Soil moisture distribution pattern of surface drip irrigated mango

Abstract

At present, Pakistan has been facing acute shortage of irrigation water and farmers have been using conventional irrigation methods for orchards, such as flood and basin irrigation, thus wasting huge amount of fresh water. Therefore, it is necessary to find efficient irrigation methods to cope with this major burning issue. The micro drip irrigation method is considered efficient but in the case of mango orchards there is a problem of irrigation frequency, number of emitters, and duration of flow from emitters to meet water demand. Considering the above, an experiment was conducted in the experimental field of the Sindh Agriculture University, Tandojam, by installing the drip system with two circular peripheries of lateral lines in clay loam soil covering the entire canopy of a mature mango tree. The radius of the first and second periphery around the tree trunk was 100 cm and 150 cm, respectively. Four emitters with 4 dm3∙h –1 discharge of individual dipper were fixed in each periphery. Emitters were tested for six different irrigation times, i.e. 1, 2, 3, 4, 5 and 6 h, to observe the moisture distribution pattern. Hydraulic characteristics, such as density, field capacity, porosity, infiltration rate, available water and permanent wilting point (PWP), were determined using standard methods (1.4 g∙cm –3, 33%, 49%, 8 mm∙h –1, 12.41% and 20% respectively). The texture class of the soil profile was determined as clay loam at the soil depth 0–120 cm. Fifty soil samples were collected at 0–10, 10– 30, 30–60, 60–90, and 90–120 cm depths and at 0–20, 20–40, 40–60, 60–80 and 80–100 cm distances on two opposite sides of emitters. The emitters provided sufficient moisture up to field capacity in clay loam soil with flow duration of 4 h. The maximum moisture distribution efficiency was 77.89% with flow duration of 4 h at vertical depth of 0–120 cm and 0–100 cm distance horizontally among four emitters as compared to 1, 2, 3 h flow duration which under irrigated the canopy area and 5, 6 h flow duration which excessively irrigated the canopy area of the mango tree. The water demand of the mango tree was met by 4 h flow duration which provided adequate moisture to the entire canopy up to 120 cm depth in the root zone and water saving was calculated as 15.91% under the installed drip irrigation system as compared with the conventional (basin) irrigation method.