施氮水平对多花黑麦草植株氮含量及反射光谱特征的影响

植株氮含量是评价牧草群体长势、估测产量和确定最佳施肥量的重要指标。对不同施氮水平下多花黑麦草植株氮含量及冠层反射光谱特征进行了测试,分析了冠层反射光谱与植株氮含量之间的相关性。结果表明,施氮水平对多花黑麦草植株氮含量具有显著影响,植株氮含量随着施氮水平的增加有所升高。在可见光区域,冠层光谱反射率随施氮水平的增加而降低。植株氮含量与单波段反射率呈负相关关系,在波段487～718 nm范围内,相关系数绝对值都大于0.5(P<0.01)。利用敏感波段估测植株氮含量最优模型为y=4.362-0.754x₅₇₉+0.351x₇₀₀。以植被指数估测植株氮含量最佳模型为y=3.026-0.670DVI_(610,487)+4.997NDVI_(700,579)。植株氮含量估测值与实测值之间存在显著相关关系。

Plant nitrogen content of annual ryegrass and spectral reflectance response to nitrogen application level

Plant nitrogen content was a vital indicator to evaluate pasture growing situations,to estimate production and to determine optimal fertilizer application.An experiment was conducted to investigate the plant nitrogen content of annual ryegrass and the characteristics of canopy spectral reflectance under five nitrogen levels,exploring the relationship between plant canopy reflectance and nitrogen content.The nitrogen level had a significant impact on the plant nitrogen content of annual ryegrass and when nitrogen fertilizer increased from 100 to 400 kg/ha the plant nitrogen content increased accordingly.In the visible region,canopy spectral reflectance rate reduced as nitrogen level increased.There was significant negative correlation between plant nitrogen content and single-band reflectance rate and the absolute value of the correlation coefficient was greater than 0.5(P<0.01) within 487-718 nm.The optimal model of plant nitrogen content estimation by using sensitive bands was y=4.362-0.754x579+0.351x700,and the optimal model of plant nitrogen content estimation based on vegetation index was y=3.026-0.670DVI(610,487)+4.997NDVI(700,579).A strong correlation between estimated and true value of plant nitrogen content was detected(P<0.01).