Nitrogen Utilization Characteristics of Sisal on Different Nitrogen Rates, Using ~(15)N Isotope Tracer Technique
Pot experiment and15 N tracer technique were used to explore the effects of different nitrogen levels on the growth and nitrogen utilization characteristics of sisal. Four levels of nitrogen fertilizer were: none, low(0.69 g),medium(0.98 g) and high(1.24 g). The results showed that plant height, leaf length, leaf width, leaf fresh weight and water content of the leaf increased significantly when using nitrogen fertilizers. The content of N and the amount of N accumulation of the aboveground parts and roots increased as the application of nitrogen fertilizers increased. The uptake of N from the fertilizer( Ndff) by above-ground parts and roots all increased with the N rates. The percentage of N from the fertilizer(%Ndff) ranged between 24.2% and 32.6% when calculated by the tracer method, and 34.6%-53.1% when calculated by the difference method. N uptake efficiency of plants ranged between 20.0% and 22.0% when calculated by the tracer method, and 30.0%-35.7% when calculated by difference method, whereas no significant differences were found between the treatments. The results showed that(1) the uptake of N from the fertilizer was higher than from soil,(2) the N uptake efficiency of sisal was low,(3)the values of the percentage of N from the fertilizer and N uptake efficiency that calculated by the tracer method were lower than that calculated by the difference method.