Sugarbeet seeds emerged well under moderately saline conditions

 Stephen Kaffka, Kurt Hembree, Gary Peterson, and Dong Daxue

Successful stand establishment is one of the most difficult challenges for sugarbeet growers.  Saline soil conditions increase the difficulty further.   Sugarbeet is among the most salt tolerant crops, but is reported to be less tolerant at germination and emergence.  In trials in the Imperial Valley and western Fresno County, sugarbeet seeds emerged well under moderately saline conditions.  At ECe levels greater than 6 dS m-1, rates of emergence and seedling dry weight were reduced, but not final stand counts.  Priming seed before sowing moderated the effects of salinity on emergence rates and seedling growth.
 

Salt tolerant crops may be more sensitive at emergence

Sugarbeet is one of the most salt tolerant crops.   But it is reported to be less tolerant of salinity during germination, emergence, and in the seedling stage (Maas, 1986).  Growers may have difficulty establishing adequate numbers of plants under saline conditions.  Thirty to forty thousand plants are needed at harvest for good economic yields.  To counteract this problem, growers may use use more expensive sprinkler irrigation methods to reduce salt accumulation in the seed zone, or rely on soil amendments like gypsum if soils are sodic and have crusting problems.  A large portion of the western San Joaquin Valley and parts of the Imperial Valley have some salinity limitations for crop production.  Tolerant crops like sugarbeet can be produced successfully on moderately saline soils, or with saline irrigation water, but problems with successful stand establishment may otherwise limit the use of these soil and water resources.   It would be useful to have a better understanding of the emergence of sugarbeet seed under field conditions when salinity is a factor.
 

Methods

As part of a larger sugarbeet stand establishment effort, two trials were conducted in which salinity was a factor.  One took place in the Imperial Valley in September and October, 1997 at the UC Desert Research and Extension Center (DREC), and one in western Fresno County at the UC Westside Research and Extension Center (WSREC) in October and November, 1997.  In Imperial Valley, plots were either furrow or sprinkler irrigated using water supplied by the Imperial Irrigation District (Table 1).  Soil moisture during the emergence period was monitored using a time domain refractometer device (Theta meter HH1, manufactured by Delta T, Inc., Cambridge, England) and irrigation was applied as needed to maintain adequate levels of available water in the top three inches (7.5 cm) of the profile.  Three furrow irrigations and five sprinkler irrigations were used over the thirty day period of emergence to maintain adequate soil moisture in the seed zone in the Imperial Valley, while two furrow irrigations were applied in the San Joaquin Valley.  Seeds were planted at approximately 0.75 inches (2.1 cm) in depth.  Soils were sampled by collecting soil at a 0 to 2 inch (5 cm) depth.  Different irrigation treatments resulted in different salinity levels in the soil surface during emergence.  In Fresno County, seeds were planted in plots with differing initial ECe (Table 2).  To further increase differences among the plots, some were irrigated with non-saline water from the Central Valley Project canal and others with moderately saline water from a nearby shallow well (Table 1).  The plots were part of a larger group used for the study of crop response to soil and water salinity (Kaffka et al., in press).  Plots were selected from this larger group based on soil analyses from samples collected from the surface 12 inches (30.5 cm) of the plots (Table 2)
At both locations, six different seed treatments also were evaluated (Table 3).  The same seed lot of SS-781R sugarbeet seeds was used at both locations and for all seed treatments.  Film coated treatments were applied by Holly Hybrid Seeds (Sheridan, Wyoming).  Pelleted and PAT treatments were applied by Seed Systems, Inc, (Gilroy, California).  Seeds were planted in rows with 100 seeds per row using a cone planter.  Row length was 30 feet (9.15 m), and rows were 30 inches (0.76 m) apart.  Two adjacent rows were planted with each seed treatment.  The assumption was made that factors influencing emergence and establishment in adjacent rows in the same plots were similar.  In the first row, daily counts of the number of emerged seedlings were made.  In the second row, more intensive monitoring was carried out.  Half the row length was measured, and all seeds emerging in the measured area were counted and labeled daily for the first seven days after emergence began, and every other day afterwards.  Only newly emerged seedlings were counted each day.  Any seedling dying after emergence was recorded, and the cause of mortality noted if possible.   This method allows for an exact determination of the number of seedlings emerging, without underestimation due to post emergence losses.
Soils were sampled before and after the initial irrigation at WSREC and analyzed for electrical conductivity of saturation paste extracts (ECe) (Table 2).  Post irrigation samples were collected from the surface 0 to 2 inches (5 cm) of the bed surface.  Values were determined on mixed, ground samples which integrate the salinity conditions of the entire seed zone.  At the WSREC site, 20 seedlings from each plot were collected at the end of the trial by cutting them off at the soil level followed by drying.  Dry weights were compared.  Rates of emergence were estimated from plots in which daily emergence was recorded.  The number of days to reach 50 % emergence was determined using linear interpolation.
 

