William M. Iversen

Remote Sensing and Control of an Irrigation System Using a Distributed Wireless Sensor Network

Efficient water management is a major concern in many cropping systems in semiarid and arid areas. Distributed in-field sensor-based irrigation systemsoffer a potential solution to support site-specific irrigation management that allows producers to maximize their productivity while saving water. This paper describes details of the design and instrumentation of variable rate irrigation, a wireless sensor network, and software for real-time in-field sensing and control of a site-specific precision linear-move irrigation system. Field conditions were site-specifically monitored by six in-field sensor stations distributed across the field based on a soil property map, and periodically sampled and wirelessly transmitted to a base station. An irrigation machine was converted to be electronically controlled by a programming logic controller that updates georeferenced location of sprinklers from a differential Global Positioning System (GPS) and wirelessly communicates with a computer at the base station. Communication signals from the sensor network and irrigation controller to the base station were successfully interfaced using low-cost Bluetooth wireless radio communication. Graphic user interface-based software developed in this paper offered stable remote access to field conditions and real-time control and monitoring of the variable-rate irrigation controller.

Instrumentation and Control for Wireless Sensor Network for Automated Irrigation

An in-field sensor-based irrigation system is of benefit to producers in efficient water management. A distributed wireless sensor network eliminates difficulties to wire sensor stations across the field and reduces maintenance cost. Implementing wireless sensor-based irrigation system is challenging on seamless integration of sensing, control, and data communication. An automated sensor-based irrigation system was developed for an integrated wireless in-field sensor network and automated variable rate irrigation. Field conditions were real-time monitored sitespecifically by in-field sensor stations distributed across the field. Each sensor station measured soil moisture, soil temperature, and air temperature, while one weather station recorded precipitation, wind speed and direction, air temperature, relative humidity, and solar radiation. Sensors and a data logger were self-powered by a solar panel and sensory data was periodically sampled and wirelessly transmitted to a base station about 700 m away from the sensor stations. A host computer received and real-time displayed field data without interference. This paper describes details of the design and construction of wireless communication, hardware used, and the costs and benefits of the control system.

Development of Strip Tillage on Sprinkler Irrigated Sugarbeet

A project to evaluate new technologies for strip tillage of small seeded crops was initiated in fall 2003 near Sidney, Montana, for sprinkler irrigated sugarbeet (Beta vulgaris L.) to be grown in 2004. Strip till treatments were compared to conventional grower tillage practices in fifty-six 15- × 25-m (48- × 80-ft) side-by-side plots. Both treatments were flat planted with no ridges or beds. All strip tillage and fertilization was done in the fall after removal of a malt barley crop. Conventional tillage was done in the fall at the Sidney site and in the spring at the Nesson site. Thirty-centimeter (12-in.) wide strips were tilled directly into the straw residues about 20 cm (8 in.) deep using straight and paired fluted coulters and a modified parabolic ripping shank followed by a crows-foot packer wheel. Toothed-wheel row cleaners were installed in front of the straight coulter to move loose residue to the side to avoid plugging. At the same time, dry fertilizer was shanked (banded) about 8 to 13 cm (3 to 5 in.) below the anticipated seed placement location. Sugarbeet were planted about 2.5 cm (1 in.) deep with 60-cm (24-in.) spacing between rows in the spring. Toothed-wheel row cleaners were also placed in front of each row on the planter to move any residue displaced by winter storms. Operation of the strip tillage machine required about 25 tractor horsepower per row, but substantial fuel savings were realized with this system by reducing the number of tractor equipment field passes by up to 75%. In 2004, 2006, 2007, and 2008 there were no significant differences in yields or sugar production between the two tillage treatments; however, in 2005 the strip tilled plots produced about 17% greater yields (tonnage and gross sugar). This benefit in 2005 was primarily due to the standing straw stubble in the strip tilled plots that protected sugarbeet seedlings from blowing soil during a spring wind storm that severely damaged seedlings in the conventionally tilled plots where there was no surface crop residue. It was concluded that strip tillage must be considered as part of a larger cropping system that affects timing and equipment choices for planting, cultivation, spraying, and harvesting as well as tillage and other cultural practices. Based on these results, it is generally recommended that strip tillage should be performed in the fall on clay soils in eastern Montana where it has been shown to result in better seedbed conditions than spring strip tillage. Whereas lighter, sandy soils would probably produce equally well when strip tilled in the spring, which could then be combined with planting into a single pass tillage, fertilizing, and planting operation. Banding fertilizer is highly recommended under strip till to increase fertilizer use efficiencies and reduce input costs. RTK-GPS guided steering in combination with some type of mechanical steering assistance on the implements are also recommended for both strip tilling, planting, and cultivation (if needed).

