The application of organic fertilizers on farmland increases agricultural productivity by increasing the nutrient content of the soil and promoting microbial growth. The effect of application of oil cake, one of the organic fertilizers, on the growth of the jujube and soil bacterial community was evaluated by comparing it the with effects of chemical fertilizer application. Fertilizer amendment was carried out every March from 2017 to 2020 on the basis of nitrogen content after soil test.
The application of oil cake increased the length of the fruiting stem of the new branch and the number of fruit set. As a result, compared to chemical fertilizer application, the marketable yield of jujube increased with fruit yield larger than 28 mm. Fruit weight and solid content were also found to be greater in the oil cake treatment than in the chemical fertilizer treatment. On the other hand, oil cake amended soil had increased exchangeable cation content compared to chemical fertilizer amended soil.
Principal coordinate ordination plots showed clear clustering of soil bacterial communities according to fertilizer application. The species abundance indices (OTUs, Chao1, Ace) and the species diversity indices (Shannon, Inv-simpson) of the soil samples were higher in oil cake fertilized soils than chemical fertilizer treatment. At the bacterial phyla level, Proteobacteria, Bacteriodetes and Verrucomicrobia were significantly more abundant in oil cake fertilized soils than in chemical fertilized soils, indicating altered bacterial community composition. The predicted functional genes that were significantly higher in the oil cake amended soils compared to chemical fertilized soils are mainly involved in soil nutrient cycling, plant growth promotion, and organic matter degradation.
These results imply that the soil chemistry and bacterial community were changed due to the oil cake application in the jujube orchard with a consequent improvement in the growth and yield of jujube. Therefore, it is recommended that oil cake application could be used for continuous soil nutrient management in jujube orchards.