Crop canopy sensor orientation for late season nitrogen determination in corn

Increasing nitrogen use efficiency (NUE) in irrigated corn production is of great importance to overall agricultural sustainability. Studies have shown that crop canopy sensors can aid in this pursuit as they allow for the determination of nitrogen (N) requirements in split applications later in the growing season. Fertigation can also increase NUE as many split applications can be conducted. If crop canopy sensors could be used to direct N fertigation rates, overall NUE may be increased even further. However, in some cases, N differences may need to be determined later in the growing season after corn has tasseled, which can cause issues with crop canopy sensor readings. Therefore, a study was initiated to evaluate the potential of a crop canopy sensor to differentiate between N levels at two corn (Zea mays) growth stages (R1 and R3) after the corn had tasseled. The sensor was placed in three orientations to evaluate which orientation best determined the corn N status across two sensor-calculated indices while avoiding taking measurements involving the corn tassel. These orientations were (1) nadir, between corn rows (above canopy), (2) 45° off nadir within the corn canopy (below corn tassel), and (3) 90° off nadir within the corn canopy (below corn tassel). The results of this study show that N differences in late season corn can be determined by utilizing crop canopy sensors in an inter-row orientation. Results also show that the red edge normalized difference vegetation index (ReNDVI) index is superior to the normalized difference vegetation index (NDVI) index for late season N determinations in corn. These results suggest that crop canopy sensors could be an effective tool for determining N requirements of corn late in the growing season.     

Effect of nitrogen fertilizer source on corn (Zea mays L.) optical sensor response index values in a rain-fed environment

The use of optical sensors to detect nitrogen (N) deficiencies and determine in-season fertilizer recommendations has grown. Nitrogen responses are difficult to detect early in the growing season. The objective of this experiment was to determine if different N sources could deliver early season detection of N deficiencies. Four N fertilizer sources were applied at rates of 90 and 180 kg N ha^?1 across three site-years. A Greenseeker and SPAD sensor were used to measure in-season fertilizer response index (RI). When differences in sensor RI values between N rates were present, they did not occur until the V9/10 growth stage. No specific N source provided superior results that led to a reliable, early season detection of N deficiency. Reliable differences in response index values could be detected beyond the V7/V8 growth stages. For earlier detection of N responsiveness, and potential N deficiency, other management strategies should be investigated.     

不同施肥长期定位试验地夏玉米冠层光谱特征研究

以黄淮海地区典型冬小麦-夏玉米轮作区的长期定位施肥试验为研究对象,筛选对氮、磷、钾三种营养元素及产量最敏感的波段和生育期,为监测不同时期作物营养胁迫情况和估产提供依据。系统分析了氮、磷、钾单一养分缺乏和两种或两种以上营养元素同时缺乏时典型生育期夏玉米冠层反射光谱特征、收获后秸秆和子粒氮、磷、钾及产量的变化规律。结果表明,缺素使冠层光谱反射率在可见光波段增加,在近红外波段降低。作物秸秆、子粒含氮量和含钾量及产量与可见光波段反射率呈负相关,与近红外区域7601~300 nm反射率呈正相关;秸秆含磷量与各反射率的相关性不明显,子粒含磷量与冠层光谱之间无明显规律。整体上,560和810 nm分别为收获期作物含氮量在可见光和近红外两个区域的敏感波段,开花期为夏玉米氮素诊断的敏感时期;夏玉米钾素在可见光和近红外区域的敏感波段分别为680和810 nm,拔节期为诊断钾素的敏感时期。整个生育期各单波段反射率与产量均呈极显著相关关系,拔节期关系最密切。说明在明确主导养分限制的前提下,利用作物冠层光谱来监测氮素和钾素的丰缺以及准确估产是可行的。     

Comparison of two ground-based active-optical sensors for in-season estimation of corn (Zea mays,L.) yield

Thirty field experiments were conducted in North Dakota during 2011 and 2012 to compare two ground-based active-optical sensors for their relationship between sensor readings and INSEY (in-season estimate of yield). The experimental design at each site was a randomized complete block with four replications and six nitrogen (N) rate treatments: control, 45, 90, 134, 179, and 224 kg ha^?1 applied pre-plant as ammonium nitrate within five days of planting. The two sensors, GreenSeeker® (Trimble, Sunnydale, CA, USA) (GS) and Crop Circle ACS 470® sensor (Holland Scientific, Lincoln, NE, USA) (CC) were used to scan over the top of the corn at V6 and V12 growth stages. The GS INSEY and the CC INSEY were similarly related to corn yield at V6. The CC using the red-edge lens option improved the INSEY relationship to corn yield compared to the GS or the CC using the red lens option at V12.     

