Sprinkler water distributions as affected by winter wheat canopy

Sprinkler uniformity is often used to evaluate irrigation system performanc e. The measurement of uniformity is generally made from one test when no cr op is present. However, a developing crop canopy has significant potential to modify the distribution of water applied during irrigation. This study w as conducted to evaluate the influence of a winter wheat canopy on sprinkle r uniformity and on canopy-intercepted water by measuring water distributio ns above and below the canopy. The Christiansen uniformity coefficient (CU) was calculated on both a daily and a cumulative basis. The CU was higher b elow the canopy than above the canopy. Canopy-intercepted water, which is h ere defined as the sum of canopy storage and stemflow, increased with incre asing water application depth. Sprinkler uniformity had no significant effe ct on the mean amount of water interception by the canopy. The ratio of wat er interception to total water application depth for the whole irrigation s eason was between 0.24 and 0.28. The CUs calculated from the cumulative dep th caught above and below the canopy are larger than the averages of indivi dual CU values during the irrigation season. Measurement of individual CUs during the irrigation season therefore underestimates the cumulative CU. Ex perimental results also demonstrated that sprinkler uniformity in this stud y had little effect on crop yield.