Wireless sensor networks (WSNs) find wide applications in environmental monitoring. MAC protocolsplay a vital role in controlling the energy consumption in a WSN. It tells the network when and how to access the medium. Time Division Multiple Accesses (TDMAs) are well suited for these real time applications. Because it prevents radio interference, and reduces energy consumptions. In this paper a TDMA based MAC protocol was used to collect environmental data such as soil moisture and temperature of an irrigation system. The base station was collecting the data in a particular area using the sensor nodes. All nodes in the network were homogenous and energy constrained. TDMA scheduler assigned the time slots for each node and those sensor nodes turn ON/OFF their radio according to the schedule to save energy. If the collected data was less than the threshold value, the base station would inform the controller by setting the corresponding bit to perform a motor control action. In this paper two methods based on TDMA scheduling were used. The first one was a direct communication method, in which each node transmitted the data directly to the sink. The second method used data fusion (aggregation) method in which nodes were grouped into clusters to save energy. The simulation results showed that the aggregation method was providing a 10% increase in the residual energy and 13% increase in the throughput.