Impacts Of Nitrogen Fertilization On Soil Nutrient Contents And Greenhouse Gas Fluxes In Eucalyptus Plantations During Growing Season

Eucalyptus has been wildly introduced to southern China for afforestation.Fertilization is necessary in Eucalyptus plantations to sustain productivity, especially nitrogen. Synthetically studying the effects of nitrogen fertilization on soil nutrient,greenhouse emission and its interaction are important for understanding the impacts of nitrogen fertilization on ecosystem functions and improvement of fertilization in Eucalyptus plantations.In order to study the impacts of nitrogen fertilization on soil nutrient and greenhouse gas emission, combined with field control experiment and lab analysis, four nitrogen fertilization treatments（CK, 0 kg?hm-2; LN,84.20 kg?hm-2;MN,166.80 kg?hm-2; HN,333.70 kg?hm-2） were settled in Eucalyptus plantations, soil nutrient contents and CO₂, CH₄ and N₂ O fluxes were measured during growing season.The results shown:1. During the growing season, nitrogen fertilization significantly reduced soil pH.Soil nitrate concentration increased with the amount of added nitrogen, which was significantly higher in MN and HN treatments than in CK treatment. Nitrogen fertilization had no signficant effects on soil NH₄+-N、Available phosphorous、Available potassium.2.Soil nutrients changed during growing season. Soil pH decreased during the early stage of growing season, increased during the latter stage of growing season. In a month after fertilization,the soil pH had the minimum peak.However, soil ammonium and nitrate concentrations increased during the early stage of growing season and decreased at the latter stage of growing season. Soil available phosphorous showed an increased trend and available potassium showed a decreased trend during growing season.3.Nitrogen fertilization significantly increased soil CO₂ and N₂ O emission. A week after fertilization, both CO₂ and N₂ O had the flux peak and decreased by the end of growing season,the CO₂ flux had a great difference between HN treatments and CK treatments, the N₂ O flux had a great difference among all treatments. By the end of growing season, the differences among the treatments gradually disappeared.Nitrogen fertilization significantly decreased soil CH₄ absorption.The MN treatments and HN treatments was significantly lower than HN treatments. By the end of growingseason,the CH₄ flux began to pick up.4.The amount of fertilization is a curcial factor that has significant effect on CO₂、CH₄ and N₂ O. Fertilization strongly increased N₂ O emission fluex. HN treatment had a significant positive on CO₂ emission. MN and HN treatments had a significant negative on CH₄ emission.5.Soil CO₂ and N₂ O fluxes were positively correlated with soil water content and nitrate concentration, soil CH₄ flux was negatively correlated with soil water content and soil N₂ O flux was negatively correlated with soil available phosphorous.6.The amount of fertilization is a curcial factor that has significant effect on tree growing 、soil nutrients and greenhouse emission.In comprehensive consideration of the economic and ecological benefits,LN treatment of Eucalyptus growing fastest.Take the low nitrogen level N application may be more conducive to increase the economic benefits of Eucalyptus plantations.Our results showed that nitrogen fertilization had significantly impacts on soil pH,nutrient content and greenhouse gas fluxes in Eucalyptus plantations during growing season. Application of slow release fertilizer and fertilization in accordance to Eucalyptus needs might decrease the risks of nitrate leaching and greenhouse gas emission.