Hi Tom,

Depending on what you class as expensive you might have a few options..is there any spare budget for your project at all? What temperature ranges are you thinking?

If you don't have any budget and there is no other equipment available then the simplest but perhaps too labor intensive method would be to have the soil samples on a series of trays and move them from the lab (or one high temp constant temp room) to a low temp constant temp room and back again in the morning. Obviously you would need weekend access and yourself or a friend/lab technician to be able to move them twice each day. If its one tray or they are on a trolley its only a 5 minute job but the kicker is weekends if you don't have access.

If that commitment is not an option maybe speak to the lab technicians and see what equipment is laying around..there is often a stock of weird and wonderful items no one really knows are there. If you could scrounge up a timer plug or two and some low cost electric heating you might have some other options.

If you do have some budget you could leave a constant set up in one of the cooler constant temp rooms, with your samples on a heating mat (electric blanket or seed starting mat) with some insulation between them so they don't get too hot if needed. Cover the whole lot with tubs to keep the heat in and use the timers to turn them on for your 'daytime'. When they go off at night they should quickly cool down.

Hi Tom,

If the guys in you constant temperature room allow you to operate a heating lamp there, you may use a heating lamp and a time switch (altogether a bill of 40 Euro or even less) - this would lead to a temperature rise upon switching the heating lamp on in the morning and a drop again in the evening. You would have to measure one cycle to see what temperature cycle you're exactly getting from this and the constant temperature room's heating/cooling system must be fast and strong enough to deal with the energy intake into the rest of the room (maybe validate it by a temperature log over one cycle in another place in the room). As it would be a single-sided heating it might come quite close to an actually diurnal rythm in the field.

Good success!

Niko