| Rubber plantation is amongst the important tropical forest ecosystems. However, because of the continuously collection of latex from rubber trees, the cycling of plant nutrients is totally different from those in other forest ecosystems. The production management of rubber plantation had been changed greatly since the stimulated tapping system (s/2.d/3+ET2.0%) carried out from the 90’s of last century.15N isotope trace technique and the research method appllied in the nutrient cycling of forest ecosystem, had been used in order to characterize the cycling of nitrogen and phosphorus in rubber plantation.The experiment had been carried out in rubber plantation located in CATAS, Danzhou,Hainan. The results are following:The average biomass of rubber trees (Clone 7-33-97) increased 12.25t.hm-2 every year (based on the 29.19kg/plant). Rubber trees, planted in 1993,grow faster and have more biomass than those planted in 1999 and 1987. The annual uptake of nitrogen by all rubber trees is 246.80kg.hm-2 (including dry latex) and that of phosphorus is 20.33 kg.hm’2. The coefficient rates are 0.0478 and 0.0125 for nitrogen and phosphorus uptake, respectively. Rubber trees, planted in 1993,took more nitrogen and phosphorus than others, while they took up the similar amount of phosphorus as rubber trees planted in 1999。 The uptake of nutrients by rubber trees planted in 1987 is the least.The nutrition use efficiency for nitrogen and phosphorus are 54.52 and 662.10 respectively. And the highest efficiency is related to the trees planted in 1993, while the lowest efficiency is related to those planted in 1987.The dry latex production is averagely 1218.35kg.hm-2 (2.90kg/plant). The remove of nitrogen and phosphorus within latex is annually 9.81 kg.hm-2 and 3.05 kg.hm-2, respectively.The litter of leave and shoots is annually 6178.88 kg.hm-2, and the amount of litters increases with the age of trees. The return of the nitrogen and phosphorus into the soil by litters is annually 113.32 kg.hm-2 and 5.86 kg.hm-2, respectively. The recycle speed of nitrogen (1.20 y) is faster than that of phosphorus (2.53) and increases with the age of the tree.The content of nitrogen and phosphorus in soils are strongly affected by the decomposition of litters, phenophase of rubber trees, and fertilization. The total nitrogen and alkali-hydrolyzable nitrogen content was highest in the May and lowest in the March and April. The content of alkali-dydrolyzable nitrogen decreased during the Juni to November in corresponding to the growth of rubber trees. The total phosphorus content in the soil kept constant during the whole year, while the available phosphorus is the lowest at the end of phenoph ase (December to the next Feb.) of rubber trees and relatively high during May to June, and the highest in August.Annually input of the nitrogen and phosphorus through rainfall to the rubber plantation ecosystem is 6.99kg.hm-2 and 0.32 kg.hm-2, respectively. The output of nitrogen and phosphorus through surface runoff and leaching is 4.00 kg.hm"2 and 0.42 kg.hm-215N isotope trace method was used and the uptake of 15N isotope was 3.1844g/plant, the apparent fertilizer use efficiency was 21.12% averagely, which was 18.36% for rubber trees planted in 1999 and 24.09% for those planted in 1993. The residue of 15N applied in soil was decayed after the fertilization and the decay rate was decreased with the time. The residue of 15N in 5 months was 1.888g in soil for one plant, the residue rate is 12.59%, the loss rate was about 66.13%.Only after the fertilization of nitrogen, the ammonia volatilization could be detected in the second day. The most loss of ammonia volatilization happened during the 10 days after fertilization and stopped after 20 days. The loss rate of ammonia volatilization is between 3.89%-11.18%, averagely 8.33%. Temperature and rain had effect on the ammonia volatilization.Emission of NO and NO2 was detected both in fertilized and non fertilized soils in rubber plantation. The emission rate of NO in fertilized and non fertilized soils in rubber plantation was 119.11μgN.m-2.h-1 and 7.38μgN.m-2.h-1.And emission rate of NO2 was 33.55μgN.m-2.h-1 and 0.87μgN.m-2.h-1. The total emission rate of NOx (NO+NO2) was 2.524kgNOx-N.hm-2.yr-1 with emission coefficient rate of 0.42%。The bio-chemical global cycling of the nitrogen and phosphorus in the rubber plantation ecosystem investigation showed that the deficit of nitrogen is 14.40kg.hm-2.yr-1 and 26.97 kg.hm-2.yr-1 for the rubber plantation planted in 1999 and 1993 respectively, while the profit of nitrogen is 7.20 kg.hm-2.yr-1 for the rubber plantation planted in 1987. The profit of phosphorus is averagely 12.47 kg.hm-2.yr-1 for all of the rubber plantation.Summarize the information at given above, the application rates of nitrogen should be increased in the rubber plantation planted in 1999(in initial stage) and 1993(in prosperous stage), instead, decreased in 1987(decline stage). the application rates of phosphorus should be reduced in all of the tapped rubber plantation. |
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