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Title: A New Weighing Method to Measure Shoot Water Interception

item Delgado, Jorge
item Bausch, Walter
item McMaster, Gregory

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2007
Publication Date: 6/1/2008
Citation: Mauch, K.J., Delgado, J.A., Bausch, W.C., Barbarick, K., Mcmaster, G.S. 2008. A new weighing method to measure shoot water interception. Journal of Irrigation and Drainage Engineering 134: 349-355.

Interpretive Summary: Based on the results from this study and the results from Parkin and Codling (1990), Steiner et al. (1983), and Lamm and Manges (2000), it can be assumed that most of the water that contacts the shoots will be througfall or redirected to the soil via stemflow. The weighing intercepted method values presented in this paper are low and suggest that previous interception methods overestimated the intercept values or that the evaporation from a field study was at least 7 to 10 times higher than Iw or Iwadj. Some of the reported values with the difference method are 240+ mL shoot-1 and as high as 1500 and 2000 mL shoot-1. However, evaporation values as large as 1000 mL during an irrigation event that may last 15 minutes (average time a given shoot is wet) seems to be too high. The use of a balance to quantitatively measure the water intercept by the shoots with a lower variability suggests that previous values have been overestimated. We correlated an increase in LA with an increase in Iw and Iwadj. There is the potential that for older stage of growth, we will have higher values. However, our method was still 7 to 8 times lower than other field estimates of interception at a similar stage of growth (Parkin and Goding, 1990). One reason could be that the evaporation is higher under a field system than what we observed in the hydraulic laboratory. The weighing interception method still suggests that with a more quantitative method to measure interception, the values that are intercepted by the shoots are lower than those previously reported.

Technical Abstract: There is the need to develop a method that can quantitatively measure water interception from plant shoots. Corn (Zea Mays L.) Corn was grown in 13 L buckets containing Valentine fine sand (Mixed, mesic Typic Ustipsamment) under a climate-controlled growth chamber. Plants were taken out of the growth chamber for two to three hour periods for measurements of shoot water interception in a hydraulic laboratory equipped with an Accupulse system hanging from the ceiling that was used to wet the corn shoots at growth stages V7 through V13. A lightweight, movable frame-work was placed around a balance, and the bucket with corn plants were placed on the scale, one plant at a time. Water was applied until all shoot surfaces were wet and runoff from the leaves and stalk surfaces could be observed. The weighing method for shoot water interception was tested by using the balance to instantaneously measure shoot water interception during application of water and after plant surface runoff ceased. The balance, bucket, and soil surface was covered with plastic and were impermeable to water, so only the shoots were wet. Interception by the shoot of corn ranged from 31 to 47 mL shoot-1. These values were much smaller than previous values reported in the literature. The average coefficient of the variation was 9.2 percent for two studies, which was much lower than previously accepted methods. This study suggests that the weighing method for shoot water interception can be used to quantitatively and more accurately measure water intercepted by corn shoots. The weighing intercepted method values presented in this paper are low and suggest that previous interception methods overestimated the intercept values.