In the Farm Crop Production class at Barton, students learn temperature has the greatest effect on a crop’s adaptation to an area, ability to survive, and yield. Moisture is the most limiting climate factor for crop yield. Sounds simple but what does that really mean?
First, let’s tackle temperature and what exactly that means.
· Each crop plant has what are termed “cardinal” temperatures including a minimum, maximum, and optimal range. This defines the low and high temperatures a crop can exist in and the range where growth is optimal. This helps define where a crop is adapted to grow in and examining the long-term weather data, an idea of how productive it can be may be formed.
· For summer crops, the average dates of the last frost in the spring and the first frost in the fall are critical. The period of time between frosts defines the average length of the growing season. This is important in determining if you plant a full, medium or short season corn or sorghum hybrid. For soybeans it determines what maturity group suitable for an area. Simply looking at the frost-free period and average temperature, you have an idea of yield potential based on maturity of the crop (ignoring precipitation). The fuller season hybrid/variety you can plant, generally the greater the yield potential. The downside is that the greater the vegetative growth, the greater the risk of running out of water for grain production.
· Average daily highs and lows during the growing season. As more crops have moved into Kansas over the last few decades, especially into Central and Western Kansas, it’s not just a freeze that matters.  For tropical type crops like soybean, cotton and sesame, it doesn’t take a freeze to end the growing season. Temperatures on either side of forty degrees will usually stop growth and end vegetative development. A reason to select an earlier maturing cultivar so reproductive maturity is reached and quality/yield maintained and to plant late enough that a producer should avoid cold snaps in the spring.
· For crops like winter wheat, you don’t particularly worry about the frost-free period; instead a producer looks to see what average spring/early summer temperatures. What are the average temperatures during reproduction and grain fill. For cool season crops, high temperatures have a negative effect on yield even with adequate moisture. This is in part the advantage to earlier maturing wheat varieties; they are designed to flower and develop grain before high temperatures impact yield. The downside to earlier flowering is an increased risk of cold temperatures damaging wheat heads, pollination, and/or vascular tissue.
· For crops, soil temperature is as important as air temperature in determining the ability of a plant to survive and produce the desired crop.
· Keep in mind this is climate, not the weather during a particular growing season. The saying goes “Climate is what you expect and weather is what you get.”
Next week, a discussion of moisture and humidity regarding crop production.