Note: Please see pdf for full abstract with equations. Finding a direct solution to the widely us... more Note: Please see pdf for full abstract with equations. Finding a direct solution to the widely used Green-Ampt (G-A) one dimensional infiltration model has been subject of efforts for more than half a century. We derived an accurate explicit formula that appears be so far the simplest proposed model in the literature. Our approach builds upon simulating the Valiantzas’s G-A infiltration model by a second order polynomial. The proposed equation is F = Kt (0.70635 + 0.32415 √1+9.43456(S2/K2t)), with F, K, S and t being cumulative infiltration, saturated hydraulic conductivity, sorptivity and time, respectively. Relative errors (ɛ) by the application of this equation generally do not exceed ±0.3% in most practical infiltration problems faced in water resources engineering. It was both numerically and mathematically shown that absolute errors > 0.3% could only occur if Kt/F > 0.904, a criteria that could practically be the case for light textured soils like sand and loamy sand if ...
A mobile thermal-RGB imaging tool for mapping crop water stress of grapevines
2020 IEEE International Workshop on Metrology for Agriculture and Forestry (MetroAgriFor)
This study evaluates a tablet computer-enabled miniature thermal-RGB imager to map the crop water... more This study evaluates a tablet computer-enabled miniature thermal-RGB imager to map the crop water stress index (CWSI) in grapevines. Imagery data were acquired in a commercial grapevine block irrigated at four different rates (100, 80, 60, and 40% of replacement evapotranspiration [ET]). The latter three were the subsurface irrigation treatments. A custom image analysis algorithm was developed and CWSI was estimated using empirical baseline equations. RGB imaging refined the segmentation of the target canopy from background objects. Canopy-air temperature difference had significant and strong relationships with the vapor pressure deficits as per local conditions (R2: 0.72–0.85, p < 0.05). CWSI estimates for grapevines irrigated at 40% of ET were consistently the highest and were followed by for those irrigated at 60, 80, and 100% of ET rates. Study findings highlight the potential to develop a smartphone-enabled imaging and integrated application for real-time crop water stress assessment under field conditions. Our future efforts will refine these computing algorithms and develop a smartphone application for growers to assess tree-level crop water demands for site-specific irrigation management.
Advancements of Sensor-based Water Management to Maximize Crop Water Use Efficiency in Conjunction with Direct Root Zone (DRZ) Subsurface Drip Irrigation
6th Decennial National Irrigation Symposium, 6-8, December 2021, San Diego, California, 2021
Direct root-zone irrigation (DRZ) is a novel subsurface irrigation strategy initially tested in v... more Direct root-zone irrigation (DRZ) is a novel subsurface irrigation strategy initially tested in vineyards for economizing water and securing grape production in arid regions with unstable climatic patterns. However, studies are lacking on the responses of grapevine leaf carbon assimilation and deep rooting patterns to the novel irrigation strategy, which are essential for optimizing grapevine growth and alleviating extreme water stress during periods of heat and drought. Thus, a two-year field study was conducted in a commercial vineyard of Cabernet Sauvignon (Vitis vinifera L.) under a semi-arid climate in Washington, USA to compare the differences in leaf gas exchange and root distribution along the 0-160 cm soil profile, combined with measurements of specific leaf area and total carbon and nitrogen content in leaves and shoots to compare DRZ and traditional surface drip irrigation (SD) under three watering regimes. Compared to SD, significantly higher rates of net CO 2 assimilation, stomatal conductance and transpiration in leaves, which positively correlated to midday stem water potential, were found in grapevines irrigated through DRZ in both years. Meanwhile, DRZ reduced total root number by 50-60% and root length density (RLD) by 30-40% in the upper 60 cm soil at high (0.75-0.80 crop evapotranspiration) and moderate (0.60-0.65 crop evapotranspiration) irrigation rates, but no significant differences were found at low (0.45-0.50 crop evapotranspiration) irrigation rate between DRZ and SD. Higher root number and RLD were detected under DRZ within 60-160 cm soil depths, accompanied by a decreased ratio of total carbon to nitrogen content in leaves with slightly increased specific leaf area. Decreased rainfall and increased temperature in 2018 possibly amplified the positive effects of DRZ. Our study indicates that grapevines under DRZ could develop deeper roots for water uptake, which helps ameliorate water stress and improve the photosynthetic rate as well as enhance grapevine adaptation to semi-arid climates.