Plots varied in salinity

Furrow irrigation concentrates salts in the seed bed (Hanson, 1993).  ECe near the surface of flattened beds can increase up to seven times if water is applied in every furrow (Bernstein and Fireman, 1957) but changes with time and soil moisture content.  In furrow irrigated plots in the Imperial Valley,  ECe averaged 10.1 dS -1, while in sprinkler-irrigated plots, values were five times lower (2.0 dS -1).   In the San Joaquin Valley location all plots were furrow irrigated and the ECe values in the most saline plots were approximately similar to those in the Imperial Valley furrow irrigated plots (Table 2).
Salinity slowed emergence and reduced seedling weight

At the Imperial Valley site, there were no significant differences between the number of seedlings established 31 days after irrigation began (5 to 6 leaf stage) in furrow or sprinkler irrigated plots (Table 4) and no significant differences in days to 50 % emergence.
At the WSREC site, sugarbeet establishment at 38 days after initial irrigation (approximately 6 true leaves), was not significantly affected by soil salinity (fig. 1) or by irrigation treatment (using either saline or non-saline water, data not shown).  Irrigation treatments were important only in so far as they affected salinity in the seed zone.   Seed treatments influenced  establishment, with primed seed resulting in larger numbers of seedlings.  Primed seed emerged more slowly when soils were saline, but at a higher rate than unprimed seed, approximately equaling the rate of non-primed seeds under non-saline conditions (fig. 2).  Days to 50% emergence increased significantly at greater ECe levels (fig 3). It was largely unaffected on average until ECe reached 6 dS -1.  Then the rate slowed (fig 3).  Plant dry weight was affected by  ECe levels greater than 6 dS -1 as well (fig 4).  There was an interaction between seed treatments and plant dry weight.  Primed treatments were less affected than non-primed treatments.  The primed seeds emerged faster (fig 2), and because day length and soil and air temperatures were declining in late October, faster emergence resulted in greater seedling dry weights under both sets of conditions (fig 4) .
 

