Are vegetation indices derived from consumer-grade cameras mounted on UAVs sufficiently reliable for assessing experimental plots?

Recent technological advances in UAV (unmanned aerial vehicle) technology offer new opportunities for assessing agricultural plot experiments using UAV imagery. Vegetation indices (VIs) based on aerial images derived from consumer-grade cameras are a simple and cheap alternative compared to VIs derived from proximal (on-ground) sensors. The objective of this study was to assess whether VIs derived from consumer-grade cameras mounted on UAVs are reliable and whether there are any shortcomings in image acquisition and analysis that need to be addressed before their general application. This objective was investigated using a rotary-wing and a fixed-wing UAV, true colour (RGB) and colour-infrared (CIR) cameras, four different VIs (ExG, NGRDI, NDVI and ENDVI), altitudes in the range of 30–100 m, different ambient lighting conditions and two different software packages for stitching images together. Results were compared with ground-based recordings by consumer-grade cameras and multispectral sensors. Field experiments in cereals were used to evaluate the assessments. The study showed that VIs based on UAV imagery have the same ability to quantify crop responses to experimental treatments as ground-based recordings with cameras and advanced sensors. However, there are shortcomings that need to be taken into consideration: (1) angular variation in reflectance (bidirectional reflectance), (2) stitching and (3) ambient light fluctuations. Bidirectional reflectance was so extensive that it could lead to misleading conclusions in sunny conditions and this effect could be amplified further by stitching. A procedure for avoiding impacts from bidirectional reflectance is demonstrated when plots were cropped from individual images and a procedure is suggested for stitching images. Camera, VIs and image acquisition altitude were of minor importance, but fluctuating ambient lighting conditions is an issue that should be addressed in future studies.     

Estimating canopy leaf nitrogen concentration in winter wheat based on multi-angular hyperspectral remote sensing

Real-time, nondestructive estimation of crop nitrogen (N) status is highly important for precision N management in winter wheat production. Developing a new N indicator based on the direct link between spectral index and chlorophyll content is important for crop N diagnosis. In this study, we investigated the quantitative relationships between leaf N concentration (LNC) and ground-based multi-angular remote sensing hyperspectral reflectance in winter wheat (Triticum aestivum L.). Field experiments were conducted from 2011 to 2014 across different sites, cultivars, growth stages, N rates, and planting densities, and a novel Multi-angular vegetation index (MAVI_SR) was developed to improve the prediction accuracy and stability of LNC measurement. The optimum vegetation indices (VIs) obtained from 40 traditional indices reported in the literature, as well as normalized difference spectral indices (ND) and Simple Ratio Indices (SR), were tested for their stability in estimating LNC at 13 viewing zenith angles (VZAs). Overall, the coefficient of determination (r²) of spectral reflectance and traditional VIs with LNC decreased with increasing VZA in both the forward and backward scattering directions and reached maximum values at a viewing angle of −20°. Ratio index (RI-1 dB) exhibited the best linear relationship to LNC (r² of 0.837) at the −20° viewing angle, but Enhanced vegetation index (EVI-1) showed the highest r² (0.819) with LNC at the nadir direction. The relationships between the LNC and two-band combinations indicate that there are three sensitive regions with high r², which vary with VZA, usually comprising combinations of blue–red wavelengths, green–red edge wavelengths, and between-red edge wavelengths. To further analyze the relationship between the combination of the three sensitive regions and the sensitive VZAs with LNC, the MAVI_SR index in the form of MAVI_SR = (R538/R768)₋₂₀ − (R478/R634)₊₁₀ was calculated and found to be highly correlated with LNC (r² = 0.897). When independent data were fit to the derived equations, the average relative error (RE) values were 15.5%, 14.3%, and 12.6% between measured and estimated LNC using EVI-1_0°, RI-1 dB_−20°, and MAVI_SR, respectively. These results suggest that the models can accurately estimate LNC in wheat, and the novel MAVI_SR is more effective for estimating LNC than previously reported VIs, independent of years, sites, and growth periods. The results also indicate the importance of taking into account angle effects when analyzing VIs.     

