Effect of different types of organic fertilizers on the chemical properties and enzymatic activities of an Oxisol under intensive cultivation of vegetables for 4 years

The effects of different types of organic fertilizers on the chemical and enzymatic properties of an Oxisol were studied after being fertilized for four consecutive years (26 crops) in a greenhouse under intensive cultivation of vegetables. Seven treatments, consisting of five types of organic fertilizer treatments, one 'sequential application' (SA) treatment, and a chemical fertilizer treated plot were compared. The organic fertilizers used were dairy cattle dung compost (DCDC), hog dung compost (HDC), chicken dung compost (CDC), pea residue compost (PRC) and soybean meal (SBM). After 4 years of cultivation, the soils were analyzed for their chemical properties and enzymatic activities. The microbial carbon (C) and nitrogen (N), basal respiration and nitrification rate were also measured. The results showed that the SBM significantly lowered the soil pH, and that the HDC and DCDC raised the soil pH. The SBM and CDC resulted in the lowest soil electrical conductivity. The SBM had no significant effect on soil organic C and total N contents when compared with the CF plot. However, the DCDC resulted in the highest contents of soil organic C and total N. The organic fertilizers applied did not significantly affect the soil available copper, zinc, cadmium, lead and nickel. The effects of the different organic fertilizers on soil enzymatic activities depended on the types of organic fertilizers applied. The SBM and CDC often resulted in a lower microbial C (or N) and respiration rate, while in contrast DCDC and PRC resulted in high measurements. Most of the measured soil enzymatic activities in the SBM treatment, except for acid phosphatase, were the lowest. Differing contents of different heavy metals in the organic fertilizers resulted in different Mehlich III extractable heavy metal contents in the soils. From the point of view of the soil chemical and enzymatic properties, SBM is not an appropriate organic fertilizer for continuous application to an Oxisol.