Response of grain yield and water use efficiency of wheat and faba bean to partial root-zone irrigation in intercropping

Intercropping of cereal and legumes is the most common system of intercropping in which complementary effects in the consumption of environmental resources leads to increasing in production. Wheat and faba bean intercropping is a cereal-legume intercropping. Available water resources have been reduced in recent years. In this case, so many efforts have been considered to save water resources in agronomical systems. Partial root zone irrigation is a new technique for deficit irrigation which increased water use efficiency in different cropping systems including sole maize and wheat-Persian cloverand maize-mung bean intercropping. In these cropping systems, the reduction of yield was much less than the reduction of water consumption. Since there is not enough information on the effect of water deficit in wheat-faba bean intercropping, this research was aimed to evaluate the effect of deficit irrigation induced by partial root zone irrigation on yield and yield components of wheat and faba bean in sole and intercropping patterns.

This experiment was carried out in Shadegan (Khuzestan province) during 2017-18 growing season as two-factor factorial based on RCBD with three replications. The first factor was irrigation (conventional and partial root zone irrigation) and the second was planting pattern (sole wheat, sole faba bean, within row and alternate row intercropping of wheat and faba bean). Irrigation treatments were applied after seedling establishment. In each irrigation, the volume of irrigation was measured. At harvest time, grain yield and yield components of wheat and faba bean were determined. Water use efficiency was also measured. Land equivalent ratio was determined for evaluation the benefit of intercropping.

Deficit irrigation reduced spike length, grain per spike and grain yield of wheat by 9.8%, 11.9% and 24.4%, respectively. The highest spike length, grain per spike and grain yield of wheat achieved in sole cropping which was 13.2%, 16.5% and 21.8% more than that of within-row intercropping. Wheat had the highest height in within-row intercropping under conventional irrigation. The highest 1000-grain weight (40.1g) was achieved in sole cropping under conventional irrigation which was 11.6% more than that of the lowest value (35.4g in within-row intercropping under partial root zone irrigation). Wheat had the highest biological yield in within-row intercropping under conventional irrigation (11170 kg ha-1) which reduced 18% with partial root zone irrigation. With partial root zone irrigation, the reduction of wheat grain weight in intercropping was more than that achieved I sole cropping, indicating that in intercropping and deficit irrigation wheat is a weak competitor compared with faba bean which led to the reduction of growth (plant height and biological yield) and yield component (grain number and weight) of wheat. 1000-grain weight, grain per plant and grain yield of faba bean were reduced by partial root zone irrigation. The highest plant height of faba bean was achieved in within-row intercropping under conventional irrigation. Faba bean had the highest pod per plant in sole cropping under conventional irrigation. The highest biological yield of faba bean was recorded in within-row intercropping. Higher density of faba bean in sole crop stand led to higher yield compared to intercropping patterns. In intercropping, faba bean benefited from the shading of wheat for grai production. Water use efficiency (WUE) was improved by partial root zone irrigation. WUE of intercropping was more than that of sole crop stands. Land equivalent ratio was not affected by irrigation method and planting pattern. However, LER of both intercropping patterns was more than one, indicating the benefit of intercropping compared with sole cropping.

Partial root zone irrigation reduced wheat and faba bean grain yield. However, since the reduction of grain yield was much more than the reduction water consumption, partial root zone irrigation led to the improvement of water use efficiency in sole and intercropping. As a final remark, wheat and faba bean intercropping can be cultivated in partial root zone irrigation condition to improve water use efficiency.