基于近地成像光谱的小麦全蚀病等级监测

小麦全蚀病是检疫性的土传病害,对小麦生产危害极大,对其发生的监测是治理的根本。遥感技术可实时、宏观监测病害发生发展,尤其是成像光谱技术的图谱合一,可精准对病害识别和分类。该文首先通过主成分分析提取不同小麦白穗率的冠层光谱特征;再通过灰色聚类分析方法,研究白穗率等级的可分性;最后利用基于径向基(RBF,radial basis function)核函数的支持向量机对全蚀病害的近地成像高光谱图像进行分类,从而验证近地成像光谱在全蚀病监测上的可行性。研究结果显示:该方法对5种程度的小麦全蚀病白穗率的分类精度均达94%以上,Kappa值大于0.8。研究表明利用该方法,通过近地成像光谱图像可以准确监测小麦全蚀病的病情,对小麦全蚀病的治理有指导意义。     

Assessment of rhizobacteria from grapevine for their suppressive effect on the parasitic nematode Xiphinema index

The capacity of rhizobacteria isolated from grape plants to protect grapevine roots from damage by the nematode Xiphinema index was assessed in trials carried out in the growing season 2008–2009 and 2009–2010. A total of two groups of bacteria were evaluated, one comprising 49 isolates, of which 37 were assessed in previous studies, and one comprising 90 isolates not previously evaluated. Two assays were performed on the first group, one per season, and one on the second group, lasting two growing seasons. Pots of field soil (3 L) planted with two-month old Thompson Seedless vines were inoculated with 200 or 400 specimens of X. index after inoculation with 10⁶ cfu/ml of test rhizobacteria; the posts were maintained in a shaded greenhouse. Seven isolates from the first group of bacteria (Bacillus brevis, Bacillus megaterium, Cytophaga johnsonae, Pseudomonas fluorescens, Rahnella aquatilis and Stenotrophomonas maltophilia) were effective in decreasing damage in both of the assays (P < 0.05). Ten isolates from the second group (Variovorax paradoxus, Pseudomonas pseudoalcaligenes, Bacillus mycoides, Bacillus sphaericus, Bacillus thuringiensis, Curtobacterium flaccumfaciens, Pseudomonas putida, Pseudomonas alcaligenes and Pseudomonas viridiflava) resulted in the lowest number of galls per gram root. B. brevis and B. megaterium also demonstrated good activity in previous studies on grape plants and are thus promising candidates for further research.     

玉米花期耐高温品种的筛选与综合评价

以30个黄淮海地区主栽玉米品种为试材,研究高温对不同玉米杂交种的形态、叶片生理以及产量构成因素的影响,筛选玉米杂交种花期耐热性评价指标,对30个玉米杂交种花期耐热性进行综合评价。结果表明,高温胁迫阻碍了玉米雌雄穗的分化,造成植株生长中心转移,且不同基因型玉米间存在显著差异。高温处理后,穗位叶片变薄,其比叶重、叶绿素相对含量及净光合速率均有所下降,穗位叶片浸泡液相对电导率显著增加。高温胁迫使玉米果穗行粒数明显减少,百粒重及子粒产量显著下降。综合不同品种各性状耐热系数的相关性分析及逐步回归分析结果得出,产量、百粒重、穗长、穗粗和结实率可作为评价玉米杂交种花期耐热性的主要指标。     