基于夏玉米光谱特征的叶绿素和氮素水平及氮肥吸收利用研究

本文首先分析不同施 N 水平条件下夏玉米冠层在6个典型生育期的光谱特征曲线,然后计算了可见光和近红外波段光谱反射率组成的归一化植被指数(NDvI)及相应时期叶片叶绿素含量和地上部分全N含量2个重要指标以及孕穗期冠层NDVI和几个N肥吸收利用效率的相关性.结果表明,孕穗期冠层光谱反射率在近红外区域反射率最大,且其可见光和近红外区域反射率差异最大:从苗期到孕穗期,NDVI和叶绿素、全N含量的相关性逐渐增强,到抽雄期减弱,灌浆期又有所增强;整体来讲绿色归一化植被指数 GNDNI(560,760)在各生育期与不同农学参量的相关性比其他波段组合的指数好,其次为NDVI(660,760)波段组合.随着施N量的增加,N肥利用效率、收获指数和N肥收获指数、N素农艺效率以及N肥回收效率均逐渐降低,对各N肥吸收利用指数的预测以NDVI(660,760)、NDVI(660,1100)和GNDVI(560,760)较理想.     

施氮水平与模拟降雨pH值对玉米冠层NO3--N淋失的影响

为探明降雨特别是酸雨对玉米冠层氮素淋失的影响,以盆栽试验春玉米为指示作物,采用自制人工降雨器进行模拟降雨,研究施氮与不施氮（对照）条件下玉米冠层NO3--N淋失动态、数量及随生育期和降雨酸度的变化规律。结果表明,中性和弱酸性降雨淋洗,NO3--N淋失量主要由冠层氮素含量决定,而强酸雨淋洗,NO3--N淋失量受降雨pH值和冠层氮素含量共同影响。各生育期玉米冠层NO3--N淋失量随降雨pH值降低变化规律不一,生育前期降雨pH值对冠层NO3--N淋失影响较生育后期显著,在研究降雨酸度对玉米冠层NO3--N淋失的影响时,必须考虑生育期。相同pH值模拟降雨条件下,玉米冠层NO3--N淋失量随生育期推进逐渐降低：11叶期>吐丝期>灌浆期,生育前期显著高于中后期。玉米冠层NO3--N淋失量不仅与介质施氮有关,同时受降雨pH值影响,2因素在不同生育期对NO3--N淋失贡献大小有所不同,但总体看,植物体氮素丰富程度是影响冠层NO3--N淋失的主要因素。各生育期玉米冠层均存在一定数量的NO3--N淋失,尤以生育前期为甚,说明在研究农田生态系统氮素流量和冠层氮素损失时,冠层氮素淋失应予以考虑。     

基于冠层覆盖度的玉米植株临界氮浓度模型构建与产量预测

  【目的】  依据临界氮浓度稀释原理,构建基于冠层覆盖度的覆膜滴灌玉米植株临界氮浓度稀释曲线,并通过氮营养指数和氮累积亏缺量模型对玉米氮营养状况进行诊断和评价,以期达到基于该模型的玉米产量预测。  【方法】  于2019—2020年,在宁夏引黄灌区开展了4个氮肥用量(0、120、240、360 kg/hm2)田间试验,采用滴灌水肥一体化技术,氮肥按照苗期10%、拔节—大喇叭口期45%、抽雄—吐丝期20%和灌浆期25%的比例分8次随水追肥。在玉米关键生育时期测定农学参数和图像参数,分别测定了地上部生物量、植株氮浓度和产量,建立和验证基于冠层覆盖度的玉米植株临界氮浓度经验模型。  【结果】  基于冠层覆盖度的玉米植株临界氮浓度、最大氮浓度和最小氮浓度模型R2分别为0.917、0.843、0.873。临界氮浓度模型检验参数RMSE和n-RMES分别为 0.242和 11.753%。以冠层覆盖度为基础的氮营养指数和氮累积亏缺量推算出玉米最佳施氮处理为240 kg/hm2。不同生育时期氮营养指数、氮累积亏缺量与相对产量的关系极显著,R2均不小于0.922,且大喇叭口期和抽雄期R2值最高。采用独立试验验证表明,在大喇叭口期和抽雄期表现出稳定的模型性能,R2值≥0.944,n-RMSE均≤9.089%。在大喇叭口期和抽雄期,氮营养指数、氮累积亏缺量与相对产量呈极显著相关,能准确地解释受氮素限制和不受氮素限制生长条件下相对产量的变化。  【结论】  基于冠层覆盖度构建的植株临界氮浓度稀释曲线可准确判断和评价玉米拔节期至吐丝期的氮素营养状况,依据氮营养指数、氮累积亏缺量与相对产量所构建的关系模型可对玉米产量进行准确估计,其为玉米生长过程中氮肥的精确管理和产量预测提供了一种简便的新方法。     

