Comparing soil moisture under trickle irrigation modeled as a point and line source

The validity of the assumption that an irrigation event from point sources can be approximated as an infinite line source is investigated in this article. This is accomplished by comparing soil water dynamics under line and point sources. Two existing mathematical models which simulate point and line drip irrigation were used. The models consider root water uptake, evaporation of soil water from the soil surface and incorporate hysteresis in the soil water characteristic curve. The comparison was made for two soil types (loamy sand and silt). The results showed that the treatment of a point source as a line source underestimates the water content values for both the soil types. This difference decreases when the depth of comparison increases. For soil depths greater than 30cm and for time greater than irrigation duration the two models gave very close results. For the same emitter spacing and for the horizontal direction perpendicular to the drip line on the emitter spot, when the distance from the point and the line sources increases the difference of water content values increases. On the contrary, in the direction parallel to the drip line when the distance from the emitter increases (the distance from the line source remains the same) the difference of water content decreases. Lastly, differences are greater in the case of coarse grained soil than in fine grained soil.