Effects of alternate partial root-zone irrigation on the utilization and movement of nitrates in soil by tomato plants

Alternate partial root-zone irrigation (APRI) can greatly affect water conservation and yield stabilization via its physiological regulation of plants. However, most studies have not distinguished the fate of residual nitrogen in specific soil layers, and little attention has been paid to the utilization and fate of residual nitrogen in different soil layers under APRI. The aim of this study is to evaluate the fate of nitrate accumulated in different soil profiles and its potential for utilization by crops under APRI. The 15N tracer technique and simulated soil column method were used to study the effects of APRI on the movement and utilization of residual nitrate. The results showed that, compared to conventional irrigation, APRI could save 38.8% irrigation water without significant effects on tomato yield, even though the total plant biomass significantly decreased. APRI improved the absorption of residual nitrate and facilitated the transfer of nitrogen from the stems and leaves to the fruits. Compared to residual nitrate (labeled by 15N) in the upper layer (10-20 cm), nitrate in the lower layer (40-50 cm) showed less potential for absorption by tomato plants and a diminished leaching distance, corresponding to a significantly increase loss (rate). Under APRI, the 15N loss rate significantly decreased, but the utilization did not significantly decrease, compared to conventional irrigation. Moreover, APRI promoted root development, especially fine root growth, and reduced the leaching of residual nitrate in different soil layers.