同时估测土壤全氮、有机质和速效氮含量的光谱指数研究

通过系统分析我国中、东部地区5种不同类型土壤风干样本的有机质、全氮及速效氮含量与近红外(1 000～2 500 nm)光谱反射率之间的关系,进而构建了适合同时估测这3种养分含量的光谱参数及定量估算模型。结果表明,同时与3种养分指标相关较高的波段范围为1 879～1 890与2 050～2 100 nm,其中1 881和2 070 nm两个波段的反射率经多元散射校正及Savitzky-Golay平滑处理并构建而成的差值指数DI(CR1 881,CR2 070)与土壤有机质、全氮及速效氮含量具有良好的线性相关性。独立的观测资料检验显示,基于DI(CR1 881,CR2 070)的估测模型对全氮、有机质和速效氮的预测决定系数R2分别为0.83、0.79和0.72,均方根误差(RMSE)分别为0.20 g kg-1、4.71 g kg-1和23.96 mg kg-1,相对分析误差(RPD)分别为2.56、2.30和2.93。表明DI(CR1 881,CR2 070)是一种可同时估测土壤中3种养分含量的良好光谱指数。

The spectral Index for estimating soil OM, TN and AN content simultaneously using near-infrared spectroscopy

Extracting soil nutrient information using spectral analysis technology is very important for precision crop management. Difference indices (DIs), normalized indices (NIs) and ratio indices (RIs) were calculated from all available combinations with reflectance of two random bands between 1 000 and 2 500 nm, and correlated to soil organic matter (SOM), total nitrogen (TN) and available nitrogen (AN) content using dried soil samples from five different soil types in central and eastern China, then key spectral index and quantitative models for estimating SOM, TN and AN content were developed. Results show that spectral indices composed of reflectance corrected with multiplicative scatter correction (MSC) and collated with Savitzky-Golay (SG) smoothing method were highly correlated with the three soil nutrient indices. The sensitive wavebands well correlated simultaneously with the three nutrient indices were 1 879~1 890 and 2 050~2 100 nm, and DI(CR_{1 881}, CR_{2 070}) composed of the reflectance in wavebands 1 881 nm and 2 070 nm corrected with MSC and SG smoothing methods performed the best. Testing of the estimating models based on DI(CR_{1 881}, CR_{2 070}) with independent datasets from different types of soil samples resulted in validation of R², RMSE and RPD being 0.83, 0.79 and 0.72, 0.20 g kg^-1, 4.71 g kg^-1 and 23.96 mg kg^-1 and 2.56, 2.30 and 2.93 for TN, OM and AN, respectively, which indicates that DI(CR_{1 881}, CR_{2 070}) might be a good spectral index for estimating contents of the three nutrients simultaneously.