品种和生育时期对冠层光谱指数(NDVI)估测马铃薯植株氮素浓度的影响

NDVI是反映作物叶绿素相对含量及氮素水平的重要参数,但是作物品种和生育时期的变化对NDVI估测氮素营养的能力有重要影响。本研究在内蒙古阴山北麓马铃薯主产区进行了多年多品种田间试验,于2014—2016年7月上旬至8月中旬马铃薯关键生育时期,利用便携式主动作物传感器GreenSeeker获取马铃薯冠层光谱指数NDVI,对比了品种和生育时期对NDVI估测结果的影响。结果表明,块茎形成期NDVI与马铃薯植株氮素浓度相关性较差,随着生育时期的推进, NDVI与植株氮素浓度的线性相关性增强,块茎膨大期与淀粉积累期组合会显著提高NDVI与植株氮素浓度的线性建模效果。品种混合会降低NDVI的灵敏性,增加数据的离散性,基于时间序列归一化的光谱指数TNDVI能够克服这些问题,尤其是在块茎膨大期TNDVI与植株氮素浓度的拟合决定系数(R2)能够由原来的0.13提高到0.47。TNDVI对块茎形成期、块茎膨大期和淀粉积累期组合的线性估测建模R2为0.76,显著高于NDVI。株型展开型的品种在块茎膨大期和淀粉积累期更具线性拟合趋势。研究表明,马铃薯生育时期和品种对NDVI估测植株氮素浓度有显著影响,且生育时期的影响更大。构建的TNDVI光谱指数能够克服品种差异导致的块茎膨大期、淀粉积累期数据分异及饱和现象,为NDVI在马铃薯植株氮素浓度诊断应用的普适性上提供了理论依据与方法。

Effect of variety and growth period on NDVI estimation of nitrogen concentration in potato plants

The normalized difference vegetation index (NDVI) is an important parameter to reflect relative chlorophyll content and nitrogen level of crops, but NDVI’s ability to estimate nitrogen nutrition is affected by varieties and growth period. The field experiments using several varieties were conducted in the main potato producing areas at the north foot of Yinshan mountain, Inner Mongolia. From early July to mid-august in 2014 to 2016, the canopy spectral index NDVI was measured by using the pocket active crop sensor GreenSeeker during potato critical growth period. The effects of cultivars and growth stages on NDVI estimation of nitrogen concentration in potato plants were compared. The linear correlation between NDVI and plant nitrogen concentration (PNC) was poor in tuber initiation, but increased in process of growth period. The combination of tuber bulking period and starch accumulation period significantly improved the linear modeling effect of NDVI and PNC. Variety combination reduced the sensitivity of NDVI and increased the discreteness of data, which could be offset by NDVI time series normalization (TNDVI), especially the fitting coefficient of determination (R ²) of TNDVI and PNC increased from 0.13 to 0.47 in the tuber bulking period. The R ²of linear estimation model of TNDVI for the combination of tuber initiation, tuber bulking and starch accumulation period was 0.76, which was significantly higher than that of NDVI. Plant-expanded varieties had a more linear fitting trend during tuber bulking and starch accumulation. The growth period and potato varieties had significant effects on NDVI estimation of PNC, and growth period had a greater effect. The established TNDVI spectral index overcame the data differentiation and saturation phenomenon during tuber bulking and starch accumulation caused by variety difference, which provides a theoretical basis and method for the application of NDVI in the diagnosis of nitrogen concentration in potato plants.