基于无人机可见光遥感的夏玉米氮素营养动态诊断参数研究

【目的】 近年来应用无人机进行作物生长、营养和植保信息的快速提取受到广泛关注,但其对作物全生育期营养状况的动态诊断需要明确适宜的色彩参数。本研究通过田间氮水平试验,以无人机为平台利用可见光光谱对夏玉米不同生育期的冠层氮素营养进行监测,对基于可见光RGB图像的色彩参数与传统氮素诊断指标的相关性进行分析,并比较色彩参数的变异系数以探明夏玉米不同生育时期氮素营养诊断的最佳色彩参数。 【方法】 于2015年6—10月,在河北省中国农业大学曲周试验基地设置不同氮水平田间试验,以夏玉米郑单958为供试作物,设5个施氮水平:0、102、145、189和250 kg/hm2 (分别以CK、70%OptN、OptN、130%OptN、ConN表示),4次重复。分别在夏玉米六叶期 (V6)、十叶期 (V10)、吐丝期 (VT)、籽粒建成期 (R2)、乳熟期 (R4) 应用无人机可见光遥感技术获取夏玉米冠层图像,采用Adobe Photoshop软件经过一些图像处理后选用直方图程序提取图像的红光值R、绿光值G、蓝光值B、亮度值L,研究由此计算的12个色彩参数与传统氮素诊断指标 (植株氮浓度、生物量和吸氮量) 的相关性,结合相关系数和变异系数的大小综合分析筛选夏玉米不同生育时期氮素营养诊断的最佳色彩参数。 【结果】 红光值 (R)、绿光值 (G)、亮度值 (L)、绿光标准化值[G/(R + G + B)]、蓝光标准化值[B/(R + G + B)]、绿光与红光的比值 (G/R)、绿光与蓝光的比值 (G/B)、绿光与亮度的比值 (G/L)、红绿蓝植被指数 (RGBVI) 等在不同生育时期均与夏玉米的植株氮浓度、生物量和吸氮量有很好且一致的相关性,结合图像色彩参数的变异系数综合分析后,G/(R + G + B)、G/L在各生育时期与夏玉米常规的氮营养诊断指标有极显著的相关性 (P < 0.01),相关系数介于0.641～0.944之间,且变异系数小而稳定,介于0.93%～4.30%之间,优于其他光谱参数,可作为基于无人机可见光技术用于各时期氮素营养动态诊断的最佳色彩参数。 【结论】 应用无人机可见光遥感进行夏玉米氮素营养动态诊断具有结果可靠、便捷、高效、非破坏性的优点,本研究结果对应用该技术进行较大区域的作物氮素营养动态诊断提供了科学依据。      

分时段修正双源模型在西北干旱区玉米蒸散量模拟中的应用

蒸散发(ET)是陆地水循环过程的重要组成部分,同时也是区域能量平衡以及水量平衡的关键环节,精确估算ET,对于提高水分利用效率以及优化区域用水结构具有重要意义。本文利用黑河重大计划观测数据,对比了考虑CO_2浓度和不考虑CO_2浓度对玉米冠层影响的冠层阻力模型,分别将其耦合到双源的Shuttleworth-Wallace(S-W)模型中,并利用这两种模型分时段对玉米整个生育期内半小时尺度上的ET进行模拟,利用涡度相关实测数据对模型进行验证,最后分别对影响玉米冠层阻力的气象要素和影响ET的阻力参数进行敏感性分析,探寻大气CO_2浓度改变条件下黑河中游绿洲区玉米不同生长阶段的农田耗水规律。结果表明:本文所修正的考虑CO_2浓度对玉米冠层影响的冠层阻力模型耦合到S-W模型后,能够较精准地模拟玉米整个生育期不同生长阶段半小时尺度上农田耗水过程。敏感性分析表明:各生长阶段冠层阻力(r_s~c)和冠层面高度到参考面高度间的空气动力阻力(r_a~a)对ET的影响最为强烈,其他阻力参数对ET的影响不明显,ET的变化程度随着r_s~c和r_a~a的增大而减小。本文所修正的考虑CO_2浓度影响的分时段双源模型能够精准地模拟玉米整个生育期各生长阶段的ET,可为种植结构调整和土地利用方式改变以及CO_2浓度变化环境下的农田蒸散研究提供参考。     

