She Bao, Huang Jing-feng, Guo Rui-fang, Wang Hong-bin, Wang Jing
Institute of Agricultural Remote Sensing and Information Technology Application, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China; Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China; Feidong Agricultural Technology Extension Center, Hefei 231600, China.
J Zhejiang Univ Sci B. 2015 Feb;16(2):131-44. doi: 10.1631/jzus.B1400150.
The winter oilseed rape (Brassica napus L.) accounts for about 90% of the total acreage of oilseed rape in China. However, it suffers the risk of freeze injury during the winter. In this study, we used Chinese HJ-1A/1B CCD sensors, which have a revisit frequency of 2 d as well as 30 m spatial resolution, to monitor the freeze injury of oilseed rape. Mahalanobis distance-derived growing regions in a normal year were taken as the benchmark, and a mask method was applied to obtain the growing regions in the 2010-2011 growing season. The normalized difference vegetation index (NDVI) was chosen as the indicator of the degree of damage. The amount of crop damage was determined from the difference in the NDVI before and after the freeze. There was spatial variability in the amount of crop damage, so we examined three factors that may affect the degree of freeze injury: terrain, soil moisture, and crop growth before the freeze. The results showed that all these factors were significantly correlated with freeze injury degree (P<0.01, two-tailed). The damage was generally more serious in low-lying and drought-prone areas; in addition, oilseed rape planted on south- and west-oriented facing slopes and those with luxuriant growth status tended to be more susceptible to freeze injury. Furthermore, land surface temperature (LST) of the coldest day, soil moisture, pre-freeze growth and altitude were in descending order of importance in determining the degree of damage. The findings proposed in this paper would be helpful in understanding the occurrence and severity distribution of oilseed rape freeze injury under certain natural or vegetation conditions, and thus help in mitigation of this kind of meteorological disaster in southern China.
冬油菜（Brassica napus L.）占中国油菜种植总面积的90%左右。然而，它在冬季面临冻害风险。在本研究中，我们使用中国的HJ - 1A/1B电荷耦合器件（CCD）传感器，其重访频率为2天，空间分辨率为30米，来监测油菜的冻害情况。以正常年份基于马氏距离得出的生长区域为基准，采用掩膜法获取2010 - 2011生长季的生长区域。选择归一化植被指数（NDVI）作为损害程度的指标。作物损害量由冻害前后NDVI的差值确定。作物损害量存在空间变异性，因此我们研究了可能影响冻害程度的三个因素：地形、土壤湿度和冻害前的作物生长情况。结果表明，所有这些因素均与冻害程度显著相关（P < 0.01，双侧）。损害通常在低洼和易旱地区更严重；此外，种植在南向和西向坡面且生长繁茂的油菜往往更容易遭受冻害。此外，最冷日的地表温度（LST）、土壤湿度、冻害前的生长情况和海拔高度在决定损害程度方面的重要性依次递减。本文提出的研究结果将有助于了解在特定自然或植被条件下油菜冻害的发生及严重程度分布情况，从而有助于减轻中国南方此类气象灾害。
