Root system modification of faba beans ( Vicia faba L.), and its effects on crop performance. 2. Role of water stress

Abstract

This paper reports the effects of root system modification on the water use of faba beans ( Vicia faba L.) crops. Root distribution was modified through subsoiling to 45 cm depth before planting. Controls were conventionally cultivated to 20 cm depth. Irrigation (experiment 1) and early vs late spring sowing (experiment 2) were also used as treatments to assess if they interacted with the effects of subsoiling. The spring-sown crops were grown in compact Templeton silt loam under a subhumid climate, near Lincoln, Canterbury, New Zealand. Evapotranspiration (ET) was estimated by the soil water balance method, using neutron moderation to measure changes in soil water content. Transpiration (E t) was calculated from measurements of ET, crop cover, solar radiation and air temperature. All crops experienced drought stress but, although root distribution at depth was improved by subsoiling, ET and E t were unaffected in experiment 1 and the early spring sowing of experiment 2. Both ET and E t were increased by subsoiling in the late spring sowing of experiment 2, where the total amount of roots was also increased. However, in all cases compared to controls the subsoiled crops extracted more water from the subsoil, and less from the topsoil, at least until midway through podfill. There was a general trend that subsoiling increased crop water-use efficiency. Furthermore there were no significant interaction between the effects of subsoiling and irrigation on crop growth. Hence root system enlargement did not benefit crop growth simply by reducing water stress. Understanding how this occured may help improve production in drought-prone areas without making further demands upon water resources.