Study On The Solution Formula For Hydroponics Of The Leaf Vegetables Base On The Underground Water Quality In Yinchuan Plain

The nutrient solution and management is the key technology in the soilless culture. The quality of the water, which is used in these preparations, may affect the composition of solution and the effectiveness of some elements more or less, sometimes it can influence the crop growth severely, and in other words the water quality can determine the success of the soilless culture. The different water quality can sometime make the soilless crop to be performed mal-growth or reduce yields. The most of northern parts of China belong to the hard water areas, where the underground water quality is poor. Based on the analyzing the water quality, this study is to screen the solution formula which is based on the regional underground water, and is to provide the technical support for the soilless vegetable culture. The following are the main results:1. After analyzing the water samples, which were taken from the well with different depth in the greenhouse fields from Zhongwei City, Wuzhong City, Qingtongxia City, Yongning Couty, Yinchuan City, Helan Couty, and Pingluo Couty, which are along the Yellow River in Ningxia, the results showed that the quality of the most water taken from well in Yinchuan Plain is not suitable for the soilless culture, because the pH, total salt, HCO₃^-,Ca²⁺,Mg²⁺,Na⁺,Cl^-,SO₄^2- are too high to be suitable for the soilless culture. In order to develop the industry of soilless culture, the formula of the solution should be studied and screened.2. The plants absorb element of Na⁺ and Cl^- in a very fewer level, but the high concentration of Na⁺ and Cl^- in the original water can make the salt accumulation in the solution or media. The high content of Na⁺ and Cl^- in the underground water in Yinchuan Plain is regarded as an indicator of poor water quality. Though there is little inhibition to Brassica rapa L. Chinensis Group in nutrient solution by rainwater which is added NaCl by 500 mg/L （the concentration of Na⁺ is about 200 mg/L）, the inhibition is minor, and B. rapa can be cultured by Hydroponics. It indicates that leaf vegetables can be planted by Hydroponics in Yinchuan Plain.3. Under the suitable acid condition, no Ca²⁺ and Mg²⁺ added nutrient solution can fulfill the needs of plants, and no significant shortage symptoms is performed. All this indicated that Ca²⁺ and Mg²⁺ in the original water can be utilized adequately under regulating acid condition, so when the nutrient solution is prepared, Ca²⁺ and Mg²⁺ may not need to be added in according to the their content in the original water.4. In the experiments of Hydroponics at different pH, the result showed that, B. rapa grows better at pH 6.5 5.5 than at pH 7.5 8.5 in the following indexes: the morphological index, water absorption rate, pH, EC, the values of nutrients in shoot and root, inorganic nutrient uptake rate. In other words, the solution pH at 7.5～8.5 is not suitable for the growth of Chinese cabbage, and the pH 6.5～5.5 is suitable. Considering the cost, the pH in the solution in Yinchuan area can be adjusted to 6.5, and Nitrate acid or phosphate acid should be used to adjust pH, because the content of SO₄^2- is high enough in the original water.5. By means of quadratic general rotational design under the conditions of Deep Follow Technique, the concentrations of NO₃^-N, P, K and Ca in the formula of solution for B. rapa L. Chinensis, Ipomoea aquatica Forskwas studied comprehensively.（1） The regression model demonstrated the relationships between yield factor （Y） and four element factors the concentrations of N, P, K, Ca（X₁, X₂, X₃, X₄）were established. The each crop model is as following: YBrassica rapa=141.42857 + 10.55542X₁ + 6.40792X₂ + 8.05042X₃ - 7.95996X₁² - 9.66621X₂² -4.55246X₃² -4.69121X₄²+5.91688X₁X₄ YIpomoea aquatica= 89.86543 + 9.23667X₁ + 3.08000X₂ + 5.55083X₃ -5.44907X₁²- 8.84032X₂² -4.03407X₃²+2.46218X₄²+3.79500X₁X₃（2） Analysis result showed that: the effects of four factors on the yield of B. rapa, I. aquatica. increased by degrees in series of nitric-nitrogen（NO₃^-N）>potassium （K） > phosphorus （P） > calcium （Ca）.（3） By doing analysis for the model, we get the interaction between B. rapa’s N and Ca, I. aquatica’s N and K were significant; There is significant positive interaction between them in lower level and significant negative interaction between them in higher level.（4） By simulation with computer, the following fact are achieved: when the single plant yield of B. chinensis is 148.75 g, the optimal combination of these factors was that the concentrations of N, P, K and Ca should be 9.0 mmol/L, 0.5 mmol/L, 4.5 mmol/L, 3.0 mmol/L; when the single plant yield of I. aquatica is 108.81g, the optimal combination of these factors was that the concentrations of N, P, K and Ca should be 9.0 mmol/L, 0.5 mmol/L, 4.5 mmol/L, 0 mmol/L, For the content of Ca in the original water has been already 2 mmol/L, the optimum solution formula should be adjusted to be following when they are prepared: B. rapa, 9.0, 0.5, 4.5, 5.0 mmol/L;I. aquatica, 9.0, 0.5, 4.5, 2.0 mmol/L.（5） In the verification experiment of the model with B. rapa, I. aquatica, the optimum formula recommended from the model is all higher than the control in the following indexes: the growth vigor, root vigor, yield, quality and the content of total N, P, K, and the worst formula recommended from the model is all lower than the control. All these prove the model is accuracy and reliability.6. At the high content of NaCl （Na 21.7 mol/l ） the ratio of 6:2 for the NO₃^ー-N : NH₄^-N is the best in the 4 treatments （8:0, 7:1, 6:2 and 4:4） in the formula for hydroponics of B. rapa, it can significantly increase the growth and yield, dark the leaf color, and decrease the content of NO3– in the edible parts.