8 Jan., 190S.] Irrigation Methods. 31 



IRRKIATIOX METHODS. 



A. S. Kenyon, C.E., Engineer for Agriculture. 



A correspondent writes asking for some notes on the amount of water 

 necessary for the growth of different crops, the best means of applying 

 the water, the number of applications and the periods of the year for 

 watering. This makes too much of a demand upon the limited space 

 available for "Answers to Correspondents"' so that the reply is given 

 here in the ordinary pages of the Journal as being of general interest. 



In the first place, the volumes of water required for the full growth of 

 various crops will varv much. Water is directly required by plants for 

 transpiration or evaporation through the surfaces of their leaves, conse- 

 quently the amount of foliage is an important factor, and for the forma- 

 tion of their actual bulk, of which water is a large constituent, running, 

 in some cases, over 90 per cent. ; but its greatest service is in dissolving 

 and thus rendering available,' the plant foods contained in the soil. In 

 manv parts of the State, winter crops get sufficient moisture from the 

 heavens far all their requirements, at any rate with proper cultivation, 

 while the same may be said to a less degree of summer crops. The latter 

 mav be successfully grow^n, without artificial aid in watering, over large 

 areas where thev are at .present either whole or partial failures, by the 

 adoption of improved methods which are, in general, sowing in drills 

 sufficienth wide apart to permit of cultivation and, especially after rains, 

 the frequent use of the horse-hoe or scuffler, between them. But in other 

 localities — over the greater part of our Northern districts — winter crops 

 require additional moisture in many, nay, most years, and the summer 

 crops alwavs. The supply of these requirements is met by irrigation which 

 may be derived from public works under the State Rivers and Water 

 Supply Commission or from private sources, such as pumping plants or 

 by the construction of dams. It is well to bear in mind that by the Water 

 Act 1905, the water in all rivers, creeks, lakes, lagoons, or marshes, even if 

 wholly on private land, is the property of the Crown and can only be used 

 lawfully for irrigation under the authority of the Commission. True, 

 riparian owners are entitled to the free irrigation of 3 acres ; but only in 

 direct connexion with a homestead or for its service so that the exception 

 is only trifling. Licences to divert water from any source may be obtained 

 on reasonable terms and give a much desired security of tenure. 



Having obtained the water, care must be taken in applying to the 

 ground so as to make a thorough job of it. Mere soaking of the top few 

 inches only means early loss by evaporation Avith but little water reaching 

 the sul)Soil to be there stored for future use. Surface roots are 

 encouraged and a brief stimulus given the plant, too soon to be lost. As 

 water cannot be forced into the ground, sufficient time must be allowed 

 for it to .soak in add penetrate to a reasonable depth. The time necessary 

 may be as little as 14 hours but will generally amount to 24 or over. The 

 volume of water necessary will depend upon the character of the soil and 

 upon the method of distributing adopted ; the rooting character of the 

 plant will also be a factor, tomatoes and lucerne for instarre requiring 

 Aery different volumes. The volume may vary from 3 inches or under to 

 as much as 20 inches in depth over the whole surafce. The most usual 

 depth is found to be about 7 inches. One inch in depth OAer a surface of 

 one acre is equivalent to 23,000 gallons or 3,630 cubic feet. 



The best means of distributing the water so as to reach the plant's 

 roots, is undoubtedly by underground perforated pipes ; but this is a very 



