Mitigate nitrate contamination in potato tubers and increase nitrogen recovery by combining dicyandiamide, moringa oil and zeolite with nitrogen fertilizer.

Potato is considered a nitrogen (N) intensive plant with a low N use efficiency (NUE). The current study introduced an excellent approach by combining dicyandiamide (DCD), moringa seed oil (MSO), or zeolite (ZE), with N fertilizer for maximizing potato tuber yields and NUE as well as minimizing tubers nitrate (NO ₃ ^- ) accumulation. The impact of these materials on soil N availability and gaseous emissions (NH ₃ , and N ₂ O) was investigated under incubation conditions. A 2-year field experiment were carried out with seven treatments [without N (control), N fertilizer (350 kg N-urea ha ^-1 as a recommended dose; Urea _RD ), 75% of N recommended dose with DCD (Urea _75%RD +DCD), Urea _75%RD with 2% MSO (Urea _75%RD +MSO _2% ), Urea _75%RD with 4% MSO (Urea _75%RD +MSO _4% ), Urea _75%RD with 0.5 Mg ZE ha ^-1 (Urea _75%RD +ZE _R1 ), and Urea _75%RD with 1.0 Mg ZE ha ^-1 (Urea _75%RD +ZE _R2 )]. We also conducted a 40-days incubation trial with the same treatments; however, urea was added at the rate of 200 mg N kg ^-1 soil for all treatments, excluding the control. The addition of DCD, MSO, and ZE with urea under incubation conditions delayed the nitrification process, thereby causing a rise in NH ₄ ⁺ -N content and a decrease in NO ₃ ^- -N content. Ammonia-oxidizing bacteria (AOB) was inhibited (p ≤ 0.01) in treatments Urea+DCD, Urea+MSO _4% , and Urea+ZE _R2 . The highest NUE indexes were recorded in treatment Urea _75%RD +DCD. The highest NO ₃ ^- accumulation (567 mg NO ₃ ^- kg ^-1 ) in potato tubers was recorded in treatment Urea _RD . Whilest, the lowest NO ₃ ^- content (81 mg NO ₃ ^- kg ^-1 ) was in treatment Urea _75%RD +DCD. The lowest cumulative N ₂ O emissions and highest cumulative NH ₃ volatilization were observed in the treatment Urea+DCD under incubation conditions. Our findings demonstrated that N fertilizer rate could be reduced by 25%, while the tuber yields increased with an acceptable limit of NO ₃ ^- content, resulting in economical, agronomical, and environmental benefits.
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