Responses of Grain Sorghum to Varying Irrigation Frequency in the Ord Irrigation Area. PI* Evapotranspiration, Water Use Efficiency and Root Distribution of Different Cultivars

摘要

Four grain sorghum cultivars (Quicksilver, Texas 610SR, E57 and Q7844), representing early-to-late nmaturity types, were grown under different irrigation frequencies (7-day, 14-day, 28-day or 42-day nintervals or once-only-at-sowing) in the dry season in the Ord Irrigation Area. Soil water distribution, nroot distribution and evapotranspiration were determined periodically. nFrequent irrigation resulted in shallow root development and most water use was from the surface n40 cm of soil. Depth of water extraction increased with plant age and with less frequent irrigation. The ndepth of root penetration determined by direct measurement was similar to that inferred from soil water nprofiles. Water uptake per unit length of root was related to soil water content only in the 0-40 cm soil nlayers. E,/Ep (actual evapotranspiration/pan evaporation) was classified into three stages according to nthe degree of soil drying after irrigation. During the first stage, immediately after irrigation, EJEp was ngenerally close to 0.75 irrespective of cultivar, leaf area index (LAI) or irrigation interval. During the nsecond stage, linear functions adequately described E,/E, as a function of LA1 for LA1 less than 5. nDuring the third stage, which commenced when total soil water to 1.8 m declined to 545 mm, poor nrelationships between EJE, and soil water were observed. nFollowing an analysis of the soil water use data, it is believed that maximum yields of sorghum may nbe attainable with irrigation at sowing followed by three carefully timed irrigations.