Transitioning from standard to minimum tillage: Trade-offs between soil organic matter stabilization, nitrous oxide emissions, and N availability in irrigated cropping systems

Few studies address nutrient cycling during the transition period (e.g., 1–4 years following conversion) from standard to some form of conservation tillage. This study compares the influence of minimum versus standard tillage on changes in soil nitrogen (N) stabilization, nitrous oxide (N₂O) emissions, short-term N cycling, and crop N use efficiency 1 year after tillage conversion in conventional (i.e., synthetic fertilizer-N only), low-input (i.e., alternating annual synthetic fertilizer- and cover crop-N), and organic (i.e., manure- and cover crop-N) irrigated, maize–tomato systems in California. To understand the mechanisms governing N cycling in these systems, we traced ¹⁵N-labeled fertilizer/cover crop into the maize grain, whole soil, and three soil fractions: macroaggregates (>250 μm), microaggregates (53–250 μm) and silt-and-clay (<53 μm). We found a cropping system effect on soil N_new (i.e., N derived from ¹⁵N-fertilizer or -¹⁵N-cover crop), with 173 kg N_new ha⁻¹ in the conventional system compared to 71.6 and 69.2 kg N_new ha⁻¹ in the low-input and organic systems, respectively. In the conventional system, more N_new was found in the microaggregate and silt-and-clay fractions, whereas, the N_new of the organic and low-input systems resided mainly in the macroaggregates. Even though no effect of tillage was found on soil aggregation, the minimum tillage systems showed greater soil fraction-N_new than the standard tillage systems, suggesting greater potential for N stabilization under minimum tillage. Grain-N_new was also higher in the minimum versus standard tillage systems. Nevertheless, minimum tillage led to the greatest N₂O emissions (39.5 g N₂O–N ha⁻¹ day⁻¹) from the conventional cropping system, where N turnover was already the fastest among the cropping systems. In contrast, minimum tillage combined with the low-input system (which received the least N ha⁻¹) produced intermediate N₂O emissions, soil N stabilization, and crop N use efficiency. Although total soil N did not change after 1 year of conversion from standard to minimum tillage, our use of stable isotopes permitted the early detection of interactive effects between tillage regimes and cropping systems that determine the trade-offs among N stabilization, N₂O emissions, and N availability.     

内蒙古典型草原区地表干湿状况变化趋势及影响因素分析

分析气候变化对典型草原区干湿状况的影响,对于了解草原退化原因、恢复草原生态环境有重要的指导意义。本文根据FAO推荐的彭曼一孟蒂斯方程,利用典型草原区1961—2008年25个地面气象站资料,通过计算潜在蒸发量、地表干燥度指数和水分盈亏量,分析了典型草原区地表干湿状况的空间分布规律及其年代际变化趋势,并探讨了它们与气候要素的相互关系。结果表明：（1）典型草原区牧草生长季干燥度指数均在2．0以上,水分亏缺量在400mm以上,属于地表干燥、水分亏缺状态。且整个牧草生长季4—9月,地表仍以干燥、水分亏缺为主。（2）典型草原区地表干湿状况存在着明显的阶段性变化特征。20世纪60、70年代水分亏缺多、干燥度大,属于气候相对干燥时期;80、90年代水分亏缺减少、干燥度降低;2001—2008年,水分亏缺量和干燥度指数逐渐增大,甚至达历史最大值,成为气候最为干燥时期,且变干倾向显著。（3）对典型草原区地表干湿状况影响最显著的因子为降水量和相对湿度（相关系数在0．8以上）,其次为日照时数（相关系数在0．6以上）,平均气温和平均风速对其影响相对较小。     

