Effects of combined use of controlled-release urea and conventional urea on biological properties of Chrysanthemum morifolium‘Hangbaiju’

【Objectives】 The conventional urea and controlled-release urea are the commonly used N fertilizers in the cultivation of Chrysanthemum morifoliumHangbaiju. Previous researches about the two fertilizersfocused on their yield and quality effects, fewer on effects of their combined use on the soil biological characteristics. The effects of normal and minimized amount of controlled-release urea combined with conventional urea on the soil biological characteristics were studied in the paper. 【Methods】 Field experiments were carried out with two fertilization levels and six treatments. The suitable fertilization rates of N 120 kg/ha, P5O2 106 kg/ha and K2O 189 kg/ha, respectively.There were three treatment under suitable fertilization: No N fertilization with suitable application of P and K (CK1); Suitable rate of single conventional urea(Urea), 50% of N as basal fertilizer, 15% topdressing on 15 July, 25% on 15 August and 10% on 15 October (T1); Suitable nitrogen amount of controlled-release urea combined with conventional urea(RUrea), 50% of controlled-release urea (control release time 150 days) combined with conventional urea as basal fertilizer, 50% of controlled-release urea(control release time 90 days) combined with conventional urea used as top dressing on 15 August(R1). Minimized rate of N, P5O2 and K2O were 90, 80 and 142 kg/ha, respectively. The fertilization pattern was the same as suitable fertilization.There were also three treatments under minimized fertilization:No N fertilizer with P5O2 and K2O of 80 and 142 kg/ha, respectively(CK2); Minimized amount of single conventional urea (T2); Minimized fertilizer amount with controlled-release urea and conventional urea combined use (R2). 【Results】 1)The available soil N contents were higher in treatments of suitable fertilizer amount than in minimized fertilizer treatments. Compared with urea, the soil available N contents with RUrea were increased by 33.55% under suitable fertilization, and 120.35% under minimized fertilization, respectively. 2) In all treatments, the population changes of both soil bacteria and actinomyces were in shape of single-peak curve, the highest population of bacteria was in July and that of actinomyces in August. The population changes of fungi in the soil exhibited a mono-peak curve under suitable fertilization, a bimodal curveunder minimized fertilization. Compared with single urea, the population of both bacteria and fungi in the soil treated byRUrea increased by 10.39% and 39.83% under suitable fertilizer amount, respectively, the increase were 46.44% and 51.81% under minimized fertilizer amount. The amount of actinomyces in the soil treated with urea increased by 127.84% under suitable fertilizer amount compared to minimized fertilizer amount, no significant difference between the suitable and minimized fertilization ofRUrea; 3) Under minimized fertilization, the activities of peroxidase increased by 76.79% in the soil treated with theRUrea, and 164.14% in the soil treated with urea compared to suitable fertilization. The activities of soil polyphenol oxidase inurea were greater than RUrea under the same fertilization rate. The activities of soil phosphatase was higher in suitable urea thanin minimized treatment, but on the contrary in the treatments of RUrea. Under the same fertilization pattern, the urease activities in the soil treated by minimized fertilization was greater than by suitable fertilization. 【Conclusions】 Suitable fertilization was favorable to enhance the available nitrogen content, increase soil bacteria and actinomyces population, and the combined use of controlled-release urea with conventional urea has more remarkable effects than single conventional urea. When the fertilizer are the combination of controlled-release urea and conventional urea, there is no obvious difference in the actiomyces population between the suitable and minimized fertilizer amount, but with single conventional urea application, the actiomyces population is obvious higher in the soil treated with suitable fertilization than with minimized fertilization. With controlled-release urea combined with conventional urea, the suitable amount of fertilization decrease the activities of polyphenol oxidase and peroxidase, indicating that suitable fertilization with nitrogen being controlled-release urea combined with conventional urea was favorable to sustain good environment.