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The closed nutrient solution management method allows for the recycling and utilization of nutrient solutions, improving the efficiency of water and fertilizer utilization. This study was conducted to investigate the effects of changing the frequency of nutrient solution renewal and method of nutrient supply on the microbial communities composition, yield, and quality in closed soilless systems by using high-throughput sequencing technology and combining the physicochemical properties of root exudate solution. The results showed that different nutrient solution management modes had a significant impact on the structure and diversity of root exudate solution microbial communities. The abundance and diversity of microorganisms in inorganic perlites were correlative with EC. The abundance and diversity of bacterial communities in the root exudate solution of open liquid supply (CK) were higher than that of closed liquid supply, while the abundance and diversity of fungal communities in the root exudate solution of closed liquid supply (T1, T2, T3) were higher than that of open liquid supply. As the frequency of nutrient solution interval decreased, the accumulation of salt in root exudate solution and the richness and diversity of the fungal community also decreased, especially increasing the K+, Ca2+, and Mg2+ contents, which were positively correlated with potential beneficial Candidatus_Xiphinematobacter, Arachidicoccus, Cellvibrio, Mucilaginibacter, Taibaiella communities and decreasing the content of soluble protein, Vitamin C content, but not significantly increased cucumber yield. [ABSTRACT FROM AUTHOR]

Due to the remarkable health benefits of celery (Apium graveolens), its consumption has increased over time. A partial substitution of NO3− with NH4+ is recommended to limit the accumulation of NO3− in leafy vegetables. Hence, a factorial experiment with two factors, consisting of six treatments as combinations of three NH4:NO3 ratios (0:100, 20:80 and 40:60) in nutrient solutions and two harvesting times (in the morning and in the evening), was conducted on celery plants in a soilless culture system. The results showed that 100% NO3 as a sole N source significantly increased plant height, leaf number, chlorophyll, fresh weight, N, K, Ca, Mg, Fe, Mn, Zn, protein, dietary fibre, soluble sugars, nitrate, vitamin C, α-carotene, β-carotene and lutein of celery plants compared to either 80 or 60% NO3. However, this increase was not significant compared to 20% NH4:80% NO3 in terms of leaf number, fresh yield, N, Mg, Mn, protein, soluble sugars, vitamin C and α-carotene. Harvesting in the evening significantly increased K, Mg, Fe, soluble sugars, α-carotene and β-carotene, and lowered the nitrate level in celery plants. In conclusion, partial replacement of 20% NO3-N with 20% NH4-N and evening harvesting are recommended for a greater fresh yield, higher quality, and lower nitrate level.

At present, plug seedling cultures are common in China. The traditional plug has a hole on the bottom, which could cause the root growing through the bottom hole, thus the roots will be easily hurt when moving and plug needs to water frequently, which wasted water. In order to solve these problems, Beijing Vegetables Research Center(BVRC)developed the side opening plug, open double vertical holes surrounding each plug, each vertical hole is not lower than the bottom of the plug, which would help by keeping water in the plug. At the same time, it could avoid the roots growing through the bottom. To understand the effects of this new side opening plug method, tomato (Solanaceous vegetables) was used as the test materials in this paper. And we observed the effects of different opening methods in summer on seedlings' growth, development and water use efficiency. The main contents are as follows: Tomato cultivar 'Ouguan' was used as materials, to study the effects of the side opening and bottom opening plug methods on seedlings' growth and water use efficiency in summer. The test had two treatments, bottom opening and side opening; each treatment was repeated 4 times. In order to precisely control the amount of watering, the water was injected to each plug by a gun. The lower limit for irrigation was substrate water content decreasing to 50% of the maximum moisture capacity. Irrigation lower limit and upper limit was determined by the weighing method. Every time before and after irrigation, the weight of the trays were recorded. The amount of water irrigated and the outflow water were recorded. We also recorded the plant growth index. The results showed that the seedlings in side opening trays grew better than those in bottom opening trays in summer and autumn. The seedlings growing in side opening plug are higher and thicker with a larger biomass and higher seedling index (0.0178, 22.76%). During the whole seedling stage, the average watering amount is 25.58 kg of the side opening plugs, which is 11.7% less than bottom opening treatment. The results have shown that, the side opening plug method could promote the seedling growth and save water. The new tray supplies the seedling with a better environment, including water, fertilizer, gas and temperature, which make the tomato seedlings grow well, effectively increasing the biomass of the seedlings and seedling index. The new tray can also reduce the use of water and save labor. [ABSTRACT FROM AUTHOR]

