Open access publications in the SLU publication database

Abstract

During the summer of 1982 the Division of Hydrotechnics at the Swedish University of Agricu1tural Sciences bought an irrigation boom from F:a Deier1ing, West Germany. The boom, which is a prototype, is 45 m wide and equipped with 17 def1ector nozzles. Each nozzle is fitted with a pressure regulator so that the fall in pressure along the boom does not inf1uence the flow from the nozzles. The pressure requirement is low; 0.4 - 0.5 MPa (40 - 50 m water column) is sufficient as inlet pressure to an irrigator if a boom is used instead of a spray-gun. The water distribution of the boom was determined during a number of days in August, 1982. The distribution of water was uniform, but not as uniform as given by a good spray-gun under ideal conditions (no wind, correct spacing, correct working pressure). On the other hand, neither the spreading pattern of the boom nor the spacing are influenced by the wind. During the measurements the wind was so strong that it would have been impossible to irrigate with a spray-gun. In practice the boom spreads water more evenly than a spray-gun. The boom gives a very high mean intensity (ca 100 mm/h) but a German investigation reports that the water is delivered in the form of relatively small drops (d<1.6 mm). This implies that the supply will be gentle in comparison with the recurring downpours of the spray-gun. Thus, boom irrigation should be well suited for sensitive crops and soils with weak structure. When the nozzles on the boom were tested on a number of different soils the results were better than expected; surface water formation was negligible or non-existent and only in one case was puddling considerable. The proportion of very small drops is much lower in water from the nozzles on the boom than in water from a spray-gun. Consequently, as the boom spreads the water close to the soil the risk of aerosol formation will be much less than with a spray-gun. This is important when partially cleaned sewage water is used for irrigation. Measurements were also made of the water distribution pattern for individual nozzles and it was calculated that the optimal nozzle spacing was 3.0 m, which is in good agreement with the 2.8 m reported for the boom. The nozzles give double overlapping and droplet trajectories with large angles of impact. Because of this, the spreading pattern of the boom is relatively insensitive to variations in the distance to soil surface/crop. As regards labour considerations, the boom is much more complicated than the spray-gun. On account of its working width usually being smaller, the boom requires more frequent moves. With the design of the prototype, each move will, in addition, take longer to accomplish and includes a couple of heavy tasks, provided that it cannot be moved in extended form. By making a number of simple modifications both time and labour can be saved when moving the boom, but it is probably impossible to completely achieve the same flexibility as of the spray-gun. From the energy viewpoint, the boom is clearly superior to the spray-gun. mainly on account of lower working pressure but often also due to more uniform spreading and thus lower water requirement. The saving in energy may sometimes be sufficient to pay for both the boom and extra labour required by the boom. In most cases, however, other advantages of using the boom for irrigation should be considered in assessing whether there is justification in selecting the boom in favour of the spray-gun.