Leaf K/Na ratio predicts salinity induced yield loss in irrigated rice

Salinity is a major constraint to irrigated rice production, particularly i n semi-arid and arid climates. Irrigated rice is a well suited crop to cont rolling and even decreasing soil salinity, but rice is a salt-susceptible c rop and yield losses due to salinity can be substantial. The objective of t his study was to develop a highly predictive screening tool for the vegetat ive growth stage of rice to estimate salinity-induced yield losses. Twenty- one rice genotypes were grown over seven seasons in a field trials in Ndiay e, Senegal, between 1991 and 1995 and were subjected to irrigation with mod erately saline water (3.5 mS cm(-1), electrical conductivity) or irrigation with fresh water. Potassium/sodium ratios of the youngest three leaves (K/ Na-Leaves) were determined by flame photometry at the late vegetative stage . Grain yield was determined at maturity. All cultivars showed strong log-l inear correlations between K/Na-Leaves and grain yield, but intercept and s lope of those correlations differed between seasons for a given genotype an d between genotypes. The K/Na-Leaves under salinity was related to grain yi eld under salinity relative to freshwater controls. There was a highly sign ificant correlation (p < 0.001) between K/Na-Leaves and salinity-induced gr ain yield reduction: the most susceptible cultivars had lowest K/Na-Leaves and the strongest yield reductions. Although there were major differences i n the effects of salinity on crops in both the hot dry season (HDS) and the wet season, the correlation was equally significant across cropping season s. The earliest possible time to establish the relationship between K/Na-Le aves under salinity and grain yield reduction due to salinity was investiga ted in an additional trial in the HDS 1998. About 60 days after sowing, sal inity-induced yield loss could be predicted through K/Na-Leaves with a high degree of confidence (p < 0.01). A screening system for salinity resistanc e of rice, particularly in arid and semi-arid climates, is proposed based o n the correlation between K/Na-Leaves under salinity and salinity-induced y ield losses.