The country that has adopted prototypes of measurement instruments, including prototype test certificates and manufacturing licenses, enforces strict control over the production of measuring devices. Soil and fertilizer testing instruments fall under this category and must undergo inspection and verification by the metrology supervision department to ensure their performance and reliability. For instance, a filter-type photoelectric colorimetric soil and fertilizer meter must be tested for stability, repeatability, sensitivity, and linearity error, as well as its resistance to vibration, temperature, and electrical insulation safety. Before the metrology management department issues a prototype test certificate, the instrument must meet the requirements outlined in the national verification regulation JJG179-90 and pass power supply, environmental, and safety tests for electronic measuring instruments. In addition, the technical supervision department evaluates the production conditions, such as facilities, personnel expertise, technical documentation, verification capabilities, and management systems. Any deficiencies must be rectified within a set timeframe. Only after passing these assessments is the manufacturing license issued. These two certifications are fundamental guarantees for product quality. Products without proper licenses or incomplete documentation are considered non-compliant and potentially unsafe.
It is crucial to check the stability of the soil and fertilizer meter when purchasing. The testing method 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 so the display reads zero; then observing the changes in the reading. The stability error is calculated by dividing the difference between the maximum and minimum readings within three minutes by the full-scale reading. As the saying goes, "instruments are not afraid of instability, but unstable instruments are dangerous." Instruments with poor stability cannot be used effectively.
Soil and fertilizer meters typically have multiple test items, including basic parameters like nitrogen, phosphorus, potassium, and organic matter, as well as trace elements, pH, conductivity, and nutrient content in fertilizers. However, when purchasing, it's important to ensure the device can test the essential parameters: available nitrogen (including ammonium and nitrate nitrogen), available phosphorus, available potassium, and organic matter. Many soil fertility meters in China claim to measure these basics, but some lack the ability to detect nitrate nitrogen or organic matter, which limits their effectiveness in guiding fertilization. To confirm if the basic test items are complete, simply review the promotional materials or user manual.
Speed is a key factor when choosing a soil and fertilizer meter, as it directly impacts testing costs. Traditional soil analysis often takes 3–4 days, making it expensive. When selecting an instrument, consider the speed of soil pre-treatment, calibration, reagent preparation, and the use of other rapid technologies. However, many so-called "fast" meters in China merely replicate conventional methods without real innovation. Their claimed speed may refer only to one step, not the entire process, and often excludes pre-processing time. Therefore, it’s important to assess the overall testing speed rather than just the measurement time.
Choosing the right soil and fertilizer meter depends on your specific usage conditions. 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 and fertilizer stations. The former requires portable, durable, and easy-to-maintain equipment suitable for field use. The latter can opt for bench-top or portable models. When choosing a portable meter, it’s not just about the packaging, but also about the availability of all necessary tools, reagents, and miniaturized components.
Finally, after-sales service is vital for effective soil testing and fertilization. A good manufacturer should offer training, maintenance, spare parts, and reagent supply, along with guidance on converting rapid measurements to traditional values and determining fertilizer application rates. Some manufacturers focus only on selling equipment, while others provide comprehensive support. It’s best to choose a provider that collaborates with local soil and fertilizer institutions to establish a reliable service network. Always compare the after-sales service capabilities of different manufacturers before making a purchase.
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