As a facility for horticultural cultivation, soilless cultivation can realize the efficient use of natural resources and land, which is of great significance for the modernization and sustainable development of agriculture (Wang Jiuxing and Wang Zihua, 2005; Yang Qichang and Zhang Chengbo, 2005; Jiang Weijie, 2007) . Soilless nutrient supply is mainly provided by nutrient solution (Wang Zhenlong, 2008), which directly affects the growth of crops, so the preparation and management of nutrient solution is the key to the success of soilless culture (Zhang Li, 2006). At present, there are many researches on nutrient solution formulas in China, and a number of nutrient solution formulas for different crops have been formed, but there are few studies on nutrient solution management methods, especially nutrient solution concentration management and regulation.
Soilless culture has no soil buffer and microbial action. The substrate and nutrient solution are the root environment in which the plants depend. Too low a nutrient solution will result in slow growth of the crop and low biomass, while too high a concentration will result in inhibition of crop growth and even death. Studies have shown that within a suitable range, the increase of nutrient solution concentration can increase the chlorophyll content of plant leaves, promote photosynthesis (Ni Jiheng et al., 2011), improve quality (Max & Horst, 2009; Li Shao et al., 2011), and ultimately increase yield ( Zhangetal., 2015); excessive nutrient concentration inhibits plant growth (Lietal., 2001), reduces root activity (Rouphaeletal., 2012) and nutrient use efficiency (Gao Xiaoxu et al., 2014), and inhibits yield increase And quality improvement (Chen Yanli et al., 2010; NeoCleous & Savvas, 2015). Lin Duo et al. (2007) showed that low-concentration nutrient solution is not conducive to the growth of muskmelon melon plants; while high-concentration nutrient solution makes the plant grow too nutritious, and the yield and quality deteriorate. Bie Zhilong et al. (2005) showed that an increase in the concentration of nutrient solution increased the accumulation of nitrate in the plant. Studies on spinach and Chinese cabbage have shown that high nutrient concentrations cause a decrease in photosynthesis rate and an increase in nitrate content (Wang Rui et al., 2016), and decline in quality and yield (AlberiCietal., 2008). It can be seen that the management of nutrient solution concentration has an effect on photosynthesis and root activity of vegetables, which ultimately affects yield and quality. Therefore, the scientific management of nutrient solution concentration is conducive to promoting the growth and development of vegetables.
Amaranth nutrient solution hydroponic technology has solved the problem of cockroach in the production process of leeks, greatly reducing the use of pesticides, and has the advantages of fast growth rate, high yield and high vegetable yield. However, there are few studies on nutrient solution management and nutrient solution concentration in hydroponic amaranth. This experiment studied the effects of nutrient solution concentration on the growth, yield and quality of amaranth, in order to provide technical support for hydroponic cultivation of amaranth nutrient solution.
1 Materials and methods
1.1 Test materials
The experiment was carried out in a glass greenhouse of the Vegetable Research Center of the Beijing Academy of Agricultural and Forestry Sciences. The amaranth variety 791 was used as the test material, and the hydroponic facility was the amaranth hydroponic system developed by the Vegetable Research Center of the Beijing Academy of Agricultural and Forestry Sciences. The 72-hole bottomless tray was used to sow 3 seeds per hole. The seeding paper was first laid on the grid when planting. Seeds are sown on top, then covered with paper, and finally covered with a layer of moist perlite, placed in the germination box to germination, after the seeds are germinated, the tray is placed in the cultivation tank into the nutrient solution.
The normal nutrient solution formula is: Ca2+1.0mmolL-1, K+6mmolL-1, NO4-8mmolL-1, NH4+4mmolL-1, Mg2+1mmolL-1, PO43-2mmolL-1, and the pH is controlled at 6.00.3; The micro-fertilizer uses a universal formula. The nutrient solution is prepared using purified water.
1.2 Test methods
Five concentration gradients of 0.5 times (0.5C), 1.0 times (1.0C), 1.5 times (1.5C), 2.0 times (2.0C), and 2.5 times (2.5C) were set on the basis of the normal nutrient solution (C). The EC values ​​of the concentration nutrient solution were: 0.90, 1.60, 2.29, 2.90, 3.41, 4.11 mSCm-1, respectively, and the pH was adjusted to 6.00.3 using 0.1 mol L-1 NaOH, and the adjustment was performed once every 7 days. Five dishes were sown for each treatment, and three well-growing plates were selected for investigation. Each plate was randomly surveyed with 5 plants, each with a treatment area of ​​0.76 m2.
1.3 Determination project
The experiment was planted on April 5, 2012. Since the leek needs to be rooted to ensure subsequent harvests, the period from sowing to the first harvest (September 5) is longer, in order to ensure the accuracy and accuracy of the indicators, except for the yield. All indicators are measured at level 2, the second harvest time is October 3, and the third harvest time is November 7. The growth index was determined by plant height, pseudo-stem rough, leaf length, leaf width and number of leaves of the leek plant. Five plants were counted per treatment and three replicates. The fresh weight of each plant was determined by electronic balance, and then the gel was 15 min at 105 °C. The mixture was dried to constant weight at 75 ° C, and the dry mass was measured. Each treatment was repeated 3 times, and each repeated measurement was performed 3 times, and 2 strains were measured each time. The root activity was determined by reference to the method of Li Hesheng (2000).
Determination of quality index: Determination of VC content by 2,6-dichlorophenol indophenol colorimetric method (Liu Chunsheng and Yang Shouxiang, 1996); Determination of soluble sugar content by anthrone colorimetric method (Zhao Shijie et al., 2002); Coomassie blue ratio Determination of Soluble Protein Content by Color Method (Zhao Shijie et al., 2002); Determination of crude fiber content by 60% H2S04 digestion-fluorenone colorimetric method (Li Hesheng et al., 2000); Determination of nitrate content by ultraviolet spectrophotometry (Agriculture of the People's Republic of China) Industry standard NY/T1279—2007); Determination of nitrite content adopts the method of “National Standard of the People's Republic of China—Determination of Nitrite and Nitrate Content of Fruits, Vegetables and Their Products†GB/T15401-1994.
