Grain Guide 2018

4 5 6 7 8 Soil Water retention capacity : This is an impor­ tant attribute that determines the manage­ ment of the system and whether it will be pivot, overhead or drip irrigation. A bigger water holding capacity means that a larger application can be applied, and in this way rainfall can be utilised better. Smaller applications, causing lower water stress, ensure better growth conditions and higher yields – a typical application for drip irrigation. Smaller applications should be avoided with pivot irrigation, as crop losses can be high. Infiltration : The application rate of any system should adapt to the infiltration ability of the soil. The application rate of pivots can vary between 20 and 80 mm/h and the soil should have the ability to absorb the water without run-off. Distribution : With drip irrigation, it is important for lateral water movement to occur below the dripper. Generally two crop rows are serviced by one dripper line. Spacing between the drippers and the lines should therefore be such that both the crops rows can benefit from it. For seed germination, the dripper line is usually moved for better water distribution.  Topography Topography plays an important role in the layout and use of the irrigation system. As a general rule distribu­ tion laterals should be parallel to the contour and feeding lines should be parallel to the slope. The design is better adapted hydraulically and the system functions better. It is also easier to execute the soil conserva­ tion programme. When an irrigation pivot is used on a steep slope, the hydraulic difficulties can be overcome by pressure regulators, and with drip irrigation, pressure-compensated drippers can be installed. Costs will obviously be higher in both cases.  System aspects Various systems are currently available in the market. Each one is unique in the sense that the system is designed for the specific topography, soil and crop characteristics as well as the water availability on the farm. Designs should be left to expert, quali­ fied people. It is the producer who will pay for the system and it is therefore his privilege to appoint the designer and his right to ensure that the system adapts to his requirements and needs. Therefore, check the advantages, dis­ advantages, limitations and manage­ ment aspects before any system is acquired.  Costs The costs of irrigation systems depend on various factors and it is always important to obtain the capital as well as operating costs of a system. The following can be used as a guideline for the capital costs: Flood – Basin R15 000/ha Static – Sprinkle R25 000/ha  – Drip R50 000/ha Moving – Pivot R40 000/ha  – Traveling gun R20 000/ha Purchasing The choice between different systems lies with the producer’s preferences, what his neighbour says about a system, the service a firm provides in the execu­ tion, thoroughness, accuracy, aftercare, years in operation and whether the firm will still be around in a few years’ time. Financial planning is obviously also important and it is good to do a cash- flow analysis and to analyse the balance between capital costs and operating costs. It is better to make a mistake on paper than to lose a farm! To summarise It is important to consider all the different systems and to make good decisions. Calculate, talk to ex­ perts and allow a designer to design a system that suits your needs as producer, the soil and the crop. Felix Reinders, ARC-Agricultural Engineering 113 Irrigation