July 10, 2009

Irrigated crops grown in no-till may require three to five inches less water from rain or irrigation than those grown under conventional tillage, said UNL Extension Educator Steve Melvin.

Residue in no-till systems increases infiltration of both precipitation and irrigation water, Melvin said.  Because of the increased infiltration, producers can lower the pressure and/or narrow the pattern in the sprinkler system, saving both energy and water.

To take advantage of the increased infiltration and reduced evaporation that comes with no-till, producers should make sure soil is dry enough to store some rain in addition to the irrigation water before each application. They should use up to 60% of the plant-available soil water late in the irrigation season to make room for off-season moisture. If fields have a full profile after harvest, there’s no storage capacity for off-season moisture, Melvin said.

“If you leave the field fairly wet in the fall and if you start your first irrigation too soon, you deep-percolate the saved water,” Melvin said.

“It would be in the aquifer for use in future years, but it takes some nitrates and other things with it that we don’t like very well.” 

Record Stored Water Level

In no-till, as well as in conventional tillage, producers can make real savings by measuring stored soil water and irrigating accordingly.

Melvin suggests that producers get soil water monitoring equipment, which easily measures soil water to a four-foot depth.  With good information about available water, producers can use some of the water that’s stored in the second and third foot before their first irrigation. And by monitoring soil water throughout the season and comparing available soil water with charts showing the amount of water needed to mature the crop, producers can safely draw down soil water levels. Starting about August 10, they can calculate what’s left in the soil and use the plant-available water down to about four feet by the “black layer” stage of the crop.

Melvin said he hears producers argue that this method is “just mining the soil water.” 

That’s absolutely true, he says.  To achieve top yields and store off-season precipitation, Melvin recommends leaving only about 40 percent of the available soil water.  

“As far west as Imperial or Ogallala we still get enough off-season precipitation on average to refill a silt loam profile following a fully-watered crop,” he said.

With gravity systems, producers have to clean the furrows out to allow water to run through the field.  However, they can plant into the residues on top of the ridges and wait as long as possible to clean out the furrows. These methods allow gravity systems to take advantage of some no-till benefits.

“Of course, we need to measure soil moisture and take good account of it in furrow irrigation, too,” Melvin said.

Drip irrigation also allows for reduced tillage, Melvin said.  As with other systems, producers need to measure soil moisture and make best use of it.

No-till requires a little extra management and maybe a few equipment changes, Melvin said, but at the price of energy today and the limited water supply we face, it’s a good approach to take.

Faith Colburn
Communications Specialist, West Central REC, North Platte