The Chinese solar greenhouse, characterized by east-west orientation, a transparent camber south roof, and a solid north roof and east and west walls, is utilized primarily in horticulture in northern China. This design of greenhouse can keep the sheltering plants from freezing in winter because of the "greenhouse effect". However, the healthy growing of plants still needs assisted heating especially during winter nights. The coal-fired heating system (CFHs) and the natural gas-fired heating system (GFHs) both have been widely applied to heat greenhouses. However, the conventional fossil energy sources, such as coal and natural gas, are non-renewable and are the major greenhouse gas (GHG) contributors. The overusing of fossil fuel in agricultural production has been directly or indirectly related to the global climate change, environmental pollution, and energy crisis. Therefore, renewable and clean energy, such as solar, geothermal, and shallow geothermal has been increasingly applied for greenhouse heating or cooling across the world. Ground source heat pump (GSHP) technology has dual functions in heating and cooling. It is one of the most rapidly growing green technologies for heating and air-conditioning in recent years. The GSHP application for solar greenhouse heating has proven to have a high primary energy ratio or coefficient of performance (COP) in previously studies. However, the environmental performance of the GSHP in heating solar greenhouse, such as its carbon footprint, is still unknown. Systematic and long-term study of the specific GSHP greenhouse-heating was required to evaluate its carbon footprint based on life cycle assessment (LCA) method. The GSHP in a Chinese solar greenhouse was studied to evaluate its environmental performance in greenhouse heating. The environmental performance of the GSHP was analyzed based on the field test data and the performance analysis models that were developed in this study. According to the study, in a 480 m2 Chinese solar greenhouse during the winter heating period, the GSHP demonstrated stable heating effects. The shallow geothermal energy utilized by the GSHP, in the processes of energy storage, extraction, enhancement of refrigeration compression cycles, and greenhouse heating, were studied to analyze the greenhouse gas (GHG) emission inventory and emission levels based on per square meter of the greenhouse floor. An analysis method based on LCA was developed for estimating the carbon footprint of Chinese solar greenhouse heating with GSHPs in this study, the carbon footprints of a GSHP greenhouse heating system operating on coal fired power and gas fired power were analyzed and calculated according to the data collected from a solar greenhouse heated in the Beijing area. Meanwhile, the variation of global warming potential (GWP, CO2 emission equivalent or CO2-eq) of GSHP in heating a Chinese solar greenhouse from 20 to 100 a were analyzed. The GWP of GSHP greenhouse heating operating on coal fired power and gas fired power were 257 g/(m2•d) and 72 g/(m2•d). Meanwhile, the total GWP of 100a is reduced by 1.6% and 5.4% from the calculation of 20 a. Comparing the carbon footprints between solar greenhouse heating with GSHP and Venlo greenhouse heating with natural gas, the carbon footprint of solar greenhouse GSHP heating was 39% more than that of Venlo greenhouse heating when GSHPs was operating on coal fired power, but the carbon footprint of solar greenhouse heating will be only 41% of Venlo greenhouse heating when GSHPs were operating on gas fired power. The GSHP heating test was focused on a Chinese solar greenhouse in this study to estimate the environmental performance; however, the carbon footprint calculation and analysis methods are applicable to different styles of multi-span greenhouse GSHP heating analysis. [ABSTRACT FROM AUTHOR]