Effects of soil salinity and top removal on growth and yield of broadbean as a green vegetable

Abstract

In 1994 the effects of soil salinity and top removal were studied on faba bean for green consumption, grown during the irrigation-free season on a clay-loam soil which since 1988 had undergone the same irrigation treatments of increasing water salinity (0%; 0.125%; 0.25%; 0.5% and 1% of commercial NaCl). The response to salt tolerance was evaluated by using two models: The Maas and Hoffman model Yr = 100 − S(EC e ) − T) and the van Genuchten model Yr = 100/[1 + ( EC e EC e50 ) p ]. Within the range of electrical conductivity of the saturated soil extract (EC e) between 2 dS m −1 and 6 dS m −1, soil salinity reduced plant height by 60%, leaf area by 70%, total above ground dry matter by 45%, mean pod weight by 15% and the number of pods per plant (48%). Leaf dry matter and specific leaf weight (SLW) were positively related to salinity. Higher salinity stress decreased the seed yield by 67% due to a reduction in weight and number of seeds, and also affected product quality. The results obtained by analysing the salt tolerance model of Maas-Hoffman and its descriptive parameters, place broadbean for green consumption in the moderately salt-sensitive category. In terms of relative yield per surface unit, from the Maas and Hoffman model the threshold value was 1.7 dS m −1 and yield was reduced at the rate of 15% (dS m −1) −1: the salinity level at 50% yield reduction (EC e50) was 5 dS m −1, compared to 4.7 dS m −1 of the van Genuchten model. With regard to pod yield per plant, the values of parameters were 1.8 dS m −1 (threshold) and 13% (dS m −1) −1 (slope) and the salinity level at 50% yield reduction (EC e50) was 5.6 dS m −1, compared to 5.4 dS m −1 of the van Genuchten model. Top removal at the beginning of pod set was ineffective. At low soil salinity the only effect of top removal was higher early production, indicating a more efficient partition of assimilates to growing pods and, therefore, rapid pod enlargement and higher yield at the first harvest.