Effect of nitrogen rates applying controlled-release and conventional urea blend in maize

Abstract

Blending polymer-sulfur coated urea (PSCU) and conventional urea (U) for maize (Zea mays L.) fertilization can supply nitrogen (N) during the crop cycle with a single application. Proper placement of PSCU?+?U (0.15?m below and 0.1?m to the side of seed row) in band application at sowing is necessary to reduce salt stress that can decrease dry weight (DU) and N uptake (NU) of maize plant compromising maize yield. It is not clear the proper N rate in the proper placement for band application of PSCU?+?U at maize sowing to avoid salt stress. In the current literature, reduction of N rates are being recommended using PSCU?+?U without consider the probably salt stress provided by high rates of PSCU?+?U. DW and NU in maize plant as well as soil pH and electrical conductivity (EC) were evaluated in a greenhouse pot trial. N treatments were equivalent to 0, 90, 180, 360 and 540?kg N ha^?1 applied incorporated in band in two contrasting soils (Rhodic Eutrustox and Typic Haplustox) using 70%PSCU + 30%U. At V10 (vegetative leaf stage 10), DW and NU of maize aerial part had quadratic behavior in response to increase N rates in the Typic Haplustox soil. In the Rhodic Eutrustox was not observed known behavior for DW and NU in response to increase N rates. Soil pH and EC was higher in the fertilizer row than sowing row. A N rate above of 180?kg N ha^?1 using 70%PSCU + 30%U incorporated in bands can reduce DW and NU in early maize plant growth associated with salt concentration of N fertilizer in a Typic Haplustox soil, which could compromise maize yield.     

玉米作物系数无人机遥感协同地面水分监测估算方法研究

该文研究不同水分胁迫条件下无人机遥感与地面传感器协同估算玉米作物系数的可行性。利用自主研发的六旋翼无人机遥感平台搭载多光谱传感器获取内蒙古达拉特旗昭君镇试验站不同水分胁迫下大田玉米冠层光谱影像,计算植被指数,采用经气象因子和作物覆盖度校正后的FAO-56双作物系数法计算玉米的作物系数,研究作物系数与简单比值植被指数(simple ratio index,SR)、叶面积指数(leaf area index,LAI)和表层土壤含水率(surface soil moisture,SM)的相关关系,结果表明,作物系数与SR、LAI和SM的相关程度与水分胁迫程度有关,但均呈现出显著或极显著的线性关系,说明了基于这些指标建立作物系数估算模型的可能性。利用逐步回归分析方法建立了作物系数的估算模型,其估算模型,修正的决定系数、均方根误差和归一化的均方根误差分别为0.63、0.21、25.16%。经验证,模型决定系数、均方根误差和归一化的均方根误差分别为0.60、0.21、23.35%。研究结果可为利用无人机多光谱遥感平台进行作物系数估算提供技术参考。     

On‐farm comparison of variable rates of nitrogen with uniform application to maize on canopy reflectance,soil nitrate,and grain yield

