A study of 51 greenhouses in Shouguang examined the impact of chemical fertilizers and organic manure on vegetable yields through questionnaire surveys.
Results indicated that while high levels of chemical fertilizers were used, they did not significantly boost vegetable yields, whereas organic manure had a positive effect on yield.
The analysis also revealed trends over the past decade, such as a rise in organic manure use and a decrease in chemical N and P fertilizer application, leading to a more balanced N/P/K ratio in greenhouse vegetable farming.