The yield (kg) of amaranth in a nutrient solution culture tray (area of ​​0.1512 m2) at the time of harvest was taken as the yield, and the yield of the three amaranth was measured and the total yield was calculated. Yield [kg(667m2)-1]=(quality of amaranth in a single nutrient solution cultivation tray 667)/grid area
1.4 Data Processing
Data processing and analysis were performed using ExCel 2010 software and SPSS 17.0 software.
2 Results and analysis
2.1 Effect of nutrient solution concentration on the growth of amaranth
With the increase of nutrient solution concentration, the plant height, leaf length, leaf width, leaf number and pseudo-stem thickness of amaranth increased first and then increased. The plant height and leaf length of the amaranth treated with 0.5C were the highest, which were significantly increased by 8.08%, 19.21%, 31.59%, 18.41% and 10.01%, 21.98%, 33.62% and 19.27%, respectively, compared with other treatments; 0.5C, 1.0C treatment The difference in pseudo stem diameter was not significant, but was significantly higher than other treatments. The root activity of amaranth also decreased first and then increased with the increase of nutrient concentration. The root activity of 0.5C and 1.0C treatment was significantly higher than that of other treatments, and the root activity of 2.0C treatment was the lowest.
2.2 Effect of nutrient solution concentration on the quality of amaranth
The VC content of amaranth increased first and then decreased with the increase of nutrient solution concentration. The VC content of 2.0C treatment was the highest, which was 328.7mgkg-1. The soluble sugar content increased first and then decreased with the increase of nutrient solution concentration. The trend is that the highest content of 1.0C treatment is 1.49%; the content of crude fiber is the highest at 2.5C, which is 1.19%, and the difference between the other four treatments is not significant; the content of soluble protein is the highest at 2.0C, which is 2.79%. The nitrate content of amaranth plants increased significantly with the increase of nutrient solution concentration. The nitrate content of 2.5C treatment was the highest, reaching 2568.80mgkg-1, and 0.5C treatment was the lowest.
The nitrite content increased first and then decreased with the increase of nutrient solution concentration. The nitrite content of 0.5C treatment was the lowest, which was significantly lower than other treatments by 40.6%, 47.2%, 74.1% and 69.2%, respectively.
2.3 Effect of nutrient solution concentration on amaranth biomass
The fresh and dry quality of the éŸ menu decreased first and then increased with the increase of nutrient concentration. The fresh and dry quality of each plant treated with 0.5C was the highest, 2.89 g and 0.25 g, respectively. The yield of 3 amaranth showed a downward trend with the increase of nutrient concentration. The total yield was the highest at 0.5C, which was significantly increased by 9.5%, 14.2%, 31.3% and 42.3%, respectively.
3 Discussion
Nutrient solution contains all kinds of nutrients necessary for plant growth and development. The success of soilless culture production depends to a large extent on whether the nutrient solution formula and concentration are suitable, and whether nutrient solution management can meet different growth stages of plants. demand. The results of this experiment showed that with the increase of nutrient concentration, the plant height, leaf length, leaf width, pseudo-stem thickness, leaf number and root activity of amaranth decreased first and then increased. The dry and fresh quality of the éŸ menu was also observed. After the decline and the upward trend, the overall yield showed a downward trend. This is consistent with the research results of Chen Yanli et al. (2010) on Chinese cabbage. It can be seen that increasing the concentration of nutrient solution to a certain extent will inhibit the growth of amaranth. The inhibition of the growth of amaranth by high-concentration nutrient solution may be related to the increase of EC value of nutrient solution. High EC value may cause osmotic stress on root system, which leads to inhibition of root growth and hinder the absorption of nutrients. In the analysis of quality, it can be seen that with the increase of nutrient solution concentration, the content of VC, soluble protein and soluble sugar increased first and then decreased. It can be seen that the increase of nutrient solution concentration is beneficial to the quality of amaranth. The improvement is consistent with the results of Zhang Wei et al. (2013) on tomato. The supply of nitrogen in nutrient solution mainly depends on nitrate nitrogen, which leads to high nitrate content in hydroponic vegetable products. In this experiment, the nitrate content of amaranth increased rapidly with the increase of nutrient solution concentration. The nitrate content of 0.5C treatment was the lowest, and the treatment of 2.5C was the highest. The difference between the two was more than 30%. It can be seen that reducing the concentration of nutrient solution is an effective measure to reduce the nitrate content in plants. However, it can be seen from the results of the quality test of this test that the increase of nutrient solution concentration in a certain degree is conducive to the improvement of quality indicators such as VC, soluble sugar and soluble protein. Therefore, the regulation of nutrient solution concentration in soilless culture should take into account both the yield and quality factors. Further research is needed on methods for reducing nitrate content and nutrient solution formulations for low nitrate nitrogen.
4 Conclusion
1 Different nutrient solution concentrations have significant effects on the growth, yield and quality of hydroponic amaranth. The increase of nutrient solution concentration is beneficial to increase the content of VC, soluble sugar and soluble protein, but it will inhibit the growth of amaranth, reduce yield and increase amaranth. The content of nitrate and nitrite.
2 The results of this experiment showed that the highest yield of amaranth was 0.5492.14kg (667m2)-1 at 0.5C treatment (EC value 2.90), and the nitrate and nitrite content were the lowest, which was the suitable nutrient solution concentration for hydroponic amaranth.
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