Effect of fertigation frequency on soil nitrogen distribution and tomato yield under alternate partial root-zone drip irrigation

Alternate partial root-zone drip fertigation (ADF) is a combination of alternating irrigation and drip fertigation, with the potential to save water and increase nitrogen (N) fertilizer efficiency. A 2-year greenhouse experiment was conducted to evaluate the effect of different fertigation frequencies on the distribution of soil moisture and nutrients and tomato yield under ADF. The treatments included three ADF frequencies with intervals of 3 days (F3), 6 days (F6) and 12 days (F12), and conventional drip fertigation as a control (CK), which was fertilized once every 6 days. For the ADF treatments, two drip tapes were placed 10 cm away on each side of the tomato row, and alternate drip irrigation was realized using a manual valve on the distribution tapes. For the CK treatment, a drip tape was located close to the roots of the tomato plants. The total N application rate of all treatments was 180 kg ha−1. The total irrigation amounts applied to the CK treatment were 450.6 and 446.1 mm in 2019 and 2020, respectively; and the irrigation amounts applied to the ADF treatments were 60% of those of the CK treatment. The F3 treatment resulted in water and N being distributed mainly in the 0–40-cm soil layer with less water and N being distributed in the 40–60-cm soil layer. The F6 treatment led to 21.0 and 29.0% higher 2-year average concentration of mineral N in the 0–20 and 20–40-cm soil layer, respectively and a 23.0% lower N concentration in the 40–60-cm soil layer than in the CK treatment. The 2-year average tomato yields of the F3, F6, F12, and CK treatments were 107.5, 102.6, 87.2, and 98.7 t ha−1, respectively. The tomato yield of F3 was significantly higher (23.3%) than that in the F12 treatment, whereas there was no significant difference between the F3 and F6 treatment. The F6 treatment resulted in yield similar to the CK treatment, indicating that ADF could maintain tomato yield with a 40% saving in water use. Based on the distribution of water and N, and tomato yield, a fertigation frequency of 6 days under ADF should be considered as a water-saving strategy for greenhouse tomato production.