In an average precipitation level year (402 mm), the upper limit
of Grade B of the irrigation amount was chosen for the greening
stage, branching stage and budding stage, and the upper limit of
Grade C was chosen for other stages. The calculated irrigation demand
is 212 mm. Assumed that the irrigation coefficient is 0.9, the
optimum irrigation in the whole growth period is 234 mm, and the
quantities in each stage of the growth periods are given in Fig. 4.
The larger amount of water is demanded in the greening stage,
branching stage and budding stage, and smaller amount water is
needed in the last two stages. In the beginning of the greening
stage, a large amount of water should be irrigated to make sure
the soil water content can get saturated. Besides, the low precipitation
also induces the need of more irrigation although the transpiration
is not high. In the tillering stage and jointing stage, the
irrigation is large because the fierce evapotranspiration, which is
caused by the tall and flourishing plants and less constraint in
the condition of high soil water content. In contrast, in the flowering
stage and maturing stage, the irrigation is small because the
In an average precipitation level year (402 mm), the upper limitof Grade B of the irrigation amount was chosen for the greeningstage, branching stage and budding stage, and the upper limit ofGrade C was chosen for other stages. The calculated irrigation demandis 212 mm. Assumed that the irrigation coefficient is 0.9, theoptimum irrigation in the whole growth period is 234 mm, and thequantities in each stage of the growth periods are given in Fig. 4.The larger amount of water is demanded in the greening stage,branching stage and budding stage, and smaller amount water isneeded in the last two stages. In the beginning of the greeningstage, a large amount of water should be irrigated to make surethe soil water content can get saturated. Besides, the low precipitationalso induces the need of more irrigation although the transpirationis not high. In the tillering stage and jointing stage, theirrigation is large because the fierce evapotranspiration, which iscaused by the tall and flourishing plants and less constraint inthe condition of high soil water content. In contrast, in the floweringstage and maturing stage, the irrigation is small because the
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