Tillage Effects on Physical Properties in Two Soils of the Northern Great Plains

Tillage practices profoundly affect soil physical and hydraulic properties. It is essential to select a tillage practice that sustains the soil physical properties required for successful growth of agricultural crops. We evaluated the effects of conventional (CT) and strip (ST) tillage practices on bulk density (rho(b)), gravimetric water content (theta(w)), and saturated hydraulic conductivity (K(s)) at the soil surface and at 10- to 15-cm depth in two soils of the Northern Great Plains (NGP). Soil cores were collected from each plot at 0- to 10- and 10- to 20-cm depths under each tillage practice at both sites to measure rho(b) and theta(w). In-situ K(s) measurements at the soil surface and at 10- to 15-cm depth were determined using a pressure head infiltrometer (PHI) and a constant head well permeameter (CHWP), respectively, at two sites, one in North Dakota (Nesson, mapped as Lihen sandy loam) and one in Montana (EARC, mapped as Savage clay loam). The K(s) measurements were made approximately 1 m apart in the center of crop rows within CT and ST plots of irrigated sugarbeet ( Beta vulgaris L.). Tillage treatments significantly affected soil rho(b) and theta(w) in clay loam soil at the EARC site, while rho(b) and theta(w) did not differ between CT and ST in sandy loam at the Nesson site. The log-transformed K(s) at the soil surface did not differ significantly between CT and ST practices at either site. The effect of tillage on log-transformed K(s) at the 10- to 15-cm depth was significant in both sandy loam and clay loam soils at P < 0.10 and 0.05 levels, respectively. The K(s) values at 10- to 15-cm depth were 23% and 138% greater for ST than for CT at Nesson and EARC sites, respectively. Differences in soil compaction as evaluated through rho(b) data at 10- to 20-cm depth explain K(s) variations between the CT and ST systems at both sites. It was concluded that the CT operations increased soil compaction, which consequently altered rho(b), thereby reducing K(s) in the soil.

CHARACTERIZATION OF SPATIAL VARIABILITY OF SOIL ELECTRICAL CONDUCTIVITY AND CONE INDEX USING COULTER AND PENETROMETER-TYPE SENSORS

Assessment and management of spatial variability of soil chemical and physical properties (e.g., soil texture, organic matter, salinity, compaction, and nutrient content) are very important for precision farming. With current advances in sensing technology, soil electrical conductivity (EC) mapping is considered the most efficient and inexpensive method that can provide useful information about soil variability within agricultural fields. The objectives of this research study were to determine if Coulter and penetrometer-type EC sensors produce similar descriptions of soil variability, and if EC and cone index (CI) measured using a penetrometer-type sensor are correlated. The spatial variability of apparent EC (ECa) and penetration resistance expressed as CI for soil compaction were investigated with Coulter and penetrometer sensing technologies. The study was conducted in April 2005 at the research farm located near Williston, North Dakota, on a Lihen sandy loam (sandy, mixed, frigid Entic Haplustoll). The ECa and CI values generated by the penetrometer sensor were averaged over a 0- to 30-cm depth for comparison with values measured using the Coulter sensor over the same 0- to 30-cm depth. Classical and spatial statistics were used to evaluate spatial dependency and assess the overall soil variability within the experimental site. The statistical results indicated that the ECa data from both Coulter and penetrometer sensors exhibited similar spatial trends across the field that may be used to characterize the variability of soil for a variety of important physical and chemical properties. The coefficients of variation (CVs) of log-transformed ECa data from Coulter and penetrometer sensors were 11.3% and 18.9%, respectively. The mean difference, Md, of log-transformed ECa measurements between these two devices was also significantly different from zero (Md = 0.44 mS/m; t = 31.5, n = 134; P < 0.01). Soil ECa and CI parameters were spatially distributed and presented strong to medium spatial dependency within the mapped field area. Results from this study indicate the effectiveness of the ECa and CI sensors for identifying spatial variability of soil properties, and thus, the sensors may be useful tools for managing spatial variability in agricultural fields.

Passive Capillary Sampler for Measuring Soil Water Drainage and Flux in the Vadose Zone: Design, Performance, and Enhancement

