PRECISION AGRICULTURE INITIATIVE FOR TEXAS HIGH PLAINS

2001 ANNUAL COMPREHENSIVE REPORT

Texas Agricultural Experiment Station and Texas Agricultural Extension Service

Reporting Period:  January 1, 2001 – December 31, 2001

A.          Summary of Progress:

Remote Sensing – Doppler radar for site-specific estimation of rainfall for prediction of hybrid seed sorghum ergot. Sorghum ergot, caused by the fungus Claviceps africana, is favored by high relative humidity. High relative humidity in the dry and hot climate of the Texas Panhandle is exclusively associated with thunderstorms or scattered showers. Therefore, rainfall is one of the primary factors in development of the disease in the region. The best disease management practice consists of knowing when the disease occurs and taking appropriate, timely action.  Prediction of rainfall amounts, therefore, is critical for management of sorghum ergot. In general only a single weather station exists in each county and some counties have none. Therefore, the management unit for use of the stations in disease prediction can be as large as a county or greater. However, rainfall events are variable and patchy in nature even within short distances. Use of countywide management units for development of a prediction model would undoubtedly lead to erroneous conclusions.

The advent of Doppler radar has made it possible to site-specifically estimate rainfall amounts to a resolution of 2.2 square miles (Fig. 1). The Arkansas River Basin River Forecast Center (ARBRFC, Tulsa) and West Gulf River Forecast Center (WGRFC, Dallas-Ft Worth) keep archives of past Doppler radar estimates for the region. We have made arrangements to obtain their rainfall estimates based on Doppler radar. In addition, we have provided them with access to data from the North Plain Evapo-transpiration Network (NPET) weather stations. This data will be used as ground truth data for calibration of their rainfall estimates, which will be an large addition to their existing automated weather stations in the region. This will greatly improve our precision in predicting the disease. In the Texas Panhandle, during the summer months, daytime temperatures are too warm for ergot development. However, using these historical weather records, we discovered that during or following some rain events, the maximum temperatures are suppressed, and they remain within a range favorable for ergot. A manuscript based on this discovery has been accepted by the journal Phytopathology (a premier journal in plant pathology). Currently, an experiment is underway in growth chambers to determine environmental factors that affect disease development. A model that integrates precipitation estimates and environmental factors will be developed for prediction of sorghum ergot.

Figure 1.  Doppler radar rainfall estimates over the Texas Panhandle obtained from ARBRFC in Tulsa.

Remote Sensing – Infra-red thermometry for site specific measurement of crop water stress in the presence of plant diseases. Water is the single most important requirement for crop production. Many researchers have investigated the use of infra-red thermometry for predicting soil moisture, but no one has looked at the impact of plant diseases on canopy temperature. In a standard irrigation scheduling system, canopy temperatures above a threshold value indicate a need to irrigate. When a plant pathogen colonizes the root and vascular system of a plant, the flow of water to the leaves is disrupted. This results in higher canopy temperatures, even though there is plenty of water in the soil profile. Bare soil, like that in areas where a disease has killed all of the plants, also gives high temperature readings. Without taking disease into account, irrigation scheduling systems could result in over watering.

We are investigating techniques to improve irrigation scheduling in the presence of root rots. In wheat, cotton, and sugar beet fields, healthy areas and areas with varying levels of disease were identified. Diseases included take-all (Gaeumannomyces graminis var. tritici) in wheat, Phymatotrichum root rot (Phymatotrichum omnivorum) in cotton, and, in sugar beets, Rhizoctonia root rot (Rhizoctonia solani) (Fig. 2). At each spot, canopy and air temperature, soil moisture, and canopy reflectance were measured. Canopy temperature was measured with an infra-red thermometer (Fig. 3). Air temperature was measured with a thermistor. A 6-inch soil core was taken from the same area evaluated by the infra-red thermometer, and soil moisture was measured gravimetrically. Canopy reflectance was measured with a CropScan handheld radiometer at 460, 510, 560, 610, 660, 710, 760, 810, and 935 nm. This data is being analyzed to determine if assessing the crop using a radiometer set at one or more of these wavelengths will allow us to differentiate between plants that are drought stressed and those that are wilting from disease.

Figure 2 Color infra-red photograph of sugar beets showing variation between water treatments and varieties.

Figure 3. Temperature variation in winter wheat as measured by infra-red thermometry.

