Hyperspectral Estimation Model of Chlorophyll Content in Cotton Canopy Leaves under Drip Irrigation at Different Growth Stages

[Objective] This article is aimed to estimate the chlorophyll content of cotton canopy leaves in drip irrigation fields at different growth stages in northern Xinjiang and establish a model for estimating chlorophyll content in growth time series by using hyperspectral. [Method] Using Xinluzao 45 as the experimental material, the chlorophyll content and the corresponding spectral reflectance of cotton canopy leaves at different nitrogen levels and growing stages were measured, and the relationship between 12 indices and the chlorophyll content was analyzed. The estimation models of the chlorophyll content in cotton canopy leaves under drip irrigation were established. [Result] The correlation coefficient between the chlorophyll content of canopy leaves and Vogelmann red edge index was high in the four growing periods of cotton, and the correlation coefficient was 0.944, 0.907, 0.895, 0.930, respectively. And the spectral reflectivity was the highest at the flowering and boll period. The precision of the model established by the multivariate regression method is higher than that of the single exponential linear model with the determination coefficient more than 0.8 and the root mean square error smaller than that of the single exponential linear model. The model of the budding stage (y＝82.509_x1＋89.937_x2－94.438) has the best precision. [Conclusion] The chlorophyll content can be estimated by the models established at different growth stages, and the budding stage model has the best monitoring effect.     

气候适宜度在内蒙古东北部马铃薯发育期预报中的应用

为了建立内蒙古东北部马铃薯发育期预报模型,通过采用内蒙古东北部地区16个气象站,2003—2012年逐日最高气温、最低气温、日照时数、降水量、土壤水分资料和马铃薯生育期观测资料和相关农业气象指标,计算了马铃薯不同生育阶段的温度适宜度、日照适宜度和水分适宜度,进而研究了内蒙古东北部不同区域的马铃薯气候适宜度,建立了基于气候适宜度的马铃薯发育期预报模型。结果表明,大兴安岭以东,大兴安岭以西及大兴安岭山地3个气候小区域的模拟值与实际值的平均误差在2天以内,各发育期误差的平均值也在2天以内;预报检验结果表明,各区域各发育阶段预报误差的平均值,除大兴安岭山地的预报误差为3.4天外,其他区域的预报误差都在1.0天以下。预报模型效果较好,可用于该地区进行马铃薯发育期预报。     

冬小麦生物量及氮积累量的植被指数动态模型研究

利用遥感技术实时监测小麦生长状况,依据监测结果适时促控,可提高产量。本研究以高产小麦品种周麦27为试验材料,在不同试验地点设置了水氮耦合的大田试验,筛选出了适宜监测冬小麦地上部氮积累量和生物量的植被指数,并构建了不同产量水平下优选植被指数的动态模型。结果表明,(1)不同的水氮耦合模式显著影响小麦冠层光谱变化,在350~700nm和750~900nm表现相反的反应特征;(2)对2个农学生长指标反应敏感且兼容性好的植被指数主要有修正型红边比率(mRER)、土壤调整植被指数[SAVI(825,735)]、红边叶绿素指数(CIred-edge)和归一化差异光谱指数(NDSI),其与产量间相关性较好的时期为拔节至灌浆中期;(3)双Logistic模型可以很好地拟合植被指数的动态变化,高产和超高产水平下拟合精度较高(R^2>0.82),而低产水平下相对较低(R2=0.608~0.736)。比较而言,CIred-edge和SAVI(825,735)用于评价小麦长势较为适宜。研究结果对作物因地定产、以苗管理、分类促控具有重要意义。     

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。     

Estimation of litchi (Litchi chinensis Sonn.) leaf nitrogen content at different growth stages using canopy reflectance spectra

