Effects of nitrogen application rate on yield, quality, potassium uptake and utilization of daylily (Hemerocallis citrina Baroni) in protected cultivation

Objectives The purpose of this study was to identify the effects of nitrogen (N) application rate on yield, quality, potassium (K) uptake and utilization of daylily (Hemerocallis citrina Baroni) in protected cultivation, to provide theoretical support for nutrient management techniques in protected cultivation.

Methods Experiments were conducted from 2015 to 2017 at the daylily experimental station of Jiangsu Academy of Agricultural Sciences (Dingzui Town, Suqian City, Jiangsu Province). The daylily cultivar used in the experiment was ‘Dawuzui’. Five application rates of N 0, 50, 100, 150 and 200 kg/hm² (expressed as N0, N50, N100, N150, N200) were designed. The yield, quality, K uptake and utilization of daylily were analyzed at the re-greening, bolting and budding stages.

Results The N application increased the K uptake at all growth stages, and the largest increment occurred during bolting to budding stage. Compared to N0, the K uptake with N50, N100, N150 and N200 treatments significantly increased by 21.0%, 67.6%, 86.0% and 103.8%, respectively. Nitrogen application also changed the ratio of K uptake at the monitoring stages. The ratio of K uptake decreased from re-greening to bolting stage, while increased from bolting to budding stage, and N200 showed the most significant effect among the treatments. Increase of N application rate alleviated the K decrease rate at budding stage, the b values obtained in the treatments of N50, N100, N150 and N200 were 0.0051, 0.0048, 0.0045, 0.0044 and 0.0042, respectively. As the N application rate increased, the marginal effect of K uptake (i.e. increased amount of K uptake by 1 kg increase of N application) increased first and then decreased, and the daylily production efficiency of K descended steadily. In the treatments of N100 and N150, the daylily dry matter accumulation was high and more K was allocated to the reproductive organs, and the dynamic characteristic parameters of K concentration and accumulation were more optimized, which was beneficial for the yield formation and higher contents of vitamin C, amino acids, soluble sugars, flavones, and polyphenols. In the treatment of N150, the marginal effect of K uptake and production efficiency decreased, while the content of colchicine reached the highest. In treatments N0 and N50, the yields reduced, and K accumulation and economic coefficient of biomass of daylily decreased significantly, compared with other treatments.

Conclusions Under the tested condition, nitrogen application rate of 100–150 kg/hm² could promote the accumulation and transport of K, alleviate the decrease rate of K uptake in the later growth stage of daylily, thus beneficial to the formation of yield and quality related compounds as result.