Growth and Phosphorus Uptake of Oat (Avena nuda L.) as Affected by Mineral Nitrogen Forms Supplied in Hydroponics and Soil Culture

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^-₃in 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 CaHPO₄ 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.