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summary: The effect of ammonium and nitrate nutrition on maize and wheat grown hydroponically and salinity stressed was assessed from measurements of growth rate and gas exchange. In both maize and wheat the ammonium‐grown plains were much more sensitive to salinity toxicity than nitrate‐grown plants particularly when exposed to 60–80 mM salinity. Shoot growth was retarded to a far greater extent than root growth in salinity‐stressed plants of both wheat and maize with either nitrogen source. There was no significant decrease of photosynthetic rate in salinity‐stressed plants of either species fed nitrate or ammonium, except in severely wilted plants of both species fed nitrate or ammonium at the highest (80 mM) salinity concentration. The same was true for stomatal conductance, transpiration rate and transpiration ratio (water use efficiency). In nitrate‐fed wheat, raising the calcium concentration from 2 to 12 mM in the presence of 60 mM salinity produced an 11% increase in growth. This effect is ascribed to improved nitrate uptake due to calcium protection of the nitrate transporter and was not evident in ammonium‐grown wheat. Possible reasons for the differential effects of ammonium and nitrate nutrition are discussed. [ABSTRACT FROM AUTHOR]

This study was designed to test the hypothesis that disruption of the macrostructure of a previously zero-tilled soil is capable of reducing vesicular arbuscular (VA) mycorrhizal infection to a degree such that phosphorus (P) absorption is reduced. Undisturbed soil cores (within plastic cylinders) were excavated from long-term, zero-tilled plots. Soil removed from these plots, which was first subjected to structurally disruptive forces and then packed into identical cylinders, formed the disturbed comparisons. Maize (Zea mays L.), wheat ( Triticum aestivum L.), spinach (Spinacea oleracea L.) or rape (Brassica napus L.) were grown in the cores and P and zinc (Zn) absorption patterns monitored. Soil disturbance significantly reduced P and Zn absorption by maize grown in soil originating from three sites differing in local geography and/or texture Disturbance also reduced mycorrhizal infection in the three soils. A significant effect of disturbance upon the VA mycorrhizal infection of both maize and wheat roots (both mycorrhizal) and also upon the P absorption by these species was observed. None was found with respect to spinach and rape comparisons (non-mycorrhizal). Injection of benomyl, a potent inhibitor of mycorrhizal fungi, into the soil surface significantly reduced the influence of soil disturbance upon P absorption. No significant differences were found in VA mycorrhizal infection within fungicide-treated cores. We accepted our hypothesis based upon the above evidence. [ABSTRACT FROM AUTHOR]