Farmers Review Africa May/June 2017 Farmers Review Africa

Supplement over the eld out of the way of the crops. Sprinklers or spray nozzles can be Controls and movements spaced along that pipe to apply water wherever the pipe is traveling. At each e pivot's control panel operates the main functions of the machine. tower, pipe sections are connected with exible joints that allow the pipe to Depending on which control panel the pivot has, the controls will be move through a limited range without twisting or breaking. is exibility diﬀerent, but the way the pivot operates is the same. When a command is also allows vertical bending that enables pivots to climb moderate hilly entered into the control panel, an electrical signal is sent down the pivot slopes. until it reaches the Last Regular Drive Unit. 480 VAC then travels through a motor lead cable from the tower box to the engine. e LRDU moves, either Most centre pivots irrigate a circular area a quarter-mile (0.4 kilometer) in forward or reverse, as the control panel indicated. radius, although some can cover a larger area. Centre pivots are typically When a pivot moves, it is led by the Last Regular Drive Unit. e LRDU less than one-third of a mile (0.5 kilometer) in length. Most manufacturers moves until the switch arm, connecting the last span to the second-to-last oﬀer a way to adjust the speed of the pivot, and thus the amount of water tower, is pulled to an angle that activates the next tower. Both towers then being applied over a given area, a process called Variable Speed Irrigation move until the next tower is activated, and this continues down the pivot (VSI). until all towers have moved. e vast diﬀerences in crops, soils, farming practices and climatic conditions worldwide, coupled with regional diﬀerences in the availability of water and energy resources requires a diverse array of centre pivot sprinkler performance. Maximise irrigation eﬃciency Irrigation eﬃciency involves the ability to minimize water losses. Such factors as loss of water from wind dri and evaporation from the soil surface and plant aﬀect the level of eﬃciency. Meanwhile, another factor of irrigation eﬃciency is simply getting water into the soil, and controlling runoﬀ. For mechanized irrigation, the biggest single advancement towards increasing irrigation eﬃciency has been mounting the sprinkler down out of the wind on drop tubes. Enabling the success of drop tubes are products that spread the water out over a wide area, even when mounted below the truss rods of a centre pivot. ese rotating and spinning devices operating at low pressure have dual bene ts – increased soak time and low application rates. A more complete throw pattern can give twice the soak time of xed sprayheads. Why is sprinkler throw distance important? Without sprinkler performance that can apply water at an application rate that more closely matches the in ltration rate of the soil, the eﬃciency gained with drops and money saved with low pressure, is soon lost to runoﬀ. e rate at which a centre pivot applies water increases with the higher ow demands required at the outer portion of a centre pivot. By increasing the wetted throw distance of the sprinkler, the rate at which water is applied can be reduced to match the soil's in ltration rate. Look at a typical in ltration curve below with superimposed application rates for centre pivot sprinklers. It is obvious that the Rotator, which provides the widest throw distance on drop tubes, comes the closest to matching in ltration rates of the soil. e best condition for in ltration is to keep the soil surface open and apply water using a wide application width. Why be concerned with runoﬀ? Runoﬀ is one of the most environmentally sensitive issues involved in irrigation. Runoﬀ can result in unwanted water and fertilizers being carried into streams and rivers. Additionally, soil erosion is not only a pollution issue, but results in lost fertilizer and lower overall crop growth. Increased runoﬀ means lower application eﬃciency which increases operating costs www.farmersreviewafrica.com [41] FARMERS REVIEW AFRICA May - June 2017

Farmers Review Africa May/June 2017 Farmers Review Africa | Page 41