Effects of Irrigation water salinity on evapotranspiration and spinach (Spinacia oleracea L. Matador) plant parameters in greenhouse indoor and outdoor conditions

ArticleResponse of spinach to irrigation water salinity under greenhouse indoor and outdoor conditions was investigated in this study to reveal different weather conditions on salinity tolerance of the plant. For this purpose, saline waters at six different salinities (0.65, 2.0, 3.0, 4.0, 5.0 and 7.0 dS m-1 ) were applied to spinach (Spinacia oleracea L. Matador) grown in pots. Soil salinity increased linearly with increasing salinity of irrigation water. Threshold salinity is 2.35 dS m-1 and yield lost slope after this threshold is 3.51% for indoor and threshold salinity is 2.83 dS m-1 and yield lost slope is 3.3% for outdoor. Salinity harmful effect on spinach yield is higher for indoor conditions than for outdoor conditions because of higher indoor temperatures. These results apparently showed that spinach salinity response could change with changing weather conditions especially for temperature. Yield response factors (ky), which is the ratio of relative evapotranspiration decrease to relative yield decrease, were close in the cases of irrigation water salinity in greenhouse outdoor and indoor (ky = 2.4 and 2.1), respectively. Considerable water consumption decreases because of salinity were determined. Every 1 dS m-1 increment in soil salinity caused about 1.35% water consumption decrease for spinach. Therefore, depressing effect of salinity on water consumption should be considered in irrigation and salinity management to prevent excess saline water application and to protect environment

Estimation of daily reference evapotranspiration by neuro computing techniques using limited data in a semi-arid environment

In this paper, the daily reference evapotranspiration (ET0) for Bulawayo Goetz was estimated from climatic data using neuro computing techniques. The region lacks reliable weather data and experiences inconsistencies in the measuring process due to inadequate and obsolete measuring equipment. This paper aims to propose neuro computing techniques as an alternative methodology to estimating evapotranspiration. Firstly, ET0 was calculated using FAO-56 Penman-Monteith (PM) equation from available climatic data. Data was divided into training, testing and validation for neuro computing purposes. The study also investigated the effect of different normalisation techniques on neuro computing ET0 estimation accuracy. In another application, neuro-computing ET0 estimates were compared against those obtained using empirical methods and their calibrated versions. The Z-score normalisation technique for all data sets gave best results with a Multi-layer perceptron (55-1) model having RMSE, MAE and R2 values in the range 0.120.25 mm day?1, 0.080.15 mm day?1 and 0.940.99 respectively. There were no significant differences in ET0 estimation accuracy by neuro computing techniques due to normalisation technique. The Neuro computing techniques were superior to empirical methods in ET0 estimation for Bulawayo Goetz. The Neuro computing techniques are recommended for use in cases of limited climatic data at Bulawayo Goetz