Osama Mohawesh

Comparison of Hargreaves and FAO56 equations for estimating monthly evapotranspiration for semi-arid and arid environments

The objectives of this study are to compare reference evapotranspiration (ET0) computed using different forms of the Hargreaves (HG) equation with the standard FAO56PM; and to compare ET0 computed using the FAO56PM with limited data with the standard FAO56PM complete data set method. For this purpose, climatic data from 12 weather stations covering an area of ∼90 km2 of predominantly arid and semi-arid conditions are used. Ratios of ET0 estimated using the updated HG equation were closer to 1 when compared with the HG equations and ET0-est. Also, RMSE, ME and R 2 ranged from 0.235 to 0.526 mm day−1, −0.526 to 0.383 mm day−1, and 0.945 to 0.989, respectively. Therefore, the updated HG equation can be used for ET0 estimates instead of using the FAO56PM method with acceptable accuracy. In addition, it was found that the standard FAO56PM can be used with estimated solar radiation and humidity from temperature data and estimates of mean wind speed. In conclusion, this study produced two accurate methods that can be used to calculate monthly ET0 in conditions characterized by limited data, arid and semi-arid environments.

Effect of irrigation regimes on water use efficiency and tomato yield (Lycopersicon esculentum Mill.) grown in an arid environment

This study was conducted to determine the influence of irrigation regimes on yield of two tomato cultivars – TY-DANA and GS12. Experimental treatments were three irrigation intervals (2, 4, and 6 days), and three irrigation quantities (50%, 75%, and 100% of pan evaporation [Ep]). The total yield increased with increasing amount of irrigation water for both cultivars. The total yield increased about 10% and 17% for 100% of Ep treatment compared with 50% Ep treatment for TY-DANA and GS12 cultivars, respectively. The 100% Ep treatment showed the lowest irrigation water use efficiency (IWUE) (16.7 and 10.4 kg m−3), while 50% Ep showed the maximum IWUE (23.9 and 17 kg m−3) for TY-DANA and GS12 cultivars, respectively. The average fruit weight for 100% Ep treatment was usually higher than the other treatments. Generally, yield decreased using 50% Ep, however, the benefits of increasing IWUE and saving around 50% of irrigation water will help to grow crops in more areas and in managing the limited water resources in arid environments.

Effects of deficit irrigation on tomato and eggplant and their infection with the root-knot nematode under controlled environmental conditions

Deficit irrigation has been widely investigated as a valuable strategy for dry regions where water is the limiting factor in crop cultivation. Soil moisture can be one of the important factors that influence root-knot nematode (RKN) disease development. To determine how different levels of irrigation can affect disease development, irrigation regimes ranging from 20% to full field capacity (FC) were applied to tomato and eggplant plants inoculated with Meloidogyne javanica (M. javanica) under controlled conditions. In addition, in vitro bioassays were done to evaluate the effect of water potential and soil moisture content on M. javanica viability in the soil and reproduction on plant hosts. The relative egg hatching percentage decreased significantly with decreasing water potential from –0.1 to –1 MPa. The use of 80% irrigation level caused minor reductions in growth but significantly reduced nematode infection load. Nematode infection was reduced even further at lower levels of irrigation, however this also led to marked reductions in fresh and dry weights of the tomato and eggplants. Therefore, deficit irrigation could be used at a rate of 80% or 60% of FC to increase water use efficiency and reduce the level of RKN (M. javanica) infection without greatly reducing the growth performance of tomato and eggplant crops.

Field evaluation of deficit irrigation effects on tomato growth performance, water-use efficiency and control of parasitic nematode infection

Two field experiments were conducted using a common tomato cultivar (GS12) to assess the effect of deficit irrigation (DI) regimes on tomato growth performance, and on root-knot nematode Meloidogyne javanica galling and abundance. Irrigation treatments consisted of five irrigation regimes: 20%, 40%, 60%, 80% and 100% of field capacity. The results showed that DI decreased significantly leaf area, relative water content, water potential, minerals content and chlorophyll content. The 80% irrigation regime caused minor reductions in plant growth, but significantly reduced nematode infection load. Nematode infection was reduced even further at higher levels of water deficit, but this also led to marked reductions in fresh and dry weights of tomato. Total tomato yield, fruit soluble solids, and acidity were decreased with increasing irrigation water deficit. Water-use efficiency was lowest in the 100% irrigation regime and highest in the 20% irrigation regime among the irrigation treatments. The results indicated that the DI at a certain limit decreased M. javanica infection without causing significant reductions in tomato growth performance.

Greenhouse evaluation of deficit irrigation on the growth of tomato and eggplant and their interactions with Meloidogyne javanica

Deficit irrigation is considered to be an important approach for crop cultivation in dry regions where water resources are scarce. Deficit irrigation can be used also to decrease the level of infections by some moisturedependent plant pests and diseases such as root-knot nematode disease. Therefore, deficit irrigation at levels of 20%, 40%, 60% and 80% of field capacity was evaluated on tomato and eggplant in either the presence or absence of the root-knot nematode Meloidogyne javanica under greenhouse conditions. At irrigation levels of 20%, 40% and 60%, there was a significant decrease in leaf area, leaf water potential and growth parameters of tomato and eggplant compared to 80% and 100% of field capacity. In addition, a significant reduction in root galling and final nematode population occurred with deficit irrigation levels. Therefore, deficit irrigation at 80% of field capacity can be used to enhance water use efficiency and to increase the effectiveness of the current control strategies to control M. javanica without greatly affecting the growth of tomato and eggplant. However, more studies are still needed to confirm these results under different field conditions.

Root-Knot Nematode (Meloidogyne javanica) – Deficit Irrigation Interactions on Eggplant Cropped under Open Field Conditions

Abstract To investigate the influence of deficit irrigation on the root-knot nematode, Meloidogyne javanica, and its interaction with the eggplant crop, field experiments were conducted at two drip-irrigated agricultural areas in Jordan. Effects of limiting irrigation levels to 80, 60, 40 and 20% of the field capacity (FC) were compared with full irrigation (100%) treatment. Growth of eggplant plants was greatly reduced at irrigation levels of 40 and 20% FC at one field location, suggesting that the influence of deficit irrigation is field-dependant. Fruit yield was similar at all irrigation levels, except at 20% level, where a lower yield was noticed compared to 100% irrigation. Root galling of eggplant caused by the nematode was significantly lower at irrigation levels of 20 and 40% than 80 and 100% of FC, but was field-dependant at 60% of FC. The final nematode population was obviously lower at irrigation levels of 20, 40 and 60% than 80 and 100%. Thus, deficit irrigation to levels of 40 or 60% of FC can be utilised for the management of M. javanica infection in eggplant under field conditions.

Artificial neural network for estimating monthly reference evapotransiration under arid and semi arid environments

The objective of this study is to investigate the potential of artificial neural networks (ANNs) for estimating reference monthly evapotranspiration under arid and semi-arid environments. A simple leave one out data analysis was carried out; one neural network solution on six inputs and another six network solutions on five inputs for each monitoring station were done. Comparison of the results showed that the accuracy of ANNs is decreased when relative humidity, wind speed and solar or extraterrestrial radiation are excluded as input variables. The results also showed that monthly evapotranspiration could be computed with relatively good accuracy compared with local calibrated Hargreaves equation based on air temperature using trained ANNs at another location. We conclude, based on our overall results, that temperature-based method ANNs can be used with relatively good accuracy for water resource management, irrigation scheduling and management, and environmental assessment when data are not enough using trained ANNs from another location.

