Crop water requirements of date palm based on actual applied water and Penman–Monteith calculations in Saudi Arabia

This study was conducted in eight different regions of Saudi Arabia to estimate monthly and annual crop water requirements (CWR). Fields that have been selected are located in regions of the Medina (Al Ula), Tabuk (Teimaa), Makkah (Al Jumum), Al Jouf (Sakakah), Riyadh (Sodos), Qassim (Riyad Al Khabra), Hail (AL Kaedh), and East Region (Al Ahsa). The determination of CWRs was based on Penman Monteith method, field water balance, actual water applied in each field, and actual water applied by farmers in adjacent fields. The results based on Penman–Monteith method showed that the crop evapotranspiration, ETc (mm/year) of the sites in, Medina, Tabuk, Makkah, Al Jouf, Riyadh, Qassim, Hail, and East Region were 2418.75, 1940.51, 1837.76, 2259.03, 2139.23, 2207.41, 2008.23, and 2144.87 mm/year, respectively. The CWRs (m3/ha) after taking into account the proportion of cultivated area for each tree were: 9495.24, 7340.18, 7298.93, 8913.59, 8614.96, 8568.68, 7996.99, and 8510.72 m3/ha, respectively. The average date palm numbers were 100 trees/ha. The total annual CWRs (m3/tree) in these sites were 95, 73.4, 73, 89, 86, 85.7, 80, and 85 m3, respectively, as the radius of shaded area per tree is 3.5 m with an effective diameter of 90%, and the rate of leaching was 12, 8, 13, 12, 14, 11, 13, and 13%, respectively. The average overall irrigation water requirements was 8342.41 m3/ha/year (1 ha. = 100 trees). The results of water balance method showed that the water consumed for Qassim and Al Jouf was 3604.31 and 3515.25 m3/ha/year, respectively. The actual irrigation water added by a flow meter for all study sites was 11,305.0, 9463.9, 9692.0, 11,252.75, 1007.40, 10,035.0, 10,272.5, and 10,082.8 m3/ha/year, respectively, while these amounts added by the farmers in adjacent fields were 13,717, 12,277, 12,220, 13,340, 12,050, 12,880, 12,620, and 12,610 m3/ha/year, respectively.