Remote Sensing – Differentiation between Biotic and Abiotic Stresses: If remote sensing is to be of value for precision agriculture, it is important to be able to differentiate the various stresses that a crop might be subjected to. We need more detailed information about the spectral properties of crops under different kinds of stress.

Rhizomania, caused by beet necrotic yellow vein virus (BNYVV), is an important disease of sugar beets, and foliar symptoms can be similar to those caused by nitrogen deficiency. To maximize sugar yield, it is important that beets run out of nitrogen by the end of the growing season. So in fields infested with BNYVV, it can be difficult to distinguish between the yellowing caused by these two stresses (i.e., rhizomania and nitrogen deficiency) by eye. We have measured the spectral characteristics of healthy sugar beets and those of sugar beets infected with BNYVV over time, as the nitrogen content of the field decreases. Spectral properties on a whole-field basis were measured with a CropScan handheld radiometer; leaf spectral properties were measured using an ASD hyper-spectral radiometer and an integrating sphere.  Finally, spectral properties at the chemical level were evaluated through analysis of pigment extracts using a Shimadzu scanning spectrophotometer. This has been done for two years, and the data is currently being analyzed. Preliminary results indicate that a broad region through the visible portion of the spectrum can be used to distinguish between healthy beets and those with rhizomania (Fig. 4). As the season progresses, differences in spectral data collected from healthy and infected beets are reduced as nitrogen content decreases, but they are always apparent. Methods developed in this study could potentially be applied to differentiating among any stresses.

Figure 4. Regions between 450 and 700 nm show significant differences in the spectral properties of healthy beets and those of beets infected with BNYVV (rhizomania).

Remote Sensing – Development of management units for soil-borne viruses of sugar beets. Last year, we reported that the spatial distribution of BNYVV and BSBMV were generally near random. Investigations of additional fields in 2001 showed similar results. The two viruses are very similar biologically, and both viruses can occasionally be isolated from a single root prompting speculation of the possibility of synergism between the two viruses or cross protection of one against the other. For such possibilities to occur, the two viruses have to be spatially associated. The association of the two viruses was determined using grid soil samples in 11 fields (Texas, Colorado Minnesota, N. Dakota). The association of the viruses ranged from 0 to 42% of all grids having both viruses with a mean of 11.2%.  A manuscript containing details of the investigations is now in progress for publication in the refereed journal Plant Disease.

Remote Sensing – Purchase of hyper-spectral aerial imaging system. Aerial imagery is a useful tool in precision agriculture. Several groups in the Precision Agriculture program have had trouble purchasing satellite data in a timely fashion. For studies evaluating disease, insects, or nematodes, timing of image acquisition is especially critical. Each PI in the Precision Agriculture program agreed to tax themselves at a rate of 10% of their budget, with the funds to go towards purchasing an aerial imaging system. These funds, along with grants from Resource 21, Texas Cattle Feeders Association, Texas Corn Producers Board, Texas Sorghum Producers Board, and Texas Wheat Producers Board totaled more than $130,000. Due to the great diversity of research in the program, it was decided to purchase a hyper-spectral unit that could be configured for various uses. The unit was purchased and delivered in August 2001, and approximately $6,000 left over from initial funds was available to support flights for the first year. The vendor provided training to several Precision Agriculture faculty members and staff in September 2001. Since then, we have flown the unit several times and optimized methodologies for agricultural systems (Fig. 5 and Fig. 6). The instrument provides up to 60 spectral bands that are as narrow as 1.6 nm and as wide as 10.4 nm wide in the 428 nm to 906 nm range. Spatial resolution is between 1 m and 4 m. This unit provides a unique capability to the Texas Precision Agriculture Program.

Figure 5. AISA hyper-spectral imager installed in a Cessna 172.

Figure 6. A hyper-spectral image of a feedyard. The spectral plot in the lower right shows spectra for caliche, manure, and vegetation.

Systems Agriculture – Effect of interactions between water availability and plant population on the incidence of aphid populations and maize dwarf mosaic virus in grain sorghum. A study was initiated cooperatively among our group and Dr. Jerry Michels and Dr. Bill Payne to look at the impact of agronomic variables on insect incidence and viral population in grain sorghum. Past studies by Dr. Michels have shown a relationship between populations of corn leaf aphids and green bug. He has also shown relationships between water availability and plant populations on aphid populations. Both aphids vector maize dwarf mosaic virus (MDMV), but it was unclear if either aphid could cause a significant level of MDMV in the field. The study was designed to separate the effects of each aphid on virus level under different levels of water availability and plant populations. Unfortunately, green bug never reached a significant population in 2001. High corn leaf aphid populations resulted in an average MDMV infection of 5.2% in the field, but no effect on yield was observed. This is likely due to high levels of adult plant resistance to MDMV in sorghum. Data is being analyzed to determine the impact of plant population and water availability on corn leaf aphid populations.

B.          Education/technology transfer:

During the year members of the plant pathology project gave numerous PA presentations at field days, crop tours, commodity research meetings, and grower meetings. We also provided tours to various groups including scouts, students, visiting scientists, etc. during which we presented overviews of our PA project.

C.          Milestones achieved: 

This year we completed work on several projects. 2001 was the final year for fieldwork needed for evaluation of infra-red thermometry for irrigation management in the presence of disease.  Fieldwork was also completed for the study assessing differentiation between biotic and abiotic stresses using remote sensing technology. The results for these will be compiled, and manuscripts will be submitted for publication this year. A manuscript on the relationship between weather and development of sorghum ergot has already been submitted. The acquisition of the hyper-spectral imaging system will greatly enhance our ability to do future remote sensing work.

D.         Publications:

Harveson, R.M. and C.M. Rush. 2001. The influence of irrigation and cultivar blends on the severity of multiple root diseases of sugar beets. Plant Disease 85: 2002 (in review).

E.            Precision agriculture proposals:

PROFIT (Preproposal).  Integrated Management of Stalk Rot in Sorghum by Genetic Resistance and Precision Irrigation.  $49,420

PROFIT (Preproposal).  Interactions Among PET-based Irrigation, Plant Populations, and Insecticide Seed Treatments and Their Relationship to Pests and Profitability of Sorghum.  $78,336

Resource 21.  Purchase of Hyperspectral Radiometer.  $25,000.

Southern Minnesota ND R&D Board.  Remote Sensing of Beet Necrotic Yellow Vein Virus and Interactions with Beet Soilborne Mosaic Virus.  $21,000

Texas Cattle Feeders Assoc.  Purchase of a Hyperspectral Remote sensing System for Use in Studies of Feed Yard Dust Management. $7,000

Texas Corn Producers Board.  Acquisition of a Hyperspectral Remote Sensing System for Precision Agriculture Research in Corn.  7,000

Texas Sorghum Producers Board.  Integrated Management of Stalk Rot in Sorghum by Genetic Resistance and Precision Irrigation.  $30,720

Texas Wheat Producers Board.  Acquisition of a Hyperspectral Remote Sensing System for Precision Agriculture Research. $7,000

USDA-SRIPM.  Studies on the Survival of Claviceps africana and Development of a Model for Risk Assessment and Management of Sorghum Ergot.  $103,980

F.           Precision Agriculture meetings attended/papers (posters) presented:

Bredehoeft, M., S. Roehl, J. Fischer, J. Lamb, D. Humburg, D. Lamker, C. M. Rush.  2001.  Relationship of nitrogen rate on sugar beet yield, quality, and spectrum images in a spatial orientation.  Vancouver, B.C.  February 28, 2001.  ASSBT.

Piccinni, G.,  C. M. Rush, K. C. Steddom, and G. J. Michels.  2001.  Interactions between plant population and PET-based irrigation in grain sorghum yield.  ASA-CSSA-SSSA.

Rush, C. M., G. Piccinni, G. J. Michels, K. Steddom, and W. A. Payne.  2001.  Relationships among plant populations, PET-based irrigation, aphid populations, and incidence of MDMV.  Nashville, TN.  February 19, 2001.  NGSP/SICNA.

Steddom, K., M. Bredehoft, and C. Rush.  2001 Comparison of visual and remotely sensed Cercospora leaf spot ratings on sugar beets.  Vancouver, B.C.  February 28, 2001.  ASSBT.

Steddom, K., G. Heidel, D. Jones, and C. Rush.  2001.  Remote detection of beet necrotic yellow vein virus.  Salt Lake City, Utah, August 24, 2001.  APS.  Phytopathology 91:S84.

Steddom, K., G. Heidel, D. Jones, and C. Rush.  2001.  Use of remote sensing technology for detection of beet necrotic yellow vein virus and beet soilborne mosaic virus.  Vancouver, B.C.  February 28, 2001.  ASSBT.

Workneh, F., Villanueva, E., and Rush, C. M. 2001. Relative within-field distributions of beet necrotic yellow vein virus and beet soilborne mosaic virus in sugar beet fields. Phytopathology 91:S96.

G.         Other developments: