University of California (UC) researchers are unlocking new management practices which could help cotton growers save water through deficit drip irrigation, plus better manage weather challenges in the fall months.

At the 2014 Beltwide Cotton Conferences in New Orleans, La. in January, UC Cooperative Extension (UCCE) Cotton Specialist Bob Hutmacher discussed ongoing research on deficit irrigation in drip-irrigated cotton to save water with minimum crop yield and quality losses.

UC Cooperative Extension Farm Advisor Steven Wright, Tulare and Kings counties, discussed tweaks in the fall defoliation process which could allow Pima cotton growers to harvest earlier and reduce the threat of damage and harvest delays associated with fall rains and the related fog and dew.

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Last year, California cotton growers produced about 300,000 acres of cotton, mostly in the San Joaquin Valley (SJV). Two-thirds of the crop (200,000 acres) was Pima with the remaining 100,000 acres in Acala.

Hutmacher says a fast-growing trend over the last five years in the SJV is to grow cotton with drip irrigation (surface- or subsurface-placed systems) to improve the water application efficiency and reduce the crop’s water needs.

He says as much as 25 percent of the crop may be irrigated with drip today with the 75-percent balance watered by furrow, border, or level basin irrigation.

At Beltwide, Hutmacher discussed several field trials conducted in Fresno County on drip irrigated cotton and the impact that deficit irrigation can have on cotton yield and quality.

“Drip irrigation in cotton can do a pretty effective job of applying water and during some targeted periods the water can be successfully applied at a deficit level,” Hutmacher said. “Basically the grower irrigates in amounts less than peak plant water use rates.”

The unused water from deficit irrigated cotton can be used for other crops in the grower’s overall water and crop management systems.

The timing of Hutmacher's deficit sdrip irrigation research is perfect, though somewhat coincidental. After several consecutive years of drought, California Governor Jerry Brown in mid-January declared a drought emergency in the Golden State Overall, this will mean less water available for crop production, including annual crops like cotton.

Hutmacher’s research findings are good news for cotton growers using deficit drip irrigation.

“Relatively mild water stress created with a 15-25 percent cutback in irrigation water in the mid-to-late season from peak bloom on had a relatively limited impact on yield (5-10 percent less yield) and no significant impact on fiber length and strength,” Hutmacher said.

He warned though not to cutback water any further. A 40-percent reduction in applied water, for example, could result in more than a 25-percent yield loss.

Deficit drip all in the timing

Deficit drip irrigation should be a targeted approach by stressing the plant only at times when the least damage is done.

“The best times to deficit irrigate are early in the season before match head square and during the boll filling and maturation period in the late summer,” Hutmacher told the crowd.

“Do not greatly reduce water applications from mid square development through peak bloom; typically from mid-June into mid-July. If you do, this increases the chances of water stress-related fruit (yield) losses.”

This water management technique can save 3-4 inches of water or more in most years; water now available for other crops or to spread across more production acres.

“The fiber length, strength, and micronaire numbers still look good with this level of deficit irrigation and should not be affected to the point of a discounted price level,” Hutmacher said.

Hutmacher’s trials included nine varieties of Pima and Acala cottons. Deficit irrigation had about the same relative impact across all tested varieties, although there were varietal differences in attained yields. Field studies will continue this year.

When deficit drip irrigating cotton, Hutmacher said the effective soil volume that root systems explore for water and nutrients can be greatly reduced. It is important that growers supply nutrients to the plant through drip fertigation to maximize the delivery to the root zone. Dry nutrient applications with drip are less effective.

Overall, as California growers brace for more water cutbacks, Hutmacher says, “Cotton will still have a place in California agriculture as it uses less water than corn and alfalfa, and not much more water than a high yielding wheat field.

Deficit irrigation is one method to help growers manage the water shortage and still produce a high quality cotton crop.

Earlier Pima defolation and harvest

Switching gears to Pima cotton defoliation in California, UCCE Farm Advisor Steven Wright discussed the always tricky process of Pima defoliation and harvest in the late-season cotton before traditional fall rains arrive. If harvested too early, Pima yield and fiber quality can be reduced. The same can be true if the crop is harvested late.

“As we move into late October and November, there is a greater risk of rainfall which can trigger fog and dew,” Wright said. “These conditions can delay the start time for harvest until late in the morning, or even mid-day.”

Pima is a popular crop with growers due to the price premium paid for the extra-long-staple cotton and fiber quality.

Wright’s research has focused on whether Pima harvest aid product applications can be started earlier to escape possible exposure to late-season rain and other poor weather conditions without much negative impact on yield and fiber quality loss.

The short answer is yes.

The traditional time to begin harvest aid applications in Pima cotton in California is when cotton reaches 3-4 nodes above cracked boll (NACB).

In the UCCE Pima defoliation research conducted at the West Side Research Center in Fresno County from 2009-2013, various cotton varieties were defoliated at 4-5 NACB and 6-7 NACB with multiple applications of defoliation products, including different rates of Ginstar, Ethephon, and other products.

The field trial results suggest that Pima cotton can be defoliated 7-14 days earlier than the original 3-4 NACB timing with minimal impacts on yield and fiber quality.

Wright offered these tips for Pima growers interested in the earlier defoliation and harvest of a vigorous Pima crop.

  • Consider your own experience on how many days of harvest is needed from the harvest of the first field to the last field.
  • Keep an eye on the 1-14 day weather forecast.
  • Determine the last harvest date deemed an acceptable risk. Count back about 21 days from the desired harvest dates. Start with the defoliation program on those dates regardless of the plant’s maturity stage (NACB) of the plant.
  • Consider this approach in some fields but not all fields. Growers can start some harvest operations at an earlier date when weather conditions are more favorable.

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