Drip Irrigation Reduced Fertilizer Nitrogen Loss from Lettuce Field—A Case Study Based on 15N Tracing Technique

Abstract

Nitrogen losses under different irrigation modes have been evaluated by many studies, yet it is not very clear whether the lost N sources are from the soil or fertilizer. In order to quantitatively investigate the effects of different irrigation modes on fertilizer N loss, we used the 15N-labeledurea (15N abundance of 19.6%) as fertilizer and the lettuce (Lactuca sativa var. angustana iris) as the plant material to conduct a field experiment under three different lower limits of drip irrigation, including 75% (DR1), 65% (DR2) and 55% (DR3), accounting for the field water capacity. A furrow irrigation treatment (FI) with the same irrigation regime as DR2 was used as the control. The fate and balance of 15N under these treatments were studied. The results showed that, after the lettuce harvest, 36.9–48.8% of the applied fertilizer 15N remained in 0–80-cm soil, 32.6–39.4% was absorbed by plants, and 18.6–26.3% was lost via pathways such as volatilization or leaching. Under the same irrigation regime, 15N loss caused by FI (26.3%) was significantly (p < 0.05) higher than that byDR2 (18.9%). Moreover, FI increased the amount of total 15N, mineral 15N and organic 15N in the deeper soil layers (60 cm depth and below), leading to a potential risk of 15N leaching. The soil 15N residue was relatively lower under DR1, while the crop-absorbed15Nor15N loss was atthe highest level among the three drip irrigation treatments. The correlation analysis results showed that increasing the total irrigation amount or increasing the irrigation frequency might increase the15N loss. We concluded that using drip irrigation instead of furrow irrigation with controlling the lower irrigation limit at 65% is conducive to improving crop 15N utilization and reducing 15N loss from lettuce fields.

Optimization of a Lower Irrigation Limit for Lettuce Based on Comprehensive Evaluation: A Field Experiment

“…For each DI system, the water amount for DR1, DR2, or DR3 was calculated using the following equation [ 13 ]: where M represents the irrigation amount (m 3 ); S represents the irrigated area (m 2 ); r represents the bulk density (kg/m 3 ); h represents the planned wetting layer depth (0.2 m); Q is the field capacity (%); q 1 represents the upper irrigation limit, q 2 represents the irrigation lower limit (75%, 65% or 55%), and 0.95 is the irrigation coefficient.…”

“…For each DI system, the water amount for DR1, DR2, or DR3 was calculated using the following equation [13]:…”

NxO emissions in response to the irrigation lower limits under different irrigation modes in a lettuce field

“…In this study, the converted furrow irrigation quota according to DR2 was consistent with the local practice. The irrigation quota was calculated as [19] :…”

“…Furthermore, the correlation between N 2 O/NO emission and possible influencing factors was also analyzed. However, different irrigations may cause different distribution of water and N in soil profile [19] . Soil capillary action will promote water and nitrogen to accumulate to the surface soil, therefore affecting the NO x emission.…”

“…Many studies showed that the irrigation amount (irrigation quota) affects the emission of nitrogen oxides from agricultural land [9] . The research by Chen et al [10] showed that the soil N 2 O emission increases gradually as irrigation quota increased, N 2 O emission under 60% and 80% irrigation quotas decreased by 19.1% and 8.0% respectively compared to under full irrigation quota. Du et al [11] employed the static box in-situ gas sampling method and found that average cumulative N 2 O emission by full irrigation is 1.27 times than that by deficit irrigation.…”