甘蓝型冬油菜(Brassica napus)干物质积累、分配与转移的特性研究

采用不同的模型, 定量地研究了不同播期不同基因型油菜干物质积累、分配与转移规律. 结果表明: 油菜总干物质积累动态可拟合成Logistic模型. 油菜根、茎枝、叶干物质分配呈现出多项式函数的变化规律, 角果干物质分配表现为Logistic曲线的变化特征. 晚播油菜干物质冬前优先分配给叶, 角果发育成熟期优先分配给角果并主要给籽粒     

The Effects of Timing of an Interim Harvest on the Yield and Composition of Lablab purpureus

Lablab purpureus was grown in two field experiments in consecutive years to evaluate the effects of the timing of an interim harvest on the yield and nutritive value of the harvested material and the subsequent regrowth, which was determined from the second and final harvest. Delaying the first harvest to 50–70 days post-sowing increased the total (first plus second harvests) dry matter (DM) yield, with a greater first harvest and reduced second harvest DM yield. The delay also reduced the crude protein concentration of the first harvest and tended to increase its modified acid-detergent (MAD) fibre concentrations. The delay increased the crude protein concentration and decreased the MAD fibre concentration of the second harvest. The total crude protein yield of both harvests increased with late interim harvesting. The first harvest plant calcium concentration increased and phosphorus concentration decreased with a delay in the interim harvest. It is concluded that, in the difficult growing conditions of the Sahelian zone of sub-Saharan Africa, delaying the interim harvest of Lablab purpureus until 50–70 days post-sowing will have beneficial effects on total dry matter and crude protein yields.     

播种期对2个不同类型棉花品种产量和产量构成的影响

 适期播种是棉花丰产的重要措施,品种类型常影响播种期。为确定不同类型棉花品种的适宜播期,采用裂区设计,以品种类型（早发型鲁棉研21号和后发型鲁棉研28号）为主区,播种期（4月上旬早播、4月下旬中播和5月上旬晚播）为副区,于2009—2010年在山东临清研究了品种类型和播种期对棉花产量和产量构成的影响。两年的试验结果表明：品种和播期对棉花产量有显著的互作效应,而且主要是由于铃数和衣分的变化所致;早发型品种4月下旬播种产量最高,比4月中旬播种增产6.3%,5月上旬播种与4月中旬播种产量相当;后发型品种4月中旬播种产量最高,比4月下旬和5月上旬播种分别增产4.8%和12%。在鲁西北棉区地膜覆盖栽培条件下,早发型品种以4月下旬播种为宜,可以适当晚播,直到5月上旬;后发型品种应适当早播,以4月中旬为宜,晚播会显著减产。     

The Effect of Sowing Date on the Yield and Quality Formation of Different Cultivars of Cotton under Machine-Picked Conditions in the Coastal Saline-alkali Area of Eastern Hebei Province,China

[Objective] The effects of sowing date on the yield and quality formation of two different cotton cultivars were studied under machine-picked conditions in the coastal saline-alkali area of Eastern Hebei Province, China to identify the optimal sowing date and harvest method to improve cotton yield and quality consistency. [Method] The experiments were conducted in the state-run Haixing farm in Hebei Province during 2017 with a cotton crop seeded in 2016. The hybrid cotton Jiza 2 and conventional cotton Shikang 126 were used in this experiment. Varieties were tested using three sowing dates: April 15 (B1), April 25 (B2), and May 5 (B3) as the main plot. Six harvest dates were also used as subplots in this experiment: September 10, September 20, September 30, October 10, October 20, and October 30. [Results] The lint yield of Jiza 2 was nearly 1 400 kg·hm^－2 when the sowing date was May 5. Conversely, the highest lint yield for Shikang 126 was obtained when the cotton was sown on April 25. The yield associated with different sowing times was mainly formed in September, with this month accounting for more than 75% of yield. The fiber quality was better in September than October. The fiber quality of Jiza 2 was improved with a delay inthe sowing date. The best fiber quality for Shikang 126 was obtained with the April 25 sowing date. There was a small difference between the micronaire, fiber length, and length uniformity with different September harvest times. The fiber quality index was optimized and the consistency of the micronaire, upper half mean length, and length uniformity were higher with Shikang 126 before September 20 when sown on April 25. [Conclusion] Comprehensive consideration of yield and quality index indicated that hybrid cotton Jiza 2 performed best when sown on May 5 and harvested for the first time at the end of September. The conventional cotton Shikang 126 should be sown around April 25 and harvested for the first time on the last ten-day of September.     

