Efforts To Meet Urgent Need For Irrigation Facilities In Citrus Orchards

Bay of Plenty Times, Volume LXXVI, Issue 14636, 3 April 1948, Page 4

Efforts To Meet Urgent Need For Irrigation Facilities In Citrus Orchards

The Primary Producer

EQUIPMENT ALREADY INSTALLED IN 26 UNITS AT KERIKERI

Equipment fcr the irrigation of citrus trees has _alreacly been installed in no fewer than 29 orchards at uimm, ■ • p Everett orchard instructor, Kaikolie, m the how /ealand Journal of Agriculture. Results of the application ot even relatively small quantities of water are distinctly encouraging and this article is intended as a guide to irrigators in tnat locality. . i i . On many occasions since the first commercial citrus orchards were planted at Iverikeri in 1929 individual growers have considered seriously the possibility of providing water ±or_ irrigation. The mean'monthly rainfall at Kerikeri is about b.obm., and the lowest mean for any month is Jin., hut frequently periods occur when the surface soil to»a depth of about bin. is believed to lack sufficient moisture tp maintain citrus trees in full vigour.

The factors mainly responsible for bringing about that condition and accentuating the consequent ill effects on the trees are: —

1, The crumb structure of the soil permitting the rapid loss of soil moisture by evaporation to a greater depth than in soils that are more binding.

2. The porous nature of the soil permitting excess water to drain away rapidly. 3, A low water table (probably more than 15ft. below the soil surface in most orchards).

4. The firmly-compacted nature of the subsoil, tending to _ confine the development of the main feeding roots of citrus trees to the surface soil. Observations made over many years by old-established orchardists, and supported by rainfall records in more recent years, indicate that reiatively-dry periods occur mainly from October to March and that when they occur, particularly during October, November, or December, they invariably _ have an adverse effect on the setting of the fruit from the main spring blossoming or cause on appreciable dropping of the fruits shortly after setting, resulting in lighter crops. The exceptionally severe drought periods experienced during the 1945-46 and 1946-47 seasons, together with the ■.evidence secured from an extensive series of soil moisture tests taken in orchards at Kerikeri during the 1945-46 season, still further demonstrated the need for orchard irrigation.

Several streams- traverse cr skirt the fruit-growing area, and the water in all of these has' been analysed and found suitable for irrigation. These streams have also been • measured to ascertain the quantity of water available in drought periods. Present Equipment The urgent need for the irrigation of orchards in the 1945-46 sesaon and again in 1946-47 induced many growers to install pumps and pipelines from adjacent streams or bores to their orchards. One of those installations was completed in 1945 and several more early in 1946, but a far greater number were not completed until the 194647 season. In many cases where the only water available is from bores concrete reservoirs have been built, ranging in capacity from 5000 to 40,000 Most of those reservoirs are near the residences of the owners, and when the reserve of water is not required for irrigation the reservoirs are used as swimming pools. The pumps installed to supply water to individual orchards have capacities varying from 120 to about 1500 gallons an hour. :

During the 1946-47 drought period most irrigators applied from 80 to 100 gallons a tree at each irrigation, but in at least one case about 600 gallons a tree was applied. The number of waterings during that season ranged from one to seven and the frequency of applications varied from 10 to 21 days, with few exceptions, during rainless periods. Intervals between waterings in excess of 21 days were necessary in some orchards because insufficient water was available fcr the applications to be made more frequently. In most cases the water is carried through the centre of the orchard in permanent mains of galvanised piping. From the mains the water is taken at right angle along the rows df trees, a variety of rubber and canvas _ hose and piping‘being used fcr this purpose. In some orchards light, portable pipelines with quick-counlmg devices are used to convey the water from the main. These are fitted with roses or spray jets at tree intervals. Where the water supply is adequate the portable laterals are placed- / midway between the trees and the water sprayed as far as the trees on either side, thereby irrigating the whole of the area. Where the water supply _ is insufficient for complete irrigation a supplementary irrigation is secured by placing the lateral pipes beside the trunks of the trees and allowing the water to be sprayed upward into the branches; the foliage breaks the spray and the water falls under the spread of the trees. In other instances a tap is fitted to the lateral pipeline opposite each tree,* or several lengths of rubber hose are used to convey the water from one tap to a number of trees. In such cases a sprinkler is attached to the outlet end of each hose or no spraying device is used and the water is allowed to flow at will. Uniform Flow Of Water Where the water is being carried from the lateral pipeline to _ individual trees by rubber hose, it is possible., to water four trees at one time from a single tap by the use of a distributor having a single intake and four outlets. To give a uniform flow of water from each outlet when operating on uneven ground, the aggregate size of the sour outlet apertures must be less than the size ' of the intake aperture. Where the pump capacity was 250 gallons an hour a locally-made distributor of the following dimensions appeared to give satisfactory service; A cross of 2in. galvanised pipe had all ends fitted with a reduction socket of a size to fit into the hose that conveys the water to the trees. Inside each reduction socket the aperture was reduced to rlin. diameter by welding in a nut of suitable dimensions. On the top centre of the cross was cut a hole, over which was fitted a short' upright length of pipe, to which was attached a length of lin. hose conveying the water from the portable lateral pipeline. So far no systematic trials have been undertaken in the area co determine the effects cf complete or supplementary irrigation or to ascertain the minimum quantity of water or the frequency of application necessary to maintain trees in full vigour. Until , that data has

