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Higher water use efficiency needed for profitable cotton production

Laser leveling, shortened irrigation runs, furrow bullets and a host of other technologies have combined to make California row crop growers the most efficient furrow irrigators in the world.

However, irrigation efficiency in the 70 percent range is no longer good enough as California agricultural water supplies dwindle and water quality deteriorates.

University of California Extension cotton specialist Bob Hutmacher and UC Cooperative Extension farm advisors Dan Munk (Fresno County) and Blake Sanden (Kern County) say all cotton growers will need to raise irrigation efficiencies to even higher levels to keep cotton profitable.

It is all about producing the most cotton for the least amount of water. This could mean reducing acreage to maximize available water supplies. It could mean not taking a crop full season to reduce water use and cost. It is already meaning reduced pre-irrigation and looking more closely at deficit irrigation without reducing yields. The later may not be that bad, according to Hutmacher who has shown that a little stress may not only save water, but it can increase yields.

Where three to four acre feet of water were the norm for producing a cotton crop in years past, as little as 24 inches of applied water is producing a normal crop today.

Not everyone can grow cotton on so little water, Hutmacher, Munk and Sanden told growers and consultants at the recent annual winter cotton grower meting held in conjunction with the California Cotton Growers Association annual meeting in Visalia.

However, most could get close with new irrigation systems, particularly drip irrigation.

Row crop drip system installations have picked up dramatically in the past five years on the West Side of the San Joaquin Valley, mostly targeting higher value crops like tomatoes, lettuce, garlic and onions. However, cotton has benefited from the efficiencies and low water use of drip primarily because ground is rotated to cotton from high value crops. Lately growers have been installing low water use drip for cotton because systems have become cheaper.

Hand move sprinklers have also been used more recently in pre-irrigation and early season irrigation to save water. Now mechanical irrigation, center pivots and lateral moves, are being installed in the valley.

Munk said 20 160-acre center pivots have been installed in Western Fresno County within the past six months.

A few lateral and center pivot mechanical irrigation systems have been installed over the years in California. However, they have not caught on like they have in other parts of the country for a variety of reasons.

Munk said today's mechanical systems are more reliable with lower maintenance and are more adaptable to intensive Western irrigation. Drop nozzles and socks and irrigation furrow dikes also are making the systems more suitable for Western irrigated agriculture. They are also more attractive to growers because they can be used to apply herbicides, fertilizer and can be modified for variable rate irrigations based on soil types across a field. The cost and availability of labor to irrigate crops is another reason growers are installing mechanical systems.

In an Australian test of a lateral move versus furrow irrigation, Munk said there was a 37 percent water savings with the lateral and a 10 percent yield increase for a 70 percent increase in water use efficiency.

In a trial in Kern County, Sanden compared furrow, hand-move, solid set sprinklers, drip and sprinkler irrigation for germination followed by drip irrigation during the season. Non-furrow irrigation systems cost more per acre, almost double in some cases. However, irrigation efficiency increased from 70 percent for furrow to up to 90 percent for drip.

It would take up to a half bale more per acre to justify the costs of the pressurized lower water application systems, but Sanden said moving from lower efficiency to more expensive higher water use efficiency systems will pay off.

Using $30 per acre water, Sanden said cotton revenue from subsurface drip with a production cost of $750 per acre still netted from $210 per acre to almost $1,200 per acre over three crop years.

Hutmacher says too much water early actually can set back cotton yields. Slight water stress early could result in a beneficial, smaller plant that would be more amenable to late season water stress due to water shortages or higher water costs.

Hutmacher said stressing cotton 1.5 to 2 bars in leaf water potential with delayed irrigation has helped manage cotton without a major impact on yields.

“We are talking about stressing to 16 to 18 bars,” he explained. Taking it to the 22 bar level is too draconian and could hurt yields.

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