土壤不同形态钾含量与土壤颗粒的关系

土壤含钾矿物同其他矿物颗粒一起均分布在不同粒级的土粒中，这些土粒在不同的土壤中构成了不同的配合比例，形成不同的土壤质地的属性。统计表明，〈0．05mm与〈0．01mm粒级间呈极显著线性相关（r=0．896^＊＊，n=92），相关分析表明，不同粒级的土粒与不同形态钾间呈显著线性或曲线显著相关，而全钾只与〈0．05mm粒径的土粒呈极显著相关（r=0．234^＊＊，n=73），全钾与速效钾的数量关系通过全钾、〈0．05mm、〈0．01mm粒级与速效钾系统相关组合的算式以数学的方法计算速效钾含量。     

玉米苗期施用缓/控释氮素肥料养分释放特点与土壤生物活性研究

采用盆栽试验,模拟田间生态环境,测定施用不同种缓/控释氮素肥料,玉米苗期土壤尿素态氮、硝态氮、铵态氮含量,脲酶、硝酸还原酶活性、微生物量碳和氮含量变化趋势,比较玉米苗期氮素养分释放、土壤生物活性特点。研究表明,玉米苗期,施用SA nBPT U肥料,尿素态氮和NH4 -N的积累量最多,对土壤脲酶活性有显著的抑制作用;SA U肥料,硝态氮最多;MMA nBPT U肥料,尿素自膜内迁移到土壤中的量较少,硝态氮和微生物量最少。包膜与脲酶抑制剂nBPT相结合的缓/控释肥料,对减少硝态氮的生成效果最为明显。施用nBPT U肥料,微生物量最多。施用不同种缓/控释氮素肥料,土壤硝酸还原酶活性普遍增强,脲酶抑制剂nBPT对土壤硝酸还原酶活性无显著作用;施用不同种缓/控释氮素肥料土壤微生物量碳、氮的变化趋势一致。丙烯酸树脂包膜与脲酶抑制剂相结合的缓/控释肥料控释效果最好。     

固体水释放规律及其对土壤容积含水率的影响

本文通过土壤容积含水率变化，研究了无苗条件下固体水的释放规律，得出了不同试验阶段固体水的释放规律、保水时效性及其与环境因素的关系。同时，固体水对柠条种子发芽率的作用明显，最佳的是固体水0．75kg处理，其次为固体水1．0kg、0．5kg、0.25kg处理，对照最差。自然模拟干旱条件，使用固体水明显改善土壤水分保存状况，而至少使苗木维持2个月生存期。     

Litter quality and nitrogen release in tropical agriculture: a synthesis

 Litter of high quality is required for increased soil organic matter turnover and improved crop production in tropical agroecosystems. Studies on litter quality using plant residues have produced inconsistent results. This study reports on previously published data on litter quality, in an attempt to define universal chemical determinants controlling N release in tropical agriculture. N concentrations and polyphenol/N ratios are determinants of the N release of plant residues with limited N concentrations, i.e. of <2% and <1%, respectively. Lignin levels and lignin/N ratios were not observed to be good predictors of N release. The C/N ratio was found to be the best determinant of N release for a wide range of residue N concentrations. More specifically, critical levels of C and plant nutrients which limit the enzyme activities of microbial decomposers were found to be important for determining nutrient release. Received: 9 February 1999     

冲积潮土镁的释放特征及相对植物有效性

Experiments including two in laboratory and one in greenhouse were carried out to study non-exchangeable magnesium release from fluvo-aquic soils sampled from Daxing and Changping counties located in the suburbs of Beijing and Mg relative availability of the two soils to plants.In a batch experiment in labortory the soils were incubated under wet conditions and alternation of dry and wet conditions and determined for amount of Mg relesed at the 4th,8th and 12th week,respectively,after extraction of exchangeable Mg with 1molL^-1 NH4Ac.The amount of Mg released from the soil of Daxing was higher than from the soil of Changping,which was in accordance with the fact that the soil of Daxing had higher contents of all forms of Mg than that of Changping.There was little difference in Mg release from soils between wet conditions and alternation of dry and wet conditions.About 1%-2% of the total non-exchangeable Mg might be released within 12 weeks of incubation.restoring about 30%-35% of the original soil exchangeable Mg.Results of the experiment on kinetics of Mg release from the soils through continuous extractions with 0.5molL^-1 NH4Ac(pH7.0) on a continuous flow apparatus in laboratory showed that Mg released rapidly in the beginning,decreased sharply with time and kept stable at 60 and 240 min for the soile of Changping and Daxing,respectively,Among the five mathematical models used to describe the kinetics of Mg release,the parabolic diffusion equation best fitted the cumulative Mg release,indicating that diffusion of Mg out of the soils might be the controlling processa.The experiment of exhaustive cropping with 1 crop of tomato(Lycopersicon esculentum Mill.) followed by six crops of corn(Zea mays L.)in greenhouse showed that soil exchangeable Mg decreased remarkably with cropping .After three crops,the percentage of the total plant Mg uptake that came from soil non-exchangeable Mg was 29.5% for the soil from Changping and 35% for the soil from Daxing,About 50% of the total Mg uptake by plants in the six crops was believed to come from the soil non-exchangeable Mg form.     

