小白菜（Brassica rape L. ssp. chinensis）又称不结球白菜、青菜、油菜等。菜秧是小白菜的幼龄植株，原产中国，喜冷凉，生长适宜温度为18-20℃，高温强光天气会导致“夏淡季”，即喜凉性叶菜供应不足。在4-10月，防虫避雨棚内温度过高，超过小白菜正常生长温度范围，夏季的高温强光对小白菜生长更是不利。因此，根据播种期温光特点，探究合适的种植密度及遮阳条件，有效缓解高温强光对小白菜的伤害，促进小白菜生长，提高产量，改善品质，对小白菜的周年生产有重要意义。 本试验根据不同播种期的温光环境特点，探寻不同播种期下，生长密度和遮阳率对小白菜生长发育的影响，明确不同播种期下较适宜的生长密度和遮阳率，保证小白菜的周年供应及良好的产量和品质。此外，根据不同类型的小白菜在各播种期的产量和品质的表现，确定适栽品种，为小白菜的优质高效生产体系的建立提供依据。主要研究结果如下： 1.以品种‘青蓝’和‘抗热605’为材料，在防虫避雨棚中设置1125株/m2<上标!>，875株/m2<上标!>，625株/m2<上标!>，375株/m2<上标!> 4个密度，播种期分别为4月9日、5月17日和8月18日，共3个播种期，研究了不同播种期下生长密度对小白菜生长及产量和品质的影响。结果表明，4月9日和5月17日播种的小白菜，‘抗热605’在实际生长密度分别为1131.33株/m2<上标!>和1146.67株/m2<上标!>下产量高，品质好；‘青蓝’在实际生长密度分别为1226株/m2<上标!>和1216.67株/m2<上标!>下产量和品质最好。8月18日播种的小白菜实际株数减少，需要增加播种量以保证能达到最适宜的密度。根据8月的温光特点，‘抗热605’和‘青蓝’分别在773.33株/m2<上标!>和777.33株/m2<上标!>的生长密度下栽培品质较好，产量较高。4月9日、5月17日和8月18日播种时，均以‘抗热605’产量较高，品质较好。 2.以‘抗热605’、‘青蓝’和‘黄玫瑰’为材料，在防虫避雨棚中栽培，设置遮阳率为0%（CK）、30%、45%、60%、75%共5个处理，采用遮阳网覆盖，实际遮阳率为0%、29.3%、43.2%、54.2%、62.6%，分别于6月6日、7月17日和8月18日播种，研究不同播种期下遮阳处理对小白菜生长发育、产量和品质的影响。结果表明，6月6日播种，‘抗热605’在不遮阳下产量最高，在30%的遮阳率下品质较好；‘青蓝’在45%的遮阳率下产量最高，在30%遮阳率下品质最好；‘黄玫瑰’在45%的遮阳率下产量最高，在30-45%遮阳率下品质最好。6月6日播种的小白菜以品种‘黄玫瑰’，采用遮阳率为30-45%的遮阳网覆盖效果较好；7月16日和8月18日播种，提高遮阳率对增加小白菜产量效果明显，3个品种均以60%的遮阳率产量最高，45%的遮阳率下品质较好。7月16日播种以‘黄玫瑰’为宜，8月18日播种以‘抗热605’为宜。

Non-heading Chinese cabbage is also called green vegetable, ‘youcai’ and Chinese little greens, etc. Non-heading Chinese cabbage seedling is the seedling stage of Non-heading Chinese cabbage (Brassica rape L. ssp. Chinensis), native to China. It adapts to cool and the optimum growth temperature is 18-20℃. High temperature and strong light will lead to ''''''''summer off-season'''''''' , which is known as lack of green leaves vegetables supply. From April to October, temperature exceeds the growth temperature of non-heading Chinese cabbage seedling in rain-shelter and insect-proof cultivation in plastic tunnel. What’s more, the temperature and light conditions in summer are unfavorable to the growth of non-heading Chinese cabbage seedling, which is easy to cause growth disorders. According to the characteristics of temperature and light, suitable planting density and shading rate can effectively alleviate the damage caused by high temperature and strong light, which is conducive to the growth, yield and quality improvement of non-heading Chinese cabbage. The experiment was based on the characteristics of temperature and light in different sowing dates, 2 cultivation measures (density and shading rate) were adopted to investigate the effects of density on growth of non-heading Chinese cabbage in different sowing date to find suitable density under different sowing dates. According to the environmental characteristics of high temperature and strong light, we select the appropriate shading rate to ensure good yield and quality in different periods. In addition, by means of the yield and quality of different types of Chinese cabbage at different sowing dates, we can make clear the suitable cultivar in different sowing date. The aim was to put forward a set of cultivation techniques to deal with different sowing dates, providing experience for the production of high quality and efficiency. The main results are as follows: 1.We used non-heading Chinese cabbage ‘Qinglan’ and ‘Kangre605’ as materials, which was cultivated in insect-proof and rain-shether plastic tunnel, and setted up 1125 plant, 875 plant, 625 plant and 375 plant per square, sowing in April 9th, May 17th and August 18th. The effects of growth density and sowing date on the growth, yield and quality of non-heading Chinese cabbage were studied. The results show that using the density of 1131.33 and 1146.67 plants per square sowing of ‘Kangre605’ in April 9th and May 17th could achieve high yield and good quality. Using the density of 1226 and 1216.67 plants per square sowing of ‘Qinglan’ in April 9th and May 17th could have a high yield and good quality. 773.33 plants per square sowing of ‘Kangre605’ and 777.33 plants per square sowing of ‘Qinglan’ in August 18th would achieve high yield and good quality. However, seedling number is reducing in August 18th, and we need to increase the amount of seedling to ensure a suitable density. What’s more, ‘Kangre605’ has higher yield and better quality in April 9th, May 17th and August 18th according to our research. 2.In order to study the effects of sowing date and shading rate on the growth, yield and quality, we used non-heading Chinese cabbage seedling ‘Kangre605’, ‘Qinglan’ and ‘Huangmeigui’ as the object of study and cultivated in insect-proof and rain-shether tunnel with shading rate 0%, 30%, 45%, 60%, 75% while the actual shading rate is 0%, 29.3%, 43.2%, 54.2% and 62.6% after covering sun-shade net sowing in June 6th , July16th and August 18th respectively. The results show that in June 6th, ‘Kangre605’ had high yield in no shading treatment and good quality in 30% shading rate. ‘Qinglan’ had high yield in 45% shading rate and good quality in 30% shading rate.‘Huangmegiui’ had high yield in 45% shading rate and good quality in 30-45% shading rate. In a word, using the variety of ‘Huangmeigui’ had a best effect and covering sun-shade net with 30-45% shading rate could improve the production and quality in June 6th. Sowing in July 17th and August 18th, increasing shading rate had a obvious effect on yield improvement, the shading rate of 60% made a higher yield and 45% shading rate made better quality. In summary, it’s more suitable to use ‘Huangmeigui’ in July 16th, and ‘Kangre605’ in August18th.