Water and nitrogen distribution under subsurface drip fertigation as affected by layered-textural soils

Laboratory experiments were conducted using a plexiglass box to investigate the effects of soil textures, layed structure and emitter discharge rates on the distribution of water nitrate nitrogen and ammonium nitrogen from a buried source. A uniform sandy (S), a uniform sandy loam (L), and a sandy-over-sandy loam (SL) soil were tested. The results indicated that the sandy-loam interface existing in the SL soil limited the downward movement of water while increased the horizontal water movement, resulting in an accumulation of water and nitrate nitrogen in the sublayer soil underneath the interface. The distribution of nitrate nitrogen concentration was also controlled by input concentration and initial concentration of soil nitrate nitrogen. A nitrate nitrogen concentration approximating the input nitrate nitrogen concentration was found in the proximity of the buried source and the concentration decreased as the distance from the source increased under the tested conditions that input nitrate nitrogen concentration was substantially higher than the initial nitrate nitragen concentration. For both uniform and layered soils, an increasing emitter discharge rate resulted in greater water content and nitrate nitrogen concentration around the source. Measurements of ammonium nitrogen showed that there existed an extremely high ammonium nitrogen concentration in the 5-10 cm proximity of the buried source because of the adsorption. No significant influence of soil texture and emitter discharge rate on ammonium nitrogen distribution was found. The results obtained from the study suggest the importance of thoroughly considering soil texture and layed-structure, initial conditions of water and nitrogen, buried depth and discharge rates of emitters, water and fertilizer applied, and input concentration in the design and management of subsurface drip irrigation systems.