Brian G. Leib

FIELD EVALUATION AND PERFORMANCE COMPARISON OF SOIL MOISTURE SENSORS

Agricultural producers who choose to supplement their crops’ water requirement are able to determine irrigation scheduling practices better when the soil water content of their fields is known. The objective of this study was to statistically evaluate numerous sensors for their ability to accurately estimate water content in a 90-cm soil profile, based on calibrated neutron probe measurements. The sensors tested were Irrometers, Watermarks, EnviroScan, Troxler Sentry, AquaTel, AquaFlex, Trime, AquaPro, and GroPoint. The sensors were field tested at different water content levels and a variety of irrigation frequencies over a 3-year period in a Warden silt loam soil (Coarse-silty, mixed, mesic, Xerollic Camborthids) planted to alfalfa. The default factor calibration was used to estimate the soil water content from all sensors except the neutron probe, which was calibrated for the soil using the gravimetric moisture content method. The Irrometer and Watermark sensors utilized a local soil water retention relationship in order to convert soil water potential into volumetric water content. The results suggest that most sensors were able to follow the general trends successfully as soil water content changed during the growing season, and there was significant correlation between the sensors and the neutron probe readings. Although sensor trends were similar, visual and statistical analyses indicated that the actual measured values varied significantly between the sensors and the calibrated neutron probe measurements. Therefore, a soil specific calibration of each sensor would have been necessary to obtain a high degree of absolute accuracy in soil water content measurements. The results suggest that irrigators can still use uncalibrated sensors to improve their watering schedules by setting irrigation trigger points that may relate only to a specific sensor in a specific soil. These trigger points cannot easily be related to different soils, different sensors, and other sources of information such as extension fact sheets and research publications, however, because the actual water content measurements may not be correct.

WISE: a web-linked and producer oriented program for irrigation scheduling

The Washington Irrigation Scheduling Expert (WISE) Software was developed to meet the needs of Washington state irrigators. WISE was written in JAVA with NetBeans DeveloperX2 components to allow cross platform operation and easy access to reference evapotranspiration from Washington states sixty Public Agriculture Weather System stations. The graphical user interface is intuitive and helps the user input their field-specific parameters such as crop type/timing, soil moisture status and irrigation system specifications. WISE employs a short-term water balance that can be adjusted for existing soil-moisture conditions. WISE is not a black box calculation of when and how much to irrigate since important steps are displayed and made apparent to the user. This feature also makes WISE an educational tool that teaches the principles of irrigation scheduling.

Perspectives on delineating management zones for variable rate irrigation

Up to 40% of soil available water content variance was explained by pie shape zoning.Dynamic zoning strategy may be needed if soil spatial arrangement varies by depth.Soil ECa and satellite images were useful attributes for irrigation zone delineation. This study aimed at investigating the performance of multiple irrigation zoning scenarios on a 73ha irrigated field located in west Tennessee along the Mississippi river. Different clustering methods, including k-means, ISODATA and Gaussian Mixture, were selected. In addition, a new zoning method, based on integer linear programming, was designed and evaluated for center pivot irrigation systems with limited speed control capability. The soil available water content was used as the main attribute for zoning while soil apparent electrical conductivity (ECa), space-borne satellite images and yield data were required as ancillary data. A good agreement was observed among delineated zones by different clustering methods. The new zoning method explained up to 40% of available water content variance underneath center pivot irrigation systems. The ECa achieved the highest Kappa coefficient (=0.79) among ancillary attributes, hence exhibited a considerable potential for irrigation zoning.

Erosion Control Practices Integrated with Polyacrylamide to Reduce Sediment Loss in Furrow Irrigation

In the Lower Yakima River Basin of Washington, surface irrigators need to reduce sediment loads exiting their fields in order to comply with newly established water quality standards. The goal of this research was to assess methods for improving the water quality of return flow from furrow irrigation by combining a patch application of polyacrylamide (PAM) with an additional erosion control practice in the tailwater ditch. A study was conducted in 2001 and 2002 that combined PAM with: 1) surge irrigation, 2) grass filter strips, 3) check dams, and 4) surface drains. In order to test the treatments under different cultural practices and slopes, the study was conducted at three site: two vineyards with silt loam soils at 1.2% slope in both the furrows and the tailwater ditch, and a cornfield with silt loam and sandy loam soil at 0.2% slope in both the furrows and the tailwater ditch. During irrigation events, sediment samples were taken and outflow rates were recorded at periodic intervals to determine sediment concentration, run-off volume, and sediment load from each treatment. At all sites and at all monitored irrigations, the control plot, which had only the patch application of PAM, produced sediment concentrations greater than the total maximum daily load standard of 56 mg.L-1 for the Lower Yakima River. All four erosion control practices in combination with PAM were more effective in reducing sediment load at the vineyards as compared to the cornfield. Only the grass treatment with PAM was consistent in reducing sediment concentrations below 56 mg.L-1 in both the vineyards and the cornfield.

