By the methods of field experiment, laboratory analysis, and in situ investigation, this paper studied the effects of different tillage conversion on the carbon sequestration capability of farmland soil doubled cropped with wheat and corn. Compared with conventional tillage (CTA), conservation tillage practices benefited the accumulation of soil organic carbon, among which, notillage plus straw returning (NTS) increased the organic carbon accumulation in 0-5 cm soil layer by 18.0%, rotary tillage plus straw returning (RTS) increased this accumulation in 0-5 and 5-10 cm soil layers by 17.6% and 25;0%, respectively, and conventional tillage plus straw returning (CTS) increased the organic carbon in 10-30 cm soil layer by 31.8%. After the conversion from CTA to NTS, the carbon emission from farm operations decreased by 54.3 kg·hm^-2·a^-1; while the conversion from CTA to CTS and RTS resulted in an increase of this emission by 46.9 kg·hm^-2·a^-1 and 34.4 kg·hm^-2·a^-1, respectively. Considering of the accumulation of soil organic carbon and the carbon emission from farm operations, it could be concluded that the conversion from CTA to conservation tillage changed this farmland soil from carbon source to carbon sink, and the RTS among the three conservation tillage modes resulted in the highest soil carbon sequestration (1011.1 kg·hm^-2·a^-1).

采用大田试验、室内分析与生产调研相结合的方法，研究了耕作方式对农田生态系统固碳能力的影响.结果表明：少、免耕以及秸秆还田等保护性耕作措施有利于土壤有机碳的累积；免耕秸秆还田（NTS）方式0～5 cm土层土壤有机碳累积量比传统耕作（CTA）方式高18.0%，旋耕秸秆还田（RTS）0～5和5～10 cm土层比CTA分别高17.6%和25.0%，而翻耕秸秆还田（CTS）方式10～30 cm土层土壤总有机碳累积量比CTA高31.8%；CTA转变为NTS后，源于农田投入的碳排放减少了54.3 kg·hm^-2·a^-1，而转变为CTS、RTS后，分别增加了46.9 kg·hm^-2·a^-1和34.4 kg·hm^-2·a^-1；综合土壤碳累积与农田投入碳排放可知，传统耕作转变为保护性耕作方式后可实现由“碳源”向“碳汇”的转变，而CTS、RTS、NTS 3种耕作方式中以RTS的固碳能力最强,达1011.1 kg·hm^-2·a^-1.

以沈单16和郑单958玉米单交种构成的六世代群体为材料，利用自行设计的玉米茎秆穿刺仪，对玉米地上第三茎节中部椭圆形短轴垂直于茎秆进行穿刺，测定玉米茎秆穿刺阻力。通过P₁、P₂、F₁、F₂、BC₁和BC₂ 6个世代联合分析法，以玉米茎秆穿刺阻力为性状，研究控制玉米茎秆倒伏性的基因遗传分离规律。结果表明，该性状在两个单交种的F₂分离世代群体均呈双峰分布，BC₁和BC₂群体分离世代呈多峰分布，说明玉米茎秆耐穿刺性遗传为多基因数量性状控制，且符合一对加-显主基因＋加-显-上位性多基因遗传模型(即D模型)；主基因遗传力为34.5%~45.7%，多基因遗传力41.6%~56.3%，两者在控制玉米茎秆耐穿刺遗传特性上都具有重要作用。这一研究结果为玉米抗倒伏性状的有效选择提供方法和理论依据。

