Irrigation Cutoff  Dates for Sugarbeets in the Tulelake Region

In the Tulelake region near the Oregon border, sugarbeets are grown on organic soils reclaimed from shallow lakes.  Groundwater is present continuously throughout the season at approximately 4 feet in depth in most fields.  Typically, April and May planted beets are irrigated until mid-September and harvested in October.  However, environmental restrictions may reduce farm water supplies in the future.  To determine if sugarbeets could be grown with less irrigation water, five irrigation cut-off treatments were applied in 1995 and 1996  to replicated, large plots at approximately two week intervals starting in mid-July.  Results from these trials suggest that farmers can save 6 to 8 inches of irrigation water by cutting off irrigation to sugarbeet crops 7 to 8 weeks before harvest under these soil and climate conditions.

Sugarbeets have been grown only for a few years in the Upper Klamath Basin of California and Oregon.  Despite a short growing season of 150 to 160 days, yields of 25 to 30 tons of roots and 9,000 to 11,000 pounds of sugar per acre are achieved.  This makes the basin one of the most productive short season locations for sugarbeet in the world.  The beets produced are stored in large piles for up to three months starting in fall, and shipped as needed to Woodland for processing.  Because of freezing temperatures in the fall, the Upper Basin is the only location producing beets for California factories where beets can be stored for an extended period .  These roots fill an important niche in factory operations.  By doing so they help maintain the beet crop as a rotation option for farmers in other locations in the state as well.

Growers in the Tulelake and Klamath Irrigation Districts may  be faced with reductions in water supplies for irrigation in the near future.  Mandated minimum flow rates in the Klamath River could reduce water supplies available for crop production, especially in dry years, or in late summer and fall in many normal ones.  If irrigation of sugarbeet during late summer can be reduced or curtailed without loss of economic yield, less water may need to be diverted for irrigation but farm incomes will be protected, meeting both environmental and economic objectives.

All crops need adequate amounts of water for economic yields.  There is a linear relationship between dry matter yield and crop evapotranspiration (ETc).  This relationship for sugarbeet is illustrated using an irrigation study carried out on the Davis campus (fig. 1).  In that experiment, irrigation was withheld for increasingly longer periods.  Compared to adequately irrigated treatments, moisture stress imposed early in summer reduced the yield of fall harvested beets significantly.

Despite the adverse effects of prolonged moisture stress, irrigation commonly is withheld from beet crops towards the end of the crop production period.  Because sugarbeets are among the deepest rooted of the annual crops, they are able to recover water at depth in the soil profile.  Also, modest losses in root yield following irrigation cutoff  typically are compensated by small increases in sucrose percentage, resulting in similar gross sugar yields.  To improve this practice, irrigation cutoff experiments have been performed in Imperial, Kern, Fresno, Yolo, and Glenn counties.  In the hot interior valley regions of California, irrigation may be stopped without economic loss from three to four weeks prior to harvest, depending on location, season, and the soil’s available water content.  Similar results also have been reported from the Pacific northwest and plains states where irrigation is used.  In one experiment in the Delta region of California on organic soils, sugarbeets, once established, were able to grow throughout the summer period without irrigation, recovering water from a shallow subsurface water table at a depth of  3 to 4 feet.  Root and sugar yields were lower, however, from unirrigated treatments than for treatments supplied with supplemental irrigation (Henderson et al., 1968).  In a second experiment carried out above a shallow water table in the Delta, sugar yields were unaffected or tended to be marginally greater when irrigation was cut off in mid-August, compared to mid-September for an October-harvested crop (Hills et al., 1981).

Current practice in the Tulelake region is to cease irrigating about four weeks prior to harvest, but there is no experimental basis for this practice.  Because a shallow water table is present on most locations in the region, sugarbeets should be able to recover soil moisture from deeper in the profile, and compensate for a modest loss of root yield through an increase in sucrose percent.  It may be possible to cut off  irrigation of sugarbeet for longer than four weeks prior to harvest, saving one or more irrigations.

The objectives of this research were: 1.  To evaluate the effects of different irrigation cut off periods on root and sugar yield, 2.  To monitor changes in root yield and sucrose accumulation, and 3.  To evaluate changes in gravimetric soil moisture and other soil properties possibly influencing water quality in the region as a function of sample date and depth in the soil profile.

Five irrigation cut off treatments

Plots were established at the lease lands site of the Intermountain Research and Extension Center (IREC) in Tulelake. The IREC site is located on soils with physical and hydrologic characteristics common to most of the farms in the Tulelake Irrigation District (Tulebasin series: mixed, mesic Andequeptic Haploquolls).  These soils are lucustrine sediments derived from volcanic ash and diatomite.  They are high in organic matter (from 10 to 15 %).    Plots were 26 by 90 feet, were separated from each other by 26 foot wide buffer plots, and reasonably simulated farm conditions.  Five irrigation cutoff treatments were replicated three times using a randomized complete block design.  The cutoff dates and the amount of water applied as irrigation or occurring as rainfall during the growing season in both years are reported in Table 1. All plots were irrigated uniformly until the first irrigation cut off treatment was initiated.   Best irrigation practices are not adequately defined for sugarbeets in the Tulelake region because the crop was recently introduced.  Cutoff treatments were chosen to provide a wide range of comparisons.

Root and soil samples

Roots were sampled from each treatment when cutoffs were imposed and subsequently at each successive cutoff date and again at final harvest.  Roots were weighed and analyzed  for sucrose and impurities such as Na, K and amino-N compounds.   Soil samples were collected from the surface to four feet deep in one foot intervals, weighed and oven dried.  Gravimetric moisture content, salinity as electrical conductivity of a saturated paste extract (ECe), N, and P content were analyzed from samples collected at one foot increments to 4 foot in depth at each cut off date.  Final harvests and soil samples were collected in mid-October.

Root and sugar yields

Root and sugar yields were not significantly different between years (Table 2), allowing for combined analysis of both years’ data.  In both years, root yields increased from 23 to 28 t ac-1 as the cutoff period decreased, but sucrose percent declined from greater than 19 % to 18.5 % with late-season irrigation (4 weeks before harvest), resulting in near equivalent gross sugar yields over the last three cutoff dates (fig. 2).  There was a non-significant tendency for sugar production to decline with September irrigation.

Soil moisture and nutrient contents

In both years, beets in cut-off treatments reduced the soil water content in the surface two feet compared to fully irrigated treatments, but there were no significant differences in soil moisture content deeper in the horizon (fig. 3).  Soil nutrient contents were not affected by cut-off treatments but changed through the season (Table 3).  Data for soil NO3-N indicate a significant decline throughout the profile as the season progressed, while there were no obvious trends for soil NH4 and P (fig. 4).  Salinity (ECe) increased with increasing depth in the profile, and was significantly lower in the fully irrigated treatment (fig. 5).

Can Irrigation be cut off earlier in Tulelake?

The Tulelake region is unusual in many ways.  Much of the land is reclaimed from shallow lakes which left soils high in organic matter (approximately 6% total C in the surface foot) with excellent tilth.  These organic soils are underlain with saturated, impervious clays which restrict subsurface drainage.  To remove excess soil moisture, drainage ditches surround most fields and the water table is maintained at approximately 4 feet throughout the growing season by pumps which remove water from the drains.  Crops capable of rooting to the depth of four feet can use some of the water present in the soil profile throughout the growing season.

In these trials, sugarbeets recovered some of their seasonal water requirement from the perched water present in the soil profile.  Despite the presence of water throughout the growing season at three to four feet in depth, moisture stress in the upper part of the profile, where the majority of roots occur, reduced root and sugar yields in the most severe cut off treatments.   At 7 to 8 weeks before harvest, however, (late August) adverse effects from irrigation cutoff on gross and recoverable sugar yields were not observed.  Near equivalent amounts of sugar were produced with less irrigation, increasing the efficiency of sugarbeet irrigation.  Carefully managed deficit irrigation seems in this way to be a beneficial practice in the production of sugarbeets in this region.  These results agree well with earlier work on sugarbeets carried out in the Delta region on organic soils with shallow water tables (Henderson et al., 1968; Hills et al., 1990).

If irrigation water deliveries are reduced in the near future in the Upper Klamath Basin because of regulatory limitations, especially late in the growing season, farmers growing sugarbeets should be able to produce economic crops, provided that subsurface soil moisture is present.  Late season irrigation requirements for potato and onion crops result in water being present in the region’s delivery canals and drains, possibly contributing to the maintenance of shallow water tables throughout the district.  If irrigation deliveries were curtailed for these crops as well, shallow water tables may fall, and beet crops might suffer more severe yield loss as well.

No trials were conducted on the region’s mineral soils, which have deeper unsaturated zones  and hold less available water than the organic soils in the region.  The results reported here are not applicable to those soil conditions.  It is more likely that the experience of farmers elsewhere in California will pertain to these soils, suggesting not more than a three to five week cutoff period.

Conclusions:

1.  Root yields were reduced by increasing the length of the cutoff period from 4 to 5 weeks to 12 weeks.
2.  Sucrose concentration was variable but tended to be higher in beets grown with longer cutoff duration.
3.  Gross sugar yields were equivalent when irrigation was cutoff at any time over the last 4 to 8 or 9 weeks of the growing season in both years.
4.  Farmers can save 6 to 8 inches of irrigation water by cutting off irrigation to sugarbeet crops 7 to 8 weeks before harvest under these soil and climate conditions.  This may allow them to produce an economic beet crop even if irrigation supplies are curtailed late in the season, provided subsurface moisture is available.

References:

Ghariani, S. A. (1981).  Impact of Variable Water Supply on Yield-determining Parameters and Seasonal Water Use Efficiency of Sugar Beets.  PhD thesis.  University of California, Davis. 153 p.

Henderson, D.W.F., F.J. Hills, R.S. Loomis, and E.F. Nourse.  1968.  Soil moisture conditions, nutrient uptake and growth of sugarbeets as related to method of irrigation on an organic soil.  J. Am. Soc. Sugar Beet Tech..  15:35-48.

Hills, F.J., S.R. Winter, and D.W. Henderson (1990).  Sugarbeet. p795-810.  In: Stewart, B.A. and D.R. Nielson (eds.).  Irrigation of Agricultural Crops.  Amer Soc. Agron., Madison, WI. 1218p.

List of figures:

Figure 1.  Relative yield vs ETc (inches) for spring planted-fall harvested beets grown on a Yolo loam soil in Davis.  Symbols represent different irrigation cutoff dates.  Data from Ghariani (1981).

Figure 2.  Root yields (fresh weight), percent sucrose, and gross sucrose yields for 1995 and 1996 growing seasons combined.  Error bars are LSD(0.05) (SAS Institute, Cary, North Carolina).

Figure 3.  Soil moisture by depth in the profile at the final harvest (mid-October) in 1995 and 1996.  There were significant differences at the 0 to 1 and 1 to 2 foot depths, but not deeper in the profile.  Error bars are the standard deviations of the means.  Soils in the Tulebasin series hold 0.3 to 0.5 inches of available water per inch (4 to 6 inches per foot) depending on depth in the profile and organic matter content.

Figure 4.  Average nutrient contents in the 0 to 4 foot profile at harvest in 1995.  NO3-N declined from greater than 20 mg kg-1 to less than 10  mg kg-1 during the July to October period.

Figure 5.  Electrical conductivity (ECe) of soil samples at the final harvest (mid-October) from the 12 week, 8 to 9 week, and 4 week cut off treatments.  Error bars are for LSD(0.05).

Acknowledgments:

Partial funding for this work was provided by the California Sugar Beet Industry Research Committee.  Spreckels Sugar company analyzed the root samples.
 
 

Submitted by :

Stephen R. Kaffka
Extension agronomist
Department of Agronomy and Range Science
University of California, Davis.
916-752-8108
srkaffka@ucdavis.edu

and

Gary R. Peterson, (Staff Research Associate, Agronomy and Range Science, UC Davis)
Don Kirby, (Acting Superintendent-Intermountain Research and Extension Center)