Troy Peters

Impact of sustained deficit irrigation on spearmint (Mentha spicata L.) biomass production, oil yield, and oil quality

Crop response to deficit irrigation is an important consideration for establishing irrigation management strategies when water supplies are limited. This study evaluated the response of native spearmint to water deficits applied using overhead sprinklers in eastern Washington, US. Five levels of irrigation were applied ranging from full irrigation (100%) to 5% of weekly averaged full crop water needs. Soil water monitoring with soil water balance was used to estimate soil water deficits for irrigation scheduling and soil water use. Mint oil yields, oil components, dry matter production, and the water-use efficiency of the spearmint were assessed. There was significant reduction in fresh mint hay (harvested biomass) yield with increasing water deficit. However, spearmint oil yields remained generally uniform across irrigation treatments at the first cutting but decreased at the driest plots during the second harvest due to a loss of plant stand. The wet harvest index and water-use efficiency improved significantly for both harvests with increasing water deficit. Hay yield, oil yield, wet harvest index, and water-use efficiency are pooled across sides and replicate blocks to provide trends with changes in maximum evapotranspiration. The three major monoterpenes show changes suggesting less mature oil yields. The study demonstrates the feasibility of sustaining native spearmint yields under managed deficit irrigations for deficits not lower than 0.5 ETc.

Analytical Determination of Distribution Uniformity for Microirrigation Tapered Laterals Laid on Uphill and Horizontal Slopes

AbstractThe uniform distribution of water delivered through microirrigation emitters on a lateral line is an important objective that greatly affects a system’s efficiency. Among the various uniformity parameters, distribution uniformity (DU) is one of the most frequently used indexes in industry. In this study, an easy-to-use analytical method for directly calculating the DU of tapered microirrigation laterals laid on horizontal or uphill slopes is developed. The proposed equations are derived assuming that the system’s hydraulic characteristics and the ground slope are the only factors affecting the DU. A comparison test with a numerical stepwise solution indicates that the proposed analytical method is reasonably accurate and can be used to evaluate the system uniformity. The results also show that the accuracy of the method increases as the total number of outlets increases or the value of the emitter exponent approaches unity.

Modified G and GAVG Correction Factors for Laterals with Multiple Outlets and Outflow

Anwar’s friction correction factor, G, and the average correction factor, GAVG, are used to compute the head loss resulting from friction and to calculate the required inlet pressure in horizontal tapered sprinkler laterals with multiple outlets. As a result of their being developed by using a discrete outflow model, which consists of a finite number of operating outlets, the previous approaches for determining these factors required tables or the solving of relatively complex formulas that may be cumbersome. In addition, use of these factors is subject to certain errors when the Darcy-Weisbach equation is used because they are developed assuming a constant friction factor along the lateral. In this study, considering the continuous flow-rate variation concept, at first, two simple and direct equations for calculating the G and the GAVG factor were developed. The proposed equations are then adjusted for the case in which the variability of the friction factor should be considered. The validity of suggeste...

Adjusted friction correction factors for center-pivots with an end-gun

A new method for calculating total friction head loss in center-pivots with an operational end-gun was developed. The proposed methodology is based on adjusting the previous friction correction factors for center-pivots with end-guns in order to correct their paradoxes and shortcomings. Equations presented in the current work are developed for center-pivots with a finite number of outlets along the lateral and constant outlet spacing and discharge as well as constant discharge and variable spacing. The proposed formulas depend on the number of outlets along the supply pipeline, the exponent of velocity term in the friction formula used and the distance that water is jetted by the end-gun. All equations reduce to the well-established equations for the friction correction factor when the end-gun is turned off. The equations presented here compare well to the stepwise friction calculation method, yet correct slight errors in the way that these friction correction factors were calculated in the past.

