Effect of different N rates on yield and benefit of edible sunflower in Inner Mongolia

Inner Mongolia Autonomous Region (IMAR) is the main sunflower-growing region, with area and production accounting for over 50% of the total in China. In IMAR, 80% of the sunflower is produced for edible nuts. The amount of nitrogen (N) required for producing 100 kg achenes is 3.8 to 4.9 kg N/ha. Farmers frequently over apply N fertilizers, resulting in low N use efficiency and low benefit. Therefore, the purpose of this project was to study the effect of various N rates on sunflower yield and benefit, providing the scientific basis for selecting the right rate of N in sunflower production.

Field experiments were conducted in Wuchuan, Jining, and Linhe counties of IMAR. The edible sunflower species used in the experiments in Wuchuan, Jining, and Linhe were 3638, SH363, SH361, respectively. Sunflower was planted using plastic mulch with five N fertilizer application rates of 0, 100, 150, 200, 300 kg N/ha, and three replicates for each treatment. The replicates of 36 m² each were randomly arranged in the field. All treatments received the same amount of phosphorus (P) and potassium (K) fertilizers at 90 kg P₂O/ha and 90 kg K₂O/ha. All P and K, and 30% of N fertilizers were row-banded basally before sowing and the remaining 70% of N was topdressed with irrigation. The crop was under drip irrigation in the Wuchan and Jining trials, while flood irrigation was used in Linhe.

Nitrogen fertilization significantly increased achene yield. The maximum yield was obtained in the 200 kg N/ha treatment at all the three locations. Achene yield increased from 15.5 to 28% at Wuchan, 11 to 23% at Jining, and 14 to 23% at Linhe, over the N control plots. Agronomic efficiency was 2.5 to 6.8, 1.5 to 5.5, and 1.8 to 5.7 kg achene/kg N; and N recovery efficiency was 17 to 41%, 15 to 44%, and 16 to 44% at the three sites, decreasing as the N application rate increased. Based on the relationship between N rates and achene yields, the N rate for maximum achene yield was 194 kg/ha in Wuchuan, 183 kg/ha in Jining, and 190 kg/ha in Linhe, with the corresponding yields being 5,970, 4,740, and 4,805 kg/ha, respectively. The economic optimum N rate, at which the marginal seed value equals the marginal fertilizer cost, was 183 kg N/ha in Wuchuan, 168 kg N/ha in Jining and 175 kg N/ha in Linhe, resulting in the maximum profits of US$940, 635, and 665/ha, respectively.