Not one cropping season is ever the same, and conditions vary greatly from region to region. Some years experience hotter temperature norms, and others have cold snaps. Both extremes put pressure on crop growth and its ability to reach maturity. How exactly? We’ll dive into both of these weather extremes and how crops cope.

Hotter Temperatures

Heat can affect a crop’s ability to mature in more ways than one. Hotter daytime and nighttime temps tend to accelerate plant processes and affect crop growth, development, photosynthesis, respiration, water transpiration, grain fill, and nutrient cycling. The magnitude of high temperature or drought stress also depends on the stage of the crop.

High daytime temps can also have an effect on the corn pollination processes critical for crop development and yield. When the pollen shed occurs, silks must emerge and be fertilized by viable pollen in order for kernels to develop. In cases where there are high temperatures and inadequate soil moisture, pollination and fertilization can reduce the seed set.

Temperatures greater than 95 degrees Fahrenheit coupled with low relative humidity will remove moisture from exposed silks, and pollen is generally no longer viable when temperatures go above the mid-90s. However, most pollen shed occurs in the morning when it’s cooler.

Heat stress on soybeans can cause a variety of yield-degrading components. Early season stress may cause flower abortion and, subsequently, pod abortion. Late-season heat stress can reduce seed size and set on pods. The greatest potential for yield reduction can come at R4 (full pod set) to beginning R5 (beginning seed set) where both pod and seed development occur.

Rapid dry-down can also cause soybean pods to become brittle and more likely to shatter when combining.

Hotter nighttime temperature affects yield in a couple of different ways. First, high nighttime temperatures result in more heat unit accumulation. Over time this results in the speed-up of developmental time. What this really means is if high nighttime temperatures occur during reproductive grain fill, then the grain fill period will be shortened.

Second, high nighttime temperature results in high respiration rates at night when photosynthesis is not active. The result is that plant sugars are used for energy rather than growth. During vegetative growth, this means less biomass production and less stem elongation. During reproductive stages, this results in fewer plant sugars available for grain fill and, subsequently, fewer and/or lighter kernels.

Colder Temperatures

When colder temperatures occur, the opposite happens, and maturity is either slowed or halted completely depending on the conditions. If freezing events (28 degrees Fahrenheit or lower) occur before the crop reaches maturity, damage to the plants is highly likely. The more severe the damage, the lower the yields. The effects of the damage will not be immediately apparent and will progress over time. Here’s what you need to monitor for after a frost event:

Signs of Frost-Damaged Corn

• Small, misshapen, soft kernels
• Undeveloped starch structure; pithy kernels
• Test weights progressively below 52 lb/bu depending on maturity (in 1993, some corn was less than 40 lb/bu)
• Average protein (7.5 to 8.0 percent) in corn heavier than 45 lb/bu, lower protein in corn lighter than 45 lb/bu
• High breakage susceptibility; many fines (material smaller than whole kernels) generated in handling
• Lower digestibility when compared with normal corn, especially for test weights below 45 lb/bu
• Little or no increase in test weight after drying (test weight will tend to decrease if frost kills the plant before physiological maturity)
• Variable amino acid levels
• Moisture meters generally read low in immature corn
• Surface drying of kernels, giving deceptively low (by 1 to 2 percent) moisture readings on dried corn

Signs of Frost-Damaged Soybeans

• Green or elongated yellow soybeans that shrink to a smaller-than-normal size after drying
• Reduced extractable oil content (below 16 percent), complete extraction of oil difficult, and poor oil quality
• Higher moisture (by 1 to 2 percent) than indicated by moisture meters
• Slower field drydown

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