The estimation of crop nitrogen status in fresh vegetation leaf using field spectroscopy is challenging due to the weak responses on leaf/canopy reflectance and the overlapping with the absorption features of other compounds. Although the spectral indices were proposed in the literature to predict leaf nitrogen content (LNC), the performance of selected spectral indices to estimate the LNC is often inconsistent. Moreover, the models for nitrogen content estimation changed with the growth stage. The goal of this study was to evaluate the performance of published indices, ratio of data difference index (RDDI) and ratio of data index (RDI) developed by band iterative-optimization algorithm in LNC estimation. The correlation analysis, linear regression and cross validation were used to analyze the relationship between spectral data and LNC and construct the best performed estimation model. The study was conducted by the data of five growing seasons of litchi from the orchards in Guangdong Province of China. Results showed that the relationship between chlorophyll (Chl) related spectral indices and LNC varied with the growth stage. Even in flower bud morphological differentiation stage and autumn shoot maturation stage, there were not significant correlations between the proposed spectral indices and LNC. Besides it is difficult to estimate the LNC by the general model across the growth stages due to the integrated effects of cultivar, biochemical, canopy structure, etc. The band iterative-optimization algorithm can improve the sensitivity of spectral data to LNC to some extent. The optimal RDDI performed better than other indices for the synthetic dataset and the dataset in each growth stage. And the sensitive bands selected in the optimal indices at each growth stage are not consistent, which are not only related to the Chl absorption but also other biochemical components, such as starch, lignin, cellulose, protein, etc. In general, the LNC can be estimated by the optimized CR-based RDDI indices in autumn shoot maturation stage, flower spike stage, fruit maturation stage, and flowering stage with the R² > 0.50 and RMSE < 0.14. Although there were the significant relationship between RDIs and RDDIs in flower bud morphological differentiation stage, the highest R²s of the model developed by RDDIs and RDIs were less than 0.50 in cross validation. This study indicated that the applicability of canopy reflectance to estimate litchi LNC was closely related to the growth stage of litchi. Growth stage-specific models will be preferred for estimating litchi LNC estimation.     

水稻透射光谱与氮含量的相关性研究

采用小区试验研究了水稻叶片氮含量与透射光谱的相关性。用“秀水110”建立诊断模型,再用“协优9308”进行检测,分析一阶导数光谱与叶片氮含量的相关性。结果表明,一阶导数光谱与氮含量显著相关,相关系数可达R2=0.74。预测模型可达R2=0.84。与一阶导数光谱相比,还建立了3个植被指数：蓝波段透射光谱氮指数(BETNI)、波段透射光谱氮指数(YETNI)和红波段透射光谱氮指数(RETNI),并分别计算了它们在这三个波段的特殊波长的值。在这些特殊波长处,3个指标与氮含量的相关性明显比单叶片的透射光谱的相关性显著。YETNI610,YETNI630,YETNI643,YETNI652,and RETNI能够很好的预测氮含量;对于“协优9308”的预测结果显示YETNI570,YETNI592和RETNI最优。分析结果显示,透射光谱的氮指标（YETNI570,YETCI592,and RETNI）能够最好地预测氮含量。     

养分综合管理对马铃薯抗冻性的影响

内蒙古马铃薯生产中面临倒春寒和秋早霜的冻害威胁,特别是秋早霜如果较重将造成产量的大幅下降。因此,尽可能提高马铃薯抗冻性对内蒙古马铃薯产业发展具有重要意义。本文从养分综合管理的角度出发,研究了马铃薯叶片矿质元素含量以及叶面积指数与马铃薯抗霜冻性的关系。结果表明,马铃薯叶片中氮磷钾含量以及叶面积指数均与其抗霜冻性存在相关关系,其中,氮肥处理的叶面积指数变化与霜冻损害评分的相关性最为显著,相关系数达-0.948,该处理下叶面积指数变化对霜冻损害评分影响幅度达到1.6,同样为各处理中最高值。     