Various soil water samplers are used to monitor, measure, and estimate drainage water, fluxes, and solute transport in the vadose zone. Passive capillary samplers (PCAPs) have shown potential to provide better measurements and estimates of soil water drainage and fluxes than other lysimeters designs and field sampling methods. Twelve automated PCAPs with sampling surface dimensions of 31 cm width × 91 cm long and 87 cm in height were designed, constructed, and tops of the samplers were placed 90 cm below the soil surface in a Lihen sandy loam (sandy, mixed, frigid Entic Haplustoll). The PCAPs were installed to continually quantify the amount of drainage water and fluxes occurring under sugarbeet (Beta vulgaris L.) and malting barley (Hordeum vulgare L.) crops treated with 30 mm (low replacement) and 15 mm (high replacement) irrigation frequencies. Drainage water was extracted, collected, and measured periodically (weekly from May to mid-August, biweekly until late September, and monthly thereafter until mid-November). This design incorporated Bluetooth wireless technology to enable an automated datalogger to transmit drainage water and flux data simultaneously every 15 min to a remote host. Real-time seamless monitoring and measuring of drainage water and fluxes was thus possible without the need for costly time-consuming supportive operations. The mean difference (Md) values between manually extracted and logged drainage water for high frequency (Md = 0.80 mm) and low frequency (Md = 0.26 mm) irrigations were small and not significantly different from zero. The Root Mean Square Error (RMSE) of 2.46 and 7.83 mm for high frequency and low frequency irrigations, respectively, were also small. Despite small variations in drainage water results, our novel PCAP design provided an accurate and convenient way to measure water drainage and flux in the vadose zone. Moreover, it offered a significantly larger coverage area (2700 cm2) than similarly designed vadose zone fluxmeters or PCAPs. In the course of one years field testing, we incorporated several additional enhancements such as PCAP container, tipping bucket and datalogger unit, all of which we recommend for optimal performance.

Development of combined site-specific MESA and LEPA methods on a linear move sprinkler irrigation system.

A site-specific controller, hardware and software systems were developed with the capability to switch between either mid-elevation spray application (MESA) or low-energy precision application (LEPA) methods. These systems were field tested and used to manage site-specific irrigations under a linear move sprinkler system and simultaneously varied water application depths by plot as the machine traveled back and forth across the field. The controller and modifications to the water application methods utilized off-the-shelf components as much as possible. The linear move system was modified so that every plot could be irrigated using either MESA or LEPA methods. A programmable logic controller (PLC)-based control system was utilized to activate grouped networks of electric over air-activated control valves. Both the depth and method of irrigation were varied depending on the location of each plot in the field as provided by a low-cost WAAS enabled GPS system mounted on the machine. When not being used, low-cost pneumatic cylinders lifted the LEPA heads above the MESA heads to avoid spray interference when the MESA mode was operating over a specified plot width and length. The control system was used on fifty-six 15- × 24.4-m (50- × 80-ft) plots as well as several other adjacent research projects in which there were a mix of crops and a prescribed set of management experiments. While this particular application was designed specifically for a large, complex agronomic research project to address artificially imposed spatial variability water management, the same controllers, valves and general software could be easily adapted to field scale commercial irrigation.

Spatial Variability and Correlation of Selected Soil Properties in the Ap Horizon of a CRP Grassland

Knowledge of the spatial variability of soil properties in agricultural fields is important for implementing various precision agricultural management practices. This article examines spatial variation of selected soil physical and chemical properties and explores their spatial correlation in the Ap horizon of a Lihen sandy loam soil (sandy, mixed, frigid Entic Haplustoll) within a field of grass-alfalfa Conservation Reserve Program (CRP) land. Soil measurements were made on a 16 x 36-m grid sampling pattern. Soil properties including penetration resistance (PR), bulk density (rho b), and gravimetric water content (theta m) were measured by collecting undisturbed soil cores from 5- to 10-cm and 20- to 25-cm depths. Additional disturbed soil samples were collected for particle size distribution, electrical conductivity (EC(e)), and pH analysis. The two depths were averaged for the assessment of spatial distribution, relationships and interpolation of soil properties. Soil saturated hydraulic conductivity (K(s)) and total porosity (epsilon(T)) for the 0- to 25-cm depth were estimated from rho b , theta m , and volumetric water content at field capacity (FC) level. Soil properties were analyzed using both classical and geostatistical methods that included descriptive statistics, semivariograms, cross-semivariograms, spatial kriged and co-kriged prediction maps and interpolation. Results indicated that small to moderate spatial variability existed across the field for soil properties studied . Furthermore, cross-semivariograms exhibited a strong negative spatial interdependence between soil PR and theta m, epsilon(T), and lnK(s). Spatial variability of soil theta(m), rho b, PR, ECe, pH, and clay content and their spatial correlation in the Ap horizon of the CRP grassland were attributed to a combination of previous farming practices, topographic characteristics, vegetation history, soil erosion, and weather conditions at this site.

