Effects Of Light Intensity On Physicochemical And Biological Properties Of Tobacco Floating Seedling Substrate

Floating seedling,as the main method of raising seedlings in flue-cured tobacco in China,have certain advantages,but in actual production of some areas,problems such as low emergence rate,uneven emergence,salinization of substrates,and growth of green algae have occurred.In order to solve such problems,this experiment explores the effects of different light intensities on the physical and chemical properties of the substrate by measuring the electrical conductivity,bulk density,moisture content,porosity,and pH value of the substrate under different light treatments;Under different conditions,different light treatments were set up to explore the optimum light intensity and duration of tobacco seed germination,and the effect of light intensity on the occurrence of green algae.The results showed that:(1)Under 100% and 60% light transmittance,the electrical conductivity of the substrate in the nursery hole gradually increased from bottom to top,and under 30% and 0% light transmittance,the conductivity of each part of the substrate in the nursery hole tended to be consistent.Under the light transmittance of 60%,the conductivity of the substrate at the upper and the middle respectively decreased by 11.5% and 15.8%,which compared with that under natural light intensity.The electrical conductivity of each part of the substrate changed significantly with treatment time during the first 14 days of seedling,and stabilized at the 14 th day(P<0.05).The bulk density of each part of the substrate tended to be stable under 60%,30% and 0% light transmittance.With the increase of the treatment time,the bulk density of the upper and middle of the substrate gradually increased and were significantly lower than the natural light treatment in the shed,but there was a certain threshold for the increase of the bulk density(P<0.05).The effect of low light on the bulk density of the substrate was mainly in the lower part of the substrate during the first 7 days of the floating seeding,and mainly in the middle and lower parts during 7-14 days.The light transmittance of 60%,30% and 0% could increase the moisture content of the upper part of the substrate,and the light transmittance of 60% could significantly increase the moisture content of each part of the substrate.On the 14 th day,the moisture content of the upper,middle and lower parts of the substrate increased by 11.4%,10.3% and 3.7% compared with CK under the 60% light transmittance,and in addition to the light transmittance of 0%,the moisture content of the substrate gradually decreased with the rise of the position(P<0.05).Under the 0% light transmittance,the moisture content of each part of the substrate was basically the same,and this effect continued to appear during the first 14 days.The light transmittance of 60%,30% and 0% could increase the porosity of the substrate,which appeared in the various parts of the substrate during the first 7 days,and the porosity of the upper part and the lower part of the substrate increased greatly during 7-14 days,and the porosity of all parts of the substrate increased significantly and tended to be consistent under the light transmittance of 60%(P<0.05).The pH value of each part of the substrate fluctuated with the change of position,showing a trend that the pH value gradually decreased with the upward movement of the position,and this trend became more obvious with the treatment time increased.Under the light transmittance of 60%,the pH value of each part of the substrate changed slightly,and the fluctuation was relatively gentle.(2)The occurrence of green algae on the substrate surface gradually weakened with the decrease of light transmittance.Under 60%,30% and 0% light transmittance,the area of green algae on the substrate surface without seeding respectively decreased by 48.8%,72.1% and 92.4%,and after seeding decreased by 42.9%,63.9% and 92.9%.Under the incubator,the growth of green algae gradually decreased with the decrease of light intensity,so reducing the light intensity can effectively inhibit the growth of green algae.(3)Under the conditions of floating seedling,the light transmittance of 60% could significantly increase the germination potential and germination rate of tobacco seeds,respectively increased by 42.1% and 9.5%,and the growth of tobacco seedlings was optimal under this light transmittance.Too high or too low light intensity or too short light duration under incubator conditions were not conducive to the germination of tobacco seeds,but a certain weak light treatment was conducive to improving the germination potential and germination rate of tobacco seeds.And the longer the light duration under this condition,the greater the light intensity,the better the growth of tobacco seedlings.(4)In order to improve the nursery effect of floating seedling of tobacco and reduce the occurrence of green algae on the substrate surface,the seedling tray can be covered before the period of little cruciform in actual production.The light transmittance is about 60%,that is,the light intensity is about 3000 Lux.