The trend toward reduced-till and no-till farming for soil and water conservation is shown graphically in an article published in the New York Times May 11, 1982, entitled "Erosion Wary Farmers Are Sparing Traditional Plow". The necessity for sub-surface application of fertilizers for efficient utilization of plant food, as indicated by research done by TVA's NFDC, universities, and agriculture experiment stations, has resulted in many proposals for solving this problem. Some of these are outlined in the article entitled "Making Fertilizer More Efficient" in the periodical "Big Farmer", April 1982 edition.
TVA scientists have stated that broadcast application of nitrogen fertilizers on no-till soils can result in losses as high as 40 percent, and the author of the "Big Farmer" article states "Efficiency standards for broadcasting phosphorous range from 10 to 30 percent." There is little doubt that even the most "backward" farmer is aware of the tremendous increase in cost of fertilizers, and the necessity for its efficient placement, which is bound to result in the adoption of sub-surface application.
Most methods of sub-surface placement in reduced-till or no-till farming involve the use of a cutting coulter running ahead of a knife or chisel plow with a liquid fertilizer application tube extending down the back of the knife or plow. Theoretically this may seem to be a good method, but the development of numerous such applicators since 1952 has proved that this method is not practical for general use. In hard ground it is practically impossible to apply enough force on coulters to keep them in the ground, and even if this can be done (by using only a minimum number) their life is very short because they are subject to bending, breakage and bearing and spindle failures. In soft ground coulters may not cut the trash, but push it below the surface where it will be caught by the applicator blade or chisel plow and tear out wide trenches in the soil. Further, unless the coulter is kept in exact alignment with the applicator blade, trash will wedge between the coulter and the blade, and tear out large chunks of soil. It is practically impossible in normal usage to keep the coulter and knife aligned for any length of time, because driver-operators will nearly always turn the machine to some degree with the tools in the ground.
Jet injection of agricultural liquids into the soil in no-till farming, i.e. without appreciable disturbance of the soil, has been proposed. Among the earliest of these proposals is that disclosed in my U.S. Pat. No. Re 25,307, Dec. 25, 1962, which had as its principal object the continuous injection of anhydrous ammonia, at the bottom of a slot cut by a coulter, with a high pressure (e.g. 2000 psi) traveling jet having a velocity of the order of at least 700 feet per second and a fineness of the order of about 0.007 to about 0.050 inch in diameter. Another proposal is that disclosed in the Baldwin et al U.S. Pat. No. 3,012,526, Dec. 12, 1961, which had as its principal object the successive injection of slugs of agricultural liquids with a high pressure (e.g. 500-1500 psi) traveling intermittent jet having a fineness of 0.080 inch in diameter. For this purpose Baldwin used a high pressure reciprocating pump and a spring-closed valve in the injection nozzle set to open at a predetermined pressure to receive liquid from the pump and create the successive high velocity slugs at the jet nozzle.
Such proposals, however, have not become commercial because of their lack of efficiency in terms of liquid placement or equipment cost and life. The sub-surface placement of a continuous band of liquid along a plant row is impractical because at normal application rates, i.e. gallons per acre, the jet must be so fine that extremely high pressures must be used to achieve sufficient penetrating power. Further, the necessary extremely small nozzle orifice would clog up constantly. Intermittent injection of liquid along a plant row has its advantages over continuous injection in that nozzle size may be increased and the jet accordingly can achieve the same penetrating power as a continuous fine jet with reduced pressure. A larger nozzle also is not so susceptible to clogging.
The arrangement shown in the aforementioned Baldwin et al patent, however, is uneconomical and impractical. It requires a separate pumping cylinder for each valved injection nozzle or injector because it is impossible to build all injectors so they will operate at the same speed and discharge at the same rate if supplied by a single central pump. It is not feasible to build a variable stroke pump of over 3 cylinders, and therefore the Baldwin et al pump, which may require 8 or 9 cylinders, must be a constant stroke pump. Any change in application rate requires the changing of the drive ratio from the tractor power take off (PTO) to the pump, which will require the operator to have on hand an almost infinite number of sprockets for providing the desired application rate--an impractical requirement. The spacing of the injections along a row cannot be controlled since the spacing depends upon the application rate. If the injector is designed to make an ejection at each average distance of 12" of travel at an application rate of 50 gallons per acre, the on centers spacing at 25 gallons per acre will be 24", and at 70 gallons per acre will be 8.6", which will require the injector to operate at 14.3 cycles per second at a ground speed of 7 mph. At this speed the inertia forces of the large valve spring, piston, and other heavy moving parts will become so high that the valve will not cycle properly and the flow to the nozzle will be throttled by the valve, reducing the discharge pressure to the extent that there will be little penetration.
Therefore, it is seen that the pressure responsive intermittent injector method, like the continuous injection method, does not provide a satisfactory method for injecting liquids into the soil.