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1、wWIRELESS NETWORK FOR IRRIGATION CONTROL AND SENSING Variations in plant water and nutrient demand and environmental regulations to protect water quality provide significant justification for sitespecific irrigation and fertigation systems. We have developed wireless valve controllers that selfassem
2、ble into a mesh network. Mesh networking means that controllers pass messages to extend the effective communication range without using highpower radios. Solar energy is collected with a 200mW panel to operate each controller node without yearly battery replacement. Nine nodes were tested in a mesh
3、network, and each properly responded to commands. Measurements of battery voltage, solar panel voltage, enclosure temperature, and external sensors were transmitted every 10 min. Irrigation schedules were stored locally on each node and executed automatically. Schedules for each node were unique, ba
4、sed on the needs of the particular area being irrigated. Internal clock drift was an average 6.3s per day. Clock offset was removed using daily time stamps. Onehop transmission range using 916MHz radios varied from 20.9 m with a whip antenna at ground level to 241.1m with a dipole antenna at 3 m. No
5、de commands were acknowledged after an average of 2.7s per hop. Charge consumption was approximately 7.03mAh per day for the node circuit and 1 mAh per day for battery selfdischarge. The solar panel produced 26.0 to 81.3 mAh in direct sunlight and 6.5 to 13.7mAh in shade. Node operation is expected
6、to be continuous with occasional sunlight exposure. Soil moisture, pressure, temperature, and other environmental sensors will be used for feedback control and detection of problems. Such a network of intelligent valve controllers will allow growers in orchards, vineyards, nurseries, greenhouses, an
7、d landscapes to develop management practices that improve water and fertilizeruse efficiency. Conventional irrigation management provides water and nutrients uniformly across an entire field and ignores the reality that demand varies due to differences in soil, topology, and plant water and nutrient
8、 status. For sitespecific management, large plots are divided into several smaller management units based on variable site characteristics and each is provided individualized water and nutrient input to maximize profits, crop yield, and wateruse efficiency, and lessen environmental impacts. The bene
9、fits of sitespecific management have been reported for many years. Matching nitrogen delivery with plant needs has increased fertilizeruse efficiency and net returns in some field crops and reduced nitrate leaching in potato crop simulations . Variablerate application of granular fertilizer based on
10、 individual tree size in citrus reduced overall nitrogen application by 38% to 40% compared to conventional treatment. It seems logical that the benefits of variablerate granular fertilization would be seen for variablerate fertigation as well. Spatially variable management has also been shown to in
11、crease profits from corn and improve yield in potatoes and grain sorghum . Sitespecific irrigation has been most thoroughly tested in center pivot and linear move systems for field crops . Much less development has occurred for fixed irrigation systems, which are used in highvalue permanent crops an
12、d commercial horticulture. Sitespecific technology for fixed irrigation would be applicable in orchards, vineyards, landscapes, nurseries, and greenhouses, each of which has unique management challenges. The water and nutrient demand of trees, plants, and vines are impacted by variations in soil con
13、dition, elevation, or microclimate. When applied uniformly, water and fertilizer may leach in light textured soils and pool in heavy soils. Planting on steep slopes,as occurs with some vineyards and orchards, creates difficulty in preventing runoff and maintaining irrigation uniformity due to pressu
14、re variations. Commercial nurseries and greenhouses contain many different varieties of ornamental plants in close proximity to one another and must deal with continually changing inventory and strict environmental regulations. A single valve typically controls water flow to many emitters, and if th
15、ere are plants of differing size or water requirements, some will receive too much water, while others will receive too little.Irrigation control for landscapes in arid parts of the U.S. is also important since a significant amount of water is used for public turfgrass and ornamentals. Converting co
16、nventional fixed irrigation systems to allow sitespecific delivery of water and nutrients would create many small management units, each with a valve that must be independently controlled. Additionally, each should have the capability to read infield sensors such as temperature and soil moisture, which are commonly used for closedloop irrigation control. Sitespecific control for fixed irrigation systems has been limited. TorreNeto et al. used latching s
