MITCHELL BAALMAN’S well is drying up. This is bad news for a farmer of thirsty crops in parched north-western Kansas. Four years ago Mr Baalman and other local farmers realised that unless they started saving water there might not be enough left for their children and grandchildren to irrigate the soil. So they are trying something new: voluntarily cutting back on the amount they use, even though they will grow less.

The Ogallala Aquifer runs from South Dakota to Texas. In many places water is pumped far faster than the aquifer can recharge naturally from rivers and rainfall. The consequences of overuse are not always clear. But Kansas now has an unusually detailed portrait of groundwater use and its implications for future farm production, thanks to research by academics at Kansas State University (KSU).

The researchers say that by 1960 only 3% of the aquifer had been used but by 2010 30% had gone. Consumption will peak in 2025, but because of gradual improvements in the efficiency of water use farm productivity will go on rising until 2040. In the west-central district, which has always had less water, wells are being abandoned and some areas are being converted to dryland farming.

The problem is that irrigation, which is necessary in drier parts of the state, is far more productive. David Steward, the study’s lead author, says that over the past 30 years the productivity of maize (corn) farming in irrigated Kansas peaked at 12 tonnes per hectare, against four tonnes on drylands. (These figures may underestimate the impact of irrigation, because some places are too dry to grow maize at all.) The market value of the agricultural output of the state’s western congressional district is the highest in the country.

The study suggests that in many areas it may well be worth cutting back on extraction, just as Mr Baalman has done, because of improving efficiency. A gallon used tomorrow will be more productive than one used today. This will also push back the date of peak production and slow the eventual rate of decline. For example, reducing pumping by 20% would slash production to the levels of 15 or 20 years ago, but delay the peak until 2070.

Water has seeped into the state’s politics, too. In recent years Sam Brownback, Kansas’s governor, has approved a series of laws intended to help farmers preserve water. One eliminated a requirement that they pump a minimum amount each year to retain their extraction rights. Another created multi-year water accounts, to encourage conservation in wet years so there is more in dry ones. A third allowed local groups to organise cuts in consumption. Mr Baalman’s group was the first, another will start after the harvest, and a third is in development. Tracy Streeter, director of the Kansas Water Office, says the dry spell (some areas are in their third year of drought) and the study by KSU has accelerated local discussion over water.

The KSU paper also spells out a bleaker point: that unthinkable cuts of about 80% are needed to make groundwater use in Kansas truly sustainable. The best that farmers in the state’s irrigated areas can hope for is to delay the eventual decline of the productivity of their land. That is worth aiming for, but as the water runs out, decline will eventually come.