FIVE-ACRE FIELD
| Without Sewage. | With Sewage. | ||
|---|---|---|---|
| Lot 1. | Lot 2. | Lot 3. | Lot 4. |
| 20,814 | 33,244 | 60,602 | 73,564 |
| 18,294 | 62,514 | 77,299 | 71,766 |
| 11,069 | 49,851 | 78,231 | 80,941 |
| Aver. 16,725 | 48,536 | 72,044 | 76,434 |
It will be noticed that, whereas without sewage the amount of green grass was about eight tons on an acre and a quarter in the field, from lot No. 2 twenty-four tons were cut, from lot No. 3 thirty-six tons, and from lot No. 4 thirty-eight tons. Evidently the amount of sewage applied did not proportionately increase the yield in lots 3 and 4, and it may be said that a depth of sewage or water of more than twelve inches per acre has, in general, been found to be not merely unnecessary, but undesirable. The table does not show the number of cuttings made during the season, but the custom on the farm is to cut frequently, at intervals of perhaps two or three weeks, no time being given for curing the hay.
The crops suitable for growth on irrigated fields have been found by experience to be grass and root crops, such as beets, turnips, and the like. Mr. Wilcox, in writing of the requirements of different plants, suggests celery as a garden crop that needs a great deal of water. Beets, carrots, parsnips, and turnips are favorite plants for irrigated fields. Cabbage and cauliflower are benefited by abundant irrigation during the first part of their growth, but after the heads of the cabbage plants are half-formed, further excessive use of water is undesirable. The use of irrigating water in orchards has been practised with great success not only in the recent irrigation areas of the West, but along the Hudson River and in New England. The size of the fruit is increased by irrigation, and it is said that the bloom is much improved.
Methods of Applying the Water
In distributing the water or sewage over the soil in the case of a single house, no elaborate methods are required. In the case of large farms supplied with sewage from a considerable population, elaborate systems of piping or open-channel conduits are required, and the problem of working out and adjusting the necessary sizes and grades becomes a complicated matter for which engineering knowledge and experience are required. But for the small flow which comes from individual houses and from the small area involved, no such elaborate preparations are required. The essence of the distribution consists in carrying the water onto the field to be irrigated at such a low velocity that no surface soil or valuable manures are washed away; and in adjusting the volume of the flow and the requirements of the soil, there are three characteristic conditions which require different treatments.
In the first place, the area may be practically level and the crop raised may be either grass or grain. In such a case the sewage should be led onto the field which may properly be enclosed on four sides with a low, that is, six to twelve inches, earth-dike, and at each irrigation the field may be flooded about two inches deep. The next irrigation would probably not be required for a week, so that this method requires a number of beds to be worked one after another and, except where the soil is very dense, so much so that percolation is very slow, this method is not suitable because of the slow rate at which the sewage is delivered.
The second method of distribution, and one more suitable for the conditions under discussion, is to lay out the field in parallel beds from three to six feet wide and from forty to one hundred feet long. These beds are separated by furrows into which the sewage is discharged. If the grade of these furrows is properly adjusted to the porosity of the soil, that is, made about six inches in one hundred feet for open, sandy loam, and about two inches in one hundred feet for fine, clay loam, the soil will absorb the needed moisture as the sewage flows over it and there should be no ponding or excess of water at any point of the field. By dividing the field into three parts, or in arranging the flow of sewage so that it enters only two or three furrows at a time, the flow can be so changed from day to day as to furnish all parts of the area with the irrigating water, and at the same time not overload and choke the soil particles. On the beds may be planted and grown whatever vegetables are desired. A good basis for determining the area and length of furrows required is to provide a length of thirty feet of furrow for each person of the household. The total length thus obtained should not, however, be made continuous, but should be arranged in three parts, or in multiples of three, so that one-third of the total length only may be used on any one day, the other parts serving for other days, so that a rotation is practised.
Fig. 48.—Distribution of Sewage and Arrangement of Check Levees on a Hillside.