养分专家系统推荐施肥对马铃薯产量及肥料利用率的影响

为评价马铃薯养分专家系统在内蒙古马铃薯养分管理中的应用效果,在内蒙古马铃薯主产区武川县和乌兰察布市集宁区进行马铃薯养分专家系统推荐施肥定位试验。以农户习惯施肥（FP）和测土配方施肥（ST）为对照,同时设置养分专家系统推荐施肥处理（NE）、不施氮肥处理（NE-N）、不施磷肥处理（NE-P）及不施钾肥处理（NE-K）,研究马铃薯养分专家系统推荐施肥对马铃薯产量、养分利用效率以及经济效益的影响。结果表明,NE处理与FP处理相比,增产幅度可达4.22%~11.98%,与ST处理相比增产幅度为0.34%~10.02%;同时,NE处理氮肥利用效率较FP处理提高17.29%~23.00%,较ST处理提高6.21%~21.26%。本研究初步认为:通过优化推荐施肥量和施肥方法,在内蒙古马铃薯主产区养分专家系统可提高马铃薯产量和肥料利用率,同时有效降低化学肥料对马铃薯农田环境的污染风险。     

内蒙古地区不同品种马铃薯适水种植研究

根据内蒙古地区46个气象站点1965—2014年逐日降水和平均气温资料,利用GIS软件进行空间插值做出了马铃薯发芽期、块茎形成期、块茎膨大期的旬平均温度和降雨量空间分布图,根据国内外对几种主要马铃薯品种耗水规律的研究,选择出内蒙古各地区适宜种植的马铃薯品种。结果表明：在降雨量为400~450 mm的内蒙古东北部部分地区,适宜种植菜用品种‘克新1号’、淀粉加工品种‘陇薯3号’和油炸薯条品种‘布尔班克’;在降雨量为300~400 mm的东部大部分地区,最适宜种植菜用型品种‘费乌瑞它’和‘克新1号’,其次适合油炸品种‘夏波蒂’、‘布尔班克’和‘大西洋’;而在降雨量为200~ 300 mm的中部地区,适宜‘费乌瑞它’、‘夏波蒂’、‘布尔班克’的种植,但不会达到最优产量;而在降雨量偏少的中西部地区,若存在灌溉条件,可通过覆膜等措施种植‘费乌瑞它’、‘夏波蒂’、‘布尔班克’;而在降雨量为100 mm以下的西部地区,由于块茎形成期的温度超过块茎生长的最适温度,该地区并不适宜马铃薯的种植。该研究结果可为内蒙古地区马铃薯种植提供参考意见。     

单作套作大豆叶片氮素积累与光谱特征

种植模式和氮肥水平直接影响作物的生长和氮素的吸收,无损、即时监测大豆叶片氮素水平对大豆生产中的氮肥精确管理十分重要。本研究设置4个氮肥水平,分析单作套作下大豆在不同生育时期叶片氮素动态和光谱特征,明确对叶片氮素敏感的光谱特征参数,构建单作套作大豆通用的叶片氮素积累量估测模型。结果表明,随大豆生育时期的推进,单作套作种植模式下的大豆冠层叶片氮素积累量均呈现单峰变化趋势,最大值出现在N3处理下的结荚期,两种模式两年最大值平均分别为8.70 g m~(–2)和8.38 g m~(–2);不同生育时期和种植模式的大豆冠层原始反射光谱的变化规律与冠层叶片氮素变化规律均为先增加后降低,原始反射光谱在700~1000 nm波段的反射率以结荚期为拐点先增大后减小,最大反射率达到60%~70%左右;通过对单作套作大豆冠层光谱一阶导数变换,红边幅值呈现先增加后降低的趋势,同时红边位置随叶片氮积累量的增加和减小出现"红移"与"蓝移"现象。经波段自由组合和回归分析表明,以DSI(771、755)构建的线性(y=–1.249+3.209x,R~2=0.847)和乘幂(y=–1.470x~(1.676),R~2=0.872)模型能较精确地估测不同生育时期大豆冠层叶片氮素状况。