EFFECTS OF SOIL-SALINITY AND TOP REMOVAL ON GROWTH AND YIELD OF BROADBEAN AS A GREEN VEGETABLE

In 1994 the effects of soil salinity and top removal were studied on f aba bean for green consumption, grown during the irrigation-free seaso n on a clay-loam soil which since 1988 bad undergone the same irrigati on treatments of increasing water salinity (0%; 0.125%; 0.25%; 0.5% an d 1% of commercial NaCl). The response to salt tolerance was evaluated by using two models: The Maas and Hoffman model Yr = 100 - S(ECe - T) and the van Genuchten model Yr = 100/[1 + (ECe/ECe50)(p)]. Within the range of electrical conductivity of the saturated soil extract (ECe) 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 p od weight by 15% and the number of pods per plant (48%). Leaf dry matt er and specific leaf weight (S:LW) were positively related to salinity . Higher salinity stress decreased the seed yield by 67% due to a redu ction in weight and number of seeds, and also affected product quality . The results obtained by analysing the salt tolerance model of Maas-H offman and its descriptive parameters, place broadbean for green consu mption 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 (ECe50) was 5 dS m(-1) compared to 4.7 dS m(-1) of the van Genuchten model, With regard to pod yield pet plant, the values of parameters were 1.8 dS m(-1) (t hreshold) and 13% (dS m(-1))(-1) (slope) and the salinity level at 50% yield reduction (ECe50) was 5.5 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 h igher early production, indicating a more efficient partition of assim ilates to growing pods and, therefore, rapid pod enlargement and highe r yield at the first harvest. (C) 1997 Elsevier Science B.V.