CIMMYT和中国硬质春麦在4种CIMMYT不同处理环境中产量和蛋白品质性状分析

灌溉、播期和垄作等栽培方式对小麦产量和蛋白品质性状具有重要影响。将21个中国和CIMMYT硬质春麦品种于2000—2001和2001—2002年度分别种植在CIMMYT的Obregon试验站4种处理环境中。结果表明，所有性状均受品种和处理环境的显著影响，产量和沉降值同时还受品种和处理环境互作效应的显著作用，在进行产量和品质改良时应考虑品种与处理环境间的互作。充分灌溉和适期播种有利于提高产量，减少灌溉迟播垄作则有利于提高蛋白含量和沉降值。Rayon F 89产量、蛋白含量和沉降值均较高；龙麦26产量、蛋白含量和沉降值显著高于其他光敏感品种。充分灌溉适期播种垄作利于提高Rayon F 89等的产量和Weaver等的沉降值，充分灌溉适期播种平播利于提高Seri M 82等的产量和Attila等的沉降值，充分灌溉迟播垄作利于提高龙麦26等的产量和Super Seri#1等的沉降值，减少灌溉适期播种垄作则利于提高Rayong F 89等的产量和Weaver等的沉降值。     

长沙烟稻轮作区烤烟正常与推迟采收条件下的适宜晚稻品种筛选

为了筛选出适应长沙烟稻轮作区不同烟叶采收期的晚稻品种,模拟烤烟正常采收与推迟采收两种条件,以15个晚稻品种为材料开展了大田品种比较试验。结果表明：（1）从全生育期角度,6月18日播种条件下,所有品种均适合作烟后晚稻种植,而6月28日播种条件下仅湘丰优103、隆香优130、深优9520、湘丰优9号、金优284、丰源优299、丰源优272能够正常成熟;（2）从产量角度,6月18日播种条件下,两优527、丰源优272和隆香优130产量可达8000 kg/hm2左右,是烟稻轮作区烟叶正常采收条件下烟后晚稻品种的首选;6月28日播种条件下,丰源优272、湘丰优103、深优9520和湘丰优9号是较佳选择,产量可达7600kg/hm2以上;（3）相关分析表明,产量与每穗粒数呈显著正相关,与经济系数呈正相关,因此选择穗型较大、经济系数较高的晚稻品种易获得高产。结果对长沙烟区烟后晚稻品种选择具有一定指导作用。     

‘越光’作麦茬夏稻栽培适宜播期（秧龄）的研究

旨在探明不同播期对‘越光’生长发育及其产量的影响,确立‘越光’在黄淮区域作麦茬夏稻栽培的适宜播期,阐明‘越光’适期播种高产的生长发育特点。以‘越光’为试验材料,连续进行了2年的田间试验,2013年设T₁（5月1日）、T₂（5月11日）、T₃（5月21日）、T₄（5月31日）4个播期处理,6月27日移栽,2014年与2013年播期处理相同,6月30日移栽,随机区组设计,3次重复。2013年的试验结果表明,T₃（5月21日播种,秧龄37天）产量最高,为6681.8 kg/hm²,T₄（5月31日播种,秧龄27天）产量次之,为 6533.2 kg/hm²,两者之间差异不显著;2014年的试验结果表明,T′₃（5月21日播种,秧龄40天）产量最高,为6866.4 kg/hm²,T′₄（5月31日播种,秧龄30天）产量次之,为6647.4 kg/hm²,两者之间差异不显著。2年试验中均以5月21日播种的综合农艺性状最好,5月31日播种的次之,表现为分蘖集中、蘖位较低,一次大分蘖所占比例大,群体整齐,后期不早衰,抗倒伏能力强,灌浆成熟期延长,落黄好,产量高,品质好。试验得出的结论是：‘越光’在黄淮区域作麦茬夏稻栽培适宜播期为5月下旬,适宜秧龄为35天左右（6叶1心）,10月1日前后成熟,全生育期127天左右;适当晚播是避免早衰、防止倒伏、提高单产的关键技术措施。     

