In April we entered into that period of the year where we are actually losing more water from the soil than we are gaining from rainfall. This last month of April we had one-tenth more rainfall than the average, 1.3 inches. At the same time the estimated actual loss of soil moisture was about 1.9 inches. From now on through to the end of September we will be experiencing a net loss of soil moisture. This information is linked to the Coupeville area. The north end of Whidbey Island will have somewhat similar losses, but the south end will fare somewhat better, although not much. When evaluating the Soil Water Loss from the Everett area it shows the month of May as the first month of the season where a loss begins to occur. September losses are about the same for Coupeville and Everett. When we refer to water losses we typically use the term Evapotranspiration. This term refers to soil water losses from the result of evaporation and transpiration. Plants growing on the soil use water to keep cool causing transpiration through leaf surfaces to occur. Water losses also take place through deep percolation. Deep percolation refers to water moving downward out of the root zone. Gravity is the force causing this, but only occurs when the soil is near saturation. Percolation losses become important only when over-irrigating. Let us deal with how you can go about managing water losses in your lawn and yard this summer. There are a few things you need to take into account which will help you do a better job. First, you will want to determine what kind of soil you have. Coarse, sandy soils have less water-holding capacity than fine soils such as clay. The smaller the soil particle size the greater the water-holding capacity. Coarse soils may store from 1/2 to 1 1/2 inches of water per foot of depth. Medium-textured soils may store 1 1/2 to 2 1/2 inches and clay soils can store up to 3 inches in that depth. To determine the type of soil you have, simply dig up a bit of it and feel it. Often this is aided by the use of a small bit of water. If the soil is very sandy, it will feel very gritty. The more silt and clay present will make it feel less gritty and more like smooth paste. Organic matter present will help hold moisture and it will give additional ability for the soil to infiltrate the soil depths. Excessive organic matter on the surface of the soil will actually reduce water infiltration. The degree to which plants use water in their root zone is dependent on temperature, humidity, sunlight and wind. All of these factors come into play creating transpiration. In addition, those plants which completely cover the soil will influence the retention of water. For example, low-growing ground covers tend to act as a mulch over their own root zone. Lawns pose a special problem for retaining water. Whenever a lawn is cut the leaf surface is reduced and transpiration is reduced. If, however, the lawn is sparse the rate of evaporation will go up since the soil is exposed to wind and sun. Lawns kept in a vigorous state will provide mulching-type cover even when properly cut and will require somewhat less water. In deciding how much irrigation is needed it is useful to get a feel for how deep the root zone is. For grasses you can estimate two feet on well established lawns. New lawns will have less root depth. Many of the ground covers will have rooting depths of two to three feet. Larger shrubs and trees can have much greater depths. Irrigation scheduling should take into account the root zone depth. Irrigate so the entire root zone is recharged. Over-irrigation will tend to leach nutrients down past the root zone, especially nitrogen. Full recharge of the root zone will allow less frequent irrigations. The old concept that roots will grow to water is false. What is true is that roots will grow where there is water. They will not grow without water. By deep irrigating you set up a situation where roots can be encouraged to grow. As the soil dries out near the surface, root growth slows or ceases at that level. Those roots located deeper in the root zone will still have moisture to continue growing. Irrigating only the top few inches of the soil promotes root growth only at that level of the potential root zone. Hence, when hot weather arrives the rapid depletion of soil moisture catches the plant unprepared since there are fewer roots at deeper depths. The plant wilts. Prevention of wilting in a situation such as this is to water frequently so the shallow root zone is always charged. The bottom line is to water less frequently, but more deeply each time. Sandy soils will require more frequent watering since they are not able to hold as much water. Here are some figures you can use as a guide to watering this summer for different crops or plants. In these months you can expect to have to replace the listed amount of water during the month. MONTH INCHES TO ADD MAY 1 (Raspberry plants will need about 3 inches) JUNE 3.4 (An additional inch for Raspberries) JULY 4.5 (An additional inch for Raspberries) AUGUST 3.3 (An additional inch for Raspberries) SEPTEMBER 2 (1/2 inch less for Raspberries) OCTOBER 3 If your soil is sandy plan on irrigating more frequently and less frequently for clay-type soils. To determine when you have applied an inch simply use a tin can placed in the sprinkler spray pattern. Ideally you should be able to get by with one irrigation each week, as long as the soil allows the water to enter without runoff. In some situations on lawns you may find the water simply will not penetrate. This is often due to an excessive build-up of thatch on the surface. Also contributing to this problem is soil that is very dry which becomes hydrophobic. The way to overcome this situation is to be sure that area gets watered more frequently until the soil becomes wet, then not to let it dry out completely. Once in awhile it is necessary to use what we call wetting agents. These compounds act to break the surface tension of the water, hence making it wetter. They are typically sprayed on the area that is having a problem. When water is applied it interacts with the wetting agent. Once you have identified a trouble spot, remember it from year to year. This summer the WSU-Extension Volunteer Weather Network will begin reporting temperature and rainfall figures for various sites around Whidbey Island. You can use this information to get a feel for how much additional help or lack of help you are getting from mother nature. This information will be printed in the Whidbey News-Times each week and will cover the previous week's weather. This information is unique in that it is one of the first times where a number of sites around Whidbey Island have been reported on at one time. The Volunteer Weather Network was set up to determine the extent to which we have micro-climates around Whidbey Island. The major kind of data collected involves maximum and minimum temperatures and rainfall. This data is then used to calculate Heat Units and accumulated rainfall for the various sites. Listed below is a table of the accumulated rainfall for various sites around Whidbey Island. This data is for year 1987 only. ACCUMULATED RAINFALL AREA LOCATION TO THE END OF APRIL Strawberry Point 8.28 inches Polnell Point 5.12 NAS Whidbey 6.16 Coupeville 6.24 Houston Road 9.79 Clinton 12.30 Data and graphs are available at the WSU-Island County Extension Office indicating what the Long Term Standards are for Coupeville and NAS Whidbey and what the rainfall picture has been like.

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