The agricultural development of reclaimed coastal areas in Jiangsu Province is significantly hindered by high soil salinity and an inadequate irrigation and drainage infrastructure. Optimizing the layout of subsurface drainage systems has been identified as an effective means of reducing soil salinity, with the proper designation of engineering parameters being crucial. This study applied 12 treatments (T1–T12) consisting of four different spacings of subsurface drainage pipes (6 m, 11 m, 15 m, and no subsurface drainage pipes) and three observation wells at varying distances from the drainage outlet (5 m, 25 m, and 45 m). Results showed that all three subsurface pipe spacing treatments significantly reduced soil salinity compared to natural drainage, with a smaller subsurface pipe spacing treatment leading to better salt-reducing effects. The farther the distance from the measuring point to the drain, the higher the salinity. As the burial depth of the outlet decreased and spacing between the subsurface drainage pipes decreased, the salinization rate of the 0–60 cm soil layer was higher, while the salt accumulation in the 60–80 cm soil layer was more severe. Therefore, a subsurface drainage pipe spacing of 6 m and an outlet burial depth of 40 cm are recommended as more suitable choices to effectively control salt concentration in the soil. The research aimed to provide scientific reference data and technical support for the optimized design of subsurface drainage engineering parameters while promoting efficient desalination of saline-alkali areas worldwide.

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-absorbed ¹⁵N or ¹⁵N 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 the ¹⁵N 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.

Subsurface drainage and organic fertilizer application are two important measures for improving saline–alkali soils, while the effects of different drainage spacings combined with organic fertilizer application amounts on alfalfa growth and coastal saline soil properties have seldom been evaluated. This study designed subsurface drainage pipes at four spacing distances, including 0 m (CK, without subsurface drainage), 6 m (S1), 12 m (S2), and 18 m (S3), and three organic fertilizer application amounts, including 3000 kg/ha (N1), 4500 kg/ha (N2), and 6000 kg/ha (N3), to observe the effects of different combinations of subsurface pipe spacings and organic fertilization amounts on alfalfa yield, quality, soil salinity, and nutrients. The results showed that the yield of alfalfa increased with higher fertilization amounts and smaller spacing between drainage pipes. The highest yield occurred in the S1N3 treatment, and the three batches reached 1268.5 kg/ha, 3168.0 kg/ha, and 2613.3 kg/ha, respectively, significantly (p < 0.05) higher than CK for all three batches. The increase in organic fertilizer amount resulted in an increase of 0.5–9.3% in the crude protein content, a decrease of 1.8–3.4% in the neutral detergent fiber content, and a decrease of 1.3–5.5% in the acid detergent fiber content for alfalfa plants. Under CK, the contents of quality indicators in alfalfa were the highest. For the drainage treatments, the quality indicator contents were overall at a higher level under S3. Subsurface drainage had a reduction effect on the salinity of all the 0–80 cm soils. For the surface soil, it was detected that smaller spacing was beneficial for reducing soil salt content, while higher fertilization amounts increased the salt content. S1 reduced the soil salt content by 36.3–46.1% compared to CK; however, N3 increased the salt content by 7.0–16.2% compared to the other two fertilization treatments. In addition, smaller spacing between the subsurface drainage pipes generally reduced the soil’s available nitrogen, and total nitrogen increased the C/N ratio but had no significant effect on the organic matter. It was concluded that the spacing between subsurface drainage pipes and the application amounts of organic fertilizer have remarkable impacts on alfalfa yield and quality, mainly by changing the soil salinity and nutrient status.

The accurate and efficient management of water and nitrogen is of significance for the intensive production of field-cultivated flowers. To investigate the effects of different irrigation and nitrogen application modes on the growth, development, and nitrogen use of Orychophragmus violaceus, three nitrogen application doses of 120, 160, and 200 kg/ha and three irrigation treatments of 50 + 30 mm (overwintering water and regreening water), 75 + 45 mm, and 100 + 60 mm were implemented. The ¹⁵N isotope tracing technique was used to investigate the fertilizer nitrogen use, soil nitrogen residue, and nitrogen balance of Orychophragmus violaceus, and the entropy weight coefficient evaluation model was employed to optimize the water and nitrogen strategy. Results showed that after the application of water and nitrogen, the fresh yield of Orychophragmus violaceus increased by 21.4–49.3%, W2N3 possessed the most obvious effect on promoting yield increase, and the fresh yield reached 31.1 t/ha. The highest plant nitrogen use efficiency (39.1%) was detected in W2N2, but no significant (p > 0.05) difference of nitrogen use efficiency was found between W2N2 andW3N2. After the peak flowering period, 23.8–39.1% of the fertilizer nitrogen was absorbed by the plants, 44.3–59.2% remained in the soil, and 13.7–21.6% was lost via deep seepage, a gaseous state, or other unknown ways. A higher application amount of water or nitrogen increased the risk of nitrogen loss. Among the treatments, W2N2 treatment has the highest entropy weight coefficient evaluation value of 0.905, indicating that W2N2 was the water–nitrogen coupling mode with optimal comprehensive benefits. It was recommended that 75 mm of overwintering water and 45 mm of regreening water combined with a 160 kg/ha nitrogen application amount is the suitable water and nitrogen regulation scheme for Orychophragmus violaceus.

Human-dominated landscapes have become a serious threat to amphibian populations worldwide. In such landscapes, concrete structures act as barriers to migration, fragmenting habitat and causing mortality. In China, concrete irrigation channels, which play an important role in agriculture, impede the movement of anuran amphibians. To promote the sustainable development of irrigated agriculture, we performed behavioral experiments to examine the ability of a common Chinese frog species (Pelophylax nigromaculatus) of four different body sizes to use corridors along a gradient of six different slopes to escape from irrigation channels. We found that body size was positively related with frogs’ ability to climb the ladders. Most frogs could not escape if the slope was ≥65 degrees, but all frogs could successfully navigate a ladder with a slope of 45 degrees. Based on our experimental results, we propose a simple improved design for amphibian ladders that would greatly improve the success of frogs in escaping from irrigation channels. This research is expected to provide scientific reference data and technical support for frog conservation in the study area, as well as the development of ecological restoration of irrigation districts throughout the world.

Irrigation has a significant impact on NxO (N2O and NO) emissions from cultivated land, yet the N2O or NO emission among the irrigation lower limits under different irrigation modes has not been well compared. In an irrigated lettuce field, three DR (drip irrigation) lower limits were designed, including 75% (DR1), 65% (DR2) and 55% (DR3) field capacity, and one FI (furrow irrigation) lower limit (65% field capacity). The N2O and NO emission fluxes and soil nitrogen (N) forms were determined, and the linear correlation between these indicators was analyzed. Results showed that under the same irrigation regime, the N2O and NO emissions from furrow irrigation treatment increased by 36.8% and 45.2% respectively compared to that from drip irrigation treatment. The cumulative N2O and NO emissions under DR3 were 30.2% and 28.6% higher than under DR1, respectively. Moreover, DR1 was also the lowest among the four treatments in soil NO3--N concentration. The N2O and NO emission fluxes were more correlated to soil NH4+-N (r=0.88 and 0.76) or NO2--N (r=0.90 and 0.80) concentration than soil NO3--N and soluble organic N, indicating that N2O and NO were mainly produced by the soil nitrification process. When the irrigation regime was the same, N2O and NO emissions were lower with drip irrigation than with furrow irrigation. Besides, drip irrigation with small quota but high frequency reduced N2O and NO emission compared to that with large quota but low frequency. Keywords: nitrous oxide, nitric oxide, drip irrigation, furrow irrigation, soil nitrogen DOI: 10.25165/j.ijabe.20231604.7961 Citation: Hou M M, Xiao Y, Zhu Q Y, Chen J N, Huang H, Jin Q, et al. NxO emissions in response to the irrigation lower limits under different irrigation modes in a lettuce field. Int J Agric & Biol Eng, 2023; 16(4): 159–167.