Compensating for saline conditions by using primed seed

Delayed seedling emergence can result from water stress and water stress results from increasing salinity (Ayers, 1952).  Salinity levels of 6 to 12 dS -1 are thought to reduce and delay emergence in sugarbeets (Maas, 1986).  These observations were based for the most part on trials in which chloride type salts were mixed with soil or other media and these mixtures then used for emergence trials in pots or trays (Ayers, 1952).  In our trials, in which salts were primarily of the sulphate type rather than the chloride type and seeds were planted in the field, emergence was not significantly reduced at soil salinity levels up to approximately 10  dS m-1, somewhat higher than predicted.  At the WSREC site, emergence was delayed in plots with  ECe’s greater than 6 dS m-1.  Salts had become thoroughly mixed throughout the seed zone as a result of many years of saline water application.
Seedling dry weight declined at WSREC in response to increasing ECe .   In the fall, with declining day length and temperatures, earlier emergence should result in greater seedling weight.  Water stress in saline plots may also have contributed to reduced seedling growth rates, though this was not determined directly.
Seed treatments which provide advantages under non-saline conditions, seem to provide similar advantages under saline ones as well.  Primed seed in saline plots emerged at the same rate as non-primed seed in plots with low  ECe.  Similar results were found with cotton (Shannon and Francois, 1977).  Primed seed is advanced physiologically by exposure to water prior to planting.  This reduces the time required after planting and re-imbibition of water for the physiological events preceding germination.
There were no significant correlations between emergence and irrigation treatments at the Imperial Valley site.  Plots at that site had been treated uniformly prior to this experiment and initially were non-saline.  The soil salinity differences observed were transient effects resulting from differences in irrigation method.  When furrow irrigation is used on soils in arid regions, salts move with the water and concentrate near the center and surface of the bed (Bernstein and Fireman, 1957).  Soil salinity continues ot change with time since irrigation and soil moisture levels.  Our sampling methods homogenized the surface 2 inches (5 cm) of soil and apparently did not adequately characterize the soil-water environment experienced by the seeds.  At the WSREC site in contrast, plots had been salinized for several years and soil samples reflected non-transient soil conditions.
 

Conclusions

1.  In the Imperial Valley, transient differences in soil salinity increases in the surface two inches resulting from furrow irrigation did not affect final plant populations or rate of emergence  in carefully irrigated plots.

2.  In soils at WSREC that had accumulated moderate amounts of predominantly calcium sulphate salts, seedling dry weight and the rate of emergence declined at ECe  levels greater than 6 dS m-1.   Final plant populations were not significantly affected by soil and water salinity.

3.  The rate of emergence of primed seed in saline plots equaled that of unprimed seed in non-saline plots.

4.  Seedling dry weight was reduced at ECe greater than 6.0 dS m-1.
 

References

Ayers, A. D. (1952).  Seed germination as affected by soil moisture and salinity.  Agron. J. 44(1):82-84.

Bernstein, L. M. and Fireman, M. (1957).  Laboratory studies on salt distribution in furrow irrigated soil with special reference to pre-emergence.  Soil Science 83(4): 249-263.

Hanson, B (1993).  Salt distribution under furrow irrigation.  p 51-54. In : Hanson, B.L., Grattan, S.R., and Fulton, A. (Eds.).  Agricultural Salinity and Drainage.  University of California Irrigation Program.  University of California, Davis.

Kaffka, S. R., Daxue, D., and Peterson, G.R. (In press).  Saline water can be applied to sugarbeets.  Calif. Agric.

Maas, E.V. (1986).  Salt tolerance of plants.  Appl. Agric. Res. 1(1):12-26.

Shannon, M.C., and  Francois, L..E. (1977).  Influence of seed pretreatments on salt tolerance of cotton during germination.  Agron. J. 69:619-622.

List of Tables

Table 1.  Quality of irrigation water used in trials in Imperial Valley (Desert Research and Extension Center) and western Fresno County (Westside Research and Extension Center)

Table 2.  ECe before and after irrigation at the Westside Research and Extension Center (dS-1 m).

Table 3.  Seed treatments used in both trials.

Table 4.  Final establishment and days to 50 % emergence for the Imperial Valley Trial.

List of Figures

Fig. 1.  Final establishment for different seed treatments at WSREC.  Results are grouped by plots with ECw < 5.0 (dark bars) and ECw  > 5.0.  Error bars are standard errors.

Fig. 2.  Days to 50 % emergence by seed treatment.   Results are grouped by plots with ECw < 5.0 (dark bars) and ECw  > 5.0.  Error bars are standard errors.

Fig. 3.  Relation between average rate of emergence and ECe at WSREC.  Error bars are standard errors.

Fig. 4.  Seedling dry weight as a function of seed treatment and soil ECe at WSREC.  Error bars are standard errors.    Results are grouped by plots with ECw < 5.0 (dark bars) and ECw  > 5.0.
 
  Related Articles: