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991.
本文初步研究了攀枝花市不同年龄与生境的麻疯树老树,分析了老树特征与衰老的环境诱导结构限制现象。结果表明:(1)麻疯树衰老树体相对地径(16 cm~62 cm)、树龄(15 a~41 a)、冠幅(3 m×3 m~8.5 m×8.5m)、高度(2 m~6.96 m)较大,一级枝较大,有一定比例的枯死枝;(2)新梢小(枝径0.7 cm~1.12 cm;长度7 cm~28 cm之间),生长量低,萌生枝稀少,生殖枝比例偏低(趋近于30%以下);(3)单枝坐果量低(0~3个),干果重量1.65 g,千粒重490 g,壳比例30%,适合度偏低;(4)生境肥沃时树龄偏大,衰老程度弱,而生境瘠薄时树龄小,衰老程度强烈;(5)不考虑环境异质性,则衰老为树体结构限制的结果,新梢大小小于分支阈值,丧失了树体发育的能力而成为限制生长的因素。综合分析,麻疯树老树指标是分支率,在分支率为1时衰老启动;形态上衰老为环境诱导结构限制的产物,而结构限制可能是衰老的主观因素。 相似文献
992.
回归分析法是构建单木生物量模型进而估算群体生物量的基本方法。本文研究了攀枝花市马店河一个麻疯树4年人工林生物量与生产力模型的构建过程,运用相关生长定律分析参数合理性,并筛选了适宜的模型构建参数。首先,用地径、高度、D2H、树冠直径、冠幅、枝下高、树冠垂直投影体积这些灌木生物量测定中经常采用的外部形态指标构建麻疯树单木生物量模型,得到拟合性最好的幂函数、抛物线、对数函数模型。其次,采用树体构型指标,如枝条数量(不同年龄枝级)与分支率(总体分支率、)参数构建单木生物量模型,得到相关性不等的幂函数、抛物线模型。用年龄平均法与直径增量法同时估算了麻疯树单木生产力,分别为Pa=4.93±3.92 kg.a-1,Pd=4.59±3.82 kg.a-1,方差分析差异不明显。经回归,获得单木生产力模型。通过排序,获得对生产力贡献较大的因子,并对筛选的因子进行多元回归,得到Y=∑AiXi(其中Ai为第i个常数,Xi为第i个变量,i为测定变量总个体),提高了估算的精确度。分析表明,地径、冠幅直径、冠幅、冠幅垂直体积都能较为准确的估算单木生物量、生产力,但生殖生物量估算相关系数在0.8以下(0.607〈r2〈0.753),精确度不高,表明生殖自身特性的独特性。 相似文献
993.
994.
耕作、残茬及施肥管理对土壤有机质动态变化影响的情景分析 总被引:7,自引:0,他引:7
Based on data from 10-year field experiments on residue/fertilizer management in the dryland farming region of northern China, Century model was used to simulate the site-specific ecosystem dynamics through adjustment of the model's parameters, and the applicability of the model to propose soil organic carbon (SOC) management temporally and spatially, in cases such as of tillage/residue/fertilization management options, was identified v/a scenario analysis.Results between simulations and actual measurements were in close agreement when appropriate applications of stover,manure and inorganic fertilizer were combined. Simulations of extreme C/N ratios with added organic materials tended to underestimate the measured effects. Scenarios of changed tillage methods, residue practices and fertilization options showed potential to maintain and enhance SOC in the long run, while increasing inorganic N slowed down the SOC turnover rate but did not create a net C sink without any organic C input. The Century model simulation showed a good relationship between annual C inputs to the soil and the rate of C sequestration in the top 20 cm layer and provided quantitative estimations of changes in parameters crucial for sustainable land use and management. Conservation tillage practices for sustainable land use should be integrated with residue management and appreciable organic and inorganic fertilizer application, adapted according to the local residue resource, soil fertility and production conditions. At least 50% residue return into the soil was needed annually for maintenance of SOC balance, and manure amendment was important for enhancement of SOC in small crop-livestock systems in which crop residue land application was limited. 相似文献
995.
本文以团山沟单元小流域作为流域系统产沙的源地,将其它中小流域输沙模数与单元小流域侵蚀模数之比定义为泥沙输移比,系统的研究了岔巴沟流域次暴雨泥沙输移比的时空变化特征及降水水文影响因子和地貌形态因子的综合影响。研究发现,从长远来看,流域系统的侵蚀与产沙可达到平衡,但就次降雨或年度而言,流域系统经常处于泥沙滞留和滞留的泥沙重新侵蚀搬运的状态。降雨量、径流系数、降雨时间、水流平均含沙量能很好的表达岔巴沟各流域次暴雨泥沙输移比,在考虑地貌形态因子的影响后,得到了岔巴沟流域次暴雨泥沙输移比的降水水文因子与地貌形态因子关系的综合表达式。 相似文献
996.
