The country that has selected prototypes of measurement instruments, including prototype test certificates and manufacturing licenses for measuring devices, maintains strict control over the production of such equipment. Soil and fertilizer testing instruments fall under the category of measuring instruments and must undergo inspection and verification by the metrology supervision department to assess the performance and reliability of their prototypes. For example, a filter-type photoelectric colorimetric soil and fertilizer meter must be tested for stability, repeatability, sensitivity, and linearity error, as well as vibration resistance, temperature resistance, and insulation safety. It must meet the requirements outlined in national verification regulations, such as JJG179-90, along with tests on power supply, environmental conditions, and safety before a prototype test certificate can be issued. In addition, the technical supervision department evaluates factors like production facilities, staff expertise, technical documentation, verification capabilities, and management systems. Any deficiencies must be corrected within a set timeframe before a manufacturing license is granted. These two certifications are essential for ensuring product quality. Products without proper licensing or incomplete documentation are considered non-compliant and potentially unsafe.
Checking the stability of a soil and fertilizer meter is crucial when purchasing equipment. The process involves: turning on the power and allowing the instrument to warm up for 5–10 minutes; covering the instrument with a shading cover and adjusting it to zero; then observing the reading changes over three minutes. The difference between the maximum and minimum readings divided by the full-scale value gives the stability error. As the saying goes, "instruments are not afraid of instability, but unstable instruments are not reliable." Unstable or unqualified instruments should not be used.
Soil and fertilizer meters typically have a wide range of test items, including nitrogen, phosphorus, potassium, organic matter, trace elements, pH, conductivity, and nutrient content in fertilizers, among others. However, when purchasing, it's important to ensure the device can handle the basic soil fertility tests—available nitrogen (including ammonium and nitrate), available phosphorus, available potassium, and organic matter. Many meters in China claim to offer these tests, but some may lack the ability to measure nitrate nitrogen or organic matter, which limits their effectiveness for guiding fertilization. To confirm the completeness of the basic tests, review the product’s promotional materials or user manual.
Speed is a key factor in reducing testing costs. Traditional soil analysis often takes 3–4 days, making it expensive. When choosing a soil and fertilizer meter, consider the speed of pre-treatment, calibration, reagent preparation, and other rapid technologies. Although many Chinese meters claim to be fast, most still use conventional methods and do not offer real-time measurement. Some manufacturers report only the time for a single step, not the entire process. Therefore, it’s important to evaluate the overall test speed when making a purchase.
Choosing a soil and fertilizer meter that suits your specific usage conditions is essential. There are two main types of users: those without laboratories, such as rural agricultural stations, farms, and mobile agrochemical services, and those with laboratory facilities, like county soil testing centers. The former requires portable, durable, and easy-to-maintain instruments suitable for field use, while the latter may prefer bench-top or compact models. For portable meters, ensure that all necessary tools—such as balances, washing bottles, and cleaning cloths—are lightweight, easily accessible, and minimally packaged.
Finally, after-sales service plays a vital role in the effective use of soil and fertilizer meters. A reliable manufacturer should provide training, maintenance support, spare parts, reagents, and guidance on converting rapid measurement results into conventional values. They should also help determine fertilizer application rates based on test results. Some manufacturers focus only on selling equipment, while others offer comprehensive support. It’s best to choose a provider with a strong service network, ideally connected with local soil and fertilizer agencies or agrochemical service units. When purchasing, compare the service capabilities of different manufacturers to ensure long-term support and optimal performance.
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