Nitrate Accumulation in Spinach Grown at Different Temperatures1

Nitrate accumulated in spinach plants that did not receive additional fertilizer N when temp was increased above 15°C. When 50 mg N/kg soil was added the NO 3 concn increased above 10°C and with 200 mg N/kg soil NO 3 increased with temp increments above 5°C. When N fertilizer was added the NO 3 concn decreased with a subsequent increment in temp from 25°C to 30°C. The effect of N fertilizer on NO 3 accumulation became more apparent with each 5°C rise in temp to 25°C. Either N fertilizer or a temp rise from 5°C to 25°C led to a significant increase in the total N concn of the plants. Changes in total N were correlated with changes in NO 3 -N when N fertilizer was added to the soil or when the temp was changed. Nitrite did not accumulate appreciably at any of 6 temp or 3 N fertilizer levels used.