Nitrogen Uptake And Utilization Of Greenhouse Cherry Tomato Based On ¹⁵N Isotope Tracer And Coupling Effects Of Water And Nitrogen

Facility agricultural production has become an important part of modern agricultural production,contributing to the consolidation and expansion of rural poverty eradication and the promotion of the rural revitalisation strategy.However,the intensive greenhouse production is always accompanied by an excessive application of water and nitrogen fertilizers,resulting in a serious waste of water and fertilizer resources and a series of environmental problems（atmospheric pollution,land degradation and so on）.The key to further improving the utilization of water nitrogen by vegetable crops and to reduce the amount of water and nitrogen applied in order to reduce environmental pollution is to find an optimal combination of economic and environmental benefits and to determine a reasonable amount of irrigation and fertilizer application.Aiming at the problem of low water and nitrogen use efficiency in facility cultivation,a study on the mechanism of nitrogen transport and uptake in greenhouse cherry tomatoes based on ¹⁵N tracing and the coupling effect of water and nitrogen was carried out,which is of guiding significance for guiding cherry tomatoes to save water and fertilizer and improve quality and efficiency.In this study,cherry tomato（‘Pink Rose M-2’）was planted in a greenhouse.Three irrigation levels（I100:100%ET₀,I80:80%ET₀ and I60:60%ET₀,where ET₀ is the reference crop evapotranspiration）and five nitrogen application rates(N450:450 kg N ha^-1,N360:360 kg N ha^-1,N270:270kg N ha^-1,N180:180 kg N ha^-1 and N0:0 kg N ha^-1)were applied to study the response of growth,yield,quality,water and nitrogen use efficiency and economic benefits of cherry tomato.Additionally,explore the mechanism of high nitrogen use efficiency of cherry tomato under the combined effect of irrigation amount（I100:100%ET₀ and I60:60%ET₀）and topdressing nitrogen fertilizer date（M1:24/31 DAT（2019/2021）,M2:38/48 DAT and M3:52/62 DAT）.Based on a three-year of spring trial of cherry tomato,the main results are as follows:（1）Analyze the effects of different water and nitrogen management on growth characteristics of cherry tomatoThe polynomial function was able to accurately simulate the measured normalized root length density distribution（R²=96.52%,RMSE=0.17）.The improved polynomial function(L_{nr d}（z_r）=（1-z_r）（A+Bz_r+Cz_r ²）)was able to satisfy the physical significance of the normalized root length density at all soil depths while maintaining the highest simulation accuracy.Excessive or severe water and nitrogen deficits resulted in smaller areas of root length density concentration.Heavy deficit irrigation and N stress not only inhibited the growth of root length density,but also accelerated its senescence.The response of root length density to N application at harvest depended on the amount of water applied,and among the I60 treatments,the N270 treatment produced the highest values of root length density at harvest,whereas the highest root length densities were produced in the N360 treatments in the I80 and I100 treatments.The root length densities of the I80N360 treatments（averaged over the two years）showed the optimum distribution of the root system.Both water level and nitrogen application significantly affected the growth of cherry tomato.（2）Reveal the fate of the effects of different water and nitrogen management and topdressing N fertilizer at different dates in the soil-cherry tomato systemPlant uptake of nitrogen derived from ¹⁵N-labelled urea（Ndff）showed an increasing trend with the increase in irrigation and the postponement of the date of the topdressing N application（I100>I60,M3>M2>M1）.The I100M1 treatment had the largest percentage of plant N uptake（64.9%on average）,whereas the I60M3 treatment had the highest percentage of ¹⁵N residue in the soil（65.5%）.The fate of ¹⁵N-labelled urea was significantly influenced by irrigation amount and date of topdressing N fertilizer application.Reducing the irrigation amount and post-delay of topdressing N fertilizer application significantly reduced soil N losses,but similarly resulted in lower N uptake by cherry tomato plants and increased the rate of ¹⁵N residue in soil 0-60 cm.Straw,fruit and aboveground N concentrations and N accumulation increased and then decreased with increasing water application,and the maximum values were obtained in the I80 treatment.Increasing N application increased straw,fruit and aboveground N concentration and N accumulation,but the differences were not always significant.Increased irrigation reduced nitrate-N concentrations in the top 0-20 cm of soil and nitrate-N residues in the 0-50 cm