Scheduling (or timing) of irrigation is vital to getting the most out of an irrigation system investment. Monitoring soil moisture is the usual way to schedule irrigation, and there are several methods: gypsum blocks, tensiometers, push-in capacitance meters and neutron probes.

There also are several checkbook-type programs to help farmers keep track of moisture accumulation and consumption. "The Scheduler" from the Natural Resources Conservation Service (NRCS) is one such program.

University of Missouri researchers have come up with a simple, but workable, device to alert a farmer when his crops need a drink. The gadget can be built from off-the-shelf parts for about $100.

The nerve center of the irrigation flagger is a tensiometer buried in the field. When soil moisture drops to a preset level, the tensiometer closes contact points, sending an electrical signal to the flagging device. The flagger itself consists of two flashlight batteries, a low-voltage electric motor, a garden-gate type latch, and a red flag on one end of a counterweighted rod.

When the tensiometer sends a dry-soil signal, the motor trips the latch, which releases the flag. The flag is raised by the counterweight on the opposite end of the rod, and stands well above the surrounding crop. It can be easily seen from a road or alley alongside the field.

Without leaving his pickup, a farmer can tell if it's time to crank up the irrigation rig.