containing tritium and bromide was. applied during the first 11.5 days of the study. Thereafter, water was applied without tracers for an additional 64 days. Both water movement and tracer movement were monitored in the subsoil during infiltration and redistribution. The experimental results indicate that water and bromide moved fairly uniformly during infiltration and the bromide moved ahead of the tritium due to anion exclusion during redistribution. Comparisons between measurements and predictions made with a two‐dimensional model show qualitative agreement for two of the three water content measurement planes. Model predictions of tritium and bromide transport were not as satisfactory. Measurements of both tritium and bromide show localized areas of high relative concentrations and a large downward motion of bromide relative to tritium during redistribution. While the simple deterministic model does show larger downward motions for bromide than for tritium during redistribution, it does not predict the high concentrations of solute observed during infiltration, nor can it predict the heterogeneous behavior observed for tritium during infiltration and for bromide during redistribution.

The Las Cruces Trench Site: Characterization, Experimental Results, and One‐Dimensional Flow Predictions

A comprehensive field trench study was conducted in a semiarid area of southern New Mexico to provide data to test deterministic and stochastic models of vadose zone flow and transport. A 4 m by 9 m area was irrigated with water containing a tracer using a carefully controlled drip irrigation system. The area was heavily instrumented with tensiometers and neutron probe access tubes to monitor water movement and with suction tubes to monitor solute transport. Approximately 600 disturbed and 600 core samples of soil were taken to support deterministic and stochastic characterization of the soil water hydraulic parameters. The core sample‐based saturated hydraulic conductivities ranged from 1.4 to 6731 cm/d with a mean of 533 cm/d and a standard deviation of 647 cm/d, indicating significant spatial variability. However, visual observation of the wetting front on the trench wall shows no indication of preferential flow or water flow through visible root channels and cracks. The tensiometer readings and the neutron probe measurements also suggest that the wetting front moves in a fairly homogeneous fashion despite the significant spatial variability of the saturated hydraulic conductivity. In addition to the description of the experiment and the presentation of the experimental results, predictions of simple one‐dimensional uniform and layered soil deterministic models for infiltration are presented and compared to field observations. These models are presented here to provide a base case against which more sophisticated deterministic and stochastic models can be compared in the future. The results indicate that the simple models give adequate predictions of the overall movement of the wetting front through the soil during infiltration. However, the models give poor predictions of point values for water content due to the spatial variability of the soil. Comparisons between the one‐dimensional infiltration model predictions and field observations show that the use of the layered soil model rather than the uniform soil model does not consistently improve the accuracy of the predictions for this particular field application. This result illustrates that increasing the spatial resolution of the deterministic characterization of the site in the vertical direction does not always improve the model predictions. Uncertainties due to horizontal spatial variability and due to other difficulties associated with experimental characterization appear to be more significant.

Soil matric potential sensor measurements in real-time irrigation scheduling

Soil matric potential, a measure of the holding strength of the soil matrix for water, is a critical variable in crop yield, runoff, evapotranspiration and irrigation scheduling. A method for real-time in-situ measurement of soil matric potential ( ψ m) has been developed and tested. The accuracy of the measurement is dependent upon the calibration of the soil matric potential sensor (SMPS) against known standard pressures and independent of salinity, temperature and soil texture. The SMPS has a linear voltage response between −10 and −300 J/kg; and depending upon the data acquisition system used, the resolution of the soil matric potential measurement ranges from 2.5 to 5.5 J/kg. The response time of he SMPS to change in pressure plate pressures is less than 24 h between −10 and −100 J/kg but increases rapidly to several days for soil matric potential lower than −120 J/kg. SMPS were used to monitor soil matric potential in field soil in real time and to control drip irrigation systems automatically by initiating irrigation when a preset threshold was exceeded and terminating irrigation cycles when the time needed to apply 1.2 mm of water had elapsed. The timing of the irrigation cycle is a function of the irrigation method used, the hydraulics of the irrigation system, the soil physical properties and the crop water requirements.

Título en español

Se diseñó un sistema, utilizando tubos de material plástico, para estudiar el uso de la técnica de riego por goteo y del suministro de abonos en un Oxisol muy intemperizado, lixiviado, de fertilidad relativamente baja y ácido. Se utilizó el pimiento como cosecha indicadora. Todas las parcelas recibieron una aplicación inicial a voleo, de un abono 10-4.4-8.3 a razón de 80 kg/ha. Se utilizó un diseño de bloques completos aleatorios con cuatro tratamientos y seis repeticiones. Los tratamientos fueron como sigue: 1. N y K inyectados en el sistema de riego por goteo, P aplicado en franjas; 2. N, P y K aplicado en franjas; 3. N, P y K a voleo; y 4. Testigo-sin N, P, K fuera del aplicado inicialmente a voleo en todas las parcelas. En todos los tratamientos, excepto el control, se aplicaron 56.8 g/planta de un abono 10-10-10 y todos recibieron riego por goteo. Se hicieron dos siembras: una en la temporada de sequía y otra en la lluviosa. Los rendimientos de pimiento fueron significativamente diferentes entre todos los tratamientos en la temporada de sequía. En la temporada lluviosa las diferencias en rendimiento no fueron significativas entre el tratamiento en que se inyectó N y K en el sistema de riego y el tratamiento en que se aplicaron estos nutrimentos en franjas. Sin embargo, se obtuvieron rendimientos significativamente más altos con estos dos tratamientos que con el que se aplicó el abono a voleo. Estos tres tratamientos fueron superiores al testigo. El sistema de riego por goteo parece ser un método prometedor para el uso y suministro de agua y nutrimentos en los Oxisols de las regiones tropicales.