In addition to sink and source, drain is also an important factor in crop yield forming. Being the organ of drain, vascular bundle (Vb) has been studied widely in recent years. In rice and wheat, researches showed that the number and area of Vb in culm (neck-panicle, branch) were positively correlated to panicle characters; cultivation factors, such as planting density, fertilizer and chemical regulator, affected the development of Vb; the Vb structure was mainly determined by cultivar type. In maize, the related studies, which started later than those in rice and wheat, have focused on the relations between Vb structure and sink capacity of ear and kernel. There are very few reports based on maize cultivar type or genotype. In maize production, vertical-type cultivars are commonly utilized. Researches showed that high yield of vertical-type cultivar is contributed by its sufficient source and large sink, however, the function of drain was seldom mentioned. The present experiments were designed to compare Vb structure and function of maize ear in cultivars with different plant types and ear types.
We choose three types of maize hybrids as tested materials, namely Yedan 4, Yedan 13, and Shendan 7, corresponding to vertical-small-ear type, vertical-large-ear type and horizontal-large-ear type, respectively. The number and area of Vb, phloem, xylem, the number and diameter of vessel were measured using bare-handed sections. The quantity of bleeding sap from ear-stalk and its sucrose content were determined. The effects of planting density and plant growth regulators on Vb structures and function and sink capacity were initially explored.
The number of big Vb and total Vb, the average area of single big Vb, total area of big Vbs, total area of all Vbs in ear-pedicel (ear-axis) of Yedan 13 and Shendan 7 (large-ear type) were significantly superior to those of Yedan 4 (small-ear type). The relative area and density of ear Vb of Yedan 4 and Yedan 13 (vertical type) were larger than those of Shendan 7 (horizontal type). The vertical -large-ear type Yedan 13 had certain superiority on the quantity and transportation rate of bleeding sap from ear-stalk. Planting density had a significant effect on the number and area of ear Vb and the response of cultivars to planting density was different. Dealing with plant growth regulators GA₃ and 6-BA could increase the number and area of big Vb in ear-pedicel. Volume of fresh grain, endosperm cells of single grain and 1000-kernel weight were also raised.

选用不同株型和穗型的3个玉米高产杂交种掖单4号、掖单13和沈单7号，利用植物显微技术与生理生化相结合的方法，比较了不同品种间果穗维管束发育的差异及对种植密度的响应，激素对维管束发育的调控。结果表明，在穗柄（轴）大维管束数、总维管束数、单个大维管束的平均面积、大维管束总面积、维管束总面积上，大穗型品种掖单13和沈单7号显著优于小穗型品种掖单4号；在维管束密度及维管束相对面积上，则紧凑型品种掖单4号和掖单13大于平展型品种沈单7号；密度对果穗维管束的数目、面积及穗粒库容影响显著，不同类型品种间对密度的反应有差异；促进类生长调节剂GA3和6-BA处理能显著增加穗柄内大维管束的数目和面积，显著增加籽粒体积，提高单粒胚乳细胞数和千粒重。

Lodging is an important factor to limit grain yield of summer maize. This study is to investigate the effects of potassium (K) application rate on the lodging resistance of summer maize under high yield cultivation conditions to that providing a reference of reasonable cultivation way. Two cultivars of summer maize (Zea mays L.), Denghai 661 (DH661) and Zhengdan 958 (ZD958), were used and six levels of K application rates were designed. The results showed that the grain yield and bleeding sap were increased at the first, and then gradually decreased with the increment of K application rate. Applied K could enhance rind penetrometer resistance by 17.9%, 25.57% in maximum for DH661 and ZD958. But the increase in different internodes was different. The increased vascular bundles especially the small vascular bundles, per unit area of crease rection of internode, were the key reason to improve stalk puncture strength. DH661 and ZD958 reached the highest yield at the K application rate of 180 kg ha^-1 and 240 kg ha^-1 respectively.

