Growth and yield of barley (Hordeum vulgare L.) as affected by salinity and mixed ammonium and nitrate nutrition.

Abstract

Absorption and utilization of N by plants has been shown to be affected by the N form supplied and salinity. This study was conducted to determine the growth and N uptake of barley grown in modified Hoagland-Arnon nutrient solution containing different NH₄⁺-N / NO₃⁻-N ratios and various salinity levels in the growth chamber. The first experiment was conducted to study the N uptake rate at five different NH₄⁺-N/NO₃⁻-N ratios and three salinity levels (0, 6 and 12 bars). No ¹⁵N was applied in this experiment. The second experiment was conducted with the same objectives with modification in the salinity levels based upon the results of experiment 1. The salinity levels were 0 and 8 bars. The third experiment was similar to the second experiment except the duration of the study that was 45 days instead of 30 days. The NH₄⁺-N/NO₃⁻-N ratios were 0/100, 25/75, 50/50, 75/25 and 100/0. The total N concentration in all treatments was 100 ppm. Solutions were sampled after every 15 days during all experiments and analyzed for ammonium and nitrate concentration. For the short term ¹⁵N uptake study (experiments 2 and 3), either ammonium labelled ¹⁵N or nitrate labelled ¹⁵N was added to each NH₄⁺-N/NO₃⁻-N treatment for 6, 12, and 24 hours period on the last day of experiment 2 and 6, 12, and 18 hours period on the last day of experiment 3. Mixed N nutrition resulted in greater accumulation of whole plant-N than plants receiving only NO₃⁻ or NH₄⁺ as the source of N. Labelled nitrate recovery was highest in the 50% NH₄⁺ treatment. The same trend was evident from the solution sample analysis. In all the three experiments, plants produced significantly higher dry matter yields when grown with mixed N nutrition than with NH₄⁺ or NO₃⁻ alone. Total dry matter production, nitrogen uptake, root and shoot N contents, ¹⁵N content and water uptake decreased with increasing salinity levels in all the three experiments. The plants fed with ¹⁵NO₃⁻ source inhibited nitrate uptake more severally under saline conditions than the NH₄⁺-fed plants under similar conditions. Salinity and N nutrition interaction was found significant in all experiments.