Recent development in canopy optical‐sensing technology provides the opportunity to apply fertilizer variably at the field scale according to spatial variation in plant growth. A field experiment was conducted in Ottawa, Canada, for two consecutive years to determine the effect of fertilizer nitrogen (N) input at variable‐ vs. uniform‐application strategies at the V6–V8 growth stage, on soil mineral N, canopy reflectance, and grain yield of maize (Zea mays L.). The variable N rates were calculated using an algorithm derived from readings of average normalized difference vegetation index (NDVI) of about 0.8 m × 4.6 m, and N fertilizer was then applied to individual patches of the same size of NDVI readings (0.8 m × 4.6 m) within a plot (2184 m²). Canopy reflectance, expressed as NDVI, was monitored with a hand‐held spectrometer, twice weekly before tasseling and once a week thereafter until physiological maturity. Soil mineral N (0–30 cm depth) was analyzed at the V6 and VT growth stages. Our data show that both variable and uniform‐application strategies for N side‐dressings based on canopy‐reflectance mapping data required less amount of N fertilizer (with an average rate of 80 kg N ha^–1 as side‐dressing in addition to 30 kg N ha^–1 applied at planting), and produced grain yields similar to and higher nitrogen‐use efficiency (NUE) than the preplant fully fertilized (180 kg N ha^–1) treatment. No difference was observed in either grain yield or NUE between the variable‐ and uniform‐application strategies. Compared to unfertilized or fully fertilized treatments, the enhancements in grain yield and NUE of the variable‐rate strategy originated from the later N input as side‐dressing rather than the variation in N rates. The variable‐rate strategy resulted in less spatial variations in soil mineral N at the VT growth stage and greater spatial variations in grain yield at harvest than the uniform‐rate strategy. Both variable‐ and uniform‐application strategies reduced spatial variations in soil mineral N at the VT stage and grain yield compared to the unfertilized treatment. The variable‐rate strategy resulted in more sampling points with high soil mineral N than the uniform‐rate strategy at the VT stage.     

Biomass accumulation and N status in grain maize as affected by mineral and organic fertilizers in cool climate

Abstract

Expansion of grain maize to marginally suitable cool climate regions requires a better understanding of the nitrogen (N) economy of the crop. This study was aimed at yield formation in response to different type of fertilizers. Field experiments with short-season maize variety were conducted in Akademija, Lithuania, in 2015 and 2016. In spring, before sowing, ammonium nitrate, pelletized cattle and poultry manures, green waste compost were incorporated at a rate equivalent to 170?kg N ha^?1. Crop N status, based on SPAD measurements, started to differ significantly at the end of the vegetative period with higher values in treatments applied with ammonium nitrate and lower with organic fertilizers. Under favorable conditions maize produced more grain per cob and higher yield. Agronomic N use efficiency (AE_N) of pelletized organic fertilizers in the unfavorable season (AE_N 2015: 0.1–4.9) was poor and significantly lower than in the favorable season of (AE_N 2016: 4.9–11.2).     

基于无人机图像参数对滴灌条件下玉米氮素营养的动态诊断

于2018和2019年在宁夏平吉堡农场进行滴灌水肥一体化氮肥梯度试验，以天赐19为试验材料，设6个氮素水平，即 0 （N0）、90（N1）、180（N2）、270（N3）、360（N4）和450（N5）kg·hm⁻²，在玉米拔节期（V6）、小喇叭口期（V10）、大喇叭口期（V12）、吐丝期（R1）和乳熟期（R3）利用无人机搭载数码相机获取玉米冠层图像，利用Matlab编写代码开发的数字图像识别系统提取玉米冠层图像红光值R、绿光值G、蓝光值B，研究基于此计算的10个冠层图像参数指标与氮素营养指标间的相关性，筛选出稳定性好且敏感度高的图像色彩参数，构建玉米氮素营养诊断指标与图像参数间关系模型并进行验证，以探究利用无人机图像进行宁夏引黄灌区滴灌玉米拔节-乳熟期氮素营养动态估测的可行性。结果表明：冠层图像参数指标绿光与红光比值(G/R)、绿光标准化值（NGI）、红绿蓝植被指数(RGBVI)与植株氮含量和叶片氮含量相关性高且变异系数小，可作为氮素营养诊断的潜在最佳色彩参数；将最佳色彩参数与植株氮含量和叶片氮含量分别进行回归模型构建，幂函数模型可以更好地预估玉米氮素营养状况；利用2019年相同氮素试验进行模型验证，发现NGI与植株氮浓度和叶片氮浓度实测值与估测值的R2分别为0.738和0.689，检验指标RMSE为2.594和3.014，nRMSE为13.125%和13.347%，预测精度和准确性高于G/R和RGBVI。故选择NGI作为滴灌玉米拔节−乳熟期氮素营养动态诊断的最优参数，参数NGI与植株氮浓度的关系模型（N_P=4.967×106NGI^14.26）R²为0.707，与叶片氮浓度的关系模型（N_L=1.707×106NGI^12.88）R²为0.654。说明应用无人机图像技术可以较好地对宁夏引黄灌区玉米拔节−乳熟期氮素营养状况进行动态估测，构建的氮素营养诊断模型可为宁夏引黄灌区滴灌玉米氮肥精准配施提供理论依据。     

