| | Since the start of spring, it's been cooler and drier than normal across the province. Alberta Environment's precipitation maps for May this year show that Lethbridge was recording the best conditions with 56 per cent of normal precipitation, while Calgary was at 23 per cent, Red Deer - 42 per cent, Edmonton - 33 per cent, Drumheller - 25 per cent and Lloydminster - 28 per cent. Basically, across most of southern, central and even north-central Alberta, precipitation conditions were much drier than normal for the month of May and the trend continued into mid-June.
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For crops such as wheat, barley or canola, a certain amount of moisture is needed to not only initiate germination, but to take the crop through the vegetative growth stages to the point where it will produce grain.
"It takes at least four inches (100 mm) and often closer to five inches (125 mm) of water to get a wheat or barley crop from germination to the point where it will head-out and produce grain, and it's about the same for canola," says Dr. Ross McKenzie, agronomy research scientist with Alberta Agriculture and Rural Development, Lethbridge. "The amount of moisture needed is a bit variable because if you have a cool spring, the crop doesn't need quite as much moisture for transpiration, and more moisture will go into vegetative growth."
While the province finally got some much-needed heat in mid-June, heat also means that the crops need to use some of the available moisture for transpiration to keep cool. Temperatures that stay around the 20° C range are ideal as crops are able to use more of the available moisture for growth as opposed to transpiration to keep cool.
"Cereal crops at the tillering stage will use approximately 2 to 3 mm of water per day. Most crops in Alberta are now at the stem elongating stage where they will need about 3 to 5 mm of water a day," says McKenzie. "When the temperatures go up over 25° C, these crops will need more moisture, about 5 mm per day.
"If we assume 5 mm per day for a seven day period, that's 35 mm which is almost an inch and a half of water needed for one week at the stem elongation stage. When crops hit the heading stage, usually at the end of June to early July, they use up to 7 to 8 mm of water per day, so in a three-day period the crop will be using an inch of water under ideal conditions. That means that water use is fairly substantial from mid-June to late-July. If moisture is lacking during this period, significant yield reduction can occur."
Once the crop is to the point where it starts producing grain, Alberta Agriculture research trials across the province have shown that for approximately every five to seven bushels of wheat a crop will produce it needs an additional inch of rain; for barley, calculations show that for every seven to nine bushels an inch of precipitation is needed; and, for canola, three and a half to four bushels will be produced for every inch of precipitation.
"During June, the first thing that water stress will demonstrate is a reduction in growth, in leaves and stem," says McKenzie. "Once there is limited moisture available, cell expansion and division within the plant slows down. The effect is that plants will reduce the production of enzymes and proteins needed for growth. If the plant is lacking moisture, the stomata will close and wilting will start. If this becomes advanced, in some severe cases wheat and barley plants will start sloughing off tillers, which would translate into significant yield loss. Oilseed crops are affected by reduced branching. If moisture is limited when seed is filling, yield potential and seed quality can be greatly reduced."
Cereal crops set their yield potential at the 5- to 6-leaf stage. The number of tillers that the plant will set and the actual size of the head, or number of potential seeds, is determined by environmental conditions at that stage of growth. If there is moisture stress at that stage, while yield potential is being set, the ultimate potential can be reduced. Oilseed crops such as canola or mustard are more adaptable and can adjust their yield potential later into the reproductive growth stages by increasing or decreasing the amount of branching and the amount of flowers produced in response to soil moisture conditions.
Contact:
Dr. Ross McKenzie
403-381-5842 |
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