CHLORIDE ENHANCEMENT OF WHEAT RESPONSES TO AMMONIUM NUTRITION

Calcium chloride combined with an enhanced ammonium supply (EAS) (0.5: 1 Ca/NH4 molar ratio) has increased yields of horticultural crops. Gre enhouse experiments were conducted to determine if Ca or Cl promote wh eat (Triticum aestivum L., cv. Len) responses to an EAS. Wheat was gro wn in a Shano silt loam soil (coarse-silty, mixed, mesic Andic Mollic Camborthid) with 0 to 400 mg N kg(-1) applied as (i) 100% NO3-N suppli ed by Ca(NO3)(2); (ii) 50% NO3-N supplied by Ca(NO3)(2), 50% NH4-N sup plied by urea with a nitrification inhibitor (NI) (50:50 NO3/NH4, 0.5: 1 Ca/NH4 molar ratio); (iii) 50:50 NO3/NH4 + CaCl2 (1:1 Ca/NH4); (iv) 100% NH4-N supplied by urea with a NI; and (v) NH4 + CaCl2 (0.5:1 Ca/N H4). Grain yield averaged 9 to 30% less for the NH4 and 50:50 NO3/NH4, but 15 to 37% more for the NH4 + CaCl2, than for the NO3, indicating that CaCl2 promoted the response to an EAS. A response to CaCl2 added to the 50:50 NO3/NH4 treatment, in which the NO3-N was supplied as Ca( NO3)(2), suggested that the response to CaCl2 was due to the Cl rather than the added Ca. The individual roles of Ca and CI in EAS responses were evaluated in a second experiment by combining Ca, CI, and Ca + C l with NO3 and NH4 (300 mg N kg(-1) soil)in a factorial design. There was no effect of added Ca on grain yield with either N form. Furthermo re, grain yield was higher for the NH4 + Cl than for the NH4, NH4 + Ca , or NO3 treatments, indicating that supplemental CI elicited wheat re sponses to an EAS. Chloride also stimulated Ca uptake, which may have played a secondary role in the EAS response.