   Summer Storms - August 11, 1999 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County This summer's monsoon season is really off to a great start. During July, 1999, Yavapai County Flood Control District reported 4.25 inches of precipitation in Camp Verde and 7.44 inches on top of Mingus Mountain. This is a fairly wide range, but this is to be expected from our quirky summer storms. July precipitation at your location is probably somewhere between these two figures if you live in the Verde Valley. The amount you receive depends on local storm patterns, topography, and luck. For backyard gardeners, the summer monsoons are usually a welcome sight. Both mild and intense storms have their distinct benefits on the environment. Gentle rains infiltrate into and percolate through the soil and providing moisture for plant roots, keep the air cooler, and make weeds much easier to pull. Gentle monsoon rains are rarer than the lively thunder showers that typify our monsoon season. The intense gully-washers scour stream channels, move sediment, and deposit it when the energy in the flowing water is dissipated. On the rangelands surrounding our cities and towns, the warm season perennial grasses are greened up and once again growing. The lush green hills are always a welcome sight. Once the soil is recharged, subsurface and overland flow of water increases. This water movements combined with the very intense rains have started to fill up dry cattle tanks and reduce hardships on our local ranchers. What's good for cattle is not always good for our other local agricultural producers. High flows play havoc with irrigation ditches, and the moisture makes it difficult to harvest vegetable and hay crops. The Verde River and associated tributaries experienced very high flows from storm runoff on July 26 and 27. Those living in Cottonwood/Clarkdale may have noticed that Bitter Creek really got moving during these storms. Bitter Creek runs into the Verde River from the Jerome area. This particular event moved large amounts of materials downstream into the Verde River including ten vehicles from a nearby auto salvage yard. This rainfall event is nicely chronicled on the Verde NRCD web site http://www.nrcd.org/verde. Thundershowers also bring impressive lightning displays. These violent, and often dangerous, outbursts help plants grow by converting atmospheric nitrogen to plant available nitrogen. Let's take a brief look at how lightning assists with this conversion. The earth's atmosphere is roughly 78% nitrogen gas. However, this pure gas form (N2) is totally unavailable to plants. As we know, lightning can release large amounts of energy. The energy from lightning is great enough to break the bonds connecting the two nitrogen atoms in nitrogen gas. When this occurs, oxygen from the atmosphere combines with the nitrogen to form nitrogen oxide (NO). In the next step, nitrogen oxide reacts with other oxygen atoms to form nitrogen dioxide (NO2). The resulting nitrogen dioxide readily combines with water in the atmosphere to form nitric acid (HNO3). Nitric acid is easily dissociated (broken apart) to release nitrate (NO3+) which is an available form of nitrogen to plants. This process is called atmospheric nitrogen fixation. As a side note, similar reactions also take place when we burn fossil fuels (i.e. acid deposition). Okay, the chemistry lesson is over. You can wake up now. Seriously, the nitrogen fixed by lightning during our monsoon season is probably significant enough to increase plant growth in our gardens and landscapes. Unfortunately, it is difficult to quantify amounts and therefore research is limited. By the way, there are a variety of other ways that nitrogen gas can be converted to a plant available form by living organisms: soil bacteria, phytoplankton in the oceans, blue green algae, actinomycetes, etc. These are all biological nitrogen fixation processes. The University of Arizona Cooperative Extension has publications and information on gardening and landscaping. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |