|Irrigation management is recognized as one of the major components which have to be increased in order to obtain a corresponding increase in yield, i.e grain number per spike and grain size. In order to achieve these increases, the wheat or barley seed crops should not be subjected to moisture stress at any stage of the growth cycle. The seasonal water requirements is in the range of 450-500 mm.
The period of minimum water use covers the germination, tillering and jointing stages. The root system extends to a depth of over 70 cm during the first eight weeks. The soil should be wet to this depth either before planting or by an irrigation shortly after planting. A light irrigation immediately after planting encourages even germination.
There is no benefit from induced water stress in the early stages since this may reduce tillering and adversely affect spikelet initiation. However, water use in the first months is small and once the soil has been wet to 70 cm only one further irrigation on sand and clay loams, or two on sand veld soils, will be necessary between emergence and shooting, i.e. up to about six weeks.
The period of increasing water use covers the growth stages from shooting to ear emergence. Water stress can substantially reduce yields, and irrigation should ensure a moist soil at this stage, i.e. about eight weeks after emergence. In the cool weather up to the end of July an irrigation of 50 mm every ten days on sandveld soils, or 80 mm in fourteen days on sand clay loam soils will be sufficient.
The period of maximum water use about four to six weeks, i.e. from about mid July to August, starts with ear emergence at about nineteen weeks after sowing and continues through flowering and grain formation to the soft dough stage. The crop uses water at about 4-5 mm/day and irrigation of 50 mm in seven to nine days on sandveld soils, or 80 mm in ten days on sand clay loam soils, will usually be sufficient. Lack of moisture during this period will adversely affect both grain number per spikelet and grain size, and may result in sterile ears at harvest.
The period of decreasing water use starts at the end of the soft dough stage, i.e. at about 15 weeks from planting and continues through the hard dough stage to ripening.
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