Seed Priming Enhances the Performance of Late Sown Wheat (Triticum aestivum L.) by Improving Chilling Tolerance

In rice–wheat systems, late sowing of wheat is the major reason of low yield. This yield reduction is principally due to lower and erratic germination, and poor crop establishment because of low temperature prevailing. The present study was conducted to explore the possibility of improving late sown wheat performance by seed priming techniques. Seed priming strategies were: on‐farm seed priming, hydropriming for 24 h, seed hardening for 12 h and osmohardening with KCl or CaCl₂ for 12 h. Seed priming improved emergence, stand establishment, tiller numbers, allometry, grain and straw yield, and harvest index. However, seed priming techniques did not affect plant height, number of spikelets, number of grains and 1000 grain weight. Osmohardening with CaCl₂ gave more grain and straw yield and harvest index compared with control and other priming treatments, followed by osmohardening with KCl and on‐farm seed priming. Improved yield was attributed principally to better stand establishment and improved number of fertile tillers. Seed priming techniques can be effectively used to improve the performance of late sown wheat.     

适期晚播对不同密度冬小麦产量和茎秆抗倒性能的调控效应

(方法)本试验在宽幅播种条件下,以大穗型冬小麦品种泰农18为材料,设计常规播期10月10日和适期晚播10月20日2个播期处理,各播期下分别设置225、375和525万/公顷3个种植密度,(目的)研究了播期和密度互作对冬小麦产量及产量形成、茎秆重心高度、基部节间机械强度和茎秆抗倒指数的影响,以期明确适期晚播对密植高产冬小麦产量和茎秆抗倒性能的调控效应。(结果)研究结果表明,播期和种植密度显著影响冬小麦的产量和抗倒性能。各播期间适度密植(375万/公顷)可通过提高穗数获得高产,且在两播期间无显著差异。适度晚播显著提高各密度冬小麦抗倒指数;在晚播条件下,随种植密度增加,小麦重心高度提高的幅度、基部节间机械强度降低的幅度显著低于常规播期,从而使得适期晚播密植小麦的抗倒能力仍可维持在较高水平。(结论)适度密植小麦可通过适期晚播平衡其产量和抗倒能力,本试验条件下,采用375万/公顷的种植密度,在10月20日播种,可协同实现高产、稳产。     

不同生态条件下播期对机插杂交籼稻日产量的影响

为探讨不同生态条件下播期对机插杂交籼稻日产量的影响,并提出相应的丰产对策,以3个杂交籼稻品种宜香优2115、F优498和川优6203为材料,采取毯苗机插栽培方式,在四川的南部、射洪、安州和大邑4个生态点,通过分期播种,研究不同生态条件下播期对机插杂交籼稻全生育期、产量和日产量的影响。结果表明,不同生态条件下机插杂交籼稻的全生育期、产量和日产量存在差异;随着播期从3月下旬推迟至5月上旬,机插杂交籼稻播种至拔节期天数缩短,抽穗至成熟期天数增加,平均全生育期从159.5 d逐渐缩短至150.7 d,平均产量从10,260.45 kg hm~(–2)逐渐下降至7795.83 kg hm~(–2),平均日产量从64.58 kg hm~(–2) d~(–1)逐渐下降至51.95 kg hm~(–2) d~(–1)。气象因子对机插杂交籼稻产量和日产量的影响在不同生态条件下存在差异,产量与全生育期平均气温日较差、日照时数呈显著正相关,与水稻全生育期日平均温度、平均日最低温度、日平均相对湿度和降雨量呈显著负相关;日产量与全生育期平均气温日较差、日照时数呈显著正相关,而与全生育期平均日最低温度、日平均相对湿度呈显著负相关,在南部、射洪和大邑与全生育期日平均温度呈显著负相关。在四川盆地西平原区和中、东北丘陵区,冬水(闲)田或蔬菜茬口水稻最佳播期在3月下旬,选择F优498进行机插栽培可获得较高日产量;麦(油)茬水稻应在前茬收获后尽早抢栽,一般在4月下旬播种,选择F优498进行机插栽培可获得较高日产量。     