Characterization of humus-protease complexes extracted from soil

Pyrophosphate (140 mM, pH 7.1) extracts of two arable soils and one pasture soil were ultrafiltrated separating the extracted material into three fractions: A_I with nominal molecular weight (nmw) > 100 kD, A_II with nmw between 10 kD and 100 kD and R with nmw < 10 kD. Protease activity was determined in the fractions by using three different substrates: N-benzoyl-l-argininamide (BAA), specific for trypsin; N-benzyloxy-carbonyl-l-phenylalanyl l-leucine (ZPL), specific for carboxypeptidases; and casein, essentially a non-specific substrate. The derivative fractions were also analysed for their amino acid N and humic (HA) and fulvic (FA) acid contents. The organic matter of extracts and derivative fractions obtained from the pasture soil was analysed by isoelectric focusing (IEF) and that of fractions analysed by pyrolysis gas chromatography (Py-GC). Activities of the extract were monitored for their thermal stability and those of the extract and derivative fractions for their optimal pH.Due to the mechanical disintegrating action of sodium pyrophosphate over the humic substances during the fractionation process the amount of total organic C and FA in the fractions was ranked as R > A_II > A_I. The lowest amino acid N/organic C was found in the R fraction, whereas A_II fraction was rich in humic acids, carbohydrates and amino acid N and A_I fraction showed the lowest carbohydrate content. At least 70% of the total BAA- and ZPL-hydrolysing activity was associated to particles with nmw higher than 10 kD and at least 30% of these activities were present in particles with nmw higher 100 kD. Casein-hydrolysing activity was quite evenly distributed among the three fractions (A_I, A_II and R). The extracted protease-organic complexes were resistant to thermal denaturation and some of them showed optimal activity at pH values higher than 10 as a result of the polyanionic characteristics of the humic material surrounding enzyme molecules and of the presence of alkaline protease. Comparison of data obtained in Py-GC analyses and in protease activity suggests that BAA-hydrolysing activity was associated to a highly condensed humic matter and ZPL-hydrolysing activity to less resistant humic substances, while at least some of the extracted casein-hydrolysing activity was present as glyco-proteins not associated to humus. BAA-hydrolysing activity was probably inhibited by fresh organic matter of carbohydrate origin whereas lignin derived organic matter probably inhibited ZPL- and casein-hydrolysing activity.     

姜花在Cu胁迫下的耐性机理研究

采用模拟湿地盆栽试验,研究了姜花在Cu胁迫下的积累、分布、化学形态和富集能力。结果表明：（1）姜花对Cu的积累能力随Cu处理浓度的增加而增大,但各部位对Cu的积累具有明显的差异性。当Cu处理浓度≤150mg·kg。时,其积累能力表现为根〉叶〉茎;当Cu处理浓度≥200mg·kg。时,其积累能力表现为叶〉根〉茎。（2）Cu在姜花叶片细胞中的分布具有选择性,其主要分布位点为细胞可溶性部分和细胞壁部分,而在细胞器中Cu的含量较低。（3）Cu在姜花根、茎和叶中赋存的化学形态有明显差异。在根部,Cu的化学形态主要以乙醇提取态和水提取态为主;在茎部,Cu均以氯化钠提取态为主;而叶部Cu主要以活性较低的氯化钠提取态、醋酸提取态和盐酸提取态存在。（4）姜花对Cu具有一定的富集能力,但富集能力不强,当Cu浓度达到400mg·kg^-1以上时,姜花植株便出现了较明显的毒害症状并随之死亡,因而姜花尚未达到超富集植物的标准。可见,姜花在Cu胁迫下具有一定的耐受性,分布选择性和富集能力,将其运用于湿地Cu污染修复中,将极大地缓解重金属Cu污染给环境带来的压力。     

基于物元评判模型的土地整理综合效益评价方法研究

利用物元分析理论,将土地整理综合效益的等级、评价指标及其特征值作为物元,确定土地整理综合效益的经典域、节域及待判物元,应用物元和可拓集合中的关联函数建立了土地整理综合效益物元评判模型。并以山西省阳高县王官屯等二乡(镇)土地开发整理项目为例,对土地整理综合效益物元评判模型进行了实证研究,其综合效益的等级属于程度Km(P)=(-0.101,0.037,-0.431),属于"一般"等级,与模糊综合评价结果相似,符合项目区的实际情况。物元模型应用于土地整理综合效益评价作为一种初步的尝试与探索,为定量评价土地整理综合效益提供了一种新的思路。     

