IRRIGATION IN HUMID REGIONS

By R. P. Teele

In arid regions irrigation is a necessity if agriculture is to exist, and the only questions relate to methods of securing water and of applying it. In humid regions, however, agriculture is being practiced successfully without irrigation, and it becomes not a necessity, but a means of insurance against drought, or of increasing production, similar to the use of fertilizers, crop rotation, or practicing cultivation. It belongs, therefore, to an advanced state of agriculture, where new land convenient to markets is no longer available and increased demands for agricultural products must be met by securing larger returns from land already in use, rather than by bringing larger areas into cultivation. For this reason irrigation is practiced but little in the humid sections of the United States; but it may be expected to become more general in the future. On the other hand, in the thickly settled countries of Europe irrigation has been practiced for centuries in regions where the rainfall is as great as that in the eastern half of the United States, and where irrigated fields are interspersed with those that depend on rainfall alone.

Great Britain, Holland, Germany, Switzerland, Italy and France. Water is kept running over the meadows almost continuously, especially in winter, when it prevents the freezing of the ground and keeps the grass growing. In Italy marcite, a mixture of clover and Italian rye-grass, is grown in this way, and yields of 10 to 15 tons per acre to each cutting, and 8 to 12 cuttings per year, are reported. In the other countries mentioned, the meadow lands susceptible of irrigation are considered among the most valuable lands.

In the United States the irrigation of meadows in the manner just described is not practiced, but

The occasion for irrigation arises, not from a deficiency in the total amount of rainfall, but from its uneven distribution, making alternating periods of abundance and scarcity. The frequency of periods of drought of greater or less duration is well illustrated by the rainfall record of Philadelphia, which may be considered typical of the humid region. This record is taken because of the length of the period covered, 1825 to 1895. During the seventy years covered, the rainfall was at least one inch below the normal in some month of the growing season in 88 per cent of the years; dry periods of two months occurred in 56 per cent of the years; and shortages covering three months occurred in 30 per cent of the years. The frequency with which different crops will suffer depends on their ability to survive periods of drought. According to the record, crops having short growing periods will be injured in at least 88 per cent of the seasons; annual crops generally will be below the normal in about half the years; while all crops will receive too little water in about one-third of the seasons. It follows that irrigation is of greatest value for those crops that suffer most from short periods of drought, that is, for garden truck, the growing season of which covers but a few weeks; and smallfruits, which dry up and become worthless if a drought occurs at the time of ripening. It is of great value for meadows also, since the growth of grass depends on a continuous supply of water. Irrigation of meadows.

In European countries the irrigation of meadows has been practiced for centuries. This is true of

there seems to be no reason why it should not be where the large quantities of water required can be secured easily, and especially where sewage water is available. The use of sewage water in this way would be of great benefit to agriculture, would produce no unhealthful conditions where it is used, and would prevent the pollution of streams by discharging the sewage water into them, which is a growing evil.

The irrigation of meadows at times during the summer, however, is practiced to a certain extent in the humid parts of the United States. Reports from four counties in Pennsylvania,-Lancaster, Berks, Lehigh, Northampton-show about 800 acres of irrigated meadow, the yield from which is about double that from similar meadows not irrigated. With few exceptions, these meadows are on low land to which water from streams can be applied easily by gravity. The stream is tapped above the meadow and the water carried in a ditch having less grade than the stream, which will bring the water higher than the land to be irrigated. Ditches are run through the land, and the water turned out from these through cuts in the

banks and allowed to spread over the ground. In order that the land may be wet uniformly, it is necessary that the land be smooth and nearly level. Fig. 604 illustrates the method of flooding meadow land. AB is the main supply ditch, while CD and EF are smaller ditches running through the meadow. The supply ditch is dammed at A until enough water has entered CD to wet thoroughly the land down as far as EF, when the dam at A is removed, the head of CD is dammed, and the water flows down to the dam at B, which turns the water into EF, from which it flows out on the land below that ditch. The usual custom is to allow the water to run on a field continuously for three or four days, then shut it off for periods varying from three or four days to a month. When a meadow

Fig. 604. Flooding from field laterals.

is used for pasture, the best practice is to divide it, and irrigate one part while the other is being pastured. There is little expense to this kind of irrigation. There are a great many places where small streams flowing through meadows can be put to use by the construction of small dams and ditches which require almost no cash outlay and only a little labor.

Irrigation of small-fruits.

Small-fruits, as berries and currants, do not require large quantities of water, but the lack of water at the time of ripening causes small and seedy fruit, reducing both the yield and the quality. In years when such droughts do not occur there will be little benefit from irrigation, but when they do occur the benefits will be great. Experiments made by the New Jersey Experiment Station covering three years showed a very large gain from irrigation in one year and no gains in the other two years. The same is found to be true by persons raising small-fruits on a commercial basis. The profits in the dry years are more than sufficient to pay the fixed charges for the years when the equipment is not in use, as well as the expenses in years when irrigation is necessary.

Irrigation of truck gardens.

Truck gardens show the greatest profit due to irrigation, and a large number of gardeners in the vicinities of large cities practice it. Few of these persons keep records of cost and profits, but all agree to the great value of irrigation. In ordinary years it increases the yields, and in dry years it means a full crop instead of no crop, the returns in a single dry year often being equal to the first cost of providing a water-supply.

Irrigation of field crops.

Field crops are not generally irrigated, but experiments conducted by Professor King at the

Wisconsin Agricultural Experiment Station go to show that it would be profitable in many cases. Compared with average yields for the state, the average increase in the yield of clover hay on irrigated land over that from unirrigated land was 21 tons per acre; the average increase in yield of corn was 26.95 bushels per acre, and potatoes showed an increase of 83.9 bushels per acre. The annual cost of irrigation at Madison, Wis., was $6.68 per acre, not including interest on the first cost of equipment, but including all extra labor. At current prices this leaves a net profit of about $20 per acre on hay, $11 per acre on corn, and $14 per acre on potatoes. It should be noted that the returns are compared with the averages for the state, which is hardly fair, as irrigation will be practiced only by the industrious, careful farmer, and the returns should be compared with those received without irrigation by equally good farmers. Data for this are not available; but it is believed that where water can be secured cheaply irrigation of farm crops will prove profitable.

Methods of applying water.

Throughout the humid part of the United States there are in general use two methods of applying water to fruit and garden crops-in furrows and by sprinkling. The sixty plants or establishments reported in a bulletin of the United States Department of Agriculture issued in 1906 are about equally divided between the two.

The furrow system.-The furrow system has the great advantage in cheapness and simplicity, and for this reason is preferable where it can be used, but it is not adapted to all kinds of land. The

crops irrigated are, for the most part, shallowrooting, and in light sandy soils water run in furrows soon sinks out of reach of plant-roots and is lost to them. Therefore, the system is best adapted to comparatively heavy soils. Water is brought to the highest side of the tract to be watered and from there run in furrows between the rows of plants. The furrows must have only a light slope away from the ditch, or the water will run through rapidy without soaking into the soil, and waste at the lower end. If the land is nearly level, the supply ditch or pipe may be run along the highest