Influence of Sowing Dates on Yield and Oil Quality in Sunflower

Effect of sowing dates (temperature regimes) on growth, yield oil content and quality in sunflower ( Helianthus annuus L. ) was studied. Plants of early sowings which had received low temperature during 0–45 days of growth grew very poorly in height. Plant height significantly correlated with temperature at all the three growth stages. Plants sown in March produced highest yield and January sown plants recorded lowest yield. Protein content of seeds decreased where as the oil content increased with delay in sowing dates. Oil content in the seeds collected from different sowing dates showed significant differences. However, oil content was not significantly correlated with temperatures at any growth stages. Incorporation of ¹⁴C-acetate into lipids of developing seeds was increased as the sowing was delayed. Early sown plants had higher percentage of oleic acid and late sown plants had higher percentage of linoleic acid. Effect sowing dates on oil content and oil quality were discussed on the basis of temperature variation during different growth stages.     

不同播期与基本苗对小麦生长发育及产量构成的影响

为探明稻麦周年生产条件下小麦种植适宜播期和基本苗组合,于2012—2014 年在江苏省沭阳县进行了播期和基本苗组合试验,研究了不同播期（10 月10 日、10 月17 日、10 月24 日、10 月31 日和11 月7日、11 月14 日）和基本苗（180 万/hm2、270 万/hm2、360 万/hm2、450 万/hm2、540 万/hm2）条件下小麦生长发育及产量构成。结果表明,出苗率主要受播期影响,迟播降低明显;随着播期推迟小麦叶龄逐渐变小,全生育期缩短,缩短天数少于播期推迟天数。基本苗处理对出苗率和叶龄影响不大。相同生育阶段,同一播期随着基本苗的增加茎蘖总数增多,相同基本苗处理随着播期的推迟茎蘖总数减少。播期对小麦株高、穗下节间以及穗长影响明显。单产随着播期推迟先升后降,不同播期和基本苗处理对产量构成影响显著或极显著。因此,淮北地区稻茬麦遇冷冬适宜播期在10 月17—24 日,遇暖冬适宜播期在10 月17—31日,最佳基本苗360万/hm2。     

Relationship Between Cold Severity and Yield Loss in Chickpea (Cicer arietinum L.)*

Seed yield in chickpea (Cicer arietinum L.) is substantially increased by advancing sowing date from the traditional spring to early winter at low to medium elevation areas around the Mediterranean Sea. This shift, however, increases the probability of the exposure to subzero temperatures as low as -10 °C for up to 60 days in a year. These low temperatures often reduce seed yield of cold-susceptible cultivars. Yield losses from cold were estimated in two experiments conducted at Tel Hadya, Syria. In experiment 1, of 96 genotypes sown on nine dates ranging from autumn to spring during the 1981–82 season, those lacking tolerance to cold were killed and produced no yield in autumn sowing, whereas lines with cold tolerance produced nearly 4 t/ha which corresponds to a four-fold increase over spring sowing. Moderately cold-tolerant genotypes sown during early winter produced substantially more seed yield than the normal spring-sown crop. Seedlings were more cold tolerant than the plants in early or late vegetative stages. In experiment 2, in which yield loss due to cold in the field was estimated in 12 yield trials comprising 288 newly bred lines in the 1989–90 season, the regression of cold susceptibility on seed yield in each of the trials was highly significant and negative. On average, winter-sown trials produced 67 % more seed yield than spring-sown trials, but 125 out of 288 genotypes produced yield more than double in winter sowing. Early maturing lines suffered severe cold damage and many lines produced no seed.     

Growth analysis of autumn and spring sown sugar beet

Slow leaf formation in spring is regarded as the main factor limiting sugar beet yield. It is therefore expected that yield can be enhanced when plants develop leaves earlier resulting in an extended growing period. The aim of this study was to analyse leaf and storage root growth of sugar beet plants sown in autumn or very early in spring with regard to possible yield increases. In 2005/06 and 2006/07, field trials were conducted at 4 sites with 6 sowing dates: August, beginning and mid of September, and in February, March and April. Sequential harvests were conducted to follow yield formation.Field emergence of autumn sown sugar beets was fast and reached 90% whereas in early spring it was severely restricted due to low temperature. Leaf and root yield formation of autumn and spring sown sugar beets could well be described with thermal time confirming that sugar beet growth is temperature driven and day length insensitive. Despite longer growing periods autumn sown beets did not form more cambium rings in the storage root than spring sown beets. That might be partly due to the bolting process after winter. However, early spring sown beets as well did not achieve more cambium rings than plants sown in April pointing to a presumably limited ability to adapt cambium ring formation. Because of the shift to reproductive growth, autumn sown beets formed high amounts of shoot dry matter, but not much root dry matter. Furthermore, the root dry matter consisted of a lower sugar and a higher marc content and would therefore not be suitable for sugar recovery. Earlier sowing in spring did not result in a significant yield increase because the benefit from early sowing diminished throughout the season as also obvious from the distance between the cambium rings.For bolting resistant sugar beet varieties, which are expected to be available in near future, the presented data form a basis to predict yield with models. However, it has to be investigated to what extent sugar beet growth and yield formation benefits from early sowing and extended growing periods.     

