Cotton canopy reflectance under variable solar zenith angles: Implications of use in evapotranspiration models

Evapotranspiration (ET) is an important parameter in hydrologic processes and modelling. In agricultural watersheds with competing uses of fresh water including irrigated agriculture, estimating crop evapotranspiration (ET_c) accurately is critical for improving irrigation system and basin water management. The use of remote sensing-based basal crop coefficients is becoming a common method for estimating crop evapotranspiration for multiple crops over large areas. The Normalized Difference Vegetation Index (NDVI) and the Soil Adjusted Vegetation Index (SAVI), based on reflectance in the red and near-infrared bands, are commonly used for this purpose. In this paper, we examine the effects of row crop orientation and soil background darkening due to shading and soil surface wetness on these two vegetation indices through modelling, coupled with a field experiment where canopy reflectance of a cotton crop at different solar zenith angles, was measured with a portable radiometer. The results show that the NDVI is significantly more affected than the SAVI by background shading and soil surface wetness, especially in north–south oriented rows at higher latitudes and could lead to a potential overestimation of crop evapotranspiration and irrigation water demand if used for basal crop coefficient estimation. Relationships between the analysed vegetation indices and canopy biophysical parameters such as crop height, fraction of cover and leaf area index also were developed for both indices.     

综合多特征的Landsat 8时序遥感图像棉花分类方法

传统的多时相遥感图像分类大多拘泥于单一特征,本文基于多时相的Landsat 8遥感数据,开展了综合多特征的特征提取与特征选择方法研究。综合了NDVI时间序列、最佳时相反射率光谱特征以及纹理特征作为初始分类特征,并采用基于属性重要度的粗糙集特征选择算法对其进行特征约简。分类结果表明:(1)利用初始分类特征,分类的总体精度达到92.81%,棉花提取精度达87.4%,与仅利用NDVI时间序列相比,精度分别提高5.53%和5.05%;(2)利用粗糙集选择后的特征分类,分类总体精度可达93.66%,棉花分类精度达92.73%,与初始分类特征提取结果相比,棉花分类精度提高5.33%。基于属性重要度的粗糙集特征选择不仅提高了分类精度,同时有效降低了分类器的计算复杂度。     

基于GF—6卫星的棉花种植面积提取研究——以山东省夏津县为例

国产高分卫星6号（简称GF6）具有高分辨率、宽覆盖、高质量和高效成像等特点,可为农业资源遥感监测提供可靠的数据支撑。本研究以GF6卫星影像为主要数据源,综合利用遥感技术理论和方法开展对夏津县棉花种植面积的提取研究,利用同时相的哨兵2号（简称Sentinel2）影像解译结果进行对比分析。研究结果表明：基于GF6卫星的夏津县棉花种植面积提取方案高效、准确,提取精度明显优于Sentinel2卫星,进一步证明了新增了红边波段的GF6卫星能够显著增强作物的识别能力,其在大规模作物种植信息提取方面具有广阔的应用潜力。     

Evaluation on Groundwater Resources of Medium Salinity in Tarim Basin and Development and Demonstration of Under-mulch-drip Irrigation Technology for Cotton

The groundwater of medium salinity refers to the groundwater with a mineralization degree of 2-7 g/L that can be directly or indirectly used for irrigation. This paper determined the distribution area of the groundwater with medium salinity in Tarim Basin, estimated the total amount of recharge resources and exploitable quantity of the groundwater of medium salinity. The irrigation water quality assessment was conducted on the groundwater of medium salinity by using multiple factors and methods. The salt tolerance parameters and irrigation water mineralization control parameters of the cotton in under-mulch-drip irrigation were determined. The under-mulch-drip irritation technology for cotton in groundwater of medium salinity was developed and applied successfully to the demonstration area. The social, economic and ecological effects of this technology as well as the application prospect were analysed. This paper also puts forward two questions that need to be further studied     

运用气候箱模拟石河子棉区棉花冷害的试验研究

为了确定引起棉花障碍型冷害的主导气象因子,达到及时预报、减轻损失的目的,2003-2005年在新疆石河子棉区乌兰乌苏农业气象试验站内,通过智能人工气候箱实施低温处理试验,模拟2001年石河子地区发生障碍型冷害时的温、湿度变化,并做不同光照强度处理的对比试验。结果表明,棉花在花铃期遭受异常低温冷害之后,其叶片、蕾和幼铃都会出现异常脱落现象,并且其蕾和幼铃先于叶片表现出受害现象,其减少率也大于叶片;而且受害程度不仅与冷害过程中的温、湿度及光照强度有关,而且与冷害发生前所处的环境条件密切相关。     

棉花滴灌专用肥氮磷钾元素在土壤中的运移及其利用率

棉花滴灌专用肥是基于绿洲干旱区域滴灌施肥和棉花需肥特点研发的新型复合肥。通过田间试验,对比研究了滴灌专用肥与常规肥的不同养分在土壤中的运移特点及滴灌棉花的养分利用率。结果表明:在膜下滴施条件下,滴灌专用肥的氮、磷、钾养分在土壤中的移动性强于常规肥,养分在土层中的分布与棉花根系分布特点吻合度好,促进了棉花根系养分吸收,提高了养分利用率;棉花滴灌专用肥氮、磷、钾的生理利用效率较常规肥分别提高了3.62%、4.18%和1.45%,农学利用率较常规肥分别提高了29.37%、29.2%和29.38%;在等养分条件下,滴施专用肥增产籽棉6.9%。     

基于多时相中分辨率时间过程特征的江汉平原棉花种植面积变化监测

棉花是中国重要的经济作物,快速、准确地提取棉花的种植面积和分布信息,对于优化棉花种植空间格局、科学指导棉花生产及提高其管理水平具有十分重要的意义。为了探讨多时相中高分辨率影像在棉花种植面积监测中的可行性,本文以江汉平原为研究区,根据棉花物候特征,选取2012年、2014年江汉平原棉花生长关键期的多时相HJ-1A/1B卫星数据,通过分析研究区棉花不同生育期的光谱特征和归一化植被指数（NDVI）时序变化特征,对分类影像进行阈值分割、掩膜处理,最后利用决策树算法提取研究区2012年、2014年棉花种植面积。通过计算混淆矩阵评价分类精度的方法和提取面积精度方法对棉花提取结果进行评价,总体精度达到95.96%,Kappa系数为0.93,以农业局统计数据为参考,2012年、2014年HJ数据提取的棉花种植面积精度分别达到了97.91%、91.27%。因此,在不受云和降水等因素的影响下,基于江汉平原区域关键时相HJ卫星CCD影像数据,可利用该方法进行棉花种植面积监测。     

Agricultural liberalization,cotton markets and buyers’ relations in Zimbabwe, 2001–2008

The paper examines the relations between seed cotton buyers in Zimbabwe's deregulated cotton sector. It draws upon interviews with officials from cotton companies to expose the disagreements and lack of cooperation among them over side marketing of contracted seed cotton and in maintaining common industry standards. In this context, the paper discusses cotton sector reforms spearheaded by some industry stakeholders aimed to address problems in the cotton sector. Despite the companies’ official agreement to the draft reforms of 2004, there were simmering tensions and disputes that strained relations among them. The government's unwillingness to intervene and provide coordination exacerbated problems in the cotton sector. Further, the paper highlights the contradictions in neo‐liberal reforms that seek to promote competitive agricultural markets, and argue against state intervention and strong regulation of markets. It argues that there is a need to reconceptualize the role of the state in some predatory and developing countries that liberalized agricultural markets because of the multiple and uneven effects of the lack of regulation and absence of institutions in the private sector.     

干旱区膜下滴灌棉田表层土壤盐分日内动态特征

利用便携式土壤盐分计测量膜下滴灌棉田不同位置和不同深度的土壤电导率,来研究膜下滴灌条件下表层土壤电导率的日内变化特征.结果显示:干旱区一膜两管膜下滴灌条件下,窄行处土壤电导率值最低,膜间最大,宽行居中,表层土壤电导率值存在显著的日内变化特征,早晚土壤电导率值低,中午电导率值高,上午的上升速率大于下午的下降速率;窄行处相对变化幅度大,膜间绝对变化幅度大,土壤电导率值日内变化幅度随深度呈减小趋势;膜下滴灌情况下,表层土壤电导率值的变化受土壤温度和气温的影响显著,但二者相关性复杂,不同深度、不同时间段的相关性不同,膜间大多呈显著正相关,窄行大多呈非显著正相关,宽行处上午呈非显著正相关,但下午呈显著负相关.     

基于GIS的新疆棉花生产发展时空变异分析

在新疆棉花生产统计数据库建立的基础上 ,利用地理信息系统工具软件ArcView制作新疆历年棉花播种面积、单产和总产分布图 ,并以 1 980、1 985、1 990和 1 995年为例对新疆棉花生产的时间和空间分布进行分析 ,同时还分析了 1 997年棉花播种面积占耕地面积和总作物播种面积的比率分布。进入 90年代后新疆棉花生产发展迅速 ,播种面积、单产和总产都有大幅度增加 ,1 995年总产达到 30× 1 0 5t以上的县有莎车、阿克苏、沙雅、阿瓦提、麦盖提、巴楚 6县 ,主产区主要分布在南疆的库尔勒 -阿克苏 -莎车和北疆的昌吉 -博乐沿线各县 ,1 997年已有 1 4个县棉田面积占耕地面积的比率大于 5 0 %。新疆棉花生产已达到一定的规模 ,宜在稳定中求发展 ,注意防止规划和管理不善可能造成的土地退化 ,以保障农业生产持续发展。