气候变化对石羊河、大凌河流域灌溉玉米生产的影响

全球气候变化及其影响越来越受到广泛关注,生态环境已相对恶化的地区未来将可能更加脆弱.选取生态环境已十分脆弱的石羊河和大凌河流域,采用区域气候模式与CERES-Maize模型相结合的方法,模拟分析了基准气候(BS,1961-1990年)和A2、B2两种气候变化情景下2011-2100年2个流域灌溉玉米生产的变化,以了解未...     

Superoxide Dismutase Plays an Important Role in Maize Resistance to Soil CO2 Stress

CO₂ capture and storage(CCS) has the risk of CO₂ leakage, and this leakage always increases soil CO₂ concentration, and the long-term CO₂ stress damages crop production in farmland. Using maize, the growth characteristics, such as plant height and yield, and physiological indexes(osmoregulation substances and antioxidant enzymes) were explored under different simulative CO₂ leakage conditions. Further, the relationship between maize physiolo...     

结合高光谱像素级信息和CNN的玉米种子品种识别模型

玉米作为中国重要粮食作物,品种众多,易出现错分现象,影响农业安全和粮食生产。针对传统基于卷积神经网络CNN（Convolutional Neural Network）的高光谱图像作物品种识别模型所需建模样本数量巨大的问题,提出基于高光谱像素级信息和CNN的玉米种子品种识别模型。首先,获取不同品种玉米种子在400—1000 nm范围内的高光谱图像,提取样本全部像素的203维光谱信息,利用主成分分析PCA（Principal Component Analysis）算法将光谱维度降至8维。在实验中,样本的像素级光谱信息（即：样本的全部像素的光谱信息）除应用于CNN模型外,也应用于支持向量机（SVM）和K近邻分类（KNN）模型中,结果表明：在相同模型中,基于像素级光谱信息比基于米粒级光谱信息（即：每粒样本所有像素光谱信息的平均值）识别效果好;在相同情况下,CNN模型比SVM和KNN模型的识别效果好;基于像素级光谱信息和CNN的品种识别模型识别效果最稳定,依据像素级分类结果采用多数投票策略对玉米种子样本进行识别,样本识别精度高达100%（注：100%为建模集样本与测试集样本数量为0.27和0.32时的识别精度,随着测试集样本数量的增加,该识别精度将有所降低）。最后,使用t分布随机邻域嵌入（t-SNE）算法实现CNN输出特征值的可视化,验证了基于高光谱像素级信息和CNN的品种识别模型的有效性。在建模样本极少的情况下,实现了玉米种子品种的无损、高效识别,为精准农业提供了理论基础。     

Ecotoxicity of Cadmium to Maize and Soybean Seedling in Black Soil

Ecotoxicity and bioavailability of cadmium(Cd)to the maize(Zea mays L.)and the soybean(Glycine max(L.)Merr.)were investigated by acute toxicity experiment in the laboratory with black soil.Ecotoxicity and bioavailability of Cd were quantified by calculating the median effective concentration(EC50)and bioaccumulation factor(BAF).The measurement endpoints used were seed germination and seedling growth(shoot and root).The results showed that concentrations of Cd in the soil had adverse effect on the growth of roots and shoots.Seed germination was not the sensitive indicator for the ecotoxicity of Cd in the soil,while the growth of roots was the most sensitive measurement endpoint.Absorbability and transport of Cd in plants depended on the test crop species and Cd concentrations in the soil.The maize retains more Cd in its roots,while the soybean transports more Cd to the shoots from roots.     

Greater effect of canopy conductance in regulating the energy partition above the maize field in arid northwest China

The partition of available energy into evapotranspiration affected by environmental and physiological factors is critical in understanding the water cycle and optimizing the water management in the field. Our study attempted to accurately quantify the environmental and physiological control on variability in evaporative fraction (EF) based on the Penman–Monteith model. The eddy covariance method was used to measure water flux over a canopy and then calculate the EF above a maize field in northwest China in 2007. Results indicate that the EF was lower in other growth stages than in the heading stage, so the EF value in the heading stage was taken as the standard value. The decreases in EF caused by canopy conductance and environmental factors were 0.176 and ?0.026, accounting for 117% and ?17% of the total difference in EF, respectively. Such results were mainly due to the following: (1) the variation of maize canopy conductance was greater than that of the environmental factors, such as air temperature, air humidity, wind speed and radiation; (2) the EF of the maize was more sensitive to variation in canopy conductance than the environmental factor. Our study revealed that crop physiological factor played an important role in determining the energy partition processes and reducing the sensible heat flux in the maize field. Copyright © 2012 John Wiley & Sons, Ltd.     

Geographic Influences on Maize Seed Exchange in the Bajío,Mexico

To document the diversity of geographic (physical and human) influences on seed exchange, an important component of traditional agricultural systems, household surveys were conducted in four villages in the Mexican Bajío. This research reviews and contributes to an understanding of the purpose, structure, and scale of seed exchange and threats to seed movement. Based on the household survey data, the main factors that distinguish seed exchange at the village level include whether or not the same seed was grown the previous year, what farmers look for in a seed source, and where they have acquired their original seed. When the household survey data are analyzed based on gender, rather than village, different results are obtained. We discuss the diversity of possible influences on the current seed systems in four Bajío communities surveyed and address the possible consequences for agrobiodiversity conservation.     

农田N_2O通量测定方法分析

采用空气动力学方法、波文比 /能量平衡法及密闭箱法结合气相色谱分析对农田N2 O通量进行了测定。在夏天和秋天观测前的 1～ 2周 ,148和 10 9kgNhm-2 肥料被分别施入夏玉米田和冬小麦田。实验表明 :空气动力学法与波文比 /能量平衡法测定的N2 O通量在冬小麦田较为接近 ,在夏玉米田则相差较大。夏玉米冠层上方温湿梯度的细微变化可导致能量平衡法计算的N2 O通量发生较大离散 ,从而与空气动力学法的计算结果产生较大偏差。观测期间 ,微气象法和密闭箱法测定的农田N2 O日平均通量在夏玉米田分别为 18± 37和 8± 5ngNm-2 ·s-1;在冬小麦田分别为 43± 2 1和 6± 1ngNm-2 ·s-1。微气象法测定的农田N2 O通量高于密闭箱法的观测值 ,由此推测作物冠层可释放N2O ,其机制可能是土壤中生成的N2 O被作物的蒸腾液流输送到大气中。微气象法和密闭箱法测定的N2 O通量间的差异在冬小麦田大于夏玉米田 ,表明冬小麦释放N2 O的量大于夏玉米。这可能是冬小麦根系分布较夏玉米深的缘故。采用密闭箱法观测时 ,箱内气温发生变化 ,半小时内最高可增加10℃ ,因地温变化小 ,其对土壤中N2 O的生成并无显著影响。由于密闭箱法观测忽略或低估了植物释放的N2 O ,且箱内的边界层阻力可能高于箱外 ,其测定的地表N2 O通量偏小。     

WOFOST模型在东北春玉米产区的验证与适应性评价

校准与验证春玉米WOFOST模型,为模型本地化、区域化应用提供研究依据。采用东北春玉米田间观测数据,使用全局敏感性分析EFAST方法对WOFOST模型参数进行敏感性分析,结合土壤数据和同期气象数据等资料对模型进行参数校正与优化,确定春玉米的作物参数;利用独立的观测数据,对春玉米生育期、叶面积指数、各生物量等指标进行详细的验证与适应性评价。结果表明:1)针对不同区域进行作物模型敏感性分析筛选出的作物参数有一定差异,但对产量影响最敏感的前5位总敏感参数相同。2)模型对春玉米生育期的模拟较好,开花期和乳熟期的相对模拟平均误差在1 d左右,在成熟期的平均误差在3 d左右。3)模型对各生物量模拟的回归系数α与确定系数R2较好,均通过显著性检验,从模型整体模拟效果来看,地上部分总生物量和叶面积指数为89%和86%,整体模拟性能较好;残差聚集指数(CRM)为14%和4%,表明模型对地上生物量和叶面积指数的模拟值略偏低。4)通过校准模型作物参数值,WOFOST模型能够较好地模拟东北春玉米生长发育及其生物量的动态积累过程,能够应用于东北地区春玉米生产。     

Application of Multi-Temporal MODIS NDVI Data to Assess Practiced Maize Calendars in Rwanda

Crop calendar is an important tool providing relevant information on crops cycles in a specific area for effective agricultural management. Crop calendars vary in different areas given dissimilarities in agro-ecosystems’ characteristics. This research used multi-temporal MODIS NDVI stratification to assess differences in practiced maize crop calendars in various areas of Rwanda. Four (4) sample NDVI strata dominated by agriculture were purposively chosen, and 433 local farmers were randomly selected from the strata for interviews. The collected information helped to know about their maize planting as well as harvesting dates in order to generate maize calendars per NDVI strata. The generated crop calendars were later classified using k-means unsupervised classification, and produced 4 groupings of practiced maize calendars irrespective of NDVI strata. ANOVA results revealed significant differences between both the generated maize crop calendars by NDVI strata and the practiced crop calendars irrespective of NDVI strata, at p = 0.05. Moreover, chi-square tests and t-tests revealed not only a significant relationship between maize calendars and number of crop growing seasons, but also a significant relationship between maize calendars and NDVI strata, at p = 0.05. Finally, findings of this research contrasted the present conviction that there exist a single general maize calendar all over the country. Instead, the results were in accordance with the fact that Rwanda agro-ecosystems differ from East to West in terms of, mainly, altitude and rainfall patterns variations.     

Study on micro water collecting technique in dryland field of spring maize *

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