Preparation technology of nutrient solution for soilless cultivation

Preparation technology of nutrient solution for soilless cultivation

The first step of soilless cultivation is the correct preparation of nutrient solution, which is the key technical link of soilless cultivation. If it matches

The preparation method is incorrect, some nutrient elements will fail due to precipitation, or affect plant absorption, or even lead to plant death.

I. principles for the preparation of nutrient solution

The general principle of nutrient solution preparation is to ensure that there is no precipitation of insoluble compounds after preparation and when using the nutrient solution. Each nutrient solution formula has the potential to produce insoluble matter precipitation, which is inseparable from the composition of the nutrient solution. Whether the nutrient solution will produce precipitation mainly depends on the concentration. Almost any chemically balanced formula will precipitate at high concentrations. For example, Ca2+ interacts with SO42- to produce CaSO4 precipitation; Ca2+ and phosphate (PO43- or HPO42-) produce Ca3 (PO4) 2 or CaHPO4 precipitation; Fe3+ and PO43- produce FePO4 precipitation; and Ca2+, Mg2+ and OH- produce Ca (OH) 2 and Mg (OH) 2 precipitation. Under the guidance of the solubility product method of insoluble substances in practice, the precipitation in the nutrient solution can be avoided by adopting the following two methods: one is to prepare the salt compounds which are easy to precipitate, store them in separate cans, dilute and mix them before use; the second is to add acid to the nutrient solution to reduce the pH value and adjust it by adding alkali before use.

2. Preparation before the preparation of nutrient solution

1. According to plant species, growth period, local water quality, climatic conditions, fertilizer purity, cultivation methods and cost, the formula of nutrient solution is correctly selected and adjusted because there are differences in water quality and fertilizer purity among different areas. it will directly affect the composition of the nutrient solution; different varieties and growth periods of cultivated crops require different proportions of nutrient elements, especially the proportion of N, P, K In the cultivation mode, especially in the substrate cultivation, the adsorption of the substrate and the nutritional composition of the substrate will change the composition of the nutrient solution. The use of different nutrient solution formulations also involves the problem of cultivation cost. Therefore, the formula of the selected nutrient solution should be adjusted correctly and flexibly before preparation, and then it can be applied on a large scale after it is proved to be feasible.

2. Selecting appropriate fertilizers (inorganic salts) the selected fertilizers should not only consider the concentration and proportion of available nutrient elements in the fertilizers, but also pay attention to selecting fertilizers with high solubility, high purity, few impurities and low price.

3. Read the relevant materials before preparing the culture solution, read carefully the instructions or packaging instructions for fertilizers or chemicals, and pay attention to the molecular formula of the salt, the crystal water contained, the purity, etc.

4. Select the source of water and test the water quality as a reference for the preparation of nutrient solution.

5. Prepare the liquid storage tank and other necessary items. The nutrient solution is generally prepared into a mother liquid of 100 to 1000 times concentration. Each formula requires 2 to 3 mother liquor tanks. The volume of the mother liquid tank should be 25 or 50L, and the dark opaque one should be the best.

Third, the preparation method of nutrient solution

There are two preparation methods of nutrient solution: concentrated solution (also known as mother liquid) and working solution (also known as cultivation solution). In production, the concentrated reserve solution is generally diluted into the working liquid, which is convenient for preparation, and if the amount of nutrient solution is small, the working liquid can also be prepared directly.

(1) preparation of concentrated solution

The preparation procedure of concentrated liquid is: calculation-weighing-dissolving-sub-packing-preservation.

1. Calculate the amount of various compounds in the formula according to the volume and concentration multiple of the concentrated solution to be prepared. Pay attention to the following points in the calculation:

The main results are as follows: (1) soilless cultivation fertilizers are mostly industrial and agricultural supplies, often have hygroscopic water and other impurities, and their purity is low, so the dosage should be modified according to the actual purity.

(2) Ca2+ and Mg2+ contained in water should be deducted from hard water areas. For example, Ca2+ and Mg2+ in the formula are provided by Ca (NO3) 2 ·4H2O and MgSO4 ·7H2O, respectively. The actual dosage of Ca (NO3) 2 ·4H2O and MgSO4 ·7H2O is the amount of formula minus the amount of Ca2+ and Mg2+ contained in the water. However, after deducting Ca2+, the amount of nitrogen in Ca (NO3) 2 4H2O is reduced, and the reduced nitrogen can be supplemented by nitric acid (HNO3). The addition of human nitric acid can not only supplement the nitrogen source, but also neutralize the alkalinity of hard water. When the pH value in the water can not be reduced to the ideal level after the addition of nitric acid, the amount of phosphate can be reduced appropriately, and phosphoric acid can be used to neutralize the alkalinity of hard water. If the nutrient solution is sour, the amount of potassium nitrate can be increased to supplement nitrate nitrogen, and the amount of potassium sulfate can be reduced accordingly. Excluding the amount of magnesium in nutrition, the actual amount of MgSO4 ·7H2O is reduced, and the amount of sulfate (SO42-) is reduced accordingly, but because the hard water itself contains a lot of sulfate, it generally does not need to be supplemented. If necessary, a small amount of sulfuric acid (H2SO4) [Jishan Huayao] can be added. In hard water areas, the amount of calcium nitrate is small, and the deficiency of phosphorus and nitrogen is supplied by nitric acid and phosphoric acid.

two。 Weigh all kinds of fertilizers and put them in clean containers or plastic film bags, or on the plastic film spread evenly on the ground, so as to avoid loss. When weighing all kinds of salt fertilizers, pay attention to stability, accuracy and speed, and the weighing should be accurate to within plus or minus 0.1.

