Wheat growth in a saline sandy loam soil as affected by N form and application rate

Plant growth in saline soils may be increased by fertilisation, but little is known about the effect of different forms of N on wheat growth in soils with different salinity levels. The aim of this study was to investigate the response of wheat (Triticum aestivum L., cv Krichauff) to (NH₄)₂SO₄ or KNO₃ or NH₄NO₃ at 0 (N0), 50 (N50), 100 (N100) and 200 (N200) mg N kg⁻¹ soil in a saline sandy loam. Salinity was induced using Na⁺ and Ca²⁺ salts to achieve three ECe levels, 2.8, 6.6 and 11.8 dS m⁻¹ denoted S1, S2 and S3, respectively, while maintaining a low SAR (>1). Dry weights of shoot and root were reduced by salinity in all N treatments. Addition of N significantly increased shoot and root dry weights with significant differences between N forms. Under non-saline conditions (S1), addition of NO₃ − N at rates higher than N50 had a negative effect, while N100 as NH₄ − N or NH₄NO₃ − N increased shoot and root dry weights. At N100, shoot concentrations of N and K were higher and P, Ca, Fe, Mn, Cu and Zn were lower with NO₃ − N than with NH₄ − N nutrition. The concentration of all nutrients however fell in ranges did not appear to be directly associated with poor plant growth with NO₃ − N. At all N additions, calculations indicated that soil salinity was highest with N addition as NO₃ − N and decreased in the following order: NO₃−N > NH₄−N > NH₄NO₃−N. Addition of greater than N50 as NO₃ − N, compared to NH₄ − N or NH₄ − NO₃, increased soil salinity and reduced micronutrient uptake both of which likely limited plant growth. It can be concluded that in saline soils addition of 100 mg N kg⁻¹ as NH₄ − N or NH₄NO₃ − N is beneficial for wheat growth, whereas NO₃ − N can cause growth depression.