Quality testing of agricultural irrigation water

NegotiableUpdate on 03/14

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Overview

Agricultural irrigation water quality testing: The quality of agricultural irrigation water directly affects crop growth, soil ecology, and the quality and safety of agricultural products. Establishing a scientific and standardized testing system is an important technical support for ensuring the sustainable development of agriculture.

Product Details

The quality of agricultural irrigation water directly affects crop growth, soil ecology, and the quality and safety of agricultural products. Establishing a scientific and standardized testing system is an important technical support for ensuring the sustainable development of agriculture. The following will elaborate on the detection principle, core process, and technical points.

1、 Principle of agricultural irrigation water quality detection: multidimensional analysis of water body characteristics

1. Principle of physical index detection

PH value: Based on the glass electrode method, the pH value of the water body is reflected by the potential difference between the hydrogen ion selective electrode and the reference electrode. For example, when using a pH meter probe to immerse in a water sample and stir it, let it stand and read a stable value, parallel measurements need to be taken twice with an error of ≤ 0.1.

Conductivity: By utilizing the characteristic that the conductivity of ions in a solution is proportional to their concentration, the conductivity value of a water sample at 25 ℃ is measured using a conductivity meter to reflect the total dissolved salt content.

Turbidity: Using the principle of light scattering, such as a turbidity meter emitting light of a specific wavelength, the concentration of suspended particles in water is quantified by detecting the intensity of scattered light.

2. Principle of chemical index detection

Chemical Oxygen Demand (COD): Based on the oxidation-reduction reaction, potassium dichromate oxidizes reducing substances in water samples under acidic conditions. The unreacted potassium dichromate is titrated with ferrous ammonium sulfate to calculate the mass concentration of oxygen consumed by oxidation. For example, the COD limit for surface water is usually ≤ 150mg/L, and for dryland irrigation water it is ≤ 200mg/L.

Five day biochemical oxygen demand (BOD ₅): Simulate the process of microbial decomposition of organic matter, cultivate water samples in the dark at 20 ℃ for 5 days, and measure the difference in dissolved oxygen before and after cultivation. The BOD ₅ of water used for planting should be ≤ 60mg/L, and the BOD ₅ of water used for irrigating raw vegetables should be ≤ 15mg/L.

Nitrogen and phosphorus nutrients: Total nitrogen is determined by spectrophotometry, such as alkaline potassium persulfate digestion UV spectrophotometry, and hexavalent chromium is determined by diphenylcarbazide spectrophotometry. Ammonia nitrogen detection uses potassium iodide mercury to form a yellow complex with ammonia, which is quantified by colorimetry at wavelengths of 410-472nm.

3. Principles of heavy metal and microbial detection

Heavy metals: Atomic absorption spectroscopy quantitatively analyzes elements such as cadmium, lead, mercury, etc. based on the absorption characteristics of atomic vapor at specific wavelengths of light. For example, mercury detection uses cold atomic absorption method to reduce Hg ² ⁺ to mercury atoms and measure the absorbance.

Microorganisms: The filter membrane method intercepts microorganisms in the water sample through a 0.45 μ m filter membrane, and incubates them in MFC medium at 37 ° C for 24 hours, counting blue purple characteristic colonies (fecal coliforms).

2、 Core testing process: Standardized operation ensures data reliability

1. Preparation before sampling

Personnel qualifications: Testing personnel must hold CMA certification or industry professional certificates and regularly participate in skill assessments.

Equipment calibration: Key instruments such as pH meters and conductivity meters need to be calibrated with standard solutions. For example, pH meters can be calibrated with three-point buffer solutions of pH 4.01, 6.86, and 9.18.

Consumables processing: The sampling bottle is soaked in 10% nitric acid for 24 hours, then rinsed and dried. The filter membrane is sterilized at 121 ℃ for 20 minutes under high pressure.

2. Sampling and Preservation

Sampling method: Surface water samples are collected at a depth of 0.5 meters below the surface, groundwater is collected by pumping or siphoning, and recycled water needs to be washed three times in the sampling bottle.

Fixation and refrigeration: Add nitric acid to heavy metal samples until pH<2, do not add fixatives to microbial samples, store at 4 ℃, perform routine testing within 24 hours, and complete heavy metal and microbial testing within 48 hours.

3. Laboratory testing

Physical and chemical indicators: pH value is determined by glass electrode method, COD is digested and titrated by potassium dichromate method, and conductivity is directly measured by instrument.

Heavy metal detection: After the water sample is digested with nitric acid, the concentration of metal ions is determined by an atomic absorption spectrometer, and a standard curve is established for quantitative analysis.

Microbial detection: After filtering the water sample using the membrane filtration method, place the membrane in a selective culture medium and count the number of characteristic bacterial colonies.

4. Quality Control and Reporting

Blank test: Each batch of samples should be simultaneously blank throughout the entire process, and the blank value should be less than 1/2 of the method detection limit.

Parallel sample detection: Collect 1 set of parallel samples for every 10 samples, with a relative deviation of ≤ 10%.

Report preparation: The report should include sample information, testing items, method basis, results and conclusions, and the archiving period should not be less than 5 years.

3、 Technical key points: precise control of key links

Safe operation: Strong acid operations should be carried out in a fume hood and acid resistant gloves should be worn; High temperature digestion prevents the solution from exploding and boiling.

Waste disposal: The waste liquid containing heavy metals is handed over to professional institutions for treatment, and the microbial waste liquid is sterilized at 121 ℃ for 30 minutes before being discharged.

Instrument maintenance: Clean the instrument promptly after testing, such as rinsing the atomic absorption sampling system with dilute nitric acid and soaking the spectrophotometer colorimetric dish in distilled water.

Through the application of standardized testing processes and multidimensional technical principles, the quality of agricultural irrigation water can be systematically evaluated, providing scientific basis for agricultural water safety and assisting in the green and high-quality development of agriculture.