滴灌冬小麦精量穴播栽培模式效果分析

【目的】研究冬小麦精量穴播栽培模式效果,为滴灌小麦优质高产栽培技术规程提供科学依据。【方法】在不同播种量处理的示范田内样点调查,采用固定和随机取样等方法,调查与分析空穴率、基本苗、冬前总茎数、越冬总茎数、平均单株分蘖数及可能有效分蘖数、有效穗数、产量等,与龙王庙村常规播种地块对比产量和效益。【结果】获取精量穴播冬小麦播种量6.3 kg/667m²、8.3 kg/667m² 2个播种量的空穴率分别是20.6%、9.1%,基本苗分别是10.3×10⁴/667m²、14.4×10⁴/667m²,冬前单株分蘖数分别是3.1和2.8,冬前分蘖成穗率分别是98%和65%,平均单株成穗率分别是403%和283%,收获穗数分别是41.5×10⁴/667m²和40.7×10⁴/667m²、实收单产分别是628和632 kg/667m²等,精量穴播2个处理均取得了较高的产量,分别比同等条件下条播16 kg/667m²播种量处理实收单产分别增加38和42 kg/667m²,节约种子分别是9.7和7.7 kg/667m²,增加效益分别是494.16和488.84元/667m²。【结论】冬小麦产量高低与播种量没有明显关系;随着播种量的增加,平均单株成穗率和冬前分蘖成穗率逐渐减少;在肥水充足的条件下,收获穗数随着播量增加呈下降趋势;平均穗粒数随着平均穗数增加而减少;精量播种冬小麦可以节约生产成本,提高产量和种植效益;播量为6.3 kg/667m²时,冬前分蘖数与分蘖成穗数接近,有效分蘖数和收获穗数最高,平均单株成穗率达403%,冬前分蘖成穗率达98%,节本增效金额达494.16元/667m²,节本增效最多。     

Preparation of silk sericin beads using LiCl/DMSO solvent and their potential as a drug carrier for oral administration

Silk sericin (SS) was fabricated into beads using LiCl/DMSO solution as a solvent. Up to 30 % (w/v) of SS could be dissolved within 3 hours, and the shape of solidified SS depends on the concentration of SS. Ethanol was the best coagulant among alcohols, making beads with suitable mechanical strength for further application. SS beads swell more at a pH above the isoelectric point (pl) than below the pl. The pH and the presence of an enzyme greatly affect the dissolution rate of SS beads. Whereas only 10 % of SS beads were dissolved at pH 2.2 in the presence of pepsin, more than 45 % of SS beads were dissolved at pH 7.4 in the presence of trypsin. The release of drug was suppressed in a stomach-like environment while promoted in an intestine-like environment.     

赤霉素解除马铃薯块茎休眠的调控敏感位点初探

以马铃薯栽培品种“大西洋”和“中薯 3号”脱毒试管薯为试验材料。以针沾取GA3处理休眠期试管块茎不同部位 ,研究GA3 解除马铃薯块茎休眠的调控部位。结果表明 :块茎顶部对GA3 处理最敏感 ,其次是基部 ,然后是第一侧芽、第二侧芽 ,说明GA3 解除块茎休眠过程中的敏感调控部位主要是在块茎的顶部     

严寒地区保温型塑料大棚土壤蓄放热特性

土壤温度及蓄放热特性是保温型塑料大棚土壤传热特性的重要体现。因此,为定性、定量地阐明棚内土壤温度变化规律和蓄放热特性,在严寒地区生产性大棚内进行了试验测试,并通过构建大棚土壤热量平衡简化方程、温差拟合等方法对土壤蓄放热特性进行了理论分析。研究结果表明：1）土壤温度波幅随深度的增加呈乘幂函数递减,通过计算得出测试地区大棚土壤的蓄热层平均厚度约为0.55～0.80 m;2）棚内土壤横向地中传热损失占土壤总热损失的9.8%～24.7%,若将此部分热量用于提高土壤温度,则棚内土壤平均温度可提高0.3～0.5 ℃;3）天气条件对土壤蓄放热性能的影响较大：晴天日累积蓄热量比多云天多37.2%～50.6%左右,日累积放热量比多云天多44.7%～64.3%;晴天的最大蓄热流量和日累积蓄热量均是阴天的4倍以上,与蓄热性能相比,晴天与阴天的土壤放热性能差异较小。土壤蓄放热量主要受表层土壤与气温温差的影响,棚内外气温差对其影响较小。     

魔芋葡甘露聚糖/硼复合凝胶对水杨酸的缓释性研究

探讨了魔芋葡甘露聚糖-硼复合物对水杨酸的释放行为：魔芋葡甘露聚糖-硼水凝胶对水杨酸呈3个阶段释放;干凝胶的释放在室温下符合零级释放方程,而40-50℃时符合一级释放模型。试验范围内硼砂浓度对释放几乎没有影响;碱性条件下较酸性条件下慢;盐离子浓度对水杨酸的释放影响较小。