B. Late Vegetative and Mid-Pollination Conditions
Record wet conditions and cool summer slowed growth but favored pollination
The amount of time between emergence and half-bloom4 depends on the planting date, the temperatures during this period (of which the impact is measured by growing degree days5), and the sorghum hybrid. High temperature stress after growing point differentiation (approximately 30 days after emergence) delays heading6 and decreases seed set (number and size of seeds), affecting final yields. Delayed planting may result in delayed blooming (or flowering). Blooming later than normal during the growing season increases the likelihood of the crop being exposed to excessive heat at blooming, which could jeopardize yields and final grain numbers. Temperatures below 40°F during grain fill can negatively impact the ability of the plant to fill the grains, thus affecting final yields. Hybrid selection also affects the length of time from planting until mid-pollination; short-season hybrids have a shorter time from emergence to flowering than the full-season hybrids, and therefore have lower yield potential compared to the full-season hybrids.
4Half-bloom is the sorghum reproductive stage where 50% of the plants in the field are in some stage of bloom.
5Growing degree days is a parameter related to heat accumulation in order to predict plant development stages.
6Heading, the process in which sorghum heads are exerted and visible on the plant tops, occurs after boot stage and before flowering.
1. Early Harvest Area
Sorghum heading in the EHA took place from mid-July to the onset of August. Cool and wet conditions (more than 20 inches of excessive rain) dominated during the vegetative phase and the half-bloom stage. These conditions slowed plant growth and reduced nutrient uptake (thereby affecting the root systems) during the vegetative phase. However, the cool temperatures favored the blooming process, resulting in more grains per head. While normal or slightly above-average temperatures occurred during the grain fill period, the main challenge for crop development remained the wet conditions.
2. Late Harvest Area
Sorghum heading for the LHA spanned from mid-August to early October, with the largest percentage occurring during September. For the northern section of this area, if flowering took place early- to mid-September, the probability of reaching maturity before the first freeze was lowered due to the lack of accumulation of growing degree days. Late vegetative phase conditions and half-bloom phase remained wet with normal temperatures. Conditions for the grain fill period across the entire LHA changed from very wet to dry, and average temperatures were normal to above-normal. These conditions shortened grain fill and accelerated maturity.