Department of Soil Science, Punjab Agricultural University, Ludhiana 141 004, India.
Department of Soil Fertility and Microbiology, Desert Research Center, Cairo 11753, Egypt.
Sensors (Basel). 2020 Feb 19;20(4):1127. doi: 10.3390/s20041127.
To produce enough food, smallholder farmers in developing countries apply fertilizer nitrogen (N) to cereals, sometimes even more than the local recommendations. During the last two decades, hand-held chlorophyll meters and canopy reflectance sensors, which can detect the N needs of the crop based on transmission and reflectance properties of leaves through proximal sensing, have been studied as tools for optimizing crop N status in cereals in developing countries. This review aims to describe the outcome of these studies. Chlorophyll meters are used to manage fertilizer N to maintain a threshold leaf chlorophyll content throughout the cropping season. Despite greater reliability of the sufficiency index approach, the fixed threshold chlorophyll content approach has been investigated more for using chlorophyll meters in rice and wheat. GreenSeeker and Crop Circle crop reflectance sensors take into account both N status and biomass of the crop to estimate additional fertilizer N requirement but only a few studies have been carried out in developing countries to develop N management strategies in rice, wheat and maize. Both chlorophyll meters and canopy reflectance sensors can increase fertilizer N use efficiency by reduction of N rates. Dedicated economic analysis of the proximal sensing strategies for managing fertilizer N in cereals in developing countries is not adequately available.
为了生产足够的食物，发展中国家的小农会在谷物上施加化肥氮（N），有时甚至超过当地的建议用量。在过去的二十年中，手持式叶绿素仪和冠层反射率传感器作为一种通过近感来检测作物氮需求的工具，已经被研究用于优化发展中国家谷物的氮素状况。本综述旨在描述这些研究的结果。叶绿素仪用于管理氮肥，以维持整个作物生长季节的叶片叶绿素含量阈值。尽管充足指数法的可靠性更高，但在水稻和小麦中，固定的叶绿素含量阈值法被更广泛地研究用于使用叶绿素仪。GreenSeeker 和 Crop Circle 作物反射率传感器同时考虑作物的氮素状况和生物量来估算额外的氮肥需求，但在发展中国家开展的关于水稻、小麦和玉米氮肥管理策略的研究很少。叶绿素仪和冠层反射率传感器都可以通过减少氮肥用量来提高氮肥利用率。用于发展中国家谷物氮肥管理的近感策略的专门经济分析尚不完善。