3. Fertilizer dissolution will put all kinds of fertilizers in order, and after the last check, they can be dissolved separately, or the compounds that do not precipitate each other can be mixed and dissolved. Pay attention to dissolve thoroughly, add and stir until the salt is completely dissolved.

4. The sub-packaged concentrated liquid was prepared into three kinds of concentrated liquid A, B and C respectively, which were filled in three liquid storage tanks. A tank: with calcium salt as the center, all compounds that do not precipitate with calcium salt can be dissolved together; tank B: with phosphate as the center, all compounds that do not precipitate with phosphate are dissolved together; tank C: prepare chelating iron solution in advance, and then dissolve other compounds needed to weigh the C solution in a small plastic container, and then slowly pour them into the chelating iron solution, adding and stirring. The concentrated solutions A, B and C all add clear water to the volume to be prepared according to the requirement of concentration multiple, and then stir evenly. The concentration ratio of the concentrated solution should be determined according to the amount specified in the formula of the nutrient solution and the solubility of each salt, so that it will not be supersaturated and precipitated. The concentration multiple should be matched into an integral value, which is convenient for operation. Generally, it is 100,200 times higher than the balanced nutrient solution that can be absorbed directly by plants, and the trace element concentrate can be concentrated to 1000 times.

5. When the concentrated solution is stored for a long time, it should be acidified to prevent precipitation. Generally, it can be acidified to pH3~4 with HNO3 and stored in a plastic container and stored in a cool and dark place.

(2) preparation of working liquid

1. The steps of diluting a concentrated liquid are as follows:

The first step is to calculate the amount of liquid to be removed from various concentrated solutions and adjust the pH value of the water according to the requirements of the formula.

The second step is to inject 50% to 70% of the volume of the prepared nutrient solution into the liquid storage tank or other container containing the cultivation liquid.

The third step is to measure the A mother liquid and pour it into it, and start the pump to circulate 30min or stir to make it spread evenly.

The fourth step is to slowly inject the B mother liquid into the clear water entrance of the liquid storage tank and let the water source dilute the B mother liquid and bring it into the liquid storage tank to participate in the flow and diffusion. the amount of water added in this process is up to 80% of the total liquid volume.

The fifth step is to measure the C mother liquid into the liquid storage tank with water flushing to participate in the flow and diffusion. After adding enough water, circulate 30min or stir evenly.

In the sixth step, the pH value and EC value of the nutrient solution are detected by acidity meter and conductivity meter respectively. If the determination results do not meet the requirements of the formula and crops, they should be adjusted in time. The pH value can be adjusted by dilute acid solutions such as sulfuric acid, nitric acid or dilute alkali solutions such as potassium hydroxide and sodium hydroxide. After adjusting the nutrient solution, rest for some time before use, then circulate the 5~10min or so on the planting bed, and test the PH value again until it meets the requirements.

Step 7, make a detailed record of the preparation of the nutrient solution for inspection.

two。 Direct preparation

The first step is to calculate the amount of various fertilizers required according to the formula and the volume of the nutrient solution to be prepared, and adjust the pH value of the water

The second step is to prepare C mother liquor.

The third step is to inject 50% of the water into the liquid storage tank or other container.

The fourth step is to weigh various compounds equivalent to A mother liquor, dissolve them in the container, pour them into the liquid storage tank, and turn on the water pump to circulate 30min.

In the fifth step, various compounds equivalent to the B mother liquor are dissolved in the container and diluted with a large amount of clear water, then the water source flushes the B mother liquid into the liquid storage tank and turns on the pump to circulate and flow 30min. The water added in this process is 80% of the total liquid volume.

In the sixth step, after the C mother liquor is measured and diluted, it is slowly poured into the water source entrance of the liquid storage tank, and the pump is turned on to circulate until the nutrient solution is uniform.

The seventh and eighth steps are the same as the concentrated dilution method.

In the Netherlands, Japan and other countries, when large-scale soilless cultivation is carried out in modern greenhouses, two mother liquid tanks An and B are generally used. Tank A mainly contains calcium nitrate, potassium nitrate, ammonium nitrate and chelating iron, and tank B mainly contains potassium sulfate, potassium nitrate, potassium dihydrogen phosphate, magnesium sulfate, manganese sulfate, copper sulfate, zinc sulfate, borax and sodium molybdate. In order to prevent the precipitation of the mother liquor tank, it is sometimes equipped with an acid tank to adjust the acidity of the mother liquor. The whole system is controlled by computer, diluted and mixed to form working liquid.

In the process of the working liquid, it is necessary to prevent a large amount of precipitation due to the high local concentration caused by the rapid addition of the mother liquid. If these precipitates cannot be dissolved after turning on the pump cycle for a long time, the nutrient solution should be reformulated.

Operating rules for the preparation of nutrient solution

In order to ensure that there are no mistakes in the preparation of nutrient solution, it is necessary to establish a set of strict operating rules. The contents should include:

1. Carefully read the fertilizer or chemical instructions, pay attention to the molecular formula, content, purity and other indicators, check whether the name of the raw material is consistent, prepare the container containing the storage liquid, and affix the label of different colors.

2. The calculation process and final results of raw materials have to be checked three times by three staff members to ensure accuracy.

3. After all kinds of raw materials are weighed separately, put them together on the position specified in the preparation site, and finally check that there are no omissions before starting the preparation. Do not rush to operate when the materials and equipment are not ready.

4. When the raw material is dissolved with water, some reagents dissolve too slowly and can be heated; some reagents, such as ammonium nitrate, cannot be struck or shoveled with iron utensils, but can only be used with wood, bamboo or plastic utensils.

5. Establish strict records and files for inspection. The record table is shown in Table 2 Mui 8 and Table 2 Mui 9.

Table 2-8 concentrated liquid preparation record book

Table 2-9 working liquid preparation record book