The growth of tagestes erecta,petunia hybrida nana compacta and myosotis alpestris in a range of peat‐based container media

Abstract

The dry matter yield and nitrogen content of marigold (Tagestes erecta), petunia (Petunia hybrida nana compacta) and forget‐me‐not (Myosotis alpestris) plants growing in a range of peat‐based container media amended with different proportions of either sand, perlite, pumice, sawdust, bark chips or soil were studied under glasshouse nursery conditions.

Plant responses differed between species as manifested by their different correlations with measured moisture and aeration characteristics of the media. Marigold and petunia were adversely affected by excessive moisture content as demonstrated by their negative correlation with micropore water and container capacity. However, forget‐me‐not, being adapted to relatively high moisture regimes, responded adversely to increased aeration.     

增氧对粉绿狐尾藻氮素吸收及其底泥微环境的影响

为探明增氧对粉绿狐尾藻氮素吸收及其底泥微环境的影响,本研究以粉绿狐尾藻为材料进行盆栽试验,以不增氧处理为对照(CK),分别设置O₁(4 min)、O₂(6 min)、O₃(8 min)、O₄(10 min)4个增氧水平,系统研究了粉绿狐尾藻不同生长时期氮素吸收及其底泥铵态氮、硝态氮含量等的变化规律,揭示了增氧调控底泥微环境、提高粉绿狐尾藻对水体氮污染物降解能力的机理。结果表明：无论增氧与否,粉绿狐尾藻根部和地上部氮素吸收量及植株氮素积累量均随生长时间延长呈逐渐增加趋势,且地上部氮素吸收量均高于根部;与CK相比,生长前期(t₁、t₂时期)增氧8 min、中后期(t₃、t₄、t₅时期)增氧6 min对应的粉绿狐尾藻氮素吸收与积累量均最大,其中增氧6 min对应t₅时期的粉绿狐尾藻植株氮积累量为171.08 mg·株^-1。增氧使粉绿狐尾藻生长前期底泥pH...     

水田自然免耕土壤有机质变化特性研究

水田自然免耕后,土壤有机质含量比淹水平作土壤低,比水旱轮作土壤高,随着免耕时间延长,免耕土壤的有机质和活性有机质逐渐回升.免耕垄作土壤的腐殖质特别是松结合态腐殖质相对含量增多,土壤复合度增加,有利于土壤结构的改善。     

丁香芳香气味物质的收集与测定

对丁香芳香气味物质的收集与分析方法等问题进行了探讨,借助于ＧＣ及ＧＣ－ＭＳ手段对其芳香成分的结构与含量进行了测定。     

冬小麦旱地周年覆盖栽培技术

在旱地中采用周年覆盖栽培技术 (秋覆膜 ) ,对汛期降水蒸发的抑制率可达 3 0 %～ 5 0 %,比春覆膜 (对照 )多保蓄 3 172mm/hm2 以上的降水 ;秋覆膜的垄与麦沟形成微型集雨区 ,降水易向沟内径流 ,可多聚水 15 0 0mm/hm2 以上 ,两者合计多蓄水 4672mm/hm2 以上。冬春两季 0～ 10cm地积温 ,垄上与垄底分别增加约 40 0℃和 2 0 0℃。土壤内各种微生物增加 0 .66～ 1.2倍 ,土壤总孔隙度提高 4.5 1%,速效N、P2 O5 、K2 O含量分别增加 5 .88%、2 4.69%、10 .3 1%。旱地冬小麦增产 2 5 .5 %～ 40 .3 %。