Improvement of yield and quality of greenhouse-grown pepper through basal application of fulvic acid fertilizer under chemical fertilizer reduction

Objectives Fulvic acid (FA) had been proved of beneficial effects in crop growth and photosynthesis. This paper focused on the reducing ratio of total chemical fertilizer inputs after the application of FA, so to provide an effective way of reducing chemical fertilizer input and increasing yield and quality of pepper (Capsicum annuum L).

Methods A microplot experiment was conducted using ‘Changjian’ pepper as the test material in a solar-greenhouse of Shandong Agricultural University. Conventional chemical fertilizer input of N 450 kg/hm², P₂O₅ 120 kg/hm² and K₂O 900 kg/hm² was used as control (CK), and at the base of basal applying 600 kg/hm² of fulvic acid, four reducing ratio treatments of NPK fertilizers were set up as 45% (T1), 30% (T2), 15% (T3) and 0% (T4). The dry matter weight, photosynthetic and fluorescence parameters, carbon metabolism were measured at the full fruiting stage, and the quality and yields of pepper were investigated at harvest.

Results Compared with CK, T1 treatment merely increased plant height significantly, T2 treatment increased the plant height, stem diameter, total dry matter content, sugar content and sucrose synthase (SS) activity of obviously, and T3 and T4 treatments increased plant dry matter weight, photosynthetic rate (P_n), sugar content, sucrose phosphate synthase (SPS) and SS activities notably. In all the FA applied treatments, plant leaves had lower rate of transpiration rate (T_r) and higher fruit number per plant and mean single fruit weight, and the yield of T1, T2, T3 and T4 were significantly increased by 29.48%, 13.91%, 37.79% and 26.37%, respectively. However, T1 showed the worst integrated pepper fruit quality and T3 showed the best one as its higher contents of soluble sugar, soluble protein, free amino acid and vitamin C.

Conclusions Under the experimental conditions, applying FA fertilizer 600 kg/hm² could promote the growth, accumulation of dry matter, photosynthesis, activities of carbon metabolism related enzymes as well as the yield and quality of pepper. With this FA rate, total chemical fertilizer input could be reduced by 30% for keeping high quality and yield, and reducing 15% would increase the growth and activities of carbon metabolism related enzymes in fantastic range, thus increase the yield and quality of pepper. As the result is from one season, the long-term effect of FA fertilization on the reducing potential of chemical fertilizer should be further studied.