Effects of water and fertilizer management on yield and flavor of drip-irrigated winter-spring pepper in greenhouse production

Objectives We studied the effect of water and fertilizer rates on the yield and flavor quality of drip irrigated greenhouse pepper. The study was conducted to determine the appropriate soil water content at different growth stages, and proposing a water and fertilizer management scheme for high yield and aroma enhancement of pepper.

Methods In 2019 and 2020, an orthogonal fertigated (fertilized and drip irrigated) sheep horn pepper experiment was carried out in winter-spring season under greenhouse production. Special water-soluble fertilizers were used. Each of the two factors (water and fertilizer) had 3 levels to form 9 combination treatments. In 2019, the total water amounts were 1703.3 m³/hm² (W1), 2423.3 m³/hm² (W2), 3143.3 m³/hm² (W3), and the total amounts of fertilizer were 712.5 kg/hm² (F1), 1087.5 kg/hm² (F2), 1462.5 kg/hm² (F3). In 2020, 1913.3 m³/hm² (W1), 2753.3 m³/hm² (W2), 3593.3 m³/hm² (W3) of water and 412.5 kg/hm² (F1), 825.0 kg/hm² (F2), 1237.5 kg/hm² (F3) of fertilizer were applied. The total yield, commodity yield, the number of abnormal and blossom-end rot fruit were investigated, and the pungency and volatile aroma components of fresh fruit were analyzed. The soil water content in root zone was monitored during the growth period.

Results Irrigation significantly affect the yield of commercial fruit, fruit number, blossom-end rot fruit number (P<0.01), but fertilization rate or its interaction with irrigation had no such effects. W2 and W3 produced higher commercial fruit yield than W1 in the harvest collected from the fourth to tenth drip managements, and W3 achieved significantly higher commercial yield than W2 in the harvests collected in the sixth, seventh and ninth managements (P<0.05). W3 significantly reduced the yield of non-commercial fruit and blossom-end rot fruit, and increased the total N, P and K absorption than W1. The effect of irrigation amount on the content of main aroma components such as hydrocarbons, aldehydes, pyrazines and furanoids, the content of dihydrocapsaicin, and the activity of main odorants such as 2-methoxy-3-(2-methylpropyl)-pyrazine (the principal odorant) and (E, E)-2,4-nonadienal in fresh fruits were significant (P<0.01). The hydrocarbon, pyrazine, furanoids and dihydrocapsaicin components in pepper fruit in W1 were significantly higher than in W2 and W3. The aldehydes components of fruit in W1 and W2 were significantly higher than in W3. The odor activity values (OAV) of 2-methoxy-3-(2-methylpropyl)-pyrazine and (E, E)-2,4-nonadienal in W1 were significantly higher than that in W2, and that of W2 was significantly higher than that in W3. F2 and F3 treatments achieved significantly higher OAV of 2-methoxy-3-(2-methylpropyl)-pyrazine than F1. The average relative water contents of root zone soil in W1, W2 and W3 during the whole growth period were 51%, 77% and 88%, respectively. From the second drip management, the soil water contents of W2 and W3 were significantly higher than that of W1.

Conclusions Relatively less irrigation created a lower soil moisture around the root area, benefited the accumulation of odorants and concentration of the fruit juice, and improved the fruit quality, but the abnormal and disease fruit number increased. Moderately increasing fertilizer rate is also good for the accumulation of the main principal odorants. Overall, for aroma and spicy of fresh fruit as well as acceptable yield, irrigation amount of 2423 m³/hm² and fertilizer rate of 825 kg/hm² (W2F2) are recommended for winter-spring pepper production.