Project Summaries

10-777  Project Manager: E. M. Barnes

EVALUATION OF COMMERCIALLY AVAILABLE, SOIL-WATER MONITORING SYSTEMS FOR IRRIGATION SCHEDULING IN MID-SOUTH COTTON

Brian Leib, University of Tennessee

Progress in wireless technologies now provides the ability to remotely monitor crop water status conditions. These systems have the potential to significantly decrease the labor associated with collection of soil moisture data, and costs of the systems are decreasing each year. Six types of irrigation scheduling equipment were installed and used to monitor the Deficit Irrigation of Cotton experiment at the West Tennessee Research and Education Center in Jackson, TN, to determine how dependable and easy to use these systems are from a producer's perspective, as well as evaluate the overall system accuracy during 2012. The first four systems described in following summary were also evaluated in 2010.

Irrometer Wireless Monitors for Soil Tension with Edge of Field Data Collection: The Irrometer systems were based WaterMark sensors, an "electronic tensiometer" that tells how tightly water is held by the soil, measured as a tension. When the tension reaches a crop specific threshold, it is an indication that irrigation is needed. The cost of collecting soil tension and transmitting it to the edge of a field is relatively inexpensive at around $200 per monitoring site. Up to 15 monitoring sites can be wirelessly connected to a single edge of field receiver that cost $600 but most producers will not need this many monitoring locations. Installation is time consuming because each sensor required auguring a 2-inch hole within 4-inch of the desired sensor depth, sledging a 1-inch hole the final distance for a good soil contact with the sensor, wetting the 1-inch hole, inserting the sensor into the 1-inch hole, repacking the soil into the 2-inch hole, and connecting the sensor wires to the wireless transmitter.

Set-up of the interface between the sensors and the data that was downloaded to a laptop computer required close attention to detail to insure that the data being observed was linked to the correct field location. Four sets of sensor wire had to be connected to a single wireless transmitter in a known order, then four jumper switches were set to a unique identification on each wireless transmitter so that they could be individually recognized by the wireless receiver and finally each sensor was assigned a unique name on the wireless receiver that corresponded to the correct wireless transmitter and the correct wire location for each sensor. Data is downloaded to a laptop from the central receiver at the edge of the field. This approach likely has more research than producer application. In 2011, new sites were added and the sensors were "permanently" installed by burying wires and leaving after harvest.

Irrometer Wireless Monitors for Soil Tension with Radio Link to the Internet: This was the same set of sensors described with the Irrometer Edge of Field section; however, a transmitter radio was connected to the wireless receivers and a radio receiver was connected to a Web portal in the office building close to the experiment. Most of the characteristics of this system are similar to the previous system and only the changes created by the communication modification are reported. The cost per monitoring site and edge of field receiver is the same as described above with the addition of $2,000 for the radio based Web link. The data was consistently received during the time that the Web link was established. Set-up of the wireless to radio to internet system was reestablished without any difficulty in 2011. The pressure switch for tracking irrigation time got out of synch and needed to be reset by the company.

SmartField – Wireless Canopy Temperature with Cellular Link to the Internet: SmartField infrared sensors were installed in the 10 irrigation treatments that were initiated in the two soil types for a total of 20 units. The theory behind these sensors is that when the crop is water stressed, the leaf temperature increases, and so much time above a threshold temperature indicates the need for irrigation. The wireless sensors and mounting system cost $400 per monitoring site plus $3,500 for the cellular based Web link. Installation was fairly simple: the adjustable mounting bracket was driven into the ground, the sensor was attached to the mounting bracket, the battery(s) was installed in the sensor, and the sensor was aimed at the canopy. These 20 units were installed in approximately three hours by two people because no soil excavation or wires were involved. The interface set-up was also fairly simple: sensor ID was recorded with the field location, the wireless receiver/logger/cellular transmitter located at the field edge was switched on and it automatically connected with sensors via their unique ID. The sensor IDs were then renamed with the field location IDs on the Web site. Access to results only required a Web address, username, and password and the dashboard of the main program made finding the desired field location easy. Also the data was integrated so that canopy temperature, air temperature, humidity, rainfall events, and stress indexes could all be viewed on a single graph.

This system also had some operational challenges. Even at the short wireless transmission distance of 300 feet or less between sensors and receiver, connectivity was lacking for long periods in 1 of the 20 units and there were short data skips in many other units. The default stress index did not seem to provide a good indication of when to irrigate under Tennessee conditions. A different stress algorithm is needed for very humid conditions. There were no-wires to interfere with field operations but the sensors were placed above the cotton canopy and needed to be lowered for field spraying. In 2011, the cellular link to the datalogger required several weeks to establish.

AquSpy – Soil Water Content from Capacitance Probes with a Cellular link to the Internet: The AquSpy system is based on segment probes that measure soil water content at different depths in the soil profile. The sensors relate changes in the electrical properties of the soil to changes in water content (capacitance). Three 40-inch capacitance probes with 10 sensors per probe placed 4-inches apart were installed in the 1.5-inch per week starting at square, 1.0-inch per week starting at bloom, and non-irrigated treatment of very shallow loam over sand soil. The cost of 10 sensor capacitance probes for each monitoring site was very high at $2,000 with similar cost for the cellular based Web link, $2,500. Four-inch holes were hand augured and the excavated soil was sieved to make a slurry. The slurry was poured into the hole and the probe was inserted into the slurry to make good contact. The probes were connected to the edge of field logger/cellular transmitter via fairly long wire runs. Last year in a silt loam soil, a crack developed when the slurry dried and was patched as good as possible. This year in the loam over sand soil, the slurry was a mixture of both soil layers, which does not put the true soil texture next to the probe. In 2011 for a silt loam over sand, another crack developed and was patched.

