Study on Nutrient Release Characteristics of Controlled Release Urea and Its Application Effects on Rapeseed
|School||Huazhong Agricultural University|
|Keywords||rapeseed controlled release urea nitrogen recovery efficiency net income soil inorganic nitrogen|
Nitrogen plays important roles in rapeseed production. Many studies have shown that nitrogen use efficiency in rapeseed is only about34%. Nitrogen loss is a very serious problem, which not only caused lots of economic and energy losses, but also induced a series of environmental problems. Furthermore, the growth period of winter oil rape is very long, which usually needs topdressing2-3times, so a lot of labor input increases in the whole growth period. Therefore, improving the fertilizer use efficiency, decreasing application frequency, and developing simplified and high effective fertilization are key issues in rapeseed production. The application of controlled-release fertilizers (CRFs)/slow-release fertilizers (SRFs) is an important way to resolve these problems. The aim of the present study was to investigate the nutrient release characteristics of the rapeseed special controlled release urea (CRU), and to determine the effect of CRU application on the growth index yields, nitrogen accumulation, nitrogen recovery efficiency, profit of rapeseed, and soil nutrients using multi-point filed experiments. We hope the results could provide the theoretical basis for controlled release urea rational application on rapeseed. The main results were showed as follows:1The "dissolution rate in water" method was used to study the nitrogen nutrient release characteristics of rapeseed special controlled release urea (CRU). The results showed that the nutrient day average release rate increased first and decreased afterwards, reached maximum (2.6%) in30days. The initial nutrient release rate and cumulate nutrient release rate in28days were1.0%and59.2%, respectively. The period of nutrient release was50days, which met with the Chinese standards for evaluating the nutrient release characteristic of slow release fertilizers.2The "dissolution rate in soil" method was used to study the nitrogen nutrient release characteristics of rapeseed special controlled release urea (CRU) in different soils. The results showed that the cumulate nutrient release of CRU had no significant difference in three types of soil at the field temperature conditions. The N cumulative release rate of CRU is less than10%in the first day, with slow release rate in different degrees. At the beginning (1-7d), the nutrient release rate increased slowly, but it rapidly increased from the7th day to60th days after experiment, reached to60percent60days later in three types of soil, and increased very slowly after60days. The change of soil inorganic nitrogen content are similar in different soils after the CRU application, while the content of NH4+-N and NO3-N varie greatly with different trends. There was a significant positive linear correlation between accumulative nutrient release rate of CRU in soil and that in water, and its correlation coefficient (r) was greater than0.967.3The pot experiment was conducted to investigate the effect of CRU application on soil inorganic nitrogen content. The application of CRU increased soil inorganic nitrogen content obviously compared to the treatment of total N application as base (UB) between30and140day. Moreover, the peak value of NH4+-N, NO3--N and inorganic nitrogen content of the CRU treatment delayed compared to the treatment of UB. The results suggested that the CRU has more obviously slow-release effect as nitrogen fertilizer than the UB, which can guarantee the nitrogen supply in the middle and late period for the growth of rapeseed. In addition, the soil inorganic nitrogen content of the treatment of total N split application (UD) reached the peak value at the thirtieth day and the hundredth day after the experiment started.4Six field experiments were conducted to study the effect of controlled release urea (CRU) on the yield, nitrogen recovery efficiency of rapeseed and soil nutrient in the main cultivation area. The results showed that the application of CRU promoted the growth of rapeseed significantly and guaranteed the nitrogen supply in the middle and late period sufficiently. The SPAD value and green leaf number of individual plant increased significantly compared to the treatment of total N as base fertilizer (UB). The application of CRU increased the yield of rapeseed by7.1%～32.5%and the net income by525.1Yuan/hm2. The application of CRU also significantly increased dry matter, nitrogen accumulation of rape, and nutrient recovery efficiency, compared to the treatment of UB in the middle and late period. The dry matter in seedling, bud, blooming, and mature period increased by-33.5%～-10.4%,-10.2%～22.4%,2.4%～26.6%, and1.8%～23.7%, the nitrogen accumulation increased by-28.4%～-7.4%,2.4%～21.4%,5.4%～23.4%, and12.7%-21.4%, and the nitrogen fertilizer recovery efficiency increased by-8.6～-0.6(-5.2) percentage points,1.1～15.2(5.4) percentage points,2.2～16.8(10.0) percentage points, and9.3-16.8(13.6) percentage points, respectively. The soil inorganic nitrogen and available nitrogen in tillage layer soil increased1.3～15.6mg/kg and2.4-34.5kg/hm2compared to the UB treatment after the experiment, respectively. Other index including pH value, organic matter, total nitrogen, available P, and available K had no difference between the treatment CRU and UB.There was no significant difference in the growth indexes, yield, dry matter, N accumulation and N recovery efficiency between the CRU treatment and the treatment total N split application (UD), while the net income increased by78.0-760.8Yuan/hm2. After the experiment, the soil inorganic nitrogen and available nitrogen in tillage layer soil increased by0.7-13.3mg/kg and6.0-44.0mg/kg, respectively. Therefore, the application of CRU could significantly decrease the N loss.5The effect of combined application of urea and controlled release urea (CRU+U) on rapeseed was studied. The results showed that combined application (CRU+U) increased the yield of rapeseed by11.4%-12.9%, and increased the profit by488.9-1040.2Yuan/hm2compared to the treatment of total N application as base (UB). There was no significant difference in the yield and dry matter between the CRU treatment and CRU+U treatment, while the profit increased by205.3-599.0Yuan/hm2with the CRU+U treatment. In addition, the dry matter and nitrogen accumulation were UB=CRU+U>CRU, the combined application of CRU+U was beneficial to rapeseed growth in seedling stage. The dry matter and nitrogen accumulation showed CRU=CRU+U> UB in mature stage. There was no significant difference in nutrient recovery efficiency between the CRU treatment and the CRU+U treatment, while which increased by7.6percentage points compared to the treatment of total N application as base (UB). After harvest, the soil inorganic nitrogen showed CRU> CRU+U> UB in all test site. The soil inorganic nitrogen of CRU+U treatment decreased by19.6%-38.8%compared to the CRU treatment, but increased by5.0%-44.2%compared to the UB treatment.