The Effect Of Irrigation And Nitrogen On Spinach Growth,Water And Nitrogen Migration In Soil

Water and nitrogen are important factors that affect plant growth and survival.The increasing scarcity of water for irrigation and environmental pollution due to excessive use of fertilizers are the important problems in vegetable production.The objective of this study was to explore the effect of different irrigation and nitrogen treatment on growth responses of spinach,water and nitrogen use efficiency,and water and nitrogen migration in soil.It provided a scientific basis for saving water and fertilizer resources,improving water and nitrogen efficiency,increasing the spinach yield,reducing nitrogen leaching and protecting sustainable development of agriculture.A great amount of water and nitrogen fertilizer were used in spinach growth.And spinach was easy to accumulate nitrates.Spinach?Spinacia oleracea L.?was used to investigate the effects of irrigation and nitrogen.The field experiments were conducted at the Irrigation and Drainage Experimental Station located in Qingpu District,ShangHai,China.A field experiment with combination of three levels of irrigation?W₁:20 cm?W₂:40 cm?W₃:60 cm?and nitrogen fertilization(N₀:0 kg ha^-1?N₁:85 kg ha^-1?N₂:170 kg ha^-1)was employed to optimize the irrigation and nitrogen fertilizer usage of spinach for three years.Nitrogen nutrition?physiological traits,water and nitrogen use efficiency,yields and quality?,soil microorganism,and migration pattern of water and nitrogen of spinach under different regimes were determined.Main results were shown as the following.1.The effect of physiological traits under irrigation and nitrogen treatments.Leaf area was significantly influenced by water and nitrogen treatment.Leaf area and plant height increased with the increase of nitrogen application in the well-watered treatment.Total biomass of spinach was affected by nitrogen fertilizer.The total biomass got the highest value(5.04 g plant^-1)intreatment of W₂N₂ and it decreased under water deficit.The application of nitrogen fertilizer resulted in an increase in root activity and the maximum value 1.34 mg g^-1 h^-11 was obtained under W₂N₂ treatment.Water deficit?W₃?decreased the root activity.2.The effect of water and nitrogen use efficiency and quality under irrigation and nitrogen treatments.Water and nitrogen use efficiency were affected by both irrigation and nitrogen fertilizer usage.The highest WUE value(36.87 kg ha^-11 mm^-1)was observed under W₃N₂ treatment and the lowest WUE value(6.68 kg ha^-11 mm^-1)was observed under W₁N₀ treatment.Effects of irrigation levels on the WUE ranked as W₃>W₂>W₁.It was noted that WUE generally increased under lower irrigation levels.Effects of nitrogen levels on the WUE ranked as N₂>N₁>N₀.Increase in nitrogen fertilizer usage could lead to increased WUE.NUE was affected by nitrogen fertilizer.NUE reached the lowest value of 8.82%in N₂treatment while the highest value 30.59%was observed in N₁ treatment.3.Spinach yields varied significantly under different irrigation and nitrogen treatment.In general,the yield of spinach increased with the amount of nitrogen.Under W₂N₂ treatment,yield had the maximum value 12.79 ton ha^-1.But excessive nitrogen decreased the spinach production.The yield of spinach was generally more responsive to irrigation levels.Spinach yield was highest in W₂treatment and yield decreased when irrigation was excessive or deficient.The results implied that excessive nitrogen fertilizer usage,and excessive or deficit water supply reduced the yield.The highest yield was 12.79 ton ha^-11 in the treatment of W₂N₂.4.Different irrigation and nitrogen management have the different effect on the quality of spinach.The content of nitrate and oxalic acid of spinach decreased when nitrogen fertilizer increased and irrigation was short.These could seriously affected the quality of spinach.The content of nitrate was highest 554.06 mg/kg under W₃N₂ treatment and the minimum value was 123.66 mg/kg under W₁N₀treatment.The content of oxalic acid was highest 494.80 mg/100g under W₃N₂ treatment and the minimum value was 160.00 mg/100g under W₁N₀ treatment.The effect of different irrigation and nitrogen treatments on the nutritional quality of spinach was also evident.The content of Vc,soluble sugar,soluble protein and free amino acids were high in deficit treatment W₃ and they decreased under excessive irrigation.The content of soluble sugar,soluble protein and free amino acids decreased when nitrogen treatment reduced.5.The different irrigation and nitrogen treatments affected the soil microbe.Deficit irrigation could reduce the soil microbial diversity.Under the same nitrogen treatment,the effect of irrigation on microbe biomass carbon ranked as W₂>W₁>W₃.Appropriate nitrogen treatment could increase the soil microbe biomass carbon and phosphorus,but they decreased under the excessive fertilizer and deficit irrigation.Soil enzymes activity were influenced by both irrigation and nitrogen fertilizer application.When the nitrogen fertilizer increased,soil enzymes activity increased.Deficit irrigation treatment could inhibit the soil enzymes activity.Soil enzymes activity increased under appropriate irrigation treatment W₂ and it was suitable for the growth and yield of vegetable.And the highest value of microbe biomass carbon was 302.48 mg kg^-11 in W₂N₂ treatment.The results indicated soil microbial carbon,soil enzymes activity and soil microbial diversity were high under W₂N₂ treatment and they could affect the soil microbial environment.6.A more irrigation treatment produced a higher soil water content.Under the same irrigation treatment,the electric conductivity in the same soil layer was larger when the nitrogen was applied more.With the increase of nitrogen fertilizer,the soil NO₃^--N content increased in the development and middy stage of spinach.The NH₄⁺-N mostlyaccumulated in the 0-10 cm of soil layer.In the middy period,the content of NH₄⁺-N content in the 0-10 cm soil layer was between 0.18-0.31 mg L^-1 under different irrigation and nitrogen treatment.The values of NH₄⁺-N content increased with the increase of nitrogen fertilizer.The effect of irrigation on NH₄⁺-N was not significant.The HYDRUS-1D model could simulate water and nitrogen migrate in the soil through the calibration and test.7.According to the analysis of physiological traits,water and nitrogen use efficiency,quality of spinach,soil microorganisms and soil enzymes.The optimization of irrigation and nitrogen treatment was that the irrigation treatment was 30-40 cm and the nitrogen treatment was 120-170kg ha^-1.