丛枝菌根真菌对玉米生育期土壤N2O排放的影响

【目的】明确丛枝菌根真菌（arbuscular mycorrhizal fungi,AMF）影响玉米生育期土壤氧化亚氮（N₂O）排放的机制,为增加玉米产量、提高氮素利用效率、减少温室气体排放提供理论依据。【方法】采用分室（生长室和菌丝室）箱体装置,盆栽设置氮肥用量（N1：180 kg N·hm^-2;N2：360 kg N·hm^-2）和丛枝菌根真菌（M0：作物根和AMF均不能从生长室进入菌丝室;M1：只有丛枝菌根真菌能从生长室进入菌丝室;M2：作物根和丛枝菌根真菌均能从生长室进入菌丝室）双因素试验,测定玉米生长期间植株生物量、植株氮素积累量、N₂O排放量;采用Illumina平台Hiseq 2500 PE250高通量测序技术分析土壤细菌群落结构和多样性对丛枝菌根真菌的响应。【结果】氮肥用量和丛枝菌根真菌均显著影响玉米产量、植株生物量、植株氮素积累量和N₂O排放量。不同氮肥用量条件下接种丛枝菌根真菌均显著增加玉米籽粒产量、植株生物量和氮素积累量。与M0相比,N1条件下M1和M2处理产量均值分别增加38%和82%,地上部氮素积累量增加30%和52%,无机氮含量减少26%和65%;N2条件下M1和M2处理籽粒产量分别增加16%和48%;地上部氮素积累量增加9%和33%,无机氮含量减少34%和55%。与M0相比, N1条件下M1和M2处理N₂O累积排放量分别降低17%和40%,N₂O排放强度分别降低41%和67%;而N2条件下N₂O累积排放量降低26%和45%,排放强度分别降低28%和57%。NMDS 分析表明,施肥和丛枝菌根真菌均对细菌群落结构有较大影响。与N1均值相比,N2处理门水平变形菌门（Proteobacteria）和芽单胞菌门（Gemmatimonadetes）相对丰度分别降低6%和15%,而放线菌门（Actinobacteria）增加32%;属水平链霉菌（Streptomyces）增加27%,芽单胞菌属（Gemmatimonas）降低8%。与M0相比,N1条件下M1和M2处理的Streptomyces分别增加64%和205%,Gemmatimonas细菌丰度分别增加31%和53%;N2条件下M1和M2处理的Streptomyces分别增加10%和93%,M1处理的Gemmatimonas细菌丰度降低2%,M2处理Gemmatimonas细菌丰度增加56%。土壤中Streptomyces和Gemmatimonas与N₂O排放量呈显著负相关,而与玉米产量呈显著正相关。【结论】不同氮肥水平玉米接种丛枝菌根真菌均能显著降低土壤N₂O排放量,这种影响主要通过提高玉米氮素的吸收利用和改善土壤细菌群落组成实现的,其中主要增加了土壤链霉菌属和芽单胞菌属的相对丰度。     

小麦根际解钾微生物与土壤钾含量、钾素利用率及根系活力的关系

  【目的】  探讨肥料施用方式和施钾量对土壤不同形态钾含量及小麦根系活力的影响,以期为提高土壤钾素利用效率提供技术支持。  【方法】  2018—2020年连续两年,采用裂裂区设计,主区为肥料 (A):设20%有机肥 (鸡粪)+80%氮肥 (A1),100%氮肥 (A2) 2个水平;副区为施钾量 (B):设不施钾 (B1)、减量施钾80 kg/hm2 (B2)、常规施钾120 kg/hm2 (B3)、增施钾肥160 kg/hm2 (B4) 4个水平;副副区为小麦品种 (C):西农979 (C1)、豫农202 (C2)。分别在冬前、返青、拔节、开花、灌浆、成熟时,调查分析根际解钾微生物数量、土壤不同形态钾含量、小麦根系活力、钾素利用效率。  【结果】  联合方差分析结果表明,有机肥、施钾量、品种及年份对根际解钾微生物数量、土壤速效钾含量、小麦根系活力、钾素利用效率和产量的影响均达5%或1%显著水平。在小麦全生育期内,与单施化肥相比,有机肥和化肥配施条件下根际解钾微生物数量、速效钾含量、根系活力显著提高,缓效钾和矿物钾含量降低;随施钾量提高,根际解钾微生物数量、速效钾含量、根系活力、钾素利用效率提高,而施钾量过大时则有所降低;有机肥和常规施钾量配施处理的根际解钾微生物数量、速效钾含量、根系活力较其他处理显著提高,而缓效钾和矿物钾含量降低幅度最大。有机肥和钾肥配施较单施化肥处理的钾素利用效率提高2.24%,与不施钾相比,在两年中常规施钾植株钾素利用效率提高幅度最高可达75.15%,且有机肥和常规施钾配施处理下钾素利用效率提高幅度最大达4.66%。相关分析结果表明,不同生育时期根际解钾微生物数量与小麦根系活力、土壤速效钾、缓效钾或矿物钾含量呈显著或极显著正相关。  【结论】  有机肥和化肥配施可增加土壤根际解钾微生物数量,提高土壤速效钾含量而降低缓效钾和矿物钾含量。钾肥减施条件下,采用有机无机肥配施模式有利于提高土壤钾素利用率,增强小麦根系活力,本研究条件下,黄淮平原典型麦田的施钾策略是有机无机肥配施,K₂O施用量以120 kg/hm2为宜。     

