Abstract
Introduction
Development & Implementation
Dissemination Outputs
NPPET Network Value
Forecasted Plans
References
Acknowledgements

A Potential EvapoTranspiration (PET) network has been developed and implemented within the northern Texas High Plains. The network grid represents over 2 million acres of irrigated agriculture within a total area of over 4 million acres. The network system utilizes automated data acquisition units to log data on an hourly basis at multiple sites representative of different commodities grown within a 30 county area. Interrogation of the units is by phone communication. The system automatically computes and dispatches faxes to each subscriber in the early morning hours indicating PET, growing degree day units, physiological growth stage and seasonal water use from multiple planting dates. Sequential automated computer to computer transfers occur for security and functionality purposes. In addition, the system uploads to the world wide web via the internet for electronic access for individuals requiring modern and more intensive and detailed data than provided within the faxes. Illustrations of each output are provided.

All PET computations are based on the Bushland ET equation, a derivative of the modified Penman-Monteith equation, which uses well-watered grass as a reference crop rather than the classical crop of alfalfa. PET (of well-watered grass), crop physiological growth stages and growing degree heat units are currently provided for corn, sorghum, cotton, peanuts, wheat, and sugarbeets. Computations and crop coefficients are determined using the large, monolithic lysimeter facility located at the ARS facility at Bushland, TX. Planned additions to the system are disease and insect development models. Future efforts may include dust and odor control models for concentrated animal feeding operations (CAFO's).


Keywords: Automated weather network, Evapotranspiration, Irrigation management.

Irrigated agriculture accounts for approximately 60% of the water use in Texas (Texas Water Facts, 1991). Accordingly, a large part of the irrigated agriculture in the state using groundwater is in the Texas High Plains that accounts for over 85% of the water use in that area. The 26 counties surrounding Amarillo, TX alone has over 2 million irrigated acres (more than the combined total irrigated acreage of New Mexico and Arizona) and produces over $770 million in annual crop value and $1.8 billion in annual added livestock and meat value. The entire 41 county Texas High Plains region has in excess of 4 million irrigated acres making it the 3rd or 4th largest US irrigated state if it were considered by itself. Subsequently, the majority of the most intensive irrigation and associated crop production income continues to be in the northern region of the Texas Panhandle. This trend is supported by the number of wells being drilled and reworked, the availability of an adequate groundwater saturated thickness and the continued installation of center pivot sprinkler systems in the region.

While the efficiency of these sprinkler systems can be very good, especially when designed with LEPA (Lyle & Bordovsky, 1981) or a LESA (Low Elevation, Sprinkler Applied; Marek, et al.,1996) irrigation package, irrigators generally tend to over irrigate when compared to actual crop requirements. This is especially true for irrigated corn which is a major commodity within the represented area due to the intensive, major confined animal feeding industry. Additionally, winter wheat is grown for fall and winter grazing of stocker cattle before their placement into feedlots. Accordingly, there existed a need for daily ET data for numerous crops grown within this intensive northern Texas agricultural region 1) to efficiently utilize the declining groundwater supplies through efficient irrigation practice, and 2) to provide accurate water use data to these productive growers. The southern Texas High Plains currently utilize the South Plains PET Network for predicting ET (Seymour, et at., 1994). The two networks still present water use in significantly different formats to users.

The North Plains PET network has applications with deficit irrigation. In irrigation programs where full ET is not being met, a reference level can be related to full ET requirements whereby improved irrigation scheduling and water management can be implemented. The principal anticipated users of the network are: growers/irrigators/farm managers, production consultants, seed production representatives, agronomists, agricultural engineers, researchers, extension specialists, water district technicians, regulators, design engineers, city water personnel and golf course managers.

