Enhancement of Yield and Nitrogen and Water Use Efficiencies by Nitrogen Drip‐Fertigation of Garlic

Two field experiments were conducted to evaluate response of garlic yield, and nitrogen (N) and water use efficiencies (NUE and WUE) to N applied by fertigation or conventional soil application. The following treatments were included: 0, 30, 60, and 90 mg L-1 N in the irrigation water. Additional two treatments of soil application of N (single or split) equivalent to one fertigation treatment were included. Garlic was planted in two growing seasons. Irrigation was applied to replenish 80% of the Class A pan evaporation twice each week. Neutron probe readings were taken at different soil depths and used to determine crop evapotran‐spiration (ETc), WUE, and crop coefficient (Kc). Labeled N fertilizers (15N) were applied to a micro‐plots within each plot. At harvest, plant samples were taken from the micro‐plots for 15N measurements and NUE determination. Sampling from macro‐plots was used to determine yield. Results indicate that yield responded positively to N regardless of method of application. Yield increased by fertigation of 120 kg ha-1 N in the first season and by the lower rate (75 kg ha-1 N) in the second season. In both seasons, higher yield response was obtained by fertigation than by soil application of N. Split application of N at 120 kg ha-1 produced yields as high as by higher rate (180 kg ha-1 N) with single soil application in the first season. The fresh weight per head and per bulb had similar trends as the yield did. However the number of bulbs per heads was not affected by the treatments in both seasons, indicating that with zero N smaller heads were produced and yield differences were due to the size and weight of the bulbs or heads. With fertigation, N content, N derived from fertilizer (Ndff), and consequently higher NUE were enhanced due to the more efficient timing and placement of N. Nitrogen addition synergistically enhanced fruit content of phosphorus (P), potassium (K), iron (Fe), and zinc (Zn) which was higher with fertigation technique. Nitrogen fertigation enhanced plant growth, ETc, and WUE. The average Kc ranged from 0.4 at the earlier growth to 1.1 during maximum growth stages. Towards the end of the growing season, it declined to 0.6. The maximum water depletion was observed in the top 30 cm, indicating the depth of root activity. The overall results indicate that with fertigation, the yield, NUE, and WUE could be improved.