INCREASING SALT TOLERANCE OF WHEAT BY MIXED AMMONIUM-NITRATE NUTRITION

In a greenhouse experiment with wheat, sandy loam or clay soils were salinized by additions of 0, 3, or 8 g NaCl/3L pot. Ammonium and nitrate nitrogen mixtures in ratios of 0/100, 25/75 and 50/50 together with DCD, a nitrification inhibitor, were applied with irrigation water. Salinity significantly reduced dry matter yields, and N and P content in grain and stover. In accordance with previous reports, a mixed ammonium and nitrate N source produced larger dry matter and protein yields than nitrate alone, particularly in grains. The relative increases in yields and N and P accumulation, due to mixed N nutrition, were significantly higher in salinized soils and increased with increasing proportions of ammonium. Grain dry matter and N yields at medium salinity with a 50/50 N mixture, were equal to, or higher than those in non-salinized soil fertilized with nitrate only. Chloride concentrations in stover increased with salinity and proportion of ammonium in the mixed source indicating that the advantage of mixed N nutrition is not due to nitrate-chloride antagonism. Sodium concentration in plant tissues increased with salinity, but was reduced by increasing proportions of ammonium in the medium. This effect may be attributed to competition between ammonium and sodium for root uptake sites. The results obtained emphasize the effectiveness of mixed N sources to increase salt tolerance of crops such as wheat.