Agricultural irrigation units are in wide use throughout various parts of the United States to supplement inadequate rainfall and provide the necessary supply of water to grow crops. Most of these agricultural irrigation units utilize some sort of pipeline system to transport water from a water source to the field. There are various different kinds of designs such as center-pivot units, end roll systems, etc. as is known in the art and these generally have a main supply line which moves through the field as the water is applied to the land.
It is often desirable, and even necessary, to supply additives including fertilizers or other chemicals to enhance the growth of crops in what otherwise may be a dry, mineral-poor soil. An ideal way to apply these chemicals is to utilize the irrigation unit as it moves through the field. By using the irrigation systems, the fertilizer or chemical is applied throughout the same area as the water so that it is delivered to that portion of land growing crop. In addition, the water serves as a medium to transport the chemical and with a sufficient mixing and balanced application pattern, accurate proportions of additive may be applied with hardly any waste.
Another advantage to using the irrigation system is that the chemical may be applied at no additional cost as the irrigation system must sweep through the field in any event and it costs no more in equipment or in usage if instead of applying merely water, a mixture of additive and water is applied. The only additional cost is for the equipment to pressurize and inject the chemical into the main pipeline and ensure that it is being injected in the proper proportion to the amount of water flowing through the system. Thus, for what may be a very small amount compared to the cost for the entire irrigation system, a very desirable feature may be added which allows the direct application of fertilizers or other additives to the field in a controlled, proportional amount.
In the prior art, systems have been developed and used for injecting an additive at a constant rate which is calculated to match the expected rate of flow of water through the irrigation system. In these systems a constant displacement pump injects the additive into the system at a constant flow and pressure as the system sweeps through the field. While the prior art systems work relatively well for those applications in which the application rate remains relatively constant, these systems do not provide any means to vary the rate at which the additive is injected into the system as is required when the flow of water through the main irrigation system is altered. For example, in a center-pivot irrigation system which sweeps through a circular area, corner systems are often provided to at least partially irrigate the corner areas of a square of land. As can be appreciated, the corner system is only operable for a portion of the sweep through the field, i.e. when the system is adjacent any one of the four corners of a square field. Examples of a corner system owned by the same assignee as herein are Daugherty, et al., U.S. Pat. No. 3,902,668 and Seckler, et al., U.S. Pat. No. 3,802,627, the disclosures of which are incorporated herein by reference. When the corner system is on, the flow of water through the system is stepped up to maintain a constant water application for the increased amount of land being watered. Thus, an irrigation system having a corner unit experiences several changes in flow rate through a single cycle.
For any irrigation system which has a varying flow of water, the prior art systems were found to be undesirable as the proportionate mix of additive in the system varied as the flow varied. With a prior art system, a farmer had to choose between either over-fertilizing when the corner system was non-functional; under-fertilizing when the corner system was functional; or some unhappy medium between the two. This has recently become more of a problem as the cost of fertilizers and chemicals has risen dramatically making over-fertilizing very expensive. Furthermore, some types of crops and chemical combinations show up the improper use of fertilizers very dramatically such that the prior art systems are ineffective in full utilization of the growing capabilities of the field.
To solve these and other problems, applicants have succeeded in developing a system for accurately measuring the rate of water flow through the main irrigation line and periodically injecting a measured amount of chemical into the line. As the rate of water flow increases, the number of times the chemical is injected increases to maintain the preset proportional mix of chemical and water. Similarly, as the flow decreases, the number of injections decreases. The system uses a paddle wheel type flowmeter to measure the instantaneous flow rate of the water. This flowmeter also provides a totalized output which supplies a triggering pulse to a flow control timer circuit after a predetermined amount of water has passed through the system. The timer then opens a solenoid for a preset period of time, thereby injecting a predetermined amount of additive into the irrigation line. By using a scheme which changes the number of injections of a constant amount of chemical produced at a constant pressure, a less expensive constant displacement pump may be used, as in the prior art systems. A pressure relief valve and relief line return the additive to a reservoir between timed openings of the solenoid to permit continuous operation of the pump without damage to the system. A safety shutdown prevents either a continuous-on or continuous-off condition by sensing the output of the injection line, timing the on and off conditions, and shutting the system down should either of those timed conditions exceed the normal operating time periods.
Thus, applicants' system automatically varies the amount of additive injected into the main irrigation line by "pulsing on" the injection system for a preselected time period after a predetermined amount of liquid has flowed through the system. This ensures that the proper amount of fertilizer or the like is applied through all parts of the field and at varying water application rates caused by corner system cycling or the like. Applicants' system is more fully explained in the drawings and preferred embodiment which follows.