黄淮南部玉米产量对气候生态条件的响应

针对近年来黄淮南部气候条件和耕作制度变化, 2015—2016年在河南农业大学科教园区以该区主推品种郑单958为材料, 采用分期播种方法, 研究玉米产量对气候生态条件的响应, 探讨气候因子与玉米产量的关系。结果表明, 由于年际间、播期间气候因子的差异, 玉米产量差异显著, 大体表现为春播产量高于夏播, 且夏播产量随播种时间的推迟而显著降低。随着播期的推迟, 玉米苗期日均温逐渐升高, 粒期日均温逐渐降低, 有效积温减少, 生育期缩短。试验设定密度下, 百粒重对产量的贡献大于穗粒数, 而影响百粒重和穗粒数的主要气候因子是全生育期有效积温和粒期有效积温。影响玉米产量的主要气候因子是苗期气温日较差(r = 0.696^*)和日均温(r = -0.638^*)、粒期有效积温(r = 0.822^**)和日均温(r = 0.723^**)、生育期有效积温(r = 0.843^**)。因此, 生产上, 春播玉米播期由传统的4月15日左右推迟至5月1日左右, 可减少花期阴雨和高温热害影响, 表现出较好的丰产稳产性。夏播玉米在麦收后抢时早播, 不仅可争取更多积温, 还可使玉米苗期处于较低日均温、粒期处于较高日均温的有利温度条件下, 同时为推迟收获期和机械粒收创造条件。     

The Interaction of Sowing Date and Water Availability in Determining Plant Architecture, Fruiting Pattern and Yield Components of Soybean (Glycine max L. Merr.)

A 2-year trial has been carried out in northern Italy on soybean (cv. Hodgson) grown in lysimeters, comparing three soil water regimes (well-watered conditions and water stress during vegetative and reproductive stages) at two sowing dates. Plant evapotranspiration and water uptake depth were calculated from volumes of water independently supplied to eight lysimeter layers; at harvest, plant architecture, yield components and fruit distribution along the main stem and lateral branches were evaluated.
Although water stress intensity was not severe, crop evapotranspiration and water uptake depth were severely restricted by water shortage. Both low water-availability and late sowing significantly modified the architecture of plants, decreasing total height, number and length of internodes and lateral branches. Seed allocation along the stem was shifted downwards both by delaying the sowing date and by reducing the water supply; the component most responsible for yield decrease was the number of pods per plant, while unit seed weight was only slightly affected by water stress. Grain yield reduction was higher when water availability was inadequate during the reproductive phase in the early-sown crop and during the vegetative stage in the late-sown crop. This suggests that the intensity of the water shortage, plant phenological stage of stress application, as well as the date of stress application within the growing season determine the yield response of soybean.     

Incidence of and yield loss caused by maize rayado fino virus in maize cultivars in Ecuador

Three sowing date trials, each planted with one cultivar, were performed to measure the natural incidence of the Maize rayado fino virus (MRFV). The lowest incidences (1–6%) were obtained at the sowing dates normally practised in the tested regions. Earlier or later sowing dates had higher to much higher incidences (up to 18 and 32%). Two cultivar trials, one with four cultivars and one with eight cultivars, showed significant differences in incidence, ranging from 14.0% in ‘Iniap-160’ to 2.0% in ‘Cadet-2’. In one trial with plots of 1000 m², the cultivar Iniap-122 was sown at three sowing dates. In each plot, plants that developed MRFV symptoms at the 8–10 leaf stage, at the 12–14 leaf stage and at the emergence of tassels were marked. Marked MRFV-affected plants were compared with non-MRFV-affected plants in their neighbourhood to estimate yield loss due to MRFV. The yield losses at the three sowing dates were 2.5, 1.6 and 4.8%, respectively. It was concluded that the yield loss due to MRFV is quite small provided sowing is restricted to the normal sowing period.     