Comparing soil pesticide movement for a finite-element model and field measurements under drip chemigation

Abstract Soil pesticide samples were collected from a field experiment where drip chemigation of the systemic insecticide, imidacloprid, was used to protect muskmelon (cantaloupe) plants from cucumber beetles. After the soil samples were analyzed and efficacy in controlling the insect pest was determined, the finite element model lewaste was configured to simulate: (1) drip chemigation of a pesticide in raised beds under plastic mulch, (2) advective/dispersive movement of pesticide from rainwater infiltration and drip irrigation, and (3) root extraction of pesticide with soil water. Only available parameters were input to the model domain without measuring specific soil parameters at the field site and then the model was executed to simulate soil distribution of pesticide during the period of efficacy. A linear regression of measured versus predicted pesticide concentration in the soil indicated a strong relationship between the model and the field study with a slope of 0.89, an intercept of −7.05 ppb and an r 2 of 0.97. The model and soil samples also showed that the pesticide, imidacloprid, did not leach during the time frame of evaluation and that 70% of the pesticide was still located in the root zone when efficacy ceased. In addition, the model calculated that only 11% of the applied pesticide was absorbed by the muskmelon plants during the period of efficacy. These results suggest that as the plants developed from 9 to 800 g, the muskmelons outgrew the source of the pesticide instead of the pesticide source being depleted for use by the plant via leaching, uptake, and degradation. Numerical modeling of drip chemigation can help researchers understand crop production factors such as the efficacy of a pesticide in addition to the fate and transport of pesticide.

Studying uniform and variable rate center pivot irrigation strategies with the aid of site-specific water production functions

Novel site-specific water production functions (WPFs) were developed and tested.New zoning procedures for variable rate irrigation were established.The k-NN WPF accurately predicted cotton yield under supplemental irrigation.Sector zoning was predicted to enhance cotton yield under supplemental irrigation. Irrigation management has evolved into a top priority issue since available fresh water resources are limited. Water production functions (WPFs), mathematical relationships between applied water and crop yield, are useful tools for irrigation management and economic analysis of yield reduction due to deficit irrigation. This study aimed at (i) designing and evaluating site-specific WPFs (using k nearest neighbors (k-NN), multiple linear regression, and neural networks), (ii) simulating yield maps for uniform, sector control VRI, and zone control VRI center pivot systems using the site-specific WPFs, (iii) using the best WPF to investigate different cotton irrigation and zoning strategies using integer linear programming, and (iv) comparing soil-based and WPF-based zones for sector control VRI systems. A two-year cotton irrigation experiment (2013-2014) was implemented to study irrigation-cotton lint yield relationship across different soil types. The site-specific k-NN WPFs showed the highest performance with root mean square error equal to 0.131Mgha-1 and 0.194Mgha-1 in 2013 and 2014, respectively. The result indicated that variable rate irrigation with limited sector control capability could enhance cotton lint yield under supplemental irrigation when field-level spatial soil heterogeneity is significant. The temporal changes in climate and rainfall patterns, however, had a great impact on cotton response to irrigation in west Tennessee, a moderately humid region with short season environment. We believe site-specific WPFs are useful empirical tools for on-farm irrigation research.

Irrigation, Fertigation, and Plasticulture Increase Yield and Quality while Reducing Carcinogen Formation in Burley Tobacco

U.S. tobacco growers are competing in a recently deregulated market with greater supply coming from abroad and shrinking U.S. demand for their product. Tobacco production based on preplant fertilization and reliance on natural precipitation has become less profitable under current conditions. This study tests the benefit of irrigation, fertigation, and plasticulture to produce higher tobacco yield and quality while reducing carcinogens, tobacco specific nitrosamines (TSNA). Burley tobacco (TN 90) was grown at Greeneville, Tennessee (Lindside silt loam) and Springfield, Tennessee (Dickson silt loam) during the years 2005-2007. In one set of treatments, drip irrigation supplemented rainfall to supply at least 2.54 cm/wk in order to maintain soil tension at more optimal levels. Fertigation also used supplemental irrigation but applied nitrogen fertilizer in four split applications intended to better match the plants demand for nitrogen. Plasticulture used the same fertigation protocol but added a plastic mulch covering to isolate the benefits that could be obtained from increasing soil temperature. Finally, all these production practices were tested at recommended and reduced nitrogen rates, 224 to 112 kg N/ha.

Development of an on-time logger for irrigation systems

Abstract An inexpensive micro-processor and pressure switch (

Tobacco Irrigation: Supplemental Watering of a High Value, Drought Tolerant Crop in a Humid Region

125) were developed by Washington State University’s (WSU) Irrigated Agriculture Research and Extension Center (IAREC) to log the on-times of irrigation systems. The purpose of the on-time logger was to provide better information on how irrigators respond to new irrigation management techniques and to document the water/electricity savings from improved “on-farm” irrigation practices. This on-time logger was tested by installing two loggers each at two on-farm sites where irrigation controllers opened valves for predetermined operation times. At the Prosser test site, both loggers monitored the controller-designated operation times with an average ratio of 1.0 (logger on-time to controller operation time). However, at the Outlook site, both loggers recorded on-times longer than the controller operation time with ratios of 1.1 and 1.24. At the Outlook site, the loggers were located at the end of irrigation laterals that were located at the bottom of a steep hill. In addition, the sprinkler heads were located on tall risers for apple cooling. Therefore, the pressure switches did not open immediately after the zone valves were closed because water in the pipes kept pressure on the switch until sufficient drainage could occur. On-time loggers can be successfully used to monitor the impact of on-farm irrigation improvements, but care needs to be taken to set the switch tripping pressure in accordance with the irrigation system’s configuration.

Integration of Erosion Control Practices to Reduce Sediment Loads in Furrow Irrigation

A five-year field experiment was conducted to assess the potential benefits of tobacco irrigation during the rapid growth stage of development. This experiment was conducted from 2000-2004 at Springfield, Tennessee, in a Dickson fine-silty loam. Dark Fire-cured (TN D950) and Burley (TN 90) tobacco were grown. Historically, average rainfall at this location is sufficient to meet tobacco water demand. During this study, two growing seasons were above average, one season was average, while two were below average in total precipitation.