Reducing use of paclobutrazol through reasonable fertilization for high yield and quality of Sichuan main-grown Ophiopogon japonicus

Objectives A growth regulator, paclobutrazol (PP₃₃₃), is often abused in Ophiopogon japonicus production in Sichuan. Long-term over-application of PP₃₃₃ has caused soil acidification and available nutrient leaching, which reduce the yield and quality of Ophiopogon japonicus product, and impact its exportation. The purpose of this study was to buildup reasonable N, P and K fertilizer ratio to reduce the use of PP₃₃₃ in Ophiopogon japonicus production.

Methods A quadratic orthogonal rotation combination design with 4 factors and 5 levels was applied in a field experiment. Taking current fertilizer management as standard, the levels of 2, 1, 0, –1 and –2 for nitrogen fertilizer rates were 3200, 2500, 1800, 1100 and 400 kg/hm², for phosphorus fertilizer rates were 4100, 3100, 2100, 1100 and 100 kg/hm², for potash fertilizer rates were 1760, 1333, 907, 480 and 53 kg/hm², and for PP₃₃₃ were 150, 112.5, 75, 37.5 and 0 kg/hm², making total of 36 treatments in the experiment. At harvest stage, the development characters of roots and leaves, the dry weight ratio and root/shoot ratio of Ophiopogon japonicus were investigated.

Results The experimental factors had significant effects on root weight, root dry weight, leaf weight, leaf dry weight, leaf length, and root/shoot ratio, but did not affect leaf number, leaf width, tiller number, root number, fibrous root number, fibrous root length, and drying rate. With the increase of nitrogen levels, leaf length, leaf weight, leaf dry weight, root weight, and root dry weight decreased. With the increase of phosphate levels, leaf dry weight increased first and then decreased, while root to shoot ratio decreased first and then increased. With the increase of potash levels, leaf weight and leaf dry weight increased, and the fresh root weight decreased first and then increased, and ratio of root to shoot (dry) decreased. With the increase of PP₃₃₃ levels, leaf length, leaf weight, leaf dry weight, root weight, and root dry weight all decreased. Among all the factors that affected growth of aerial part of plant, PP₃₃₃ had the greatest contribution, while among the factors that affected yield, nitrogen fertilizer had the highest contribution.

Conclusions Yield can be guaranteed by appropriate fertilization and the use of PP₃₃₃ can be decreased by 41% compared with typical rate used in Ophiopogon japonicus production. For Ophiopogon japonicus yield being over 3100 kg/hm², the appropriate rate is urea 799–1051 kg/hm², single superphosphate 1904–2296 kg/hm², potassium sulphate 823.31–900.69 kg/hm² and PP₃₃₃ 44.25–58.88 kg/hm².