Effects of spraying low molecular organic compounds on growth and nutrients uptake of rape (Brassica Chinensis L.)

【Objectives】Some low-molecular organic compounds are widely used as fertilizer assistants in foliar fertilizers for their good humectants, penetrative and adhesive properties. However, little attentions have been paid to their effects on plant growth and nutrients uptake until now. Therefor, the effects of spraying low molecular organic compounds (sorbitol, sodium gluconate and glycine) on the growth and nutrients uptake and their optimum application rate were studied in this paper. 【Methods】A pot experiment was conducted with rape (Brassica Chinensis L.) as matiral. Water was sprayed as control (CK), four spraying densities of sorbitol (30, 90, 150 and 300 mg/kg), sodium gluconate (150, 300, 600 and 1200 mg/kg) and glycine (60, 120, 250 and 500 mg/kg) were designed with four replications each treatment. Treatments were implemented since the beginning of three-leaf stage of rape and four sprayings continued with a frequency of every seven days. The rape biomass, leaf SPAD values and contents of nitrate, soluble sugar, soluble protein and main nutrients of rape were measured. 【Results】1) Compared with control, the rape biomass were increased by 9.80%, 26.37% and 25.40% in the treatment of spraying sorbitol, sodium gluconate and glycine, and the best spraying density of sorbitol, sodium gluconate and glycine were 300 mg/kg, 600 mg/kg and 250 mg/kg, and the rape yields were increased by 25.60%, 31.87% and 35.87%, respectively. 2) Compared with control, spraying proper low molecular organic compounds could improve the nutrients (N, P, K) uptake, enhance the contents of soluble sugar and protein, promote SPAD values and decrease the nitrate content of rape obviously. 3) The correlation analysis showed that there was a significant correlation of quadratic curve between the spraying concentration of the low molecular organic compounds and the biomass, nutrients uptake capacity and quality of rape, respectively, which indicated that the optimal application rate of sorbitol, sodium gluconate and glycine were 150-300 mg/kg,600-1200 mg/kg and 120-250 mg/kg, respectively. 【Conclusions】Spraying low molecular organic compounds (sorbitol, sodium gluconate and glycine) could increase the biomass, improve the quality and enhance nutrients(N, P, K) uptake of rape. The low molecular organic compounds can be sprayed directly to plant leaves as the organic nutrients as well as assistants in fertilizers.