Nutrient Uptake and Apparent Balances for Rice-Wheat Sequences. II. Phosphorus

ABSTRACT

Phosphorus (P) nutrition of the rice-wheat (RW) systems of the Indo-Gangetic Plain of South Asia has become important due to the alternate flooding and drying cycles of this crop rotation. Field experiments on the RW cropping sequence were conducted at three locations of Bangladesh on three soil types. Two fertilizer doses—farmers' practice (FP) and soil-test based (STB), containing recommended amounts of P, nitrogen (N), potassium (K), and other nutrients—were compared with mungbean or maize as a third crop. The objective of the experiments was to detect P deficiency, if any, in rice, wheat, mungbean, and maize, and to compare the FP and STB doses of fertilizers in rice-wheat-mungbean and rice-wheat-maize sequences under two mungbean management practices (residue removed or retained) and one maize management practice (residue removed) in terms of P nutrition of those crops and annual system-level P removal and apparent P balance in the soil. The apparent P balance was negative with the FP dose (?1 to ?9 kg ha^?1 for mungbean sequences at Joydebpur and Nashipur) and there was soil P accumulation under both the STB dose (9–49 kg ha^?1) and zero N control (13–50 kg ha^?1) across sites. The effect of maize or mungbean as the pre-rice crop on the apparent P balance of various RW sequences was not significant. Phosphorus deficiency occurred at all sites in wheat and maize, and at Ishwordi in rice, suggesting that P fertilizer recommendations need to be revised for RW systems in Bangladesh. The results also suggest that long-term monitoring for P concentration, uptake, and balance would be necessary for improving not only the productivity and sustainability of this system but also the fertilizer P-use efficiency.     

考虑植株氮垂直分布的夏玉米营养诊断敏感位点筛选

探明夏玉米氮素营养生化指标(叶绿素a、叶绿素b、类胡萝卜素、叶片氮含量和叶片氮积累量)与叶片SPAD值垂直分布特征及两者间定量回归关系,确立基于叶绿素仪的夏玉米氮营养无损诊断敏感叶位和叶片部位,以实现氮营养时空变化的快捷和精准监测。利用2018-2019年连续2季不同氮营养水平下夏玉米关键生育期主茎各叶位(顶1叶~顶12叶,TL1~TL12)和叶片部位(每张叶片从叶片基部开始根据叶片长度每20%分为1个测试区间) SPAD值及氮营养指标数据,研究基于偏最小二乘(partial least square, PLS)回归模型的夏玉米不同位点SPAD值与氮营养指标间关系,确定可稳定指示夏玉米氮营养空间异质性变化的敏感叶位及叶片部位。结果表明,不同叶位间夏玉米叶片SPAD值和氮营养指标于植株间分布均呈典型的"钟型"特征,至TL5或TL6时达至峰值。同一叶位不同部位间SPAD值由20%至100%位点时则逐步升高,且80%~100%位点间无显著差异(P>0.05)。PLS分析结果显示,夏玉米不同叶位SPAD值与氮营养指标间模型精度决定系数(coefficient of determination, R2)和相对分析误差(relative percent deviation,RPD)范围分别为0.693~0.821和1.425~2.744。不同测试位点R2和RPD值范围则分别为0.660~0.847和1.607~2.451,满足模型精确诊断需求。此后,基于PLS模型中各叶位和叶片部位无量纲评价指标变量重要性投影值(variable importance for projection,VIP),确定顶4叶(TL4)完展叶60%~80%区间为夏玉米氮营养诊断的敏感区域,VIP值均高于临界值1.40,预测效果较为理想。研究可为实现氮营养的高效、快捷诊断和精准施氮提供参考。     

