Soybean Response to Late-Season Irrigation

TRIAL OBJECTIVE

The objective of this trial was to evaluate the response of soybean to different late-season irrigation treatments.

  

RESEARCH SITE DETAILS

Location Gothenburg, NE     
Soil Type   Hord silt loam   

Previous
Crop
Corn     
Tillage
Type
 
Strip  


 
Planting Date 5/11/2020     
Harvest Date 09/28/20  

Potential Yield
 (bu/acre)
55    
Seeding Rate
(seeds/ac)

160K


 
  • This study was designed as a randomized complete block with four replications of five treatments. 

  • A 2.9 maturity group soybean product was planted.  

  • The plots were maintained under dryland conditions with no supplemental irrigation applied until August 25. A hand probe was unable to penetrate the soil to evaluate soil moisture at that time as it was extremely dry.

  • Irrigation treatments consisted of the following with three total irrigation applications with each treatment (Table 1).

image
  • Irrigation was applied using a sub-surface drip irrigation system, and weeds were controlled as needed. No fungicides or insecticides were applied.

  • After August 25, only one precipitation event of 0.5 inches occurred on September 8, 2020.

  • Plots were combine-harvested, and a subsample of seed from each replication was taken to determine moisture content, test weight, and total weight. Statistical analysis for Fisher’s LSD was performed.

 

UNDERSTANDING THE RESULTS

image Figure 1. Impact of late-season irrigation treatments on soybean seed test weight.
  • Irrigation treatments significantly impacted test weight with seed sampled from plants receiving the dryland and 0.5-inch/week treatments having significantly lower test weights than seed from the 1.0-inch, 1.5-inch, and 2.0-inch/week treatments (Figure 1).

  • The smaller soybean seed size can be seen in the dryland and 0.5-inch/week treatments compared to 1.0-inch/week treatment in Figure 2.

image Figure 2. Soybean seed size of seed sampled from plants receiving the dryland, 0.5-inch, and 1.0-inch/week irrigation treatments.
image Figure 3. Impact of irrigation treatments on average soybean yield.

  • For this trial, irrigation treatments significantly impacted average soybean yield with plants receiving the dryland and 0.5-inch/week treatments having significantly lower average yields (bu/acre) than the plants receiving the 1.0-inch, 1.5-inch, and 2.0-inch/week treatments (Figure 3).
    • For this trial, the 0.5-inch/week treatment did not provide enough water to overcome the drought stress conditions of experienced by the soybean plants. 
    • Soybean plants during the R5 to R6 growth stages can use on average 0.2 to 0.25 inches of water per acre per day.1
  • Minimal soil moisture was available to the soybean plants toward the end of August. Plants appeared drought stressed before the start of the irrigation treatments on August 25 as seen in Figure 4. 

image Figure 4. Stressed soybean plants before irrigation on August 25, 2020.

KEY LEARNINGS

  • Based on our observations for this trial, farmers could potentially improve soybean yields by applying  late-season irrigations when it is available.
    • Because soybeans use more water later in the growing season, late-season irrigation can be a strategy in areas where water could be diverted from a short-season corn product if sufficient moisture is available in the soil profile to fill-out the corn kernels.   

  • Significant soybean yield losses could occur in years where end of season precipitation is limited and the available moisture in the soil profile is not being actively managed. Warm air temperatures at the end of August through mid-September can also negatively impact available moisture in the soil. 

 

 

Source

1Kranz, W.L. and Specht, J.E. 2012. Irrigating soybean. University of Nebraska-Lincoln Extension. G1367.

6017_R1_20

 

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