The Effect of Intercropping Lablab purpureus L. with Sorghum on Yield and Chemical Composition of Fodder

In two years the growth and composition of mixtures of sorghum with Lablab purpureus as strips, paired rows and alternate rows were compared with those of sorghum and lablab monocrops. In the first year, when sowing did not occur until 7 August, the sorghum yields were low in the monocrop and even less in the mixed crops. Lablab yield was also reduced in mixtures compared with the monocrop, but total forage yield was greater for the mixed crops compared with sorghum alone. Of the mixed cropping systems, a reduction in the yield of lablab plants and in the phosphorus and potassium content of shed lablab leaves in paired rows suggested that there was more competition for nutrients between lablab plants grown in this treatment. In the second year, earlier sowing increased sorghum growth at the expense of lablab yield in the mixed cropping systems, with the result that total forage yield was not increased when sorghum was intercropped with lablab. However, the crude protein content of sorghum stems and leaf yield were increased in mixed crops, particularly in paired and alternate rows rather than strips, demonstrating that close configuration of the legume and cereal are necessary for the cereal to obtain most benefit from nitrogen fixed by the legume. It is concluded that, when conditions are favourable for rapid sorghum and lablab growth, the sorghum will benefit more when it is grown in paired rows with lablab rather than in strips. However, the close spacing normally adopted for paired rows may encourage competition between lablab plants and increase the requirements for phosphorus and potassium fertilizer.     

Heat Shock Protein in Developing Grains in Relation to Thermotolerance for Grain Growth in Wheat

Wheat ( Triticum aestivum L.) cvs DL 153-2 and HD 2285 (relatively tolerant), HD 2329 and WH 542 (relatively susceptible), were grown under normal (27 November) and late (28 December) sown conditions. In another experiment, these cultivars were grown under normal sowing and at anthesis stage, they were transferred to control (C) and heated (H) open top chambers (OTCs). Under late sowing, wheat cultivars were exposed to a mean maximum temperature of up to 3.6 °C higher than normal sowing and in H-OTCs, mean maximum temperature was 3.2 °C higher than C-OTCs during grain growth period. Heat susceptibility index (S) for grain growth and grain yield was determined at maturity in both the experiments. The level of heat shock protein (HSP 18) in the developing grains was determined in C- and H-OTC grown plants and in normal and late sown plants by Western blot analysis. The moderately high temperature exposure increased the accumulation of HSP 18 in the developing grains. The relatively tolerant cultivars, as also revealed from S , showed a greater increase in HSP 18 compared with susceptible types in response to moderate heat stress. An association of HSP 18 with thermotolerance for grain growth in wheat was indicated.     

Development and Yield Formation of Autumn- and Spring-sown Faba Beans in Northern Germany as Affected by Seasons, Sowing Dates and Varieties

Field trials were conducted with autumn- and spring-sown faba beans in Northern Germany during four seasons to examine the expected preceding development of autumn-sown plants, its possible transformation into a higher yield potential and its dependence on sowing dates and varieties. Height, appearance of leaves, inflorescences, mature flowers, potential and actual pot set was rated weekly, and flower initiation and tillering occasionally. Comparison was made for one winter type sown in autumn and spring, and between 6 winter types and 3 spring types, in two seasons each.
Development of autumn-sown plants significantly preceded that of spring-sown in each year, regardless of the plant material used. The mean advance, diminished considerably with time due to prolonged developmental phases in autumn-sown plants which, however, did not improve vegetative, generative or reproductive potentials of main tillers. Potentials formed by the six winter types, interacted strongly with the seasons, at least in part due to changing plant densities. Thus, only a very few traits appeared typical: a short stature with few leaves for Avrissot and the opposite for Bourdon , a high number of ripening pods for Avrissot and a low number for Banner . Early compared to late sowing in autumn increased the number of leaves, and in one year even the number of mature flowers and ripening pods per tiller, but values of early sowing never exceeded those of spring sowing. Enhancement of tiller formation by early compared to late sowing diminished after spring; nevertheless about two reproductive tillers per plant in autumn-sown stands always led to a higher density of tillers than in spring-sown.