I been secured by well-planned field trials no definite system can be recommended with complete confidence. Observations made during the period of soil moisture testing mentioned indicated that permanent wilting of the foliage occurred at about the same time as the surface 6in. of soil reached wilting point, and that several weeks before the wilting of the foliage there was appreciable dropping of mature foliage and young fruits. Throughout the 1945-46 drought period the soil moisture content 6 to 12in. below the surface never reached wilting point. The extremelyshallow rooting‘system of all citrus trees in the locality is no doubt a major factor in bringing about this early adverse effect of drying out of the surface soil. Further observations indicated that where 80 gallons of water a tree was applied to 10-year-old trees showing 100 per cent, foliage wilt, and the water was spread uniformly over the area covered by the spread of the tree, the whole of the foliage resumed normal freshness in not more than four hours after the application and no further wilting occurred during the following 14 to 21 days. In another case 12 gallons of water applied to six-year-old trees showing 100 per cent, foliage wilt caused the foliage to resume normal freshness but further wilting occurred from 5 to 8 days later; in that case the water penetrated to an average depth of about 3in., and the high evaporation rate under such conditions no doubt accounted for the early resumption of foliage wilt. During drought conditions tests were made to ascertain the extent to which irrigation water spread on and beneath the soil surface when applied to a single point beneath a mature citrus tree. In one typical test where there was a gentle slope water had been applied 24 hours previously at the rate of 33 gallons an hour for three consecutive hours; the area of the soil surface wet to a greater depth than 2in. was about 5 square feet, and beneath the surface the water had spread at an angle of about 45 degrees from the margins of the wetted area and had penetrated deep into the subsoil, where there were extremely few tree roots and where the moisture content was adquate without irrigation. In all instances where the furrow system of irrigation was observed in cultivated land there was evidence of appreciable soil erosion.

General observations made in a large number of orchards during both of the drought periods referred to indicated that defoliation and dropping of young fruits began earlier in orchards sown down in pasture and mowed regularly than in comparable orchards where a fine tilth 3 to 4in. deep was maintained. Orchards thatwere cultivated in early spring and received little or no further cultivation to maintain a tilth or check weed growth appeared to show evidence of drought effect equally as early m the season as the orchards that were sown down in pasture. Factors for Consideration From the evidence at Kerikeri to date it is suggested that irrigators in that locality when planning for or carrying out irrigation give serious consideration to the following:— 1. The fact that defoliaticn and dropping of young fruits begin before the soil moisture percentage in the top 6in. reaches wilting point suggests that factors other than soil moisture are involved. Possibly the availability of sufficient nutrients is the principal factor. Analysis of Kerikeri orchai’d soils has shown that the main concentration of nutrients is extremely near the soil surface and that the buildup of nutrients in the subsoil has been relatively small, even in wellattended orchards. Therefore it follows that trees depend mainly on the top 6 or Sin. of surface soil for their supply of nutrients, and it trees are unable to draw nutrients from the surface soil to a depth of say 3 to Sin. because of insufficient soil moisture, it is logical to expect that they will be unable to maintain the vigour required to develop a full crop. Furthermore, the loss cf foliage must in turn reduce the amount of plant food available to the_ trees. The application of irrigation water before the moisture in the surface soil to a depth of 3 to Sin. has reached wilting point is therefore recommended.

2. The feeding roots of citrus develop nearer to the soil surface under the spread of the tree than beyond that area, so the area within the drip circle requires irrigating earlier than other parts. it is expected that the area outside the drip circle will require to be irrigated before the soil moisture reaches wilting point to the depth of the main leading roots if the trees are to be maintained* in full vigour. . 3. As the feeding roots are practically confined to the surface 10 or 12in of soil, and the soil moisture at a greater depth has never been known to reach wilting point at Keiikeri, the maximum use of irrigation water would be secured bv applying only sufficient to saturate il e soi M° a depth of not more than lit. lo prevent neadiessly-deen penetration of the water and to ensure an even distribution over the area to be watered ?the use of sprinklers or spray jets is essential. 4. Though no accurate tests have been made, it is estimated th*t the water required to saturate the area within the drip cixcle of a mature 9rS US O on ee tQ a T ? e ? th of lft is a bout 200 gallons. Ic is suggested ‘that irrigation installations should provide at least for the supply of this quantity of water every 10 to 14 days. o. oufficient jets or sprinklers should be provided to irrigate at least one thirty-sixth of the trees in an orchard with not less than 200

gallons each at the same time. This envisages a six-day, week and three shifts a day at about four-hourly intervals, which would enable the shifts to coincide with the ordinary breaks in work for meals, and at the end of the last watering for the day—say 9 p.m.—the system could be simply turned off, leaving the moving of pipes until the following morning. As there is an urgent need for further information on the effects of irrigating citrus trees under New Zealand conditions, all irrigators are requested to keep records of the dates of irrigating, the quantity applied per tree, and the extent of the area to which the water is applied, so that data can be accumulated and used as a guide for future operations.