Ammonium and nitrate fertilization effects on biomass yield of maize (Zea mays L.) with special emphasis on rhizodeposition.

摘要

A pot experiment was conducted to study the effect of ammonium (NH4) and nitrate (NO3) on the growth, water relations and rhizodeposition (using accumulation of sand on the root surface as an indirect measure) of two cultivars of maize (C-20 and C-77). Nitrogen was applied as ammonium sulfate or potassium nitrate at 50 or 100 mg litre-1 on the rooting medium solution and the plants were harvested 15 days after seed sowing when seed reserves were nearly exhausted. It was assumed that form and level of N were the main variables affecting plant growth besides K that was added as potassium nitrate. Data were recorded on root and shoot biomass (fresh and dry weights) and amount and water concentration of sand adhering to the roots. In general, higher levels of NH4-N had a negative effect on plant growth and a positive effect on tissue water concentration. The amount of sand adhering to the roots increased in the presence of lower levels of NH4 in both maize cultivars. The roots could adhere sand 2-3 times their fresh weight and 30-43 times the dry weight and were assumed to reflect the amount of rhizodeposits. The RAS showed significantly higher water concentration compared to the bulk sand, suggesting the presence of polysaccharides that were assumed to be released from the roots or synthesized by rhizospheric microorganisms. The water concentration of RAS was higher in the presence of NH4, suggesting a higher rhizodeposition and/or microbial synthesis of polysaccharides. Implications of forms of N in the rooting medium on plant growth are discussed.