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Rain and Summer Crops
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As of noon this past Thursday, The GMD 5 (Groundwater Management District) weather station west of Great Bend reported 2.48 inches of precipitation for the preceding 24 hour period. The highest amount for that period from their weather stations was 4.12 inches for the Stafford site with Macksville at 3.8 inches and Radium at 2.77 inches. No, this doesn’t end the drought for areas receiving this rain but it certainly eases its effects.
This precipitation should be adequate to finish the wheat crop and allow recently planted summer crops a chance to get off to a good start. The other positive for the summer crops is the moderate temperatures forecast allowing wheat kernels to develop at a normal rate and optimize the opportunity for maximum possible yield. With all the late planted corn in Kansas and the Corn Belt, there has been talk about reduced yields from late planting. It might be helpful to understand how corn proceeds in its development to understand the concern.
A crop such as winter wheat while responding to temperature and moisture as it develops has two factors key in producing seed. First, it must vernalize (undergo a period of cold temperature) before it can flower. The amount of cold needed depends on the variety and varies greatly. The second factor triggering flowering is increasing day length. While this is not as pronounced in modern wheat as in the past it plays an important role. These factors make sense evolutionarily. Wheat is a cool season plant, germinating in the fall and flowering in the spring. It would be disastrous to flower before or during winter and the species wouldn’t survive. By not flowering until being exposed to a period of cold and waiting until daylight increases, the plant minimizes the chances of flowering under adverse (freezing) conditions. Corn is a summer crop from an area where the plant needn’t worry about winter and there is more than adequate daylight for reproduction. There is no advantage for corn to be day length or cold temperature sensitive so its developmental staging is driven by heat.
Briefly, it takes the accumulation of so much heat for corn to emerge, each new leaf to emerge, tasselling, silking, seed development, and physiological maturity. This is often expressed as a relative maturity in days and can be as little as 75 days for some hybrids to over 120 days. This isn’t the best measure. A more accurate measure is GDD (Growing Degree Day) accumulation which is determined using a simple formula involving the daily maximum and minimum temperature and a baseline of 50o Fahrenheit. For our purposes, the item to remember is that when the plant hits a certain amount of heat accumulation it is at a given growth stage regardless of other weather factors. It doesn’t have the ability to idle and wait for better conditions like sorghum. Remember last year the corn was very stunted and simply died. Unlike soybeans in our area, it only has one chance to flower while soybeans here are indeterminate and flower over an extended period of time. We certainly have a long enough growing and sunlight so why the concern regarding late planting and corn yields?
Pest concerns (insects and diseases) can be more of a problem with later planting. For our area, even with irrigation, the biggest concern is extreme heat and drought right before, during and immediately after flowering. No amount of water can alleviate the total effect of heat stress. During pollination it can result in poor, uneven pollination and poor seed set. One last thing, planting in mid-April with the snow and freezes wouldn’t have helped.