Cheap communication with 433MHz radio modules

Check out this video and plan a project based on environmental sampling following by transmission of data to distant Arduino logger. Can you do two way, half duplex communication that's time stamped too.

Soil temperature

We need an intelligent ball we can bury in the ground. It monitors soil temperature over several weeks.
When we dig it up we can read off the time-stamped temperatures and graph them, An advanced model would send a radio signal above the ground for a receiver to capture. It could even be two way so that we could wake up the buried module to give us a burst of data.
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Unlike this sensor, we need to take our power supply underground.

Make and calibrate your own salinity meter.

Check out this site  and make your own calibrated salinity meter. Use for soil samples and for river water.

Measure temperature of Kaikorai Stream over time.

Make up a waterproof river temperature probe that will log water temperatures along with times tamping them.

One configuration would be :
Arduino in secure box
Temperature sensor eg the TMP36 that comes in our kit.
Real time clock (several options including this cheap one)
Somewhere to stire data. Maybe SD card; maybe using the Arduino's spare flash memory.

Experimenting with LoRa

Set up two LoRa stations and communicate simple messages.