Spontaneous determination of soil available phosphorus using highspectrum in the Northwest Plain of Shandong Province

Soil available phosphorus is a critical index for evaluating farm land quality and forms the basis for crop fertilization. It is essential to spontaneously and accurately determine soil available phosphorus for soil management and resources evaluation, which condition is met by using high spectrum technology. This paper selected 466 soil samples in the Northwest Plain of Shandong Province to determine organic matter, available nitrogen, available phosphorus and available potassium contents in the soil. Through cluster and variance analyses, 48 soil samples were used to determine the relationship between soil available phosphorus and high spectrum reflectivity. All 48 samples were characterized by approximate contents of organic matter, available nitrogen and available potassium, but significantly different contents of available phosphorus. High spectrum reflectivity of each soil sample was measured by ASD Fieldspec3 spectrometer. The reflectivity was then transformed into reciprocal, logarithm, square root, reciprocal of logarithmic, logarithm of reciprocal and their first order derivatives. Single correlation between soil available phosphorus content and high spectrum reflectivity in 350~2 500 nm as well as its every transformations was analyzed, and sensitive high spectrum band to available phosphorus selected. The established simple linear regressions between reflectivity or its transformations in sensitive high spectrum bands (as the independent variable) and available phosphorus content were optimized and verified. The results showed that 711 nm high spectrum was the sensitive band. The simulation model based the 711 nm spectrum provided the best estimation of soil available phosphorus with fit index (R²) of 0.822 1 and correlation coefficient (R²) of 0.959 1. Modeling based on a single sensitive band of high spectrum was a spontaneous, simple and reliable approach for determining soil available phosphorus.