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Plants show different growth responses to N sources supplied with either NH + 4 or NO − 3 . The uptake of different N sources also affects the rhizosphere pH and therefore the bioavailability of soil phosphorus, particularly in alkaline soils. The plant growth, P uptake, and P availability in the rhizosphere of oat ( Avena nuda L.) grown in hydroponics and in soil culture were investigated under supply with sole NH + 4 -N, sole NO − 3 -N, or a combination. Sole NO − 3 -fed oat plants accumulated more biomass than sole NH + 4 -fed ones. The highest biomass accumulation was observed when N was supplied with both NH + 4 -N and NO − 3 -N. Growth of the plant root increased with the proportion of NO − 3 in the cultural medium. Better root growth and higher root/shoot ratio were consistently observed in NO − 3 -fed plants. However, root vigor was the highest when N was supplied with NO − 3 +NH + 4 . NH + 4 supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO 4 added as P source. No P deficiency was observed, and plant P concentrations were generally above 2 g kg −1 . P uptake was increased when N was supplied partly or solely as NO − 3 -N, similarly as biomass accumulation. The results suggested that oat was an NO − 3 -preferring plant, and NO − 3 -N was essential for plant growth and the maintenance of root absorption capacity. N supply with NH + 4 -N did not improve P nutrition, which was most likely due to the absence of P deficiency. |
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