![]() If a person walks across a lawn in the evening, his or her shoes will become wet quickly. So we have conserved water, but what are the consequences? Consider a commonplace, unremarkable event that happens most spring and summer evenings – dewfall. The resident who applied 1 inch of water receives the benefit from 0.85 inches. Estimates of water loss during night-time irrigation are approximately 15%, once again depending on humidity, wind speed, and temperature. ![]() There is no sun, so solar radiation does not contribute to water evaporation. Night-time humidity is higher, which also reduces evaporation. Night-time temperatures and wind speeds are much lower, which means lower evaporative losses during irrigation. The irrigation cycle should end early enough before sunrise to allow excess water to soak into the landscape so that the leaves will dry in the normal time period. ![]() The best time of day to begin irrigation is after nightfall. In effect, the resident who applied 1 inch of water only received the benefit from 0.7 inches. Estimates of water loss during daytime irrigation range from 20% to 30%, depending on humidity, wind speed, and temperature. In addition, water applications from sprinklers are more susceptible to drift and evaporation because of the previously mentioned climatic factors and because wind speeds are typically higher during the day. ![]() It is best to take a more preventative approach and prepare plants for this stress rather than a curative approach and irrigate plants when they are already stressed. This is when plants work the hardest to deal with the stress associated with mid-day climatic factors such as high temperatures, strong solar radiation (Figure 1), and lower humidity. Evapotranspiration is greatest during the hottest hours of the day (10:00 am to 4:00 pm). Evapotranspiration is the combination of (a) the loss of water by transpiration of plants, and (b) evaporation from soil and plant surfaces. Water Conservation & Time of Dayįrom a water conservation standpoint, daytime is a poor time to irrigate. In all practicality, disease is not increased except when lawns are routinely over-irrigated. Very few people consider night irrigation to be a viable alternative due to concerns of increased disease pressure. One group suggests that early morning is the best time, while another group claims that afternoon is the best. And, I should never water more than 0.96" (either at one time, or cumulatively based on current saturation), otherwise it's a waste.The best time of day to irrigate is the subject of some debate. Alternatively speaking, I need to water my lawn with 1.064" (0.152 * 7) of water per week, so however I get to that it's what's important (it can be 0.48" every 3.15 days, or 0.3" every other day, and so on). TL DR - To keep up with losing 0.152" of water loss due to ET, I need to water my lawn every 3.15 days with 0.48" of water. For me, I'm using y = 6, and z = 0.16 (silt loam). Second, * (z) (and * (z) * 0.5), where y = root depth and z = a standardized constant based on the soil type table in the initial article (and, generally speaking, y will end up being a constant as well, I'm assuming, since root depth, once established probably doesn't fluctuate a lot?). So my first important number is 0.8(0.19) = 0.152 (how much water I'm losing daily to ET). ![]() Also, this ignores the rain variable for now.įirst, 0.8(x), where x = daily FRET number, which will be a true variable at any given point during the year. There are a couple of numbers of importance, and I'm going to stick to just the numbers.the explanations of the numbers are above. I think I have this down, but just to confirm, and maybe simplify for anyone else reading through (I had to hand-write out the equation to make sure I got it): ![]()
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