Objective:                  

To identify the effect of planting data and harvest date on sorghum sudangrass yield and forage quality in northwestern Montana

Personnel:                     

Clint Beiermann, Jessica Pavelka

Summary:

Sorghum sudangrass was planted on three dates: May 1st, May 15th, and June 1st of 2022. All planting date treatments were harvested at three distinct harvest dates: August 1st, August 15th, and September 15th. Treatments that were harvested on August 1st and August 15th were harvested again on September 15th to assess the amount of regrowth that occurred between the first harvest event and the end of the growing season (Table 1).

There was no significant difference on forage yield or plant heights between planting dates, however there was a significant increase in yield as harvest date was delayed. The September 15th harvest date showed a significantly higher yield across planting dates, with an average of 23.4 tons/A. The August 15th harvest date also had a significantly higher yield than the August 1st date, yielding 15 tons/A and 8.1 tons/A, respectively (Table 3). This trend is also true for plant height at harvest. The September 15th harvest had an average height of 147.2 cm while the August 1st harvest had an average height of 87.5 cm (Table 3). The regrowth was significantly higher for the August 1st regrowth harvest than the August 15th regrowth harvest, as the earlier harvest date had more time for regrowth. The total forage yield, a combination of main harvest and regrowth harvest was comparable, at 16.4 ton/A for August 1st and 16.7 for August 15th (Table 3).

Nitrate levels declined as harvest date was delayed. Nitrate levels were near 120 ppm for the August 1st harvest and declined to near 40 ppm by the September 15th harvest date (Figure 2). Protein levels also decreased as harvest was delayed. Protein levels were near 12% when sorghum sudangrass was harvested August 1st and decreased to near 5% by the September 15th harvest date (Figure 3). ADF levels increased as harvest was delayed, and ADF was significantly lower for the June 1st planting date, compared to earlier planting dates (Figure 4).

 

Table 1. Management information
Seeding date: 5/1, 5/15, 6/1 Field Location: X4
Julian date: 122, 135, 152 Harvest date: 8/1, 8/15, 9/15
Seeding rate: 9 plt/ft2 Julian date: 213, 227, 258
Previous crop: Canola Soil type: Creston Silt Loam
Herbicide:

2, 4-D @ 12 oz/A & Destiny HC @6.4 oz/A 6/7/22

 Tillage: Conventional
Insecticide: NA Soil residual nutrient (NO3-1, P, K lb/A): 109-16-312
Fungicide: NA Nutrient fertilizer applied (N, P2O5, K20 lb/A):

100-20-30

 

Table 2. Agronomic performance by planting date
Planting Date Weight (ton/A) Height (cm)
May 1st 16 116
May 15th 16.4 119.8
June 1st 14.1 116.4
Mean 15.5 117.4
C.V. 11.1 5.6
LSD ns ns
PR>F 0.091 0.459

 

Table 3. Agronomic performance by harvest date
Harvest Date Main Harvest *Regrowth Harvest Total Yield
  Yield (ton/A) Height (cm) Yield (ton/A) Height (cm) (ton/A)
1st August 8.1 c 87.5 b 8.3 a 83.5 a 16.4
15th August 15.0 b - 1.7 b 45.0 b 16.7
15th September 23.4 a 147.2 a - -  23.4
Mean 15.5 117.4 5 64.3  
C.V. 18.1 5.4 32.6 13.7  
LSD 2.4 5.5 1.4 7.5  
PR>F <.001 <.001 <.001 <.001  
*Regrowth harvested 15-Sep
Letters represent differences (α=0.05)

 

Figure of forage yield over harvest date

Figure 1. Forage yield

Figure of the nitrate content in ppm over harvest date

Figure 2. Nitrate content

Figure of the protein % over harvest date

Figure 3. Percent crude protein

Figure of ADF % over harvest date

Figure 4. Percent acid detergent fiber