Fate of nitrogen-15 in the subsequent growing season of greenhouse tomato plants (Lycopersicon esculentum Mill) as influenced by alternate partial root-zone irrigation

Abstract

Alternate partial root-zone irrigation (APRI) has profound impacts on the distribution of nitrogen fertilizer applied in-season. However, the fate of previous residual nitrogen in the subsequent crop growing season under APRI has seldom been studied. Our objective in this study was to investigate the effects of APRI on the reutilization, redistribution and loss of residual nitrogen in the subsequent season. To achieve this objective, in the previous season, greenhouse tomatoes (Lycopersicon esculentum Mill) were chosen as a plant material, and were treated with two irrigation patterns (APRI and conventional irrigation (CI)), two ¹⁵N labeling depths (K¹⁵NO₃ with a ¹⁵N abundance of 10.57%, labeled in the 0–20 cm and 40–60 cm soil layers, respectively) and two transplant times (early and late summer). In the subsequent season, we adopted the same irrigation patterns, but with no ¹⁵N labeled in the soil. Our results showed that 81.3–90.7% of the residual ¹⁵N from the previous season still remained in the 0–100 cm soil layer, 4.1–7.3% was absorbed by the subsequent-season tomatoes, and 2.9–14.6% was lost. The ¹⁵N reutilization rates (defined as the ratio of ¹⁵N uptake by the subsequent tomatoes to the total applied ¹⁵N) were 2.20–4.73% under the different treatments (the ¹⁵N utilization rates of the in-season tomatoes were 18.8–27.9%). Compared to CI, APRI significantly (p < 0.05) increased the plant ¹⁵N uptake and ¹⁵N reutilization rate, and APRI also contributed to a greater mineral and organic ¹⁵N amount in shallower soil layers. Overall, the tomato ¹⁵N reutilization rate was found to be significantly (p < 0.05) higher when ¹⁵N labeling was performed in the 0–20 cm soil layer compared to that in the 40–60 cm layer. Moreover, the ¹⁵N reutilization rate had a significant positive relationship with the root dry weight (R = 0.74*), root length density (R = 0.72*), soil mineral ¹⁵N (R = 0.91**) and total residual ¹⁵N amount (R = 0.88**).