Cold Temperatures and Sorghum Planting Dates?
Tip provided by: Dr. Ronnie Schnell, Texas A&M AgriLife
Sorghum producers look to early plantings to avoid late season heat and moisture stress and to reduce the risk of midge. Yet, early plantings could encounter cool air and soil temperatures that can have adverse affects on sorghum emergence and growth.
In general, the earliest recommended planting date for a given region is about two weeks after the average last frost (Figure 1). Normally, soil temperatures have warmed to sufficient levels by this date for planting sorghum. Yet, late season cold fronts and associated cold air temperatures could reduce soil temperatures below optimum levels for grain sorghum germination and emergence. Cold soil temperatures during germination could significantly delay emergence, reduce stand and early season vigor.
Sorghum will germinate quickly with soil temperatures at 65-70°F but will also germinate at temperatures as low as 50°F (expect very slow growth). Planting should not begin until soil temperatures (2 inch depth) have reached an average of 60°F over a five day period. For example, the current (March 8-12) five day average 2-inch soil temperature at Bushland, TX is 47°F (Figure 2). Make sure to determine the soil depth that is used to measure soil temperature at various weather stations. For planting, measurements from a depth of 2 inches are most relevant. However, some stations may report measurements taken at a depth 6 inches or deeper. Shallow depths will respond more quickly and drastically to changes in air temperatures while deeper soil depths are buffered from large swings in temperature. For this reason, soil temperatures from deeper depths (> 2inch) do not reflect conditions within the planting zone.
Soil temperature information can be found at:
High Plains Region – http://www.mesonet.ttu.edu/soilobsframe.html
State Wide: http://www.wcc.nrcs.usda.gov/scan/Texas/texas.html
Temple: http://www.ars.usda.gov/SP2UserFiles/Place/62060500/temple/T2014.XLS
Figure 1. The average last freeze dates for Texas.
Figure 2. Soil temperature at depths from 20 to 20 inches over a 5-day period at Bushland, TX.
For further information, contact:
Dr. Ronnie Schnell, State Wide
(979) 845-2935
Dr. Calvin Trostle, Lubbock
(806) 746-6101
