Influence of Water Deficit on Uptake and Distribution of Nitrogen in Soybeans Monitored by Soil Injected ¹⁵N

Abstract

A pot experiment was carried out in a climatic chamber to study 15N‐uptake, translocation and recovery in soybeans [Glycine max (L.) Merr.] as affected by a 13 day interval of water deficits (wd) starting at flowering. Ten or 40 mg 15N (500 or 2000 p.p.m. 15N) was injected at 0.4 m depth into the soil 3 days after flowering (3 DAF). A dose of 10 mg 15N, resulted in a translocation of 50 and 80 % to the shoot at 7 and 13 DAF, respectively; thus the uptake of 15N into the plant organs was limited by the low remaining 15N in the soil after 7 DAF. Therefore, only results referring to the 40 mg 15N application are presented here. The daily 15N‐uptake of well‐water (ww) plants during the 10 days of investigations was about c. 2.5 mg 15N, it was significantly higher than under wd at 7 DAF and tended to be higher at 13 DAF. The reduction by wd was also evident by a lower recovery of 15N (55 % instead of 75 %) at 13 DAF. In almost all leaves and pods there was a trend to a lowered translocation (mg 15N per organ) under wd when compared with the ww plants at 7 and 13 DAF; lowering due to wd was strongest and significant in upper leaves and pods at 13 DAF, whereas translocation to stems was even slightly increased. Relative accumulation of 15N (mg g−1 dry matter) in leaves, stems and pods increased from the bottom to the top indicating an higher sink activity of younger organs. Water deficits tended to lower this relative 15N‐accumulation in all leaves and pods at 7 and 13 DAF, and caused a significant reduction in upper leaves and pods at 7 DAF. Absolute and relative 15N‐accumulation in stems tended to be affected differently by wd, being unaffected or slightly decreased at 7 DAF, but increased at 13 DAF. These differential effects of wd are discussed.

Effect of Water Stress in Maize Crop Production and Nitrogen Fertilizer Fate

“…Non-recovered N can enter into the soil organic fraction, or lost by leaching, volatilization, denitrification and other ways. To quantify the proportion of N from fertilizer taken by the crops or following other destination 15 N isotope can be used (Ma et al, 1995;Gorfu et al, 2003;Herzog and Götz, 2004). This is a direct method to determine the fate of N from fertilizer through the soil and plant compartments and through the air and water (Carter and Rennie, 1987).…”