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A fi eld experiment was conducted in 2005 at the experimental station of the Arid Land Research Center, Tottori University, Japan, for comparing latent heat fl uxes from a maize (Zea mays L.) fi eld, maize transpiration, and soil surface evaporation by two diff erent methods. Th e Bowen ratio energy balance method (Method 1) was used to measure latent heat fl uxes above the maize canopy as well as between the soil surface and the canopy at 0.5-h time intervals. Th en, latent heat fl ux from maize transpiration was calculated by the diff erence between that of the maize fi eld and soil surface. In Method 2, a weighing lysimeter and sap fl ow gauges were used to measure latent heat fl uxes from the maize fi eld and maize transpiration, respectively, at 0.5-h time intervals. Th en, latent heat fl ux from the soil surface was calculated by the diff erence between that of the maize fi eld and maize transpiration. Th e coeffi cient of determination between latent heat fl uxes by the two methods was 0.72 from the maize fi eld and 0.77 from the maize transpiration. However, results indicated a low correlation between the latent heat fl uxes from the soil surface by the two methods (r 2 = 0.36). On the average, the Bowen ratio energy balance method underestimated by 6% the latent heat fl ux measured by weighing lysimeter data and overestimated by 14% that obtained by sap fl ow data resulting in a 30% underestimation of the measured latent heat fl ux at the soil surface. At daily time intervals, results were improved with relative errors around 19 and 21% for the latent heat fl uxes from the maize fi eld and maize transpiration, respectively. Finally, this study showed that the use of Method 1 for partitioning evapotranspiration at maize fi eld level is feasible. Th e use of this technique for irrigation management to improve water use effi ciency at crop fi eld level needs to be explored.

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Water application efficiency of microirrigation systems (MIS) may depend, at least partially, on algae and protozoa (biological clogging agents, BCAs) induced filter and emitter clogging. In this study we assessed the impact of BCA-induced changes on water discharge rate and distribution uniformity from (i) emitters with different water flow cross-section (CS) area, pressure compensation (PC) systems, and inbuilt filtration areas (FAs), and (ii) filters either made of urethane, sand, or disk in the Tohaku irrigation project in Japan. In a field experiment, four types of on-line emitters on each of four laterals and four types of in-line emitters on each of another four laterals were assessed for BCA-induced emitter discharge performance without using filters in the field irrigation line. The emitters' discharge rate increased with increasing CS, FA, and working pressure (WP) and decreased when the emitters were on-line in the laterals and with increasing BCA counts. Because BCAs are the only dynamic variable in the above relationship, we conclude that BCA-induced clogging is a major issue when filters were not installed in field irrigation lines. The filter performance assessment based on the number of backwashings required to restore the working pressure to the recommended level indicated that BCA filtering by the sand filter was highest, followed by disk and urethane, respectively.

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