Theoretically, this is a fairly good system of watering. There is smaller loss by evaporation from the surface than with any other system; there is less baking of the soil and the least amount of tillage is required, and in addition, tillage is never delayed because of a wet surface. On the other hand, considerable outlay is required for tile, which must be laid, lifted and stored every year, unless placed below the frost line. Percolation is too rapid and capillary action too slow in most soils. It is doubtful if this system will ever be generally used.

The most extensive system of subirrigation in the United States is at Sanford, Fla. Large tracts of waste land have been brought under cultivation and utilized in growing lettuce, celery and other crops. The tile serve both for irrigation and for drainage. An impervious bed of hardpan lies from 2 to 4 feet below the surface and the sandy or loamy top soil is about 18 inches deep. The 4-inch water mains are made of sewer tile, cemented at the joints, the 3-inch laterals of drain tile are 20 to 25 feet apart and 12 to 15 inches below the surface. Sawdust, cinders or moss are placed over the joints to prevent filling with sand. A fall of at least 1 inch in 100 feet of tile is provided for drainage. The laterals run into open ditches dug for drainage purposes. Subirrigation is an ideal system for conditions as they exist at Sanford.

133. The Overhead System Of Irrigation

The Overhead System Of Irrigation promises to revolutionize garden irrigation in the East. Numerous plans, some of which have been described, have been used to a very limited extent since the early days when Peter Henderson was a practical gardener on Long Island. None of the methods, however, became universally popular until the Skinner system was introduced in 1904. This is an overhead method used in hundreds of gardens and greenhouses. Its success, when properly installed, is universally admitted.

Nozzles For The Skinner System Of Irrigation.

Fig. l6. Nozzles For The Skinner System Of Irrigation.

The advantages of this system of watering may be summarized as follows: (1) The water falls in the finest spray, thus preventing the washing and hard incrustation of the soil; (2) the water is distributed with the greatest uniformity; (3) there is no injury to the plant by the force of the water; (4) very little labor is required to operate the system; (5) because the water falls as in a gentle shower the foliage is cleansed and the effect is to encourage the most healthful and vigorous growth; (6) insecticides and fungicides and liquid fertilizers may be applied through the water lines; (7) the cost of installation is low, considering the merits of the system. It varies from $90 to $150 an acre.

Water may be pumped directly into the system, or reservoirs may be constructed to hold it. When water from a city reservoir can be secured at a reasonable price the problem is very simply solved. A great many growers, however, pump directly into the system. The water mains or feeders should be of ample capacity to supply the nozzle lines.

All nozzle lines should be of galvanized pipe and of the size indicated in the accompanying table. The pipes are generally 50 feet apart in outdoor irrigation, and should be supported on posts about 25 feet apart. Two-inch pipe is generally used for posts, while some gardeners use cedar or locust posts.

Figure 15 shows the position of the patented drilling machine when in operation. This work must be done with the greatest care. The nozzles, also patented, are placed 4 feet apart for outdoor irrigation and 3 feet apart for greenhouse watering. They must be in perfect alignment. Different nozzles (Figure 16) are used for greenhouse and outdoor work. A patented union (Figure 17) is also required for the installation of this system.

Sizes Of Pipe For Outdoor Nozzle Lines

Calculated on outdoor nozzles placed 4 feet apart. If the nozzles are closer together larger pipe must be used.

Nozzle No.

Length of line feet

No. feet 4-in. pipe

No. feet 1-in. pipe

No. feet 1«-in. pipe

No. feet l«-in. pipe

No. feet 2-in. pipe

No. 1 Outdoor

150

150

200

130

70

250

100

150

300

100

150

50

400

90

160

150

500

90

160

150

100

600

90

160

175

175

700

90

160

175

175

100

No. 2 Outdoor

150

115

35

200

100

100

250

90

100

60

300

90

100

110

400

80

100

120

100

500

75

100

120

120

85

600

75

100

120

120

185

Distance Between Nozzle Lines For Outdoor Irrigation

Nozzle, No.

Pounds pressure

Distance between lines, feet

No. 1 Outdoor

10

40

20

50

40

56

45

56

50

54

75 and over

50

Nozzle No.

Pounds pressure

Distance between lines, feet

No. 2 Outdoor

45

60

75

60

80

56

100 and over

50

The greater the pressure the finer the spray; but after reaching a certain pressure the spray is so fine that it retards the flow of water and reduces the distance of throw. It follows that when the pressure is so high as to produce these results, the lines must be installed slightly closer together, according to the preceding table. The above pressure refers to pressure at nozzles.

Figure 18 shows the overhead system in use at the Pennsylvania State College. A lever is provided at one end of each nozzle line, by means of which the entire line is easily turned. When in operation, the line is kept in one position until a strip of land has been sufficiently watered, and then the line is turned so the spray will fall on unwatered ground. It takes only a few seconds to turn each line and the attendant may be engaged in other work, making the rounds of the pipe lines as often as may be necessary. If watering is attended to systematically, it is probably never desirable to apply more than an inch of water at a time. The numerous bulletins issued by the manufacturers of the drills, nozzles and unions give additional details concerning the installation and operation of this system.