菜地土壤中氮肥的反硝化损失和N2O排放 总被引:4,自引:0,他引:4
A field experiment was conducted on Chinese cabbage (Brassica campestris L. ssp. pekinensis (Lour.) Olsson) in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates: zero chemical fertilizer N (CK); urea at rates of 300 kg N ha^-1 (U300) and 600 kg N ha^-1 (U600), both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N ha^-1 (PCU180) as a basal application. The acetylene inhibition technique was used to measure denitrification (N2 + N2O) from intact soil cores and N2O emissions in the absence of acetylene. Results showed that compared to (3K total denitrification losses were significantly greater (P ≤ 0.05) in the PCU180, U300, and U600 treatments,while N2O emissions in the U300 and U600 treatments were significantly higher (P ≤ 0.05) than (3K. In the U300 and U600 treatments peaks of denitrification and N2O emission were usually observed after N application. In the polymer-coated urea treatment (PCU180) during the period 20 to 40 days after transplanting, higher denitrification rates and N2O fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and N2O emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N2O emissions tended to decrease. A significant (P ≤0.01) positive correlation occurred between denitrification (r = 0.872) or N2O emission (r = 0.781) flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season. 相似文献
997.
不同耕作措施下旱作农田土壤团聚体中有机碳和全氮分布特征 总被引:17,自引:3,他引:17
以连续进行12年的保护性耕作长期定位试验为研究对象,探索了传统耕作(T)、传统耕作+秸秆还田(TS)、免耕不覆盖(NT)、免耕+秸秆覆盖(NTS)4种耕作措施对陇中黄土高原旱作农田豌豆-小麦双序列轮作系统的土壤团聚体中有机碳和全氮分布特征的影响。结果表明:各处理均以≥0.25 mm团聚体为优势团聚体,且≥0.25 mm团聚体含量随土层深度增加而增加,而其他粒径团聚体含量随土层深度的变化并无明显规律。较之T处理,TS、NT、NTS处理均可提升≥0.25 mm团聚体含量和平均重量直径,NTS处理提升效果最明显。TS、NT、NTS处理土壤有机碳和全氮含量均高于T处理,其中TS、NTS处理显著高于T处理,NTS处理高于TS处理;各处理土壤有机碳和全氮含量均随土层增加而减小。较之T处理,NT、TS、NTS处理可不同程度提高各粒径团聚体中有机碳和全氮含量,NTS处理的含量最高;各粒径团聚体中有机碳和全氮含量均随土层深度增加而减小;同时,团聚体中有机碳和全氮含量随粒径减小而增加。2~5 mm和0.25~2 mm和≥5 mm团聚体含量与相应粒径团聚体有机碳含量呈极显著正相关、极显著正相关和极显著负相关;0.25~2 mm和≥5 mm团聚体含量与相应级别团聚体全氮含量分别呈极显著正相关和显著负相关。T处理不同粒径团聚体有机碳和全氮贡献率按其大小排序均为(0.25 mm)(≥5 mm)(0.25~2 mm)(2~5 mm),其他3种耕作措施各粒径团聚体有机碳和全氮贡献率在各土层中的排序各有不同,并无明显规律。 相似文献
998.
不同耕作方式对玉米根系特性及养分吸收转运的影响 总被引:1,自引:0,他引:1
999.
The stability of aggregates in the surface soil is crucial to soil erosion and runoff generation. Thus, to understand the stability and the breakdown mechanisms of soil aggregates as well as the relationship between aggregate stability and selected soil chemical properties, such as different forms of Fe and A1 oxides, organic matter, CEC and clay content, the aggregates of slightly and severely eroded red soils derived from Quaternary red clay in subtropical China were analyzed using the routine wet sieving and the Le Bissonnais methods. The results indicated that the aggregates of the severely eroded soils were more stable than those of the slightly eroded soils. Different aggregate breakdown mechanisms resulted in different particle size distribution. The slaking from entrapped air in aggregates severely destroyed the soil aggregates,especially in the slightly eroded soils. Meanwhile, mechanical breakdown and microcracking had little effect on the aggregates compared to slaking. The fragments resulting from slaking were mainly microaggregates that increased in size with increasing clay content. The main fragment size of the slightly eroded soils was 1.0-0.2 mm, while for the severely eroded soils it was 5.0-2.0 mm and 1.0-0.5 mm. Overall, more than 20% of the fragments were smaller than 0.2 mm.In addition, aggregate stability was positively and often significantly correlated with Fed, Ald, Feo and clay content, but significantly and negatively correlated to SOC. 相似文献
1000.
The mechanism of atmospheric,surface and soil water interactions( water transformation) in hillslope under natural conditions was analyzed,and a dynamic model was developed to simulate infiltration,overland flow and soil water movement during natural rainfall in hillslope,by bringing froward concepts such as rainfall intensity on slope and a correction coefficient of saturated soil water content for soil surface seal.Some factors,including slope angle,slope orientation and raindrop inclination,which affect the rainfall amount on slope, were taken into account while developing the dynamic model.The effect of surface seal on infiltration and water balance under a boundary condition of the second kind was aslo considered. Application of the model in a field experiment showed that the model simulated precisely the infiltration,overland flow and sol water monvement in hillsope under natural rainfall conditions. 相似文献