PH Regulation For CO₂ Evolution By Bio-degradation Of Organic Wastes From Agriculture And Effects Of CO₂ Enrichment On Vegetables Growth In Greenhouse

It was found in previous studies that in the course of enriching CO₂ in greenhouse with the method of fermentation of agricultural organic wastes, the duration of CO₂ sustaining release was less than two weeks, which should be related to the sharp increase of substrate pH caused by NH₃ from the fermentation In order to solve this problem, three methods for pH regulation as chemical regulation, lactic acid fermentation liquid regulation and inoculation with acid-secreting bacteria favorable to high temperature were adopted in present research to study their effects on pH regulation and CO₂ release in the process of fermentation. Furthermore, the effects of CO₂ enrichment by fermentation of organic wastes on crop yield and quality and their mechanisms were also further studied. The main results are as follows:1. Effects of different methods of pH regulation on CO₂ release from the fermentation of organic wastesThe pH change in the fermentation of organic wastes for CO₂ generation showed a quick decrease to about 5 in two days of beginning, which was caused by organic acids from the fermentation at initial period, and a sharp increase to 7.5 until the fourth day, then had been stabilized between 8-9. The increase of pH was induced by NH3 from fermentation.CO₂ release amount was closely related to the pH changes of fermentation substrate. The quantity and duration of CO₂ release was significantly promoted and extended by pH decline. Therefore, the pH increase during fermentation should be one of the important reasons why CO₂ release from fermentation of organic wastes was not sustained.The effect of three methods on the pH regulation was chemical regulation > liquid from lactic acid fermentation > inoculation with acid-generating bacteria, but the liquid from lactic acid fermentation showed the best effect on increasing CO₂ release, then the inoculation with acid-generating bacteria. Therefore, it was suggested that regulation with liquid from lactic acid fermentation could be a reasonable method because the liquid of lactic acid fermentation was easily obtained by farmers from pickle making. However, inoculation with acid-generating bacteria may also be refered to a good method due to itssimpleness and efficiency.2. Effects of fermentation of organic wastes on CO₂ concentration in greenhouse and vegetable growthIn greenhouse, crops are often suffered from CO₂ starvation in daytime because the concentration of CO₂ can be decreased to below 250 μL L^-1 around noontime. The concentration of CO₂ could be increased remarkably by fermentation of agricultural organic wastes. The average concentration of CO₂ reached to 967 μL L^-1 at 8:00 am and 492 μL L^-1 at 12:00am respectively, about 2 times as high as that in control. Furthermore, the duration for CO₂ release could be lasted to one month by pH regulation.CO₂ enrichment by fermentation of agricultural organic wastes could increase the temperature in greenhouse, which was beneficial to protecting crops from freezing damage.CO₂ enrichment by fermentation of agricultural organic wastes could promote vegetable growth and largely increase the yield and bring forward one week for marketing. It could also significantly increase the contents of Vc and crude protein, and decrease the contents of crude fibre especially nitrate in vegetables. Therefore, the quality of vegetables was markedly improved.3. Effects of CO₂ concentration on the root morphology, nutrient uptake and nitrate accumulation of vegetablesThe growth of tomato and pakchoi cabbages was seriously inhibited when CO₂ concentration in greenhouse was decreased to 150 μl L^-1, but largely promoted by CO₂ encirhed to 800 μl L^-1 as the significant enhancement on the plant height and stalk girth as well as the biomass.The ratio of root/shoot of tomato was increased significantly by CO₂ enrichment, which indicated that CO₂ enrichment could induce transporting more photosynthesis products into the roots. The total root length, root axis diameter, total root volume and root surface area of t...