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Influence of Hybrids on Cold Soil Germination in Grain Sorghum

Early season growth is one of the most critical aspects of grain sorghum production. Within 30 days following emergence, total grain numbers are being set and any stress or reduced growth will greatly inhibit yields. To minimize these risks and optimize early growth, sorghum must be planted in a timely manner and into favorable soil conditions. This typically entails good soil moisture with soil temperatures at or above 58 F. However, with potential damages and additional costs associated with sugarcane aphids (an emerging pest in the sorghum industry), growers have become interested in planting sorghum earlier as a tool for managing these pests. Earlier planting would allow the crop more time to mature unhindered by the pest as well as potentially reaching later reproductive stages prior to potential infestation, which will often result in less yield reduction (Table 1).

 

Table 1. Impact of sugarcane aphids on grain sorghum yield loss based on growth stage of infestation.

Crop stage at 20% Percent yield loss with
no applied control
Pre-boot 81 to 100%
Boot 52 to 69%
Panicle emergence 0.67
Soft dough 0.21
Hard dough <10%

Adapted from Gore, MSU.

 

While this may be an effective strategy, planting into cooler soils could result in delayed germination and emergence, as well as reduced early season vigor, lower early season root development and delayed maturity. These issues would negate the benefits of early planting by not allowing the crop to mature quicker. Many growers have looked toward hybrid selection as a way to mitigate the risks of planting into cool soils. Some hybrids have been marketed as having good cold/cool soil emergence; however, this testing is not universal and little direct comparison between hybrids has been conducted.

 

Cold Germination Tests

To determine the ability for hybrids to be planted into cooler soils, cold germination tests were conducted. Hybrids were germinated at the standard 60 F and 53 F (below the recommended temperature). Seeds were considered germinated if the coleoptile was longer than 1 inch, the typical requirement to emerge at standard planting depths. Counts were conducted at 10 days following placement into the germination chambers. Germination values at cooler conditions were subtracted from germination in standard conditions to determine the percent reduction in germination (Table 2).

 

Table 2. Percent reduction in germination associated with cooler conditions. Values were the difference of germination at 60 F and 53 F, where seed was considered germinated if coleoptile length exceeded 1 inch.

  <20% reduction in germination in cooler conditions   20 to 35% reduction in germination in cooler conditions   >35% reduction in germination in cooler conditions  
             
  Dekalb DKS 33-07
DKS 29-07
DKS 37-07
Dekalb DKS 47-07 Pioneer 84P72
      Pioneer 85Y34
85P44
Alta Grain AG 1201
          Sharp Brothers SB 4117
  Pioneer 84P68
86P20
86G32
NuTech GS 725
GS 636
Gold Source GS7016
      Advanta ADV G2106    
  NuTech GS 693
GS 663
Richardson Seed RS 124    
      Sorghum Partners SP 73B12
SP7715
   
  Advanta ADV G3247
ADV G2275
       
      Sharp Brothers SB 3217    
  Alta Grain AG 1203 Gold Source GS6717
GS7117
   
  Dyna-Gro M60GB31
M74GB17
       
  Richardson Seed Swift        
  Sorghum Partners SP 68M57        

 

Summary

Several hybrids are currently available that will only experience minor reductions in germination/emergence when planted into soils with temperatures below the optimum 58 F. It should be noted that these reductions could still be up to 20 percent. Additionally, soil temperature is only the first factor to consider when deciding whether to plant early. While soil does not typically have major swings in temperatures, similar to air temperatures, prolonged cooler conditions following planting can negatively influence the crop. Hybrid selection does provide growers with options for planting early but critical and optimal soil temperature for planting have been established because it provides better conditions for the crop to germinate and emerge.

 

Josh Lofton
Cropping Systems Specialist

 

Anna Zander
Graduate Student

 

Chase Harris
Agricultural Technician

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