Development of associated device to portable soilnitrogen detector

摘要

Nitrogen is one of the essential nutrients in soil. Compared with the traditional soil total nitrogen (TN) measurement methods, near infrared spectroscopy analysis method is time-saving, labor-saving, eco-friendly and non-destructively. In case of real-time soil TN information can be acquired from its spectra, rapid and scientific production decisions can be achieved. In situ detecting TN is a good way to use spectroscopy technology. The first generation portable soil TN detector adopted the seven sensitive wavebands (940nm, 1 050nm, 1100nm, 1200nm> 1300nm, 1450nm and 1550 nm) was developed in China Agricultural University a years ago. The detector consists of two parts, an optical unit and a control unit. The optical unit includes six near-infraredlamp-houses, a shared lamp-house drive circuit, a shared incidence and reflectance Y-type optical fiber, a probe, and a photoelectric sensor. The control unit includes an amplifier circuit, a filter circuit, an analog-to-digital converter circuit, an LCD display, and a U-disk storage component. All seven absorbance data as inputs are used to calculate soil TN content by means of the estimation model. The calculated soil TN content is displayed on the LCD display and at the same time stored in the U-disk. But it is found in experiments that the precision of this device is not able to reach ideal requirement. Analyzing the causes, some factors have interference on measurement results, such as the distance between detecting instrument and tested soil surface, surface smooth and compacting degree of the tested soil. Therefore this research provides a kind of auxiliary device of portable soil nitrogen detector, which could be used as the enclosed sample pool. It could make up the serious impacts caused bythe distance from soil surface, soil roughness, and the soil compactness in the process of detection of the multi-wavebands soil TN detector.