In previous works, we have proposed a Web-based sensor network system or "Field Server" for agricultural use that has a monitoring module with a Web server, a wireless communication module to the Internet, and a camera module for image monitoring. In this paper, we have focused on providing effective, individualized and practical monitoring to provide the information farmers need, and developed an Open Field Server that enables easy and flexible monitoring of various types of agricultural fields and contexts. Then, we deployed the Open Field Server in five different practical agricultural applications: weather monitoring for growth prediction, insect counting for pest damage forecasting, crop growth monitoring with image data, wild animal surveillance, and farm operation recognition. Through these monitoring experiments, we demonstrated the potential and effectiveness of the system in a wide variety of practical agricultural applications while our experience has pointed to areas in which the system could be further refined to achieve advanced monitoring in a wide variety of situations.