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

摘要

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~-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.