Agronomic performance of irrigated quinoa in desert areas: Comparing different approaches for early assessment of salinity stress

Quinoa is a very versatile crop, amenable to the hot agronomical conditions of the Middle East, where it is cultivated under irrigation, frequently using saline water. This study aims to compare different approaches for early detection of the effect of salinity on the agronomic performance of this crop. A set of 20 genotypes was grown under drip irrigation in sandy soil at the International Center for Biosaline Agriculture (UAE). The crop was established using fresh water (0.3 dS m(-1)) for two weeks, after which half of the trial was submitted to irrigation with saline water, (15 dS m(-1)) and this was continued until crop maturity. After eight weeks of applying each specific irrigation, pigment contents were evaluated in fully expanded leaves. The same leaves were then harvested, dried and the stable carbon and nitrogen isotope compositions (delta C-13 and delta N-15) and the total nitrogen and carbon content of the dry matter analyzed, together with the total content of K+, Na+, Mg2+, and Ca2+ ions. Genotypic and treatment effects existed for yield and biomass, as well as for the analytical traits above. The best traits in terms of correlation with biomass and yield within each irrigation regime were the Mg2+ and K+ contents and the delta N-15. A stepwise model using different traits (mainly Mg2+, K+, and delta N-15) explained 33.1 % of the variability in biomass and 56.0 % in seed yield, under saline irrigation, 52.4 % and 34.9 % under fresh water, and 42.4 % and 38.6 % under the combination of both irrigation regimes, respectively. Regardless of irrigation conditions, the results also showed that manure application causes salinity that is associated with high magnesium content. The combined analysis of ion concentrations and delta N-15 allows early evaluation of the effect of irrigation salinity and identification of the best performing genotypes under each irrigation condition.