基于无人机图像纹理和表型参数的夏玉米水分胁迫诊断

农田水分胁迫是影响作物生长发育和产量品质的重要原因。及时准确地诊断作物水分胁迫状况,对于实现精准灌溉、提高作物抗逆性和产量等具有重要意义。为优化夏玉米水分胁迫诊断方法和提高诊断精度,该研究以夏玉米为对象,利用无人机搭载六通道多光谱传感器获取2022年夏玉米拔节期和抽雄期的遥感影像数据,且同步采集夏玉米气孔导度和表型参数数据,监督分类剔除冗余背景后使用灰度共生矩阵计算得到冠层植被指数和图像纹理信息,通过贝叶斯信息准则和全子集筛选法筛选出敏感的植被指数、图像纹理和表型参数及其组合,结合极限学习机、随机森林和反向传播神经网络3种机器学习方法构建夏玉米气孔导度预估模型,并基于最优气孔导度预估模型绘制夏玉米水分胁迫状况反演图。结果表明,多光谱图像的夏玉米冠层反射率与气孔导度呈弱负相关,植被指数和表型参数与气孔导度呈极显著正相关,不同波段的图像纹理均与气孔导度有较高的相关性,其中550 nm波段最佳。植被指数用于评估植被整体健康和水分状况,图像纹理用于捕捉作物空间分布、纹理和结构特征,表型参数用于立体反映作物生理和形态信息,它们在诊断作物水分胁迫的机理上具有互补性。基于植被指数、图像纹理和表型参数构建的反向传播神经网络模型是夏玉米水分胁迫诊断的最佳模型（决定系数为0.841,均方根误差为0.043 mol/(m²·s),平均绝对误差为0.034 mol/(m²·s) ）,并显著改善了对气孔导度较低值的低估情况。绘制的夏玉米水分胁迫状况反演图呈现出广泛的应用潜力,能够便捷准确地诊断作物水分胁迫状况,以优化灌溉策略,调整资源分配。研究结果可为夏玉米的水分胁迫诊断提供一种可行而准确的方法。     

内蒙古中西部玉米临界氮浓度稀释模型的构建与验证

【目的】建立内蒙古中西部地区玉米临界氮浓度稀释曲线模型,利用相应的氮营养指数对玉米进行氮素营养诊断,并验证曲线的可靠性,以期为实现内蒙古中西部玉米合理施用氮肥提供理论依据。【方法】于2019—2021 年,分别在内蒙古中部的达拉特旗和西部的五原县、乌拉特前旗 3 个典型区域,以新玉 12、晋单42、先玉 1225、泽玉 19、宏育 203 和晋单 542 以及东农 258 为试验材料,进行建模田间试验。6 个氮肥处理包括传统氮肥 (N 400 kg/hm²)、不施氮 (对照)、推荐优化施氮 (N) 180 kg/hm² (OPT) 以及 70% OPT、130% OPT、170% OPT,分别在玉米拔节期 (V6)、八叶期(V8)、十叶期(V10)、大喇叭口期 (V12)、吐丝期 (R1)、乳熟期(R3) 和蜡熟期 (R5) 进行植株取样,测定植株地上部生物量和植株氮浓度,利用地上部生物量和植株氮浓度构建临界氮浓度稀释模型。2021 年在达拉特旗进行验证试验,设置推荐施氮示范田和传统习惯生产田,测定玉米植株地上部生物量和植株氮浓度,利用氮营养...     

夏玉米冠气温差及其影响因素关系探析

测定了夏玉米主要生育期四个不同水分处理的冠层温度、气温、土壤含水率、叶面积指数和株高,分析了冠气温差与土壤含水率、叶面积指数及株高间的关系。结果表明:不同的灌溉水质和灌溉量措施对夏玉米冠气温差有显著的影响;中午12~14时左右H1高度(2/3株高)处的冠气温差较H2高度(H1+50 cm)更能反映作物和土壤的水分特征,可以用此时刻的卫星遥感冠层温度结合地面气象站数据监测作物和土壤的旱情;80~100 cm土层的土壤体积含水率与节水灌溉处理的冠气温差之间存在良好关系(α=0.05),0~80 cm四个土层中以中午20 cm和40 cm处的土壤体积含水率与冠气温差相关关系最好且稳定,可以利用此关系评价作物的缺水状况;充足灌溉下的夏玉米主要生育期的叶面积指数与冠气温差也有显著的相关关系,节水灌溉下二者关系不显著,说明水分充足条件下叶面积指数对冠气温差的影响更大;株高与不同水分处理的冠气温差也有一定的相关关系,冠层2/3高度处二者的相关系数分别为:0.7027(淡水节水处理)、0.4150(淡水充足处理)、0.3683(咸水节水处理)、0.3062(咸水充足处理)。这为区域上遥感反演夏玉米冠气温差进而监测农田蒸散和土壤含水率提供了试验依据。