AMOUNT AND FREQUENCY OF Ininnanox. The conditions that must be taken into consideration in determining, the amount of water to be ap plied are: (I) The storage capacity of the soil, (2) the depth to which the roots of the particu lar crop penetrate, (3) the rate at which water will rise from the soil below the root zone, and (4) the dryness of the soil and the sub soil. The frequency of irrigation will be de termined by: (1) The amount of available mois ture which the soil can store, (2) the rate at which moisture is lost by transpiration through the plant and by evaporation from the soil, and (3) the degree of dryness of the soil which the plant will tolerate without injury. Where the soil is deep and mellow the roots of plants extend to a great depth and over a wide area. Thus having a wider field from which to draw supplies of moisture and plant food. the actual percentage of moisture in the soil may lie smaller without detri ment to the plant than if the root-feeding was more restricted. Again, compact, elayey soils hold moisture so tenaciously that plants growing on them begin to suffer for moisture, even when the soil contains a percentage of water which in ease of less tenacious, sandy soil would he abundant for the plant's needs. The aim in irri gating should be to apply simply enough water to meet the needs of the plant without loss in the drainage. It is well to bear in mind in attempt ing to accomplish this desired result that plants vary in their water requirements at different stages of growth. Edmond Gain reports inves tigations which indicate that at the time of plant ing the soil should have about 25 per cent. of the total amount of water which it is capable of holding, then it should fall to 15 per cent. and remain at this point until the first leaves are formed, when it should be raised quickly to nearly 40 per cent. It should he allowed to fall rapidly to about 25 per cent. and remain at this point until shortly before flowering, when it may be raised gradually to 40 per cent. and then
flowed to fall rapidly to 12 or 15 per cent., wItere it remains during fruiting and maturity. King has found that a crop of maize yielding 70 bushels per acre can be brought to maturity in 110 days with 11.75 acre-inehes of water, applied in 3 irrigations at intervals of 37 days on soil of medium texture, or in 5 irrigations at inter vals of 22 days on the most open soil. With higher yields the number of irrigations has to be correspondingly increased. A crop of wheat yielding 40 bushels per acre requires 12 acre inches of water, applied in 3 or 5 irrigations according as the texture of the soil is medium or very coarse. Barley yielding, CO bushels per acre may be brought to maturity in SS days with 12.84 acre-inches of water applied in 3 or 5 irri gations, at intervals of 20 and IS clays, on medium and coarse soils respectively. Actual practice varies widely in different parts of the world. Three to five irrigations seems to be about the average for wheat. With maize it varies from 3 in Italy to 15 in Egypt, but 5 to 7 irrigations appears to be about the average. it is usual to give only one irrigation for each crop of clovers and alfalfa. Water meadows are irri gated as often as the water-supply will permit. The practice with potatoes is to give 2 to 4 irriga tions, according to the slope and texture of the soil, beginning when the plants have nearly or quite reached the blossoming stage. In actual practice the intervals between irrigations of fruit trees and vineyards vary from 7 to 40 (lays. According to Wiekson, fruits in California re ceive 2 invites of water per month during May to August, on retentive soils, and :3 inches during the same period on coarse soils. culture the laud is kept flooded the greater portion of the time during the growth of the crop. Ac cording to :Maxwell, it is a common practice in Ilawaii to apply 200 to 250 acre-inches of water to sugar during a growing period of IS to 20 months, although experiments have shown that 100 acre-inches is ample.