Effect of nitrogen form and phosphorus source on the growth, nutrient uptake and rhizosphere soil property of Camellia sinensis L.

Abstract

The effects of nitrogen form and phosphorus source on the growth, nutrient uptake and rhizosphere soil property of tea (Camellia sinensis L.) were investigated in a pot experiment. The experiment was performed with a compartmental cropping device, which enables the collection of rhizosphere soil at defined distances from the root of tea plant. Nitrogen was supplied as nitrate or ammonium in combination with soluble phosphorus as Ca(H2PO4)2 or insoluble P as rock phosphate. The leaf dry matter production of tea was significantly greater in the treatments with NH4+ than NO3-, whereas dry matter production of root and stem was not significantly affected. Addition of phosphorus as either source did not influence the dry matter production. The concentrations of K in root, Mg and Ca in both the shoot and root supplied with NO3- were significantly higher than in NH4+ and influence of P sources was minor. On the contrary, Al and Mn concentrations were significantly larger in NH4--fed plants which could be attributed to remarkably increased availability of Al and Mn caused by acidification of the rhizosphere soil (the first 1-mm soil section from the root surface) with NH4–N nutrition. The concentration of N in shoot was also significantly higher in NH4- than in NO3-fed plants, indicating higher use efficiency of NH4–N. Whatever the phosphate source, rhizosphere pH declined in ammonium compared to in nitrate treatment. The pH decrease was much larger when no P or soluble P were applied and reached 0.85–1.30 units which extended to 3–5 mm away from the root surface. Exchangeable acidity, content of exchangeable Al and Mn were also considerably higher in the rhizosphere soils of NH4+ fed tea plants. Significant amounts of P dissolved from rock phosphate accumulated in rhizosphere of NH4+, not NO3-, suggesting that the dissolution of rock phosphate was induced by the proton excreted by tea root fed with ammonium. With soluble P addition, shoot and root P concentrations were greater in NH4+ than in NO3- treatment and it appeared that this difference could not be sufficiently explained by the available P content in soil which was only slightly higher in NH4+ treatment. With rock phosphate addition, the shoot and root P concentrations were hardly affected by nitrogen form, although the available P content was much higher and accumulated in the rhizosphere soil supplied with ammonium. The reason for this was discussed with regard to the inter-relationship of Al with P uptake.