and 0-100 cm,but increased nitrate-N concentrations in the 20-40 cm soil layer.Nitrate N residues in the 0-50 cm soil layer decreased by an average of 16.9%and 10.3%in the I100 and I80 treatments,respectively,and by an average of 6.1%and 4.6%in the 0-100 cm soil layer,compared to the I60 treatment.Regardless of the irrigation level and the year of the experiment,postharvest nitrate N residues in the three soil layers of the N application treatments（0-50 cm,50-100 cm,and 0-100 cm）showed different degrees of increase compared to the N0 treatment,with the greatest increase in nitrate N residues in the 0-50 cm soil layer（46.0%-184.0%）.The I80N360 treatment did not have a significantly lower effect and the water nitrogen use efficiency（WP,IWUE,NUE,ANUE）was higher.（3）Clarity the combined effects of water and nitrogen on yield,quality and economic performance of cherry tomatoThe yields of the three-year experiment showed a significant increase and then a significant decrease with the increase of nitrogen application.The effects of irrigation level and water-nitrogen interaction on yield and its components varied by year.Irrigation level,N application and year all had highly significant effects on cherry tomato fruit quality,but the binary and ternary interactions varied by year of trial and quality indexes.The I80N360 treatment achieved the highest yield,fruit weight per fruit and net return over the 3-year trial period.（4）Optimize water and nitrogen management in greenhouse cherry tomatoThe AquaCrop model was able to simulate canopy cover（higher R²（≥0.94）,d（≥0.97）and EF（≥0.85）,lower NRMSE（4.5%≤NRMSE≤15.7%）and RMSE（2.6%≤RMSE≤6.7%））,above-ground biomass（higher R²（≥0.94）,d（≥0.97）and EF（≥0.85））,and aboveground biomass（higher R²（≥0.94）,d（≥0.96）and EF（≥0.95））in greenhouse film-under-drip-irrigated cherry tomato well.0.94),d（≥0.96）and EF（≥0.85）,lower NRMSE（9.7%≤NRMSE≤27.1%）and RMSE(0.3 t ha^-1≤NRMSE≤1.3 t ha^-1)),and final yields(2021 values of R²,RMSE,NRMSE,d and EF of 0.77,0.34 t ha^-1,8.18%,0.88 and 0.68 in 2021 and 0.77,0.26 t ha^-1,5.53%,0.93 and 0.70 in 2020,respectively).However,the soil water content of the fully irrigated treatments was overestimated and the simulation accuracy gradually increased with increasing N application.For water consumption,there was a significant underestimation.The simulation accuracy of water productivity decreased with increasing irrigation levels,with the simulated values for the low N treatments（N0 and N180）being closer to the measured values than the high N treatments（N360 and N450）.The simulation accuracy gradually increased with decreasing irrigation level and N application,and the effect of water stress was greater than that of N application.A watering level of 80%ET₀ combined with N application of 360 kg N ha^-1（I80N360）was the optimum treatment.Considering the uncertainty of the parameters,different irrigation levels in 2019and 2021 did not significantly affect the critical nitrogen dilution curves constructed based on aboveground dry matter mass and leaf area index.The choice of a priori distribution did not affect the results of the dilution curves.The nitrogen nutrient indices calculated from the critical nitrogen dilution curves based on leaf area index and aboveground dry matter mass could all be used to diagnose the nitrogen nutrient status of the crop.The nitrogen nutrient indices of the N360,N360,and N270 treatments were all close to 1 at I100,I80,and I60 irrigation levels in 2019-2021,indicating that nitrogen was applied at an appropriate rate.Relative yield was optimal when the nitrogen nutrient index thresholds for the critical nitrogen dilution curves based on aboveground dry matter mass and leaf area index were 0.993 and 0.985,respectively.Both critical nitrogen dilution curves based on aboveground dry matter mass and leaf area index could be used to accurately diagnose the nitrogen nutritional status of cherry tomatoes in solar greenhouses.By establishing binary quadratic regression relationships between cherry tomato yield,water and nitrogen use efficiency,net income and quality（sugar-acid ratio and lycopene）and water and nitrogen inputs,it was found that cherry tomato yield,net yield,water and nitrogen use efficiency,lycopene,and sugar-acid ratio could simultaneously reach 90%of their optimum values when irrigation was 147-167 mm and nitrogen was applied at a rate of 335-424 kg N ha^-1.The results of AquaCrop model,critical nitrogen concentration dilution curve,and entropy weighting method-TOPSIS method found that the combination treatment of moderate deficit irrigation（80%ET₀）and nitrogen application of 360 kg N ha^-1 was able to achieve the optimisation of yield,economic efficiency,and water and nitrogen use efficiency.