NITROGEN FERTILIZATION AS RELATED TO THE AVAILABILITY OF PHOSPHORUS IN CERTAIN CALIFORNIA SOILS

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Abstract
The form of N fertilizer applied makes large differences in crop yields on certain light, slightly alkaline soils. For several California soils, ammonium fertilizers provide greatly increased yields over nitrate fertilizers. The physiologically acid ammonium salt (NH4)2SO4 effectively released native soil phosphate, whereas N from Ca(NO3)2 and NaNO3 did not. Response from NH4NO3 was intermediate. Alternate methods of enhancing the P supply through (a) acidification with elemental S and (b) addition of large amts. of phosphatic fertilizer, resulted in as good response to nitrate fertilizers as to (NH4)2SO4 alone.
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