The interface is fairly straight forward since each probe has an identification number which is assigned a monitoring site location ID on the Web site. Connectivity has been consistent for three years of operation. A Web site address, user ID and password were also needed. It also takes several not very obvious steps on the Web page to access the data. It seems like a nicer dashboard is available but these sensors were not set-up using that interface. Soil calibrations for capacitance probes are very site specific so we did not assume the assigned calibration was accurate. It is recommended that irrigation cycles be observed to determine the full point and the irrigation trigger. This was difficult to do in two very rainy years with a lot of run-off and no rain events during the irrigation season that were slow enough to penetrate water to the bottom of the soil profile. The antenna was located at the edge of the field and, therefore, did not present a problem for spray operations. The long wire runs were not a problem with wheel traffic picking up and breaking the wires but this has been known to cause problems. 

AquaCheck – Soil Water Content from a Capacitance Probes with a radio link to a handheld/portable datalogger: Three 40" subsurface capacitance probes with 6 sensors per probe located at 4, 8, 12, 20, 28 and 40 inches were installed in the 1.5" per week starting at square, 1.0" per week starting at bloom, and non-irrigated treatment of the deep silt loam soil. The cost for an AquaCheck system was $600 per probe, $300 per transmitter, and $1,250 for a portable handheld receiver making this one of the least expensive capacitance probe systems on the market. The capital cost is further reduced because the receiver can be transported to many sites. These are dealer prices. An 8" deep 2-foot long trench was dug by hand with a shovel. In the end of the trench closest to the crop row, a 1 ¼" hole was augured and then the probe inserted in a soil slurry, with the top of the probe set at 6" deep to avoid planting and nitrogen knifing operations. Since the probe is a fairly tight fit, very little slurry is required and soil cracking did not appear to be a problem. The antenna base and wire from the probe are set in the other end of the trench which is the middle of a crop row that is not expected to encounter wheel traffic or nitrogen knifes. Finally the trench is refilled with the wire and the antenna stand being connect to the solo transmitter. This is a completely battery operated system and no solar panels are required. In upcoming growing seasons, installation should only require connection of the wires and setting up the antenna stand. The set-up interface was fairly straight forward since each transmitter (connected to a single probe) has an identification number which is assigned a monitoring site location ID in the CropGraph software. The handheld receiver consistently connected with the transmitters at the field edge and from a line of site office located 900 feet away. Soil water content was accessed by a USB connection that uploaded the probe data from the handheld receiver to the CropGraph software on a computer. The handheld receiver did not automatically pick-up any transmitter within range but the actual identification of each transmitter had to be specified to make this wireless connection. AquaCheck will have the same calibration problems of similar capacitance probes like AquaSpy. However, the permanent location of AquaCheck subsurface probes means that the calibration or irrigation thresholds will stay the same from year to year because the probe is not being installed every year. The CropGraph software produced fairly simple graphs and does not process the data to show the movement of soil water as easily as other capacitance probe software. The antennas needed to be lowered for field operations but there was no wire on the surface and the underground wire runs were very short.

After the data was uploaded to the CropGraph program on a laptop computer, a further upload was attempted to an Internet server from which other users with CropGraph software could view the results. This additional data upload of the soil water content to the internet was not established during the growing or in subsequent attempts after the growing season. In 2012, only one of three probes collected data. It was not possible to determine why two of the probes were not working.

Decagon – Soil Water Content from Capacitance Sensors with Datalogger: Decagon EC-5 sensors were installed at two depths in both 1.0 inch/week starting at square and the non-irrigated treatments that were located in the silt loam over sand soil.  Decagon system cost $110 per EC-5 sensor and $600 for the EC-50 logger that amounts to around $500 per site. Since the EC-5 is not a cylindrical shape, a small auger hole cannot be used to install the sensor and a pit was hand dug with a shovel that was large enough to insert an arm to the desired soil depth which is limited by the length of one's arms. Soil was hand packed around the sensor for good contact. This system is wired from the sensors to the logger and from the logger to the laptop and data was consistently available when connected. Since the length of sensor wires is short, the logger had to be located in the field such that the laptop had to be taken directly into the crop for data retrieval. The same calibration problems as other capacitance probes are expected and there are less sensors per site such that tracking soil water movement was not as evident. The ECH2O utility software only downloads the data for graphing in other software like Excel. Decagon software for downloading and graphing the data is available for a fee. The data logger is low enough that it does not need to be lowered for sprayer booms and wires are not on the surface. The logger box was removed for planting and harvest operations. The Decagon was not used in this study in 2012 due to damage to the sensors over the winter.

John Deere CropSense: This system was added to the study in 2012. The soil water content from capacitance probes with a cellular link to the Internet were installed in the 0.5" per week at square increasing to 1.5" per week at bloom treatment and the non-irrigated treatment of the silt loam over sand in 2012. Four inch holes were hand augured and the excavated soil was sieved to make a slurry. The slurry was poured into the hole and the probe was inserted into the slurry to make good contact.

In 2012, cracks in the slurry were patched. The interface is fairly straight forward since each probe has an identification number which is assigned a monitoring site location ID on the Web site. Connectivity was inconsistent. One of the two probes stayed connected the entire growing season while the other probe could not maintain a connection after three attempts. The Web site to view the data was simple and useable. The antenna was located low enough in the cotton row so that it did not interfere with spray operations.

While each of the systems had some challenges, these systems are becoming more affordable and user friendly each year. It is likely at least that more of these systems (and/or another wireless system not considered in this study) will be suitable for grower use in the next one to two years.

 

Project Year: 2012
 

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