Studies On Characteristics Of Absorption, Distribution And Utilization Of Different ¹⁵N-labeled Fertilizers In Rubber Tree Seedlings

Reasonable nitrogen (N) fertilizer application is one of important approachs maintaining rubber tree growth and high latex yield. Few studies have been conducted on different N-fertizers uptake, distribution and utilization characteristics of rubber tree in recent years. To achieve this objective, greenhouse pot experiment was conducted on a Ferralsol (Oxisol) by using 15N tracer technique from 2009 to 2010. The rubber tree clone used was SCATC 7-33-97. The treatments were no N application (CK),15N labeled CO(NH2)2,15N labeled (NH4)SO4,15N labeled Ca(NO3)2 and 15N double labeled NH4NO3, the N amount was 2g N/pot. The main conclusions obtained are as follows:(1) The leaf N derived from fertilizer (Ndff,%) of all treatments increased with the time of application extended; under the same growth stage, leaf Ndff followed: NH4NO3-15N> Ca(NO3)2-15N> (NH4)2SO4-15N> CO(NH2)2-15N.(2) Ndff of different organs in four N treatments all followed:cambium> trunk> trunk bark> coarse root, fine root, and leafstalk (Ndff of the three organs were similar)> leaf. Cambium Ndff was the highest of all organs, ranged from 39.35%to 45.50% and sequence was Ca(NO3)2> (NH4)2SO4> CO(NH2)2> NH4NO3. Trunk Ndff of four N treatments ranged from 31.09% to 37.58% and they followed the sequence that Ca(NO3)2> (NH4)2SO4> NH4NO3> CO(NH2)2. Trunk bark Ndff ranged from 30.00% to 34.47% and the sequence was Ca(NO3)2>NH4NO3> (NH4)2SO4> CO(NH2)2. Ndff of the left organs ranged from 24% to 37%, leaf Ndff of four nitrogen treatments followed:Ca(NO3)2> NH4NO3> (NH4)2SO4> CO(NH2)2, leafstalk Ndff of four N treatments followed:NH4NO3> Ca(NO3)2> (NH4)2SO4> CO(NH2)2, fine root Ndff of four N treatments followed:Ca(NO3)2> NH4NO3> CO(NH2)2> (NH4)2SO4; coarse root Ndff of four N treatments followed:NH4NO3> Ca(NO3)2> CO(NH2)2> (NH4)2SO4.The N distribution rate changed obviously among different organs and in four N fertilizer treatments all followed:leaf> root> trunk> bark trunk> leafstalk> cambium. Leaf N distribution rate of four N treatments ranged from 45% to 50% and followed the sequence that NH4NO3> Ca(NO3)2> (NH4)2SO4> CO(NH2)2. Root N distribution rate of four N treatments ranged from 28.08% to 32.04% and the sequence was CO(NH2)2> Ca(NO3)2> (NH4)2SO4> NH4NO3.15N distribution rate of trunk and leafstalk ranged from 22.15% to 25.11% and the sequence of four N treatments was (NH4)2SO4> CO(NH2)2>Ca(NO3)2> NH4NO3.(3) N use efficiency and residual fertilizer N in soil were different under different N fertilizer treatments. N use efficiency of four N treatments ranged from 18.05% to 19.74% and the sequence was NH4NO3> Ca(NO3)2> (NH4)2SO4> CO(NH2)2. Percentage of residual fertilizer N in soil of four N fertilizer treatments ranged from 66.93% to 79.25% and the sequence was (NH4)2SO4> NH4NO3> Ca(NO3)2> CO(NH2)2. N loss rate of all N fertilizer treatments ranged from 2.26% to 15.02% and the trend was CO(NH2)2> Ca(NO3)2> NH4NO3> (NH4)2SO4. Due to short growth time of rubber tree seedlings after fertilization, only small part of the fertilizer-N was absorbed by rubber tree plant, and most of the fertilizer-N remained in soil.