Technical Note: Bulk Density, Water Content, and Hydraulic Properties of a Sandy Loam Soil Following Conventional or Strip Tillage

Tillage produces a more favorable soil physical environment for seed germination and plant growth. A 2‐year study was carried out to compare effects of conventional (CT) and strip (ST) tillage practices on soil bulk density ( b), water content ( w), final infiltration rate (Ir) and saturated hydraulic conductivity (Ks) for a Lihen sandy loam where sugarbeet (Beta vulgaris L.) was grown during the 2007 and 2008 growing seasons. Under each tillage system, we measured b and w using soil cores collected from the center of crop rows in all plots at soil surface (0 to 10 cm) and 10‐to 30‐cm depths. At both depths under each tillage system, we measured in‐situ Ir using a pressure ring infiltrometer (PI) and in‐situ Ks using a constant head well permeameter (CHWP). Although we noted a significant difference in b between CT and ST plots at 10‐ to 30‐cm depth in 2007, soil w did not differ significantly between CT and ST plots in 2007. In 2008, soil b and w did not differ significantly between CT and ST plots at both depths. The log‐transformed Ir was affected by tillage practice at P 0.1 in 2007 but was not significantly affected in 2008. The effects of tillage on log‐transformed Ks were significant at P 0.05 in 2007 and P 0.1 in 2008. Soil Ks values were 68% and 56% greater for ST than for CT in 2007 and 2008, respectively. We concluded that ST reduced soil compaction in the row, consequently increased total porosity, reduced b, and thereby increased Ir and Ks in the soil. Keyword. Bulk density, Infiltration, Hydraulic conductivity, Strip tillage, Sugarbeet, Soil compaction. illage is one of the most influential agricultural management practices affecting soil physical and hydraulic characteristics (Lal and Shukla, 2004). In this study, we introduced two types of tillage, the conventional tillage (CT), which consists of several separate operations using different tillage implements following the harvest of one crop in preparation for the next crop, and strip tillage (ST), which involves a single operation with specialized equipment (Evans et al., 2010) that provides alternating strips of tilled and untilled soil. Whether tillage is accomplished by CT or ST, the results of its application are unpredictable, and its effects on soil structure, macropore modifications, and other physical properties at the field scale are known to be contradictory (Lal and Van Doren, 1990; Coutadeur et al., 2002). Moreover, there is little information available regarding the effect of ST on soil physical and hydraulic properties. Tillage has been shown to temporarily improve soil porosity by creating temporary macropores that consequently increase water movement in the soil (Ahuja Submitted for review in February 2011 as manuscript number SW 9065; approved for publication by the Soil & Water Division of ASABE in May 2011. The authors are Jay David Jabro, ASABE Member, Research Soil Scientist, William Bart Stevens, Research Agronomist, William M. Iversen, Physical Scientist, and Robert G. Evans, Agricultural Engineer; Northern Plains Agricultural Research Laboratory, USDA‐ARS, Sidney, Montana. Corresponding author: Jay David Jabro, Northern Plains Agricultural Research Laboratory, USDA‐ARS, 1500 N. Central Avenue, Sidney, MT 59270; phone: 406‐433‐9442; e‐mail: jay.jabro@ars.usda.gov. et al., 1989; Ankeny et al., 1990; Bouma, 1991). On the other hand, tillage has been shown to destroy established aggregates and macropores and disrupt soil pore continuity, thus reduce water flow between the plow layer and subsoil (Bouma, 1991). Beneficial effects of tillage on pore size distribution are temporary because pore spaces that are created either collapse or are sealed during the growing season as a result of raindrop impact and wetting and drying cycles (Topaloglu, 1999). Such inconsistency of results demonstrates the need for additional studies regarding the effect of various tillage practices on soil physical properties. Infiltration rate and saturated hydraulic conductivity are considered the most important parameters describing water flow and chemical transport phenomena in soils (Reynolds and Elrick, 2002). Hydraulic conductivity is affected by bulk density and effective porosity, two commonly measured physical properties of soil fundamental to soil compaction and related agricultural management issues (Strudley et al., 2008). While tilled soil has been shown to have a lower bulk density, higher effective porosity and superior Ks than non‐tilled soil (Rosenberg and McCoy, 1992), tilled soils can also exhibited a higher bulk density, lower effective porosity, and inferior Ks than non‐tilled soils (Chan and Mead, 1989; Dao, 1996). In view of inconsistency of results and the lack of literature about the effect of ST on soil physical and hydraulic properties, objectives of our research were to compare the effects of both CT and ST on four important parameters‐‐bulk density (ρb), gravimetric water content ( w), final infiltration rate (Ir), and saturated hydraulic conductivity (Ks)‐‐in a T

Software Design for Wireless In-field Sensor-based Irrigation Management

A wireless in-field sensor-based irrigation management system is of benefit to producers in efficient water management, but implementing sensor-based irrigation control and monitoring is challenging in sensor fusion and data interface. Wireless in-field sensing and control software was developed for user-friendly interface of an integrated wireless in-field sensor network and automated variable rate irrigation. In-field sensory data was periodically sampled and remotely transmitted to a computer. Variable rate irrigation was controlled by the computer that reads information about field condition and GPS positions of sprinklers and transmits control signals to an irrigation controller via real-time wireless communication. This paper describes details of the software design using graphic user interface for wireless control and monitoring of a variable rate irrigation system.