Uptake and allocation of nitrogen from different root zones of maize under local irrigation

Effects of partial root-zone irrigation on uptake and allocation of nitrogen from different root zones of maize grown in split-root containers were studied. Maize was irrigated on both halves of the container (conventional irrigation, C), on one side only (fixed partial root-zone irrigation, F), or alternatively on both sides (alternative partial root-zone irrigation, A). Isotope-labled 15N-(NH4)2SO4 was applied to one half of the pot with (14NH4)2SO4 to the other half so that N inflow could be tracked. Results showed that in the day 15, 20, 40, the ratios of N uptake from 15N-fertilizer applied in the irrigated root zone（Fw）to that from the non-irrigated zone (Fd) of F treatment were 2.37, 2.95 and 3.41, respectively. For A treatment, the ratios of N uptake from 15N-fertilizer applied in the early irrigated zone（Ae）to that from the late irrigated zone（Al）were 1.57, 1.08 and 1.06, respectively. The percentages of plant N absorbed from soil or fertilizer in different root zones to total N uptake for three irrigation methods also indicated that the amount of N absorption from two root zones of A treatment was equal whereas for F treatment, the N accumulation in plant was mainly from the irrigated root zone. Considering the fact that root N inflow and root length in the irrigated zone were larger than those of the non-irrigated zone for F treatment, it could be concluded that both of root length and N absorption capacity contribute to plant N uptake largely. At 40 day, the percentage of 15N-fertilizer N allocation in shoot to total accumulation for A treatment was higher than that for F treatment but lower than that for C. The 15N allocation percentage of the subroot supplied with 14N-fertilizer was higher for Fd than for the others. The 15N allocation percentage of the subroot supplied with 15N-fertilizer was higher for Fd, Al and Ae than for C treatment but lower than for Fw. Our results suggest that partial root-zone irrigation increased N allocation in root system but decreased N allocation in shoot. However, for A treatment, N allocation in two subroots was equal but for F treatment, N allocation of the subroot in the irrigated zone was higher than that of the non-irrigated zone.