Improvement of water use and N fertilizer efficiency by subsoil irrigation of winter wheat

Fresh water is a limited resource and its efficient use in agriculture represents a great challenge. The objective of the investigation was, to test a new subsoil irrigation technique for obtaining high grain yields and water use efficiency in comparison with furrow irrigation still used in Middle East. Clay pipes of the subsoil irrigation had a particular porosity which allowed a controlled diffusion of water out of the pipe into the soil. The pipes were imbedded into the soil at a depth of 0.3 m. The technique was tested in field trials with winter wheat (Triticum aestivum L.) in the 1992/1993 and 1993/1994 season under arid, continental climatic conditions of Persia on a representative silty loam soil. Plot size was 5 m2.Yields were nearly twice as high under subsoil irrigation compared with furrow irrigation. With subsoil irrigation maximum grain yield (>10 Mg/ha) was already obtained with a N fertilizer rate of 50 kg N/ha. Water use efficiency (WUE) ranged from 1.64 to 3.34 in subsoil irrigation and from 0.46 to 1.2 g grain/kg water in furrow irrigation (p < 0.001). N release from soil was much higher under subsoil irrigation (111–216 kg N/ha) than under furrow irrigation (−11 to 33 kg N/ha). There were no significant differences between the irrigation techniques for the harvest index, single grain weight and the nitrogen fertiliser agronomic efficiency (AE). The apparent nitrogen recovery (ANR%) was high particularly in the subsoil irrigation treatments and decreased with N fertiliser rates. The question is raised whether this subsoil irrigation technique can be developed for the application on a large enough scale for crop production.