节水条件下盐碱农田施用有机肥的固碳及其生态系统服务价值提升效应

Carbon fixation with improved ecosystem service using organic fertilizer application under water-saving irrigation of saline-alkali farmlands

针对中国黄河中上游河套灌区不合理灌溉和施肥造成的盐碱农田碳排放加剧和生态系统服务功能退化等问题,该研究以向日葵盐碱农田为研究对象,开展连续2 a的田间试验,探讨滴灌条件下有机肥施用对盐碱农田生态系统净碳收支和生态系统服务功能价值的影响。试验设置滴灌灌水下限及施肥模式2个因素。灌水下限设置2个水平(W1:土壤基质势阈值为-20 kPa,W2:土壤基质势阈值为-30 kPa),每个灌水下限下设置3种施肥模式(CK:纯施化肥,LBF:褐煤碳基有机肥4.5 t/hm^(2),SMF:羊粪堆肥5 t/hm^(2)),采用完全随机区组设计。另设畦灌施加化肥处理作为对照(MCK)。对不同处理的生态系统净碳收支及其组成要素以及3种生态系统服务价值(农产品供给功能价值、积累有机质功能价值和气体调节价值)进行了对比分析。结果表明:相同施肥条件下,滴灌处理的土壤有机质含量、作物净初级生产力、籽粒碳输出和土壤碳排放高于畦灌处理,且这些指标的值均随土壤基质势升高而增加。相