SEEPAGE RATE FROM CERAMIC PITCHERS UNDER POSITIVE AND NEGATIVE HYDRAULIC HEAD

摘要

Picher irrigation is a traditional technique used to supply water to plants under drought conditions in arid regions. Laboratory experiments were conducted to evaluate water seepage rates from ceramic pots/pitchers, made from baked clay-sand local materials, under various environmental and hydraulic conditions. Seven ceramic pots (simulating ceramic emitters) with various dimensions were used in the experiments. Handmade ceramic pots of about 1 L in volume and 26 cm tall were used in the experiment. The hydraulic conductivities of the pots were measured using falling head method and the values ranged from 0.275 to 0.704 mm/d. Seepage rate from ceramic pots were measured in the air and when buried in the soil under constant and falling head method inside a temperature and humidity-controlled chamber. Results indicated that seepage rate is affected by various conditions including potential evaporation, soil suction pressure and moisture condition, and hydraulic head. Seepage rate from ceramic pots were higher under constant head condition and when buried inside soil than that under falling head or in the air. Seepage rates were found to increase steadily with potential evaporation but decrease gradually with increased soil moisture around ceramic pots. The value of hydraulic head seemed to have the largest effect on pitchers' seepage rate. The seepage rate under a constant head of 30 cm above the mouth of the ceramic pot tested in the experiment was 2500 mL/d but decreased to only 114 mL/d under a constant head of -25 cm below the mouth of the pot. The experiments revealed that ceramic pitchers can be used to supply water even under negative head thus eliminating the need for pressurized flow inside irrigation pipes.