Response of Allium crops to nitrogen fertilization rates and different irrigation water sources

Two field experiments with onion and garlic were carried out on clay loam soil under different water sources (i.e. fresh, drainage and mixed) in interaction with four rates of N (30%; 45 and 60 kg N fed-1, 60%; 90 and 120 kg N fed-1, 90%; 135 and 180 kg N fed-1 and 120%; 180 and 240 kg N fed-1 of the recommended rate for onion and garlic, respectively) to assess its effects on growth attributes and yield as well as following up the changes of some soil chemical properties after the growing seasons. The side effect of using low water quality on soil properties and water relations was also traced. Drainage and mixed water significantly increased the EC, pH and sodium adsorption ratio (SAR) of the soil under both crops comparing to the fresh water. This was more vigorous under 120% nitrogen rate. In soil irrigated with fresh water, EC were decreased by ~ 26.5% under the initial level on base of over all mean of nitrogen treatments. The low quality waters reflected decrements in EC values by about 10.6% under initial and increments by about 9.7% over the initial for mixed and drainage water, respectively. In meanwhile, the SAR values increased after growing seasons with all water sources, and it affected by water quality where it increased as the low water quality applied, whereas it recorded the highest value with drainage water followed by mixed water. Additionally, the application of 60 and 90% reveal a slight increase in soil chemical properties as the mixed and drainage water were used.
Fresh water treatment increased growth and crop yields for both garlic and onion compared to mixed and drainage water treatments. Increasing N rate from 30 up to 120 % of the recommended N rate significantly increased garlic yield by 53.9% and onion yield by 16.3%. The highest WUE for onion (7.44 and 6.79 kg m-3) and for garlic (3.33 and 3.00 kg m-3) resulted from 120 % of the recommended N rate with fresh and mixed water, respectively.