A unique value function for an optimal control problem of irrigation water intake from a reservoir harvesting flash floods

Operation of reservoirs is a fundamental issue in water resource management. We herein investigate well-posedness of an optimal control problem for irrigation water intake from a reservoir in an irrigation scheme, the water dynamics of which is modeled with stochastic differential equations. A prototype irrigation scheme is being developed in an arid region to harvest flash floods as a source of water. The Hamilton–Jacobi–Bellman (HJB) equation governing the value function is analyzed in the framework of viscosity solutions. The uniqueness of the value function, which is a viscosity solution to the HJB equation, is demonstrated with a mathematical proof of a comparison theorem. It is also shown that there exists such a viscosity solution. Then, an approximate value function is obtained as a numerical solution to the HJB equation. The optimal control strategy derived from the approximate value function is summarized in terms of rule curves to be presented to the operator of the irrigation scheme.

Comparing a Smartphone Irrigation Scheduling Application with Water Balance and Soil Moisture-based Irrigation Methods: Part I—Plasticulture-grown Tomato

A new smartphone irrigation scheduling application (VegApp) was compared with current irrigation scheduling recommendations and an automated soil moisture sensor (SMS)–based irrigation system in southern Georgia during Spring 2016 and 2017. Plants were grown using plastic mulch and drip irrigation following standard production practices for watermelon (Citrullus lanatus) in Georgia. The VegApp irrigation regime was based on evapotranspiration (ETo) values calculated from real-time data collected from a nearby weather station. Current irrigation scheduling recommendations use a water balance (WB) method. The WB method uses historic averages for determining ETo rates for the season. Water applied, soil water tension at 6-, 10-, and 14-inch depths, yield, and fruit quality were evaluated. In 2016, the SMS-based irrigation plots applied the least water. In 2017, the lowest amount of water was applied to plants grown using the VegApp. Total marketable yields were not significantly affected by irrigation regime. However, 45-count fruit yields were affected by irrigation in 2017. Plants grown using SMS-based irrigation had significantly higher yields of 45-count fruit than those grown using theWBmethod. Irrigationwater use efficiency (IWUE)was affected by irrigation treatment and year. The SMS-irrigated plants had the greatest IWUE, although it was not significantly different from plants grown using the VegApp irrigation program. Internal quality parameters including, firmness, hollow heart, and total soluble solids (TSS) were not significantly affected by irrigation scheduling during the study. The results suggest that overall water applications may be reduced and yields maintained when using VegApp compared with traditional WB methods of irrigation scheduling.

Development of Pedotransfer Functions for Estimating Soil Retention Curves and Saturated Hydraulic Conductivity in Jordan Valley = تطوير معادلات التنبؤ ( PTFs ) بمنحنيات الشد الرطوبي و الموصلية الهيدروليكية للترب الزراعية في وادي الأردن

Two hundred disturbed and undisturbed soil samples were collected from three depths: 0-15, 15-30 and 30-60 cm. Particle size distribution, organic matter, alkalinity, electrical conductivity, and saturated hydraulic conductivity were determined for each soil sample. The soil water retention curve for each soil sample was measured at matric potentials of 0, -20, -40, -60, -80, -100, -330, -500, -1000, -3000, -5000, -10000, and -15000 hPa. The developments of PTFs for soil hydraulic properties were done using backward multiple regression analysis. The performance of all developed PTFs showed that as more input variables were included, mean error (ME), mean absolute error (MAE), and root mean square error (RMSE) were decreased; intercept and slope also of the linear regression analysis were become closer to zero and one, respectively. The developed PTFs were evaluated using 30 independent soil samples which were not used in PTFs development. The regression coefficient, ME, MAE, RMSE, intercept and slope were relatively close to the developed PTFs. Additionally, the correlation between predicted and measured properties were not significantly different at 0.05 level. It was noticed that the developed PTFs performed well in predicting soil hydraulic properties. As a result, this suggests that the developed PTFs can be used to estimate soil hydraulic properties using the basic soil properties instead of using available PTFs which is estimation and performance should be assessed as the soils used in its development were relatively dissimilar from our soils.