In 1995, the Texas North Plains PET network was collaboratively developed by personnel of the Texas A&M University System?s Texas Agricultural Experiment Station and Texas Agricultural Extension Service of Amarillo, Texas and by personnel of the USDA?s Agricultural Research Service at Bushland, Texas. In addition, assistance has been provided toward the ongoing effort by the Panhandle Groundwater Conservation District of White Deer, Texas, the North Plains Underground Water Conservation District of Dumas, Texas, the Texas Wheat Producers Association of Hereford, Texas and the Texas Corn Producers of Dimmitt, Texas. In addition, a soil and water conservation district, a grower cooperative, a processing facility and several growers have provided support for the network. Land use of progressive growers is also recognized as a significant contribution to the implementation and success of the NPPET.

Initially, operational and data constraints setforth by the development team consisted of the following:

1) Data must be accurate and representative (scientifically based),

2) Data must be timely (daily),

3) Data must contain integrity (through scheduled maintenance and with a quality assurance program),

4) Data must be calibrated (using the large, representative lysimeter facility at Bushland ),

5) Data must be sustainable (utilize a support system), and

6) Units should meet proposed ASAE EP specifications for automated agricultural weather stations (Ley, et al.,1994).

All weather stations within the network use Campbell Scientific?s Weather Watch 2000ä microprocessors (model which is no longer available), data storage modules, modems and sensors. Each station measures the following data on a 6 second interval and outputs it on an hourly basis: soil temperatures at 2 and 6 inch depths, ambient air temperature (at 5.9 feet height), dewpoint temperature, relative humidity, vapor pressure, vapor pressure deficit, solar radiation, wind speed (at 6 feet height),, wind direction, standard deviation of the wind direction, and precipitation. Several parameters regarding maximum and minimum and total values are reported in a daily summary. Rainfall intensity is recorded for 15 minute intervals. Interrogation of the units is achieved through phone communication due to the dependability required for the region which is susceptible to severe thundershower activity the majority of the year.

All activities of the network are handled by PC computers. The operational series of events performed by the PC computers daily is as follows: wake up central PC computers, call weather stations, download data, check raw data sets, report data errors, manipulate and process data sets, archive data sets, compute PET and respective ET for appropriate crops as well as growing degree day and seasonal water use, run other model(s) such as insect and pathogenic disease development models, record model outputs, initiate fax calls, send faxes, transfer data and fax logs to backup PC computer, call PC computer system attached to the world wide web via the internet backbone and transfer data and turn all central PC computers off. All of this activity occurs and is completed before 5:00 a.m. each day.

The network was initialized with the beginning of a corn crop and followed with a grain sorghum crop. The corn crop had four planting dates from which water use, growing degree day heat units and physiological growth stages were computed for. Likewise, the grain sorghum, cotton, peanuts and soybean crops had 4 planting dates with similar information, respectively. Wheat also had four planting dates with the first dates representing wheat for grazing plantings. The crops of corn, sorghum and peanuts continue to have parameters calculated for both a nominal short season and long season variety.

Implementation of the initial network was completed within mid April in 1995. All programming and instrumentation assembly and hookup was handled by the NPPET personnel. Six locations were originally located in the network. Since that time additional stations have been added and are located as illustrated in Figure 1. Currently there are 10 stations within the NPPET network. The location of each unit has been chosen to represent a specific irrigation area that was known or anticipated to differ from adjacent locations meteorologically. In addition, sites were chosen at locations where they were supported as well as where there existed a potential irrigation related clientele. These parameters were critically addressed to enhance usefulness for fully and limited irrigation cases and especially for deficit irrigation applications.

The daily output of the network is available in two forms. The primary output is disseminated in the form of a fax to subscribers for the crops of the appropriate growing season at each location. The second means of dissemination of the network is through the world wide web via the internet system.

The fax output is illustrated in Figure 2. The fax date for this illustration corresponds to June 9, 1998 for the Wellington, TX location. It should be noticed that all the crops grown in that location are listed on the report. The fax sheet contains PET based on well watered grass (Allen, et al., 1994) for the past three days. This value is 0.29 inches which is how much water a well watered grass 4.5 inches in height used for the 24 hour period on June 9, 1998. In addition, maximum and minimum air and soil temperatures at the 2 and 6 inch depths are displayed. Ten day minimum soil temperatures for both soil depths are also indicated. These values are especially useful in determining adequate planting temperatures for producers. The fax sheet includes growing degree day heat units for the crops of cotton, grain sorghum, peanuts, corn, soybeans, sugarbeets and wheat. These values are particularly useful for those wishing to run their own models. The fax sheet reflects accumulated growing degree day values for several crops planted on the differing planting dates for the user so he/she doesn't have to keep running totals since planting. The next section contains information regarding crop ET information for each day, 3 day, 7 day and accumulated seasonal use for both a short and full season variety for the respective crop for each of 4 planting dates. The information is related for each of the crops concurrently being grown for the time period.

The world wide web site via the internet contains a menu based system that contains the faxes. It also contains the hourly micrometeorological information for each day at each location with more detailed daily summary information than is provided in the fax output. A typical and associated file of the fax file containing the hourly and summary information of June 9, 1998 for Wellington, TX is illustrated in Figure 3. The internet system uses station buttons and a directory system to navigate to the desired information of the system. The world wide web internet address of the NPPET network home page is

http://amarillo2.tamu.edu/nppet/petnet1.htm As the user becomes more familiar with the web site, one may wish to "jump" directly to the station selection page (or use a browser bookmark) at

http://amarillo2.tamu.edu/nppet/station.htm

The NPPET network currently sends out over 325 faxes to growers, consultants and agricultural related businesses each morning. This caliber of dissemination resulted in over 120,000 faxes being sent in 1998. In earlier years, the NPPET subscriber list typically decreased during the winter months and gained during the spring through summer periods. No such fluctuation was noticed in 1998 as fax user subscription was consistent with summer usage. Attribution of the constant trend was given to improved education and utilization by user clientele. Relating to the extensive outreach of the NPPET, personnel of the network visited Valmont Irrigation in Valley, Nebraska in 1999 and were pleasantly surprised to find that irrigation personnel of the firm were not only receiving one of the NPPET faxes but were intimately versed as to how to use the sheets by their irrigation representatives in the Texas area.

Utilization development of the NPPET web site is still in it's infancy, so to speak. Detailed paging counters as to actual downloads versus mere page hits are not yet in place although they are planned for the fall of 1999. On-line database querying is also strongly being considered by the NPPET development team. Special thanks are also in order to the Texas Corn Producers Board for their equipment support of the electronic site which increased performance of the NPPET web site by 20 fold.

Although many agencies and organizations have contributed to the development and establishment of the NPPET, maintenance is a necessity of the network for the needed accuracy. In 1999, the NPPET network has an annual support cost basis of approximately $25,000. This annual cost is currently being borne by the agencies associated with development of the effort. Producers in the northern Texas Panhandle state that by using the NPPET network in irrigation scheduling, they are able to save 2 inches of pumped groundwater per corn growing season without any loss in production level. Extrapolating that to the regions irrigated acreage and considering reduction for other annually grown crops yields a estimated water pumpage savings of about $10 million annually. Agricultural economists calculate that about another $8 million is saved in engine wear and repair from the reduced pumpage. More importantly, conservation of our groundwater resources is increased through use of the NPPET network data. The "worth" of the NPPET network was recently recognized by being awarded the Texas Natural Resources Conservation Commission's Environmental Excellence Award in Agriculture in 1999 upon it's first nomination, which is somewhat unusual. It's recognition at the awards ceremony in Austin was principally for not wasting water which was not needed for efficient crop production or as the video producer stated in a short video, it's tells one "precisely how much water is needed when". In addition, by not over applying irrigation water, percolation and runoff potentials of chemicals, fertilizer and soil are significantly reduced. But possibly the best testimony as to the worth of the NPPET network was recently made at the award ceremony by a progressive northern Texas grower who stated "I'd hate to irrigate in today's environment without the NPPET network!"

Another unit of the Texas Agricultural Experiment Station at Chillicothe, Texas is currently in the process of procuring a weather station to address providing accurate ET data within that area. This research station is currently scheduled to be included in the NPPET network to initially provide timely and accurate data to agricultural engineers and other scientists. At this time it is being integrated into the NPPET network to prevent "reinventing the wheel" since agricultural engineering personnel at both sites are mutually working on water use efficiency. Ultimately, producers should be educated at the value of irrigation water management and scheduling.

Besides merely adding weather stations, the NPPET personnel are currently developing and validating insect and disease models. It is not the intent of the NPPET to replace consultants or managers, but rather to provide another very accurate tool by which producers don't have to guess at water use. It is the viewpoint of the NPPET team that water use should not be a variable in a producers risk management. Model predictions can likewise be utilized by consultants and production agents to be alerted to the fact that conditions are favorable as to the potential of an outbreak of insects and/or disease. Agricultural engineers have also expressed some future interest in possibly developing and utilizing the NPPET in predicting dust control for CAFO's. While much work in development need to be done, the value of the NPPET network appears to be extensive by any computation.

For more information on the NPPET or to receive faxes, contact Leon New or Thomas Marek at the Amarillo Agricultural Research and Extension Center at 806-359-5401. Subsequently, several PET networks within the southern region of Texas has been developed using the protocols developed with the NPPET network.

1. Allen, R. G., M. Smith, L. S. Pereira and A. Perrier. 1994. An update for the calculation of reference evapotranspiration. ICID Bulletin 43(2):35-92.

2. Ley, T. W., R. L. Elliott, W. C. Bausch, P. W. Brown, D. L. Elwell and B. D. Tanner. 1994. Agricultural Weather Stations. ASAE Paper No. 94-2086. 19pp.

3. Lyle, W. M. and J. P. Bordovsky. 1981. Low Energy Precision Application (LEPA) irrigation system. Transactions of the ASAE 24(5):1241-1245.

4. Marek, T., T. Howell, L. New, B. Bean, D. Dusek G. J. Michels, Jr. 1996. Texas North Plains PET Network. Proceedings of the International Conference on Evapotranspiration and Irrigation Scheduling. American Society of Agricultural Engineers. Nov. 3-6, 1996, San Antonio, TX. pp. 710-715.

5. Seymour, R. M., W. M. Lyle, R. J. Lascano, and J. G. Smith. 1994. Potential evapotranspiration information for irrigation management in the Texas Southern High Plains. pp.653-656. In D.G. Harrison, F.S. Zazueata, and T.V. Harrison (eds.) Computers in Agriculture 1994, American Society of Agricultural Engineers, St. Joseph, MI.

6. Texas Water Facts, 1991. Texas Water Development Board, Austin, TX.

Sincere thanks are in order to the progressive growers of the Texas High Plains who support this effort and volunteered the area for the NPPET instrumentation sites. Without their support and contributions, this effort would not have progressed to the point it is today. Without the progressive vision of the agricultural engineers and scientists associated with the NPPET network and the continued support of the users, commodity groups and the associated water use agencies of Texas, it shall go no further.

This effort is part of the Texas High Plains CREET (Cooperative Research, Education and Extension Triangle).




* Agricultural Engineers, TAMU-TAES, Amarillo, TX, USDA-ARS, Bushland, TX, TAMU-TAEX, Amarillo, TX, Agronomist, USDA-ARS, Bushland, TX, Agronomist, TAMU-TAEX, Amarillo, TX and Entomologist, TAMU-TAES, Bushland, TX..

ä The mention of a trade or commercial name is made for information only and does not constitute suitability, applicability or endorsement by the TAMU-TAES, TAMU-TAEX or USDA-ARS.

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