Increasing sustainability by intercropping legume crops with sugar beet under imposed water stress

The sustainable use of soil and water resources is a goal that should be pursued to attain food security. This investigation was implemented to compare the effects of three legume intercropping systems with sugar beet on (i) enhancing sugar beet yield under imposed water stress conditions, (ii) soil N contents, (iii) land and water use efficiencies, and (iv) farmers' net income. Two field experiments were carried out in the 2018/19 and 2019/20 seasons in the El-Minia Governorate, Egypt. The treatments included the interaction between three irrigation treatments: required irrigation ((control, 100% ETc, RI) and two levels of imposed water stress (85% ETc (WS₁) and 70% ETc (WS₂)), and three intercropping systems: faba bean (FIS), chickpea (CIS) and lentil (LIS) intercropped with sugar beet. The results indicate that the application of implementing CIS and with RI attained higher average values of soil N content (SNC = 14.0 mg kg⁻¹) and net income (NI = US$3,974 ha⁻¹) than those obtained by sugar beet alone. Irrigation with WS₁ and the implementation of CIS gave a value of SNC (12.3 mg kg⁻¹) close to that obtained under sugar beet alone irrigated with RI. CIS irrigated with WS₁ attained higher averaged values of land equivalent ratio (LER = 1.34), area time equivalent ratio (ATER = 1.28), land equivalent coefficient (LEC = 0.38), water equivalent ratio (WER = 1.12), negative value of change in water use (ΔWU < 0) and NI (US$3,602 ha⁻¹) than those obtained under FIS or LIS irrigated with RI. In conclusion, implementing CIS and irrigation with RI can achieve the sustainable use of land and water. However, implementing CIS and irrigation with WS₁ can realize soil improvement, conserve irrigation water and attain higher values of LER, ATER, LEC, WER, and NI than those obtained under FIS, LIS and sugar beet alone.