模拟降雨条件下农田氮素径流流失特征研究

基于洱海流域农田径流总氮污染严重、入湖总氮负荷较高的特点,采用室外人工模拟降雨方法,研究了20、40、60 mm·h~(-1)三种雨强条件下农田径流产流过程和氮素流失特征。结果表明:农田径流的产生主要受降雨量控制,当雨量达到(20±2)mm时才会产生径流,雨强主要影响其产流后流量的增长速度以及稳流后流量的大小,雨强越大,产流增长速度越快,平稳后径流量也越大;径流中氮素流失量与降雨量呈极显著线性相关(P0.01),而且雨强越大,氮素流失速度越快,雨强60 mm·h~(-1)时线性拟合方程的斜率最大为1.28;三种雨强条件下均无明显的初期冲刷效应,不宜通过截留初期农田径流来控制农田径流氮污染;径流中氮素浓度随着降雨量增加先增大后减小,其浓度峰值受雨强影响较大,雨强大的浓度峰值高,且浓度峰值均出现在径流量趋于稳定时段附近;氮素浓度变化与悬浮物浓度变化呈极显著线性相关。建议通过加强水土流失管控及在湖周采取截蓄净化等措施有效控制洱海流域农田径流中的氮污染。     

青藏高寒草地夏秋季不同轮牧强度对牧草及绵羊的影响

本试验是在四川省阿坝州若尔盖县辖曼种羊场进行的。对种羊场的草地进行夏秋季轮牧强度试验，对轮牧小区内牧草产量、营养成份、绵羊生产性能进行测定，结果表明：从保护利用的观点着眼，草地轮牧强度应选择7．5只羊／ha，草地的可利用牧草为90％。日增重与日食量和放牧强度之间存在显著的多元线性回归关系，日增重与采食量呈正比，而与放牧强度呈反比。日采食蛋白与日增重比与日食量和放牧强度之间存在显著的多元线性回归关系，当放牧强度为3．75只羊／ha时日食蛋白与日增重比达到最低，为0．875，即绵羊对蛋白质的利用率最高。     

Influence of Soil Properties and Manure Sources on Phosphorus in Runoff during Simulated Rainfall

Runoff from agricultural fields amended with animal manure or fertilizer is a source of phosphorus (P) pollution to surface waters, which can have harmful effects such as eutrophication. The objectives of this study were to evaluate the impact of soil P status and the P composition of manure sources on P in runoff and characterize the effects of manure sources on mass loss of dissolved reactive P, total dissolved P, and total P in runoff. Soil boxes set at 5% slopes received 7.5 cm h^?1 of simulated rainfall for 30 min. Study soils included a Kenansville loamy sand (loamy siliceous subactive thermic Arenic Hapludults, a Coastal Plain soil) and a Davidson silt loam (kaolinitic thermic Rhodic Kandiudults, a Piedmont soil). Soil test P concentrations ranged from 16 to 283 mg P kg^?1. Sources of P included broiler litter, breeder manure, and breeder manure treated with three rates of aluminum sulfate (Al₂(SO₄)₃) 0, 3.9, and 7.8 kg m^?2, di-ammonium phosphate (DAP), and an un-amended control. All manure sources were surface applied at 66 kg P ha^?1 without incorporation. Water extractable P represented an average of 10 ± 6% total P in manure. Runoff samples were taken over a 30-min period. Piedmont soil contained greater amounts of clay, aluminum (Al), and iron (Fe) concentrations, and higher P sorption capacities that produced significantly lower dissolved reactive P, total dissolved P, and total P losses than the Coastal Plain soil. Runoff P loss did not differ significantly for low and high STP Coastal Plain soils. Water extractable P in manures accounted for all dissolved reactive P lost in runoff with dissolved reactive P correlating strongly with water extractable P concentration (r² = 0.9961). Overall, manures containing the highest water extractable P concentrations contributed to the largest amounts of dissolved reactive P in runoff. Manure treated with 3.9 and 7.8 kg m^?2 of Al₂(SO₄)₃ (alum) decreased dissolved reactive P in runoff by 29%. While this soil box runoff study represents a worst-case scenario for P loss, highly significant effects of soil properties and manure sources were obtained. Management based on these results should help ameliorate harmful effects of P in runoff.     

侧柏林土壤呼吸速率对不同模拟降雨量的响应

为了研究不同林龄的森林土壤呼吸速率对不同降雨量的响应规律,选取北京市鹫峰国家森林公园内的30年生和10年生侧柏林作为代表树种,进行了模拟降雨控制试验,并采用碱液吸收法,对5,10,20和50mm降雨量及连续相同频率降雨条件下不同林龄侧柏林的土壤呼吸速率进行了测定。结果表明,林龄对侧柏林的土壤呼吸速率影响有显著差异(p0.05)。30年生侧柏林的土壤呼吸速率总体上高于10年生侧柏林。与对照组相比5,10和20mm降雨量对30年生侧柏林的土壤呼吸速率有促进作用,而50mm降雨量及连续相同频率的降雨对30年生侧柏林土壤呼吸则产生抑制作用。10年生侧柏林与30年生侧柏林相比需水量较小,只有5mm降雨量条件下对其土壤呼吸速率产生了促进作用,其余模拟降雨量均对其产生抑制作用。     

模拟酸雨对台湾桤木光合特性的影响

通过模拟酸雨实验,研究酸雨胁迫（pH2．5、3．0、35、4．0、4．5）对台湾桤木光合作用的影响。结果表明,随着酸雨酸度的降低,台湾桤木叶片的净光合速率、蒸腾速率和气孔导度呈上升趋势。pH2．5时,叶片的净光合速率达最低点,比对照（CK）降低28．6％;pH4．5时,叶片的净光合速率比CK高10．2％;pH2．5时,叶片的蒸腾速率达最低点,比cK降低59．5％,而pH3．0、3．5、4．0、4．5分别比CK降低57．4％、53．1％、50．1％和34．7％。随着酸雨胁迫时间的持续,台湾桤木叶片净光合速率先降低后升高,蒸腾速率先升高后降低,气孔导度先降低后升高;胞间CO2浓度前期降低,9月达最低,其后又升高;气孔限制值先升高后降低,水分利用效率先降低后升高。     

模拟酸雨对种子繁殖香根草生理特性的影响

研究了模拟酸雨对种子繁殖香根草叶绿素(Chl)含量、光合速率(Pn)、蒸腾速率(Tr)和水分利用率(WUE)的影响.结果表明,酸雨胁迫使香根草Chl含量明显下降,模拟酸雨pH值3.5是影响香根草Pn、Tr、WUE的临界点,pH≤3.5影响明显,pH>3.5影响不明显.在pH值1.5影响下的各项生理指标均最低,在此影响下的香根草已受到酸雨严重伤害而不能恢复,其余处理均能恢复.     

放牧强度对草原化荒漠土壤种子库物种多样性和生活型的影响

2005年5～10月,在内蒙古西部鄂托克前旗境内的温性草原化荒漠进行放牧试验,以山羊为对象,研究草原化荒漠土壤种子库物种多样性及植物生活型与放牧强度的关系.结果表明:轻度放牧强度,种子库中的物种数、种子数量相当于对照的72.7%和74.9%,重度放牧强度仅为对照的31.8%和33%;丰富度指数R1、香农指数H′均表现出下降的趋势,对区照、轻度放牧区、中度放牧区、重度放牧区R1分别为3.952 416,2.985 74,2.081 59,1.426 977, H′分别为2.622 62,2.124 39,1.556 54,1.282 09;均匀性系数变化不明显,但中度放牧强度下最小,整体略呈"V"型.种子库中一年生植物生活型占90%左右.     

Rural land-use and wildland fires in the tropics

Tropical forest land is increasingly influenced by man-caused wildfires. The vast majority of the forested area burnt and cleared annually is in the tropics. The use of fire in rural land-use systems is the major cause of the wildfires. Five broad causative agencies of wildfires are presented, shifting cultivation, grazing, non-wood forest products, migration programs and the wildland/residential interface. Integrated concepts of prescribed burning and prescribed grazing may offer solutions to the tropical wildland fire problems.     

Effects of grazing and precipitation on herbage production,herbage nutritive value and performance of sheep in continental steppe

The present study highlights the effects of sheep grazing and precipitation on herbage and animal performance in a grazed steppe of Inner Mongolia. Experimental data were collected during grazing periods of four consecutive years (2005–2008), and effects were analysed across a gradient of seven grazing intensities. Variation in annual precipitation, reflected by the effect of ‘year’, was the major factor affecting herbage; i.e., the production and nutritive value of herbage increased with increasing precipitation. Herbage parameters were also affected by grazing intensity, as herbage production (HP) and herbage nutritive yields decreased, while herbage nutritive values increased with increasing grazing intensity. The grazing‐induced decrease in herbage nutritive yields suggests that decreases in HP offset the positive effect of grazing on the nutritive value. Liveweight gain (LWG) was predominantly affected by grazing intensity, as LWG per sheep and per ha decreased and increased, respectively, with increasing grazing intensity. However, responses varied among years: LWG per sheep was maximized by light grazing in the drought year and by moderate grazing the wet year. Our results showed that herbage shortage at high grazing intensities reduces LWG per sheep and thus diminishes responses in LWG per ha. Nevertheless, the highest grazing intensity provides highest animal production per ha in the short term; however, this is not sustainable in the mid‐ and long term because decreasing HP induces degradation processes. Based on our results, a reduction in grazing intensity that still provides 78% of the maximum LWG per ha meets the requirements of a sustainable grazing management.     

基于PROSAIL结合VMG模型的冬小麦叶面积指数反演方法

针对物理模型抗噪能力差且容易过拟合的问题,提出一种PROSAIL模型结合VMG(VARI（Visible atmospherically resistant index）、MGRVI （Modified green red vegetation index）、GRRI （Green red ratio index）)多元回归模型反演冬小麦叶面积指数（Leaf area index, LAI）方法。实验基于无人机影像（Unmanned aerial vehicles, UAV）,选择河南省焦作市东南部的山阳区为实验区,结合实测2个生育期冬小麦LAI数据。首先,构建RGB植被指数模型,选取其中最优VMG模型反演冬小麦LAI;然后,对PROSAIL参数敏感性进行分析,得到参数最优值,反演冬小麦LAI;最后,采用快速模拟退火（Very fast simulated annealing, VFSA）算法将两种模型结合,获得最优冬小麦LAI。结果表明：VFSA可以有效将PROSAIL模型和VMG模型结合,提高了反演精度,且优于VMG模型和PROSAIL模型,决定系数R²高于0...