Nitrate/ammonium ratio effects on nutrient solution pH, dry matter yield, and nitrogen uptake of sorghum1

Abstract

Abstract Sorghum [Sorghum bicolor (L.) Moench] seedlings were grown in nutrient solutions in a growth chamber to investigate the effects of different ratios of NO3 – and NH4 + on nutrient solution pH, dry matter yield, and N uptake. Nutrient solutions and plant tissues were assayed throughout the time plants grew in the nutrient solutions. Nutrient solution pH depended on source of N. The pH rose to near 8 with NO3 – as the sole source of N and decreased to near or below 4 with NH4 + added to the solutions. Upon depletion of NH4 + from solution, pH values rose abruptly to near 8 and remained near this value throughout the duration of the experiments. Dry matter yield was generally higher for plants grown with some NH4 + compared to plants grown with NO3 – alone. Nitrogen uptake was generally higher in plants grown with the higher proportions of NH4 +. Nitrogen concentrations remained unchanged with plant age as NO3 –/ NH4 + ratio varied. For solutions low in NH4 +, N concentrations in roots increased with...