Efficacy of unmanned helicopter in rainwater removal from cherry canopies

Developed was an in-field sensing system to monitor cherry canopy micro-climate.Unmanned helicopter was evaluated for canopy rainwater removal.Effect of flight altitude and payloads on rainwater removal was quantified. Rain-induced fruit cracking causes significant economic loss for fresh market sweet cherry growers annually. To prevent cherry cracking, timely removal of rainwater from fruit is the key. This study evaluated the efficacy of an unmanned middle-size helicopter to remove rainwater from Y-trellised cherry canopies. Helicopter downwash in hover at four altitudes, with and without a payload, was quantified with six anemometers deployed in tree canopies. Results showed that payload and altitude significantly affected hover downwash, which was greater at higher altitude of 7.6m above ground level (AGL) than lower altitude of 4.9m AGL with payload. In the absence of payload, hover downwash peaked at the altitude of 6.1m AGL. In the efficacy study, 5.0-mm rainwater was applied to cherry canopies by a rainfall simulation system, followed by the helicopter flying over canopies at three altitudes (4.9, 5.5 and 6.1m AGL), two travel speeds (1.3 and 2.7ms-1) and with or without payload. Rainwater removal at bottom (1.1m), middle (1.9m) and top (2.7m) of the canopies was calculated based on the change of leaf wetness of target canopies in 10min after rain. Overall, helicopter with payload flying 2.7ms-1 at 6.1m AGL removed significantly more rainwater (96.3%) from top section of canopies than groups without treatment (71.2%) and compared to other payload and travel speed conditions. Results also confirmed that the unmanned helicopter could provide sufficient downwash to remove rainwater effectively from bottom and middle canopy sections.

Modeling apple surface temperature dynamics based on weather data.

The exposure of fruit surfaces to direct sunlight during the summer months can result in sunburn damage. Losses due to sunburn damage are a major economic problem when marketing fresh apples. The objective of this study was to develop and validate a model for simulating fruit surface temperature (FST) dynamics based on energy balance and measured weather data. A series of weather data (air temperature, humidity, solar radiation, and wind speed) was recorded for seven hours between 11:00–18:00 for two months at fifteen minute intervals. To validate the model, the FSTs of “Fuji” apples were monitored using an infrared camera in a natural orchard environment. The FST dynamics were measured using a series of thermal images. For the apples that were completely exposed to the sun, the RMSE of the model for estimating FST was less than 2.0 °C. A sensitivity analysis of the emissivity of the apple surface and the conductance of the fruit surface to water vapour showed that accurate estimations of the apple surface emissivity were important for the model. The validation results showed that the model was capable of accurately describing the thermal performances of apples under different solar radiation intensities. Thus, this model could be used to more accurately estimate the FST relative to estimates that only consider the air temperature. In addition, this model provides useful information for sunburn protection management.

Direct Calculation of Thermodynamic Wet-Bulb Temperature as a Function of Pressure and Elevation

A simple analytical method was developed for directly calculating the thermodynamic wet-bulb temperature from air temperature and the vapor pressure (or relative humidity) at elevations up to 4500 m above MSL was developed. This methodology was based on the fact that the wet-bulb temperature can be closely approximated by a second-order polynomial in both the positive and negative ranges in ambient air temperature. The method in this study builds upon this understanding and provides results for the negative range of air temperatures (2178 to 08C), so that the maximum observed error in this area is equal to or smaller than 20.178C. For temperatures

Closure to ‘‘Analytical Determination of Distribution Uniformity for Microirrigation Tapered Laterals Laid on Uphill and Horizontal Slopes’’ by Sayed Hossein Sadeghi and Troy Peters

08C, wet-bulb temperature accuracy was 60.658C, and larger errors correspondedto very high temperatures (Ta

Closure to “Design of Zero Slope Microirrigation Laterals: Effect of the Friction Factor Variation” by Sayed-Hossein Sadeghi, R. Troy Peters, and Freddie R. Lamm

398C) and/or very high or low relative humidities(5%,RH,10% or RH . 98%). The mean absolute error and the root-mean-square error were 0.158 and 0.28C, respectively.

Energy Grade Line Assessment for Tapered Microirrigation Laterals

Based on the mathematical procedure presented in the discussion, the discusser concludes that Eq. (13) [Eq. (7)] is only valid under a limited design case where y 1⁄4 1. He justifies this statement by denoting that it is only under this circumstance that Eq. (12) reduces to (13). In the following, we show that this conclusion is incorrect: 1. Basically our reference equation for evaluating Hav is Eq. (13) and not Eq. (12). Eq. (12) cannot be considered as an exact solution of Hav because it is derived by substituting the following approximation equation: