Research On The Optimisation Of Drip Irrigation Water And Nitrogen Coupling Pattern Based On The Quality Of Wolfberry And Its Root Zone Soil

This paper addresses the problems of low water and fertilizer utilization,difficulties in yield and quality improvement,and unclear mutual feeding characteristics between soil and plant in the current drip irrigation wolfberry planting process.A two-year field trial was conducted in Runde Manor,Hexi Town,Tongxin County,a typical area in the central arid zone of Ningxia,from 2021 to 2022.Two factors of irrigation quota and nitrogen application were considered in the experiment,and three irrigation quotas were set:i.e.,irrigation of 2,160 m³·hm^-2 during the fertility period of wolfberry in the year of abundant water（28%water reduction,I₁）recommended by the technical regulations for drip irrigation cultivation as low water level;irrigation of 2,565 m³·hm^-2 during the fertility period of wolfberry in the year of level water（14%water reduction,I₂）as medium water level;irrigation of 2970 m³·hm^-2 during the fertility period of wolfberry in the year of dry water（I₃）as high water level and three N applications:i.e.,low N₁,165 kg·hm^-2,medium N₂,225 kg·hm^-2,and high N₃,285 kg-hm2,with local conventional water and nitrogen management as the control（CK）.A two-factor,threelevel completely randomised trial was used to systematically investigate the characteristics of water and nitrogen coupling on drip-irrigated wolfberry（growth,physiology,yield,quality,water and nitrogen use efficiency,and economic benefits）and root zone soil（nutrients,enzyme activities,microbial biomass,and microbial colony numbers）.The water and nitrogen management model with high yield,high quality and good soil ecological quality of drip irrigation in dry areas was constructed based on the multi-objective comprehensive judgement model,which provided a comprehensive evaluation of the growth,physiology,yield,quality,water and nitrogen utilisation rate and soil indicators of wolfberry.The main research results are as follows:（1）The comprehensive impact characteristics of drip irrigation water and nitrogen coupling on the growth,physiology,yield and quality of wolfberry were clarified.The growth and development of each growth indicators of wolfberry were mainly carried out in the spring and flowering period,and their growth and development basically stopped after entering the fruit ripening period.Each indicators were most obviously affected by irrigation quota,followed by water and nitrogen interaction,and nitrogen application had relatively the least effect.SPAD values were significantly better in the N₂ treatment under different irrigation quotas.The daily dynamics of leaf photosynthesis during the spring and fruit ripening periods were basically the same,with a single peak at 10:0012:00 am,and a second peak in transpiration rate at 14:00-16:00 pm in some treatments only.The dry fruit yields were all highest under I₂N₂ treatment,reached 2320.94 kg·hm^-2 and 2391.73 kg·hm^-2,respectively,which were 7.48%and 3.73%higher than CK,indicating that both too high irrigation quota and nitrogen application were unfavourable to the improvement of wolfberry yield.The optimal treatments for each indicator of quality of wolfberry had different degrees of improvement compared with CK,among which polysaccharides,total sugars and betaine were most obviously improved.The comprehensive evaluation of growth,physiology,yield,quality and other indexes and the water saving target showed that the growth,physiology,yield and quality of wolfberry were better when the irrigation quota and nitrogen application were 2565 m³·hm^-2 and 225 kg·hm^-2,respectively.（2）The characteristics of drip irrigation water and nitrogen coupling on water consumption,water and nitrogen use efficiency and economic benefits of wolfberry were investigated.The soil volumetric water content in the root zone of wolfberry increased with the increase of irrigation quota,and the soil layer of 0-80 cm showed a tendency of increasing and then decreasing with the increase of depth,among which the soil volumetric water content of 20-40 cm was the highest.The water consumption of wolfberry was elevated with the increase of irrigation water,I₃ enhanced the water consumption by 27 and 34.30%compared to I₂ and I₁ irrigation quota treatments,respectively,and I₂ enhanced the water consumption by 15.66%compared to I₁ irrigation quota treatment.Water use efficiency was significantly highest under I₁N₁ treatment with 40.82%and 35.72%enhanced than CK.Irrigation water utilisation gradually decreases with the increase of irrigation quotas,and the highest treatment improves by about 27%compared to the lowest treatment.The economic benefit study showed that the I₂N₂ treatment with the highest yield had the highest net return and yield-to-input ratio,with the net return reaching RMB 55,422 yuan·hm^-2 and RMB 76,230 yuan·hm^-2 in 2021 and 2022,respectively.The water-yield response coefficients Ky for fresh and dry fruit yields of wolfberry were relatively low at each fertility period and throughout the reproductive period.（3）Characteristics of the effect of drip irrigation water and nitrogen coupling on the spatial and temporal distribution of soil nutrients were revealed.The soil organic matter content showed a trend of decreasing,then increasing,and finally decreasing again during the whole reproductive period.The organic matter content basically increased with the increase of nitrogen application under the low and medium（I₁ and I₂）irrigation quotas,and showed a trend of increasing,then decreasing,with the increase of nitrogen application under the high（I₃）irrigation quota.The effects of irrigation quota,nitrogen application and their interaction effects on organic matter content were more obvious in the spring,flowering,and fruiting periods.The soil total nitrogen was mainly concentrated in the 0-60 cm soil layer,and there were differences in soil total nitrogen affected by water and nitrogen coupling in different fertility periods.In the flowering and fruiting periods,the soil total nitrogen showed a trend of decreasing and then increasing under the I₁ flooding;under the I₂ and I₃ flooding,with the increase of nitrogen application,the soil total nitrogen showed a gradual increase or a trend of increasing and then decreasing in the different fertility periods.The soil ammonium nitrogen content decreased to some extent with the increase of soil depth,but it was not obvious.Soil nitrate nitrogen decreased with the increase of soil depth,and the whole reproductive period basically showed an M-type trend,with the increase of nitrogen application,the nitrate nitrogen content basically showed a rising trend,with the increase of irrigation,nitrate nitrogen also showed a rising trend,but the increase was lower.（4）The spatial and temporal distribution of soil enzyme activity and its changing rules under drip irrigation water and nitrogen coupling were elucidated.The soil urease,sucrase and alkaline phosphatase activities decreased with the increase of soil depth,and the urease,sucrase and alkaline phosphatase activities in the 0-40 cm layer accounted for 71.24～80.14%,79.10～87.86%and 67.39～77.57%of the activities in the 0-80 cm layer,respectively.The activities of urease,sucrase and alkaline phosphatase at different fertility periods basically increased with the increase of nitrogen application under I₁ flooding,but showed a tendency to increase and then decrease with the increase of nitrogen application under I₂ and I₃ flooding.The hydrogen peroxide dismutase decreases to some extent with soil depth,but not significantly.The activities of urease and sucrase in the 0-60 cm soil layer were affected by irrigation quota,N application and their interaction effects at highly significant or significant levels,the activities of alkaline phosphatase in the 0-20 cm soil layer were affected by irrigation quota,N application and their interaction effects at highly significant or significant levels,and the activities of hydrogen peroxidase in the 0-80 cm soil layer were most significantly affected by irrigation quota at different fertility periods,with the interaction effects of water and nitrogen being the second most significant,and the effects of N application being relatively the least significant.（5）Characteristics of the effect of drip irrigation water and nitrogen coupling on soil nutrientmicrobial biomass and its stoichiometric characteristics in the root zone of wolfberry were revealed.The soil nutrient-microbial biomass in the root zone of wolfberry will change with short-term water and nitrogen regulation,and to some extent,the content will increase with the increase of irrigation and nitrogen application,but the ratio of soil nutrient and microbial biomass will not change significantly,means that the soil nutrient equilibrium will not be disrupted by the short-term water and nitrogen regulation.Under I₁ irrigation rating,increasing the amount of nitrogen fertiliser was able to significantly enhance the number of soil bacteria,fungi and actinomycetes,and the number of soil bacteria,fungi as well as actinomycetes showed a tendency to increase and then decrease with the increase in the amount of nitrogen applied under I₂ and I₃ irrigation ratings.The impacts of irrigation,nitrogen application and their interactive effects on soil bacterial,fungal and actinomycete populations were significant.（6）A water and nitrogen management model was constructed in which wolfberry,water and nitrogen use efficiency and the soil habitat in the root zone were all superior in drip irrigation water and nitrogen coupling.The multi-objective optimisation of key indicators of wolfberry growth,physiology,yield,quality,water and nitrogen use efficiency,economic benefits and soil physicochemical properties under drip irrigation water and nitrogen coupling was comprehensively evaluated through the AHP-TOPSIS model,and it was found that I₂F₂ treatment,i.e.,irrigation quota and nitrogen application of 2565 m³·hm^-2 and 225 kg·hm^-2,respectively,the drip-irrigated wolfberry growth,physiology,yield,quality,water and nitrogen use efficiency,economic benefits and soil ecological environment were optimal.This can be used as a reference for the optimal water and nitrogen management mode of drip-irrigated wolfberry cultivation in the central arid zone of Ningxia.