Experimental design and irrigation method

In the present study, the effect of different irrigation water treatments on black grams was investigated. The experimental design was a randomized complete block design with four aqueous treatments in three replications (Fig. 1). Water treatments included 50% (I₁), 75% (I₂), 100% (I₃) or the control treatment, and 125% (I₄) of crop water requirement. To determine the water requirement, meteorological parameters were obtained from the meteorological station of the Faculty of Agriculture of Urmia University, and the reference evapotranspiration (ET_o) was calculated by V3.1 ET_o Calculator²⁴. The equation used in this software to calculate ET_o is the FAO-modified Penman–Monteith equation²⁵. Using the following equation, the ET_o calculated by multiplying the crop coefficient (K_c)²⁶ was generalized to the potential evapotranspiration (ET_c) values of black gram (Table ​(Table33).

Plot layout of field experiment.

Black gram irrigation scheduling for control treatment (I₃), during 2017 growing seasons.

Immediately after transferring the seedling, an irrigation step was carried out to plant the seedlings in the field. The black gram is used as a second crop in the area while water stress was applied in mid-July (tenth irrigation) for optimal plant establishment. The irrigation water amounts for each treatment, ET_c and ET_o, during the crop growth period are presented in Table ​Table4.4. Plant irrigation was performed during the growing season using a 16 mm dripper pipe located next to each row²¹. The 16 mm dripper pipe had constant pressure and the flow rate of emitters was 4 L h^-1. At the beginning of each 16 mm pipe, a 16 in 16 mm valve was used to control water stress over time²¹. According to soil analysis, four fertilizer treatments were used to prevent nutrient deficiency²⁷ and these four treatments received equal amounts of fertilizers²⁸. Fertilizer was used as a spray and soil fertilizers (Table ​(Table11).

Irrigation amounts and ET_o (mm), during 2017 growing seasons.

ET_o: reference evapotranspiration.