COOL TEMPERATURES SLOW CROP DEVELOPMENT

    It will not be long before the Coastal Bend prairies will turn green with rows and rows of grain sorghum, especially in Nueces County.  Nueces County is typically the number one grain sorghum producing county in Texas, as this crop usually accounts for more than 40% of the local Agricultural income.
    The recent cold night-time temperatures have certainly slowed the growth of this newly planted crop.  Here is a quick review of how seedling grain sorghum grows and develops.
    Grain sorghum goes through three different stages of development after emergence - seedling development, panicle initiation and finally reproduction. The time required for the plant to go through each stage is dependent upon hybrid maturity and temperatures encountered during the growing season.
    Grain sorghum follows a predictable pattern of growth from planting through physiological maturity. The duration between growth stages is closely dependent upon the air temperatures and relative maturity of the hybrid. The number of days required for a hybrid to reach maturity depends primarily on location, date of planting and temperature.  Because daily minimum and maximum temperatures vary from year to year and between locations, the number of days from planting to physiological maturity varies and is not a good predictor of crop development. A better system to estimate crop development is the growing degree unit (GDU) system.
    So lets take a close look at what is GDU.  The GDU is equal to  (Daily max. air temp + daily min. air temp)/2 - 50.  In the last two weeks, the GDU’s have ranged from a low of two per day to a high of 25 units per day.  Needless to say, we have been very slowly accumulating GDU’s, thus very slow crop development.
    Typically it takes 200 GDU’s from the day of planting to emergence and 500 GDU’s to reach the 3-leaf stage.  From this, one can see that temperature is the driving factor at how fast this crop will grow and develop.
    The seedling development stage is dominated by vegetative growth. The plant develops leaves and tillers, which ultimately support grain formation and growth. The duration of the seedling development stage is largely dependent on air temperature and the hybrid maturity. The more leaves formed by the plant, the longer maturity. Early maturity hybrids typically produce 15 leaves per plant, while medium and late maturity hybrids produce 17 and 19 leaves each. The plant can tolerate stress from drought, hail and freezing temperatures in this stage with little negative effect on grain yields. Sunny days with temperatures below 65°F promote tillering when the plants are in the 4- to 6-leaf stage and plant densities less than three plants per foot of row also promotes tillering. Panicles of tillers are often smaller and flower later than those of the main stem. Tillers formed can compensate somewhat for low plant populations.
    With abundant soil moisture, now all our crops need are warm temperatures, so they can grow and develop normally.