Satellites help monitor and manage natural disasters such as earthquakes, floods, forest fires, or volcanic eruptions, especially where there may not be enough time to assess damage through conventional ground or aerial surveys. A 02:21 mins video titled Disaster Risk Management and Space Technology, available at https://vimeo.com/92118750, provides details. There is also Asia-Pacific Disasters: The Philippines and Thailand, available at https://vimeo.com/92214515, which spans 06:12 mins, and Space Technology and Sustainable Development, available at https://vimeo.com/92118745, which lasts 02:17 mins.
High resolution (spatial, spectral and temporal ) satellites can be used to remotely monitor plant vigor, water stress and spread of a disease of an area. Plants affected by a certain disease reflect in a different way from healthy ones, hence this can be used as a proxy for assessing the severity of the disease in terms of its stage and spatial coverage
Determination of crop biophysical and biochemical parameters including Leaf Area Index, Chlorophyll contents, nitrogen contents, xanthophyll contents etc. is possible through remote sensing and GIS.
As you konw, the earth is very complex and changable. To be short, remote sensing would give you a view of agriculture at a large scale and many research would be performed in remote sensing with its long-term and large-area monitoring