Effect of deficit irrigation on the fate of topdressing urea in a cherry tomato-soil system as assessed by 15N-labeling

Intensive greenhouse vegetable production is always associated with high doses of nitrogen (N) fertilizer application and low N use efficiency (generally less than 50 %), leading to a significant accumulation of soil N (largely in the form of NO3-). Nowadays, it is not clear how efficiently vegetables can use the N applied in varied growth stages and the effect of deficit irrigation on the N taken up by vegetables. Given this need, a two-year greenhouse cherry tomato experiment with an unlabeled large-plot experiment and 15N-labelled micro-plot experiment were performed. Specifically, all plots received the same rate of urea-N (360 kg N ha−1) applied in five split applications under two irrigation regimes (I100: 100 %ET0 and I60: 60 %ET0, where ET0 was the reference evapotranspiration). Among these, the first three topdressing N fertilizer were tracked by 15N-labelled urea to study the fate of 15N-labelled topdressing N fertilizer in a cherry tomato-soil system. The different irrigation rates were designed to explore how water available was for the fate of topdressing N fertilizer by cherry tomato. Our results indicated that during the two growing seasons, the plant N derived from the 15N-labelled urea increased with both increasing irrigation rate and delayed topdressing N fertilizer date (I100 >I60, M3 >M2 >M1). The I100M1 treatment achieved peak plant N uptake (64.9 %, two-year average), whereas I60M3 treatment maximized residual 15N retention (65.5 %) in the soil profile. Irrigation rate and topdressing N fertilizer date significantly affected the fate of 15N-labelled urea in the two experimental years. Reducing irrigation rate and postponing topdressing N fertilizer significantly mitigated soil N loss, but concurrently decreased plant N uptake and elevated 15N residual rate in 0–60 cm soil layer. Generally, in order to higher fertilizer N uptake and lower environmental loss, the N fertilizer topdressing of about 43 days after transplanting should be reduced according to cherry tomato N uptake pattern.