本研究以东经105°10′54″~107°43′43″,北纬11°48′3″~15°45′18″,湄公河干流老挝沙湾拿吉至柬埔寨桔井段,湄公河重要支流南蒙河(Nam Mun River)、色丹河(Se Done River)、色贡河(Se Kong River)、色桑河(Se San River)、斯雷博河(Sre Pok River)及其左右岸缓冲区50km范围为研究区域,分析区域内旱季(1-2月)、雨季(6-9月)土地利用及土壤侵蚀变化情况。结果表明研究区域旱、雨季土地利用变化主要表现为河道沿岸水体动态变化;旱季水体面积较雨季净减少43259公顷,占总变化面积的93.8%;雨季至旱季耕地转入占总变化面积38.0% (17514公顷),其次为灌木地(23.0%,10159公顷)和裸地(21.8%,10033公顷)。旱、雨季土壤极强烈侵蚀和剧烈侵蚀区域变化不大;旱季以轻度侵蚀、中度侵蚀增加为主,净增加面积分别为4107公顷和5864公顷,分别占总变化面积的36.9%和52.7%。增加面积主要由无侵蚀类型发展而来,体现在旱季沿岸水体面积的大幅降低。建议在其水土保持过程中,改传统稻田种植为耕作、轮作和培肥一体化的水保措施,同时增强基础设施建设,提高河岸植被缓冲带的生态护坡建设与河岸带管理,降低自然洪水或人为工程对自然林地和植被的破坏。 相似文献
1. An experiment was conducted to determine optimal non-phytate phosphorus (NPP) concentrations for White Leghorn (WL) layers (22–72 weeks) fed diet containing 38 g Ca/kg.
2. Eight diets with graded concentrations (1.5–3.25 g/kg in increments of 0.25 g) of NPP were prepared. Each diet was fed to eight pen replicates containing 88 birds in each. Performance data was evaluated in three different phases (phase I-22–37 weeks, phase II-38–53 weeks and phase III-54–72 weeks). Optimum levels of NPP were determined by fitting a quadratic polynomial (QP) regression model.
3. Egg production (EP) was not affected (P = 0.059) by the concentration of NPP and interaction between NPP and diet phase was non-significant, indicating that the lowest concentration (1.5 g/kg diet) of NPP used in the study was adequate across the three phases. However, EP was influenced by phase (P < 0.001).
4. Optimum concentration of NPP for feed intake (FI) was estimated to be 1.5, 1.71 and 2.40 g/kg diet during phases I, II and III, respectively. FI per egg mass (EM) or feed efficiency (FE) responded quadratically with NPP and also differed significantly between phases. Optimum concentration of NPP for FE during phases I, II and III was 1.5, 2.56 and 2.32 g/kg diet, respectively.
5. Egg weight (EW), EM, shell weight and thickness were not affected by NPP concentration although all of these variables (except shell weight) were influenced by phases.
6. Breaking strength of tibia and Ca contents in tibia ash were not affected by the concentration of NPP, but bone ash and P contents in tibia ash were influenced (P < 0.001) by NPP. Predicted optimal concentrations of NPP for responses for tibia ash at 44 or 72 weeks, tibia ash P at 44 weeks and tibia ash P at 72 weeks were 1.55, 2.63 and 1.5 g/kg diet, respectively.
7. Based on the results, it was concluded that WL layers required 1.5 g, 2.63 g and 2.4 g, respectively/kg diet during phase I, II and III with the calculated daily intake of 137.3, 278.3 and 262 mg NPP/b/d. 相似文献