Saturday, 15 July 2006
116-37

Temporal Effects of N Source and Timing of N Fertilization on δ15N of Chinese Cabbages and Soil.

Seok-In Yun1, Hee-Myong Ro1, Eui-Yong Yun1, and Woo-Jung Choi2. (1) Dept of Applied Biology and Chemistry, School of Agricultural Biotechnology, Seoul National Univ, San 56-1 Sillim-dong, Seoul, South Korea, (2) Dept of Biosystems and Agricultural Engineering, Institute of Agricultural Science and Technology, Chonnam National Univ, Yongbong-dong 300, Gwangju, South Korea

Natural 15N abundance in plant and soil can be used as a powerful tool to interpret the history of nitrogen fertilization. To investigate temporal variations in N isotopic composition of plant and soil as affected by δ15N and timing of N fertilization, Chinese cabbages were grown with a single or split N inputs using isotopically different N sources (organic and inorganic) in pot under greenhouse conditions, and analyzed for the δ15N of plant and soil. Composted manure (δ15N = +16.4‰) and urea (δ15N = -0.7‰) were used as organic and inorganic inputs, respectively. Seven N treatments were studied: 1) a single basal fertilization with compost or 2) urea; 3) a basal urea application followed by an additional (at 40 days after transplant, same below) compost or 4) urea application; 5) a basal compost application followed by an additional compost or 6) urea application; and 7) no N fertilization. Irrespective of N application timing, 15N-enriched organic input resulted in higher δ15N of cabbage than 15N-depleted inorganic input. The δ15N values of cabbages receiving compost were higher than +9.0, while those of cabbages receiving urea were lower than +1.0‰. In case of split N fertilization, the addition of isotopically different N sources in the middle of growth significantly affected the δ15N of whole plant, while that of isotopically similar N sources did not. Comparing plant δ15N of cabbage parts, the δ15N signals of basal and additional N inputs were evident in outer and inner plant parts, respectively. We conclude that measurements of temporal variations in δ15N of plant parts formed in different growth stages could reveal the history of N fertilization.

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