倒伏是玉米高产的重要限制因素之一。本研究旨在探讨施钾量对高产夏玉米抗倒伏能力的影响，为钾肥科学施用提供科学依据。选用登海661 (DH661)和郑单958 (ZD958)，设置6个施钾水平，研究高产条件下施钾量对夏玉米基部茎节穿刺强度、伤流量和产量的影响，并观察基部第3茎节显微结构。结果表明，施钾肥能显著提高茎秆的穿刺强度，DH661和ZD958最大提高幅度分别为17.9%和25.57%，但不同茎节提高幅度不同。伤流液的强度随着施钾量的增大先增加后减小，开花前促进作用大，吐丝期DH661和ZD958施钾180 kg hm^-2时最高，分别比对照提高24.30%和29.68%。单位面积内维管束增加，特别是小维管束增多是提高茎秆穿刺强度的关键。施钾肥可以显著提高玉米产量，随施钾量的增加，籽粒产量呈先增高后降低的趋势，DH661和ZD958分别在施钾180 kg hm^-2和240 kg hm^-2时达到最高产量。

Lodging is a major constraint to limit grain yield under increased planting density in modern maize (Zea mays L.) production. Effects of planting density on stalk mechanical and agronomic characteristics were investigated using three maize cultivars differing in lodging resistant ability,i.e. Jingke 519 (with a large spike under thinned planting density), Denghai 3719 (tolerant to high density) and Nongda 108 (a main local cultivar). Five levels of density treatment were imposed, 3.0, 5.25, 7.5, 9.25 and 12.0×104 plants ha^-1. Experiments were arranged in a split plot design with four replicates. The irrigation and fertilizer management in the experiment plot was consistent with typical agronomic practices in the local high-yield field. The results indicated that the increase of planting density would cause significant decreases in stalk crushing strength (SCS), rind penetration strength (RPS), internode diameter and dry weight (DW), percentage of dry matter and ratio of dry matter weight to length of internode (RDWL), and dramatic increase in internode length. The relationship between stalk mechanical characteristics and planting density fitted a exponential curve (y = ae^bx) significantly. The stalk mechanical characteristics were highly correlated with the agronomic characteristics. These characteristics of Jingke 519 were susceptive of the increasing planting density above 75 000 plant ha^-1, especially for these above the 4th internode was. The whole plant would have high lodging resistant ability if the dry matter accumulation was high in the 4th and above 4th internods. That the internod length enlarged slowly and diameter of internode decreased significantly with increasing plant density was an adaptability to high planting density for the resistant cultivar. When the percentage of DW of the 4th and above 4th internods was more than 7.5%, and its RDWL was more than 0.2 g cm^-1 at a week prior to anthesis, the plants would be resistant to lodging .The stepwise regression analysis revealed that the RDWL contributed positively the most to SCS and RPS. RDWL was definite as an agronomic indicator of maize stalk lodging resistant ability.

适当增加种植密度是提高玉米产量的重要途径之一，而倒伏是玉米增加群体密度的主要限制因素。2005—2006年以茎秆抗倒伏性不同的3个品种（稀植大穗型品种京科519、耐密抗倒型品种登海3719和当地主栽品种农大108）为材料，设3.0、5.25、7.5、9.25、12.0万株 hm^-2 5个密度处理，研究了种植密度对茎秆的抗倒力学和农艺性状的影响。结果表明，随着群体密度的增加，茎秆的压碎强度（SCS）和外皮穿刺强度（RPS）以及节间直径、干重（DW）、干物质百分比、单位茎长干物质重(RDWL)显著降低，而节间长度有所增加，以上这些变化在供试品种间存在着明显的差异；茎秆抗倒力学性状随群体密度呈指数曲线（y = ae^bx）变化。茎秆抗倒力学性状与农艺性状密切相关。节间伸长慢且节间变细可能是耐密品种在高密度群体下的适应性表现，而节间干物质积累、尤其高位节间的干物质积累较高的品种抗倒伏能力强。在玉米抽雄前1周茎秆第4节间以上干物质百分比大于7.5%，单位茎长干物质重（RDWL）高于0.2 g cm^-1时较为抗倒。逐步回归分析表明，单位茎长干物质对茎秆压碎强度（SCS）和外皮穿刺强度（RPS）的正向影响最大，可以作为玉米抗倒伏品种选择的重要农艺指标。