Functional Properties of Wheat Gliadins. I. Effects on Mixing Characteristics and Bread Making Quality

The effects of addition of total gliadin and gliadin subfractions on the 2 g Mixograph parameters and loaf volume data of cv. Hereward base flour were studied. The addition of increasing levels of total gliadin and gliadin subgroups to cv. Hereward base flour decreased the overall dough strength, as evidenced by decreases in the values for mixing time (MT), mixing stability (MS) and work input (WI). The decreasing order of these parameters for different gliadins was: ω1- >, γ-, > β-, > α-gliadins. The mixing tolerance, as measured by resistance breakdown (RBD) and bandwidth breakdown (BWBD), decreased as a result of addition of different fractions. However, Peak dough resistance (PDR) values increased with addition of individual groups of gliadins and gluten to the base flour. A linear relationship was found between the PDR and loaf volume when individual groups of gliadin were added to the base flour. The ω-gliadins produced the least positive effects on PDR. Addition of total gliadin and its subgroups substantially improved loaf volumes of pan breads. The ω-gliadins again resulted in a smaller increase in loaf volume.     

三轮高架作业车玉米变量施肥系统设计与试验

针对玉米追施肥机械田间作业通过性及施肥量精确控制问题,设计了一种三轮高架作业车变量施肥系统,该系统由机械排肥系统、液压传动系统和电控调速系统3部分组成。电控调速系统采用闭环控制,以STM32F103R8T6微处理器为控制核心,结合设置的施肥参数和检测到的速度信号,采用增量式PID算法控制施压系统中的电液比例流量阀来调节排肥轴的转速,实现对施肥量的控制,并显示施肥参数、作业车前进速度和排肥轴转速。室内试验表明,排肥槽工作长度为30mm,排肥量平均变异系数最小,确定了该工作长度下排肥量和排肥轴转速的拟合方程;整定PID控制参数,确定了Kp为1.2,Ki为0.02,Kd为0.4。田间试验表明,施肥量平均偏差为0.84%,平均变异系数为1.852%,实现了对玉米机械化精确追肥。     

全液压驱动高地隙履带作业车设计与试验

针对玉米、烟草等高秆作物中耕管理作业需求,设计了一种液压驱动的小型遥控高地隙履带作业车。作业车采用龙门架式车架结构,可以在田间实现跨行行走和原地转向,液压系统中采用分流集流阀以提高作业车行走的直线性。为研究重心偏移和分流集流阀对作业车直线行驶稳定性的影响,在作业车左侧车架上添加不同配重,使用SolidWorks软件对作业车重心偏移量进行精确评估,选取空载、添加2块和4块配重3种典型负载工况,对含有和去除分流集流阀的作业车行驶直线性进行仿真和样机试验。使用AMEsim软件对液压系统进行仿真表明：有、无分流集流阀时两侧马达稳定工作时转速差相对于总转速偏差分别小于1%和大于38%。样机试验表明,含有分流集流阀时偏驶率分别为4.12%、4.28%、4.62%;无分流集流阀时偏驶率为5.08%、6.54%、9.43%。仿真和试验结果表明,采用分流集流阀提高行驶直线性的液压方案可行,作业车直线行驶稳定性满足国家标准要求。