Direct root-zone irrigation is a novel subsurface drip irrigation strategy for water conservation... more Direct root-zone irrigation is a novel subsurface drip irrigation strategy for water conservation. However, a comparison with traditional irrigation methods is lacking to better define the potential advantages of direct rootzone irrigation. A two-year study was conducted to evaluate the performance of Vitis vinifera L. cv. Cabernet Sauvignon under direct root-zone irrigation and surface drip irrigation in a commercial vineyard with loamy sand soil in a semi-arid region of southcentral Washington State, USA. Plant water status, root traits, grape yield, berry morphology and composition, and crop water use efficiency were compared between irrigation methods under three irrigation rates. Compared to surface drip irrigation, direct root-zone irrigation improved grape yield by 9-12% and crop water use efficiency by 9-11% under varied climate conditions with minor effects on berry composition, which could be potentially adjusted by irrigation rate. Moreover, grapevines irrigated through direct root-zone irrigation had 48-67% and 50-54% decrease in root number, respectively, at high and moderate irrigation rates in the upper soil profile (0-60 cm) with a decrease in water stress as revealed by higher midday stem water potential. Irrigation rate was the major factor influencing berry morphology. In fact, reduced irrigation resulted in a decrease in weight, size and number of berries. We conclude that direct root-zone irrigation could be a successful tool for improving yield and crop water use efficiency, potentially encouraging deep rooting to alleviate the water stress in grapevine under seasonal drought, and offering the ability to modify berry morphology and composition by adjusting the amount of water use.
Control of Creosotebush (Larrea tridentata) with Pelleted Tebuthiuron
Weed Science, 1982
Aerial applications of pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′... more Aerial applications of pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 0.5 kg/ha reduced creosotebush [Larrea tridentata (DC.) Coville] density by up to 86% and by 99% when applied at 1 kg/ha in February or March. Grass production 32 months after treatment was 174 to 305% greater in tebuthiuron-treated plots than on untreated ran gel and, but forb production in treated plots was reduced 38% or more and the poisonous half-shrub broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. and Rusby] was reduced 94% or more.
Control of Sand Shinnery Oak (Quercus havardii) with Pelleted Picloram and Tebuthiuron
Weed Science, 1982
Sand shinnery oak (Quercus havardii Rydb.) was controlled by both picloram (4-amino-3,5,6-trichlo... more Sand shinnery oak (Quercus havardii Rydb.) was controlled by both picloram (4-amino-3,5,6-trichloropicolinic acid) and tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} in the Rolling Plains vegetational region of Texas. Tebuthiuron provided acceptable control of sand shinnery oak at rates of 0.6 to 1.1 kg/ha, but 2.2 kg/ha of picloram was required to give comparable results. Tebuthiuron pellets applied at 0.6 kg/ha controlled 79% of the sand shinnery oak within 30 to 67 months after application. Applied at 1.1 kg/ha, tebuthiuron controlled 91% (average for three locations). No differences were found between formulations of a given herbicide.
