Interaction of Water and Organic and Chemical Fertilizers on Water Productivity of Garlic in Zahak Region of Sistan Plain

In this research, the effect of different levels of irrigation water, nitrogen fertilizer, and cow manure on garlic was investigated. The experiments were carried out in a split-spilt plot design, with four levels of irrigation water depths (40%, 60%, 80% and 100% of the plant water requirement) in the main plots, three levels of nitrogen (50, 75 and 100% nitrogen) in the sub- plots, and three levels of manure (25, 32.5 and 50 ton/ha  cow manure) in the sub-plots. Nitrogen was applied in two stages and cow manure in one stage before planting. At the end of the experiment, parameters such as plant height, weight, and number of garlic, yield, and irrigation water productivities were measured. The results showed that the effects of irrigation water, nitrogen fertilizer, and manure were significant (p< 1% and <5%) on all parameters. The highest yield was obtained from 100% fertilizer application and 100% water requirement, but no significant effect was observed between treatments of 100 and 80% of water requirement. The highest amount of irrigation water utilization was obtained at irrigation level of 60% and fertilizer level of 100% (1.48 kg/m3/ha). In this regard, there was no significant difference between treatments of 60% and 80% of water requirements. The amount of allicin was reduced by reducing irrigation water and reducing fertilizer use. Increasing nitrogen fertilizer up to 75% of fertilizer requirement, amounting to 150 kg/ha, resulted in increase of allicin, but higher amounts resulted in decrease of allicin content. Therefore, due to shortage of water in the region, irrigation of this crop can be done with 80% of the plant's water requirement, without a significant effect on the yield.