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.