The direct root-zone irrigation system is a new technique to deliver water directly to the root z... more The direct root-zone irrigation system is a new technique to deliver water directly to the root zone of grapevines at specific irrigation rates and delivery depths. The response of Vitis vinifera L. cv. Cabernet Sauvignon to direct root-zone deficit irrigation was investigated in a commercial vineyard with loamy sand soil in the semi-arid lower Columbia Basin of southcentral Washington State, USA. Three irrigation rates and three delivery depths were compared for effects on grape yield and crop water use efficiency during three consecutive growing seasons. Furthermore, we investigated the influence of irrigation rate on grape quality, and used an in situ root imaging system for root phenotyping under different delivery depths for two years. Results showed that delivery depth had no significant effect on grape yield and crop water use efficiency; however, increases in delivery depth from 30 cm to 90 cm resulted in 60-70% decreased root number and 46-59% decreased root length in the upper soil profile (0-60 cm). Moderate irrigation rates (35% less water use on average) improved crop water use efficiency by 14-23% and only reducing grape yield 15-18% per individual grapevine, without sacrificing grape quality or inducing early defoliation for the first two years. Surprisingly, no significant reduction of grape yield was found in the third year, which can be attributed to cooler and wetter weather and potentially vine acclimation to the direct root-zone irrigation strategy. We conclude that direct root-zone deficit irrigation could be a convenient and efficient subsurface irrigation method to improve crop water use efficiency without reducing grape quality under seasonal drought. Future studies should compare the economic and environmental returns of direct root-zone deficit irrigation with other traditional irrigation strategies under different environmental conditions to optimize the direct root-zone deficit irrigation method.
Triclopyr for Control of Honey Mesquite (Prosopis juliflora var. glandulosa)
Weed Science, 1983
Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was aerially applied at four locations... more Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was aerially applied at four locations in Texas to determine effectiveness of the amine and ester formulations for the control of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell # PRCJG]. The ester formulation was superior to the amine in most trials. Honey mesquite control with triclopyr amine was comparable to that with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] while control with triclopyr ester was similar to that attained with a 1:1 mixture of 2,4, 5-T and picloram (4-amino-3,5,6-trichloropicolinic acid). Honey mesquite control obtained with a 1:1 mixture of 2,4,5-T and dicamba (3,6-dichloro-o-anisic acid) was intermediate between that with the 2,4,5-T and picloram mixture and that with 2,4,5-T alone. Efficacy of triclopyr increased as rates were increased from 0.3 to 0.6 kg ae/ha and from 0.6 to 1.1 kg/ha. Triclopyr formulations were effective when applied in either water or diesel ...
In this study, 3D light detection and ranging (LiDAR) and an inertial measurement unit (IMU) were... more In this study, 3D light detection and ranging (LiDAR) and an inertial measurement unit (IMU) were integrated on a ground vehicle for mapping tree fruit crops. A custom interface was developed in robot operating system for synchronous communication with hardware modules and for continuous field data collection. Point cloud data processing methods were developed for reconstruction and estimation of canopy parameters including height, voxel grid and convex hull methods-based volume and gap fractions in the canopy. The system was tested in apple tree and grapevine canopies. Overall, the mobile 3D LiDAR mapping system provided realistic representation of the canopy compared to the manual methods. For apple trees, the manual canopy volume measurements were strongly correlated to volume derived from the mobile 3D LiDAR mapping system (Convex hull: r = 0.81, Voxel grid: r = 0.51). The voxel grid method adequately considered gaps in the canopy during volume estimation and performed better than the convex hull method. The system was also evaluated for estimating canopy growth in grapevines with different rates of subsurface irrigation treatments. Deficit irrigation treatments did not show any significant effect on the canopy growth due to a high moisture content in the soil, resulting from high winter snowpack prior to that particular season. Nonetheless, the 3D LiDAR mapping system was able to aid in visualization of the temporal changes in canopy growth during the growing season. Change in vine canopy volume for the treatments followed a similar trend to the area ratio estimated from normalized differential vegetation index images derived from small unmanned aerial system based multispectral imagery. Overall, the 3D LiDAR based canopy mapping system and pertinent data mining algorithms can be the useful tool to the growers in rapid assessment of perennial fruit crop canopies for real-time management decision making.
Management of Sand Shinnery Oak for Control of the Boll Weevil (Coleoptera: Curculionidae) in the Texas Rolling Plains
Journal of Economic Entomology, 1985
... Three cone-shaped cages, measuring 33 cm in diameter at the base and 56 cm tall, were placed ... more ... Three cone-shaped cages, measuring 33 cm in diameter at the base and 56 cm tall, were placed in each plot ... growing season following treatment, when plants eventually died, and this response was typical of other tebuthiuron treatments on shinnery oak (Ja-coby and Meadors ...
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