  We present the design and implementation of a shortest path tree based,
energy efficient data collection wireless sensor network to sense various
parameters in an agricultural farm using in-house developed low cost sensors.
Nodes follow a synchronized, periodic sleep-wake up schedule to maximize the
lifetime of the network. The implemented network consists of 24 sensor nodes in
a 3 acre maize farm and its performance is captured by 7 snooper nodes for
different data collection intervals: 10 minutes, 1 hour and 3 hours. The almost
static nature of wireless links in the farm motivated us to use the same tree
for a long data collection period(3 days). The imbalance in energy consumption
across nodes is observed to be very small and the network architecture uses
easy-to-implement protocols to perform different network activities including
handling of node failures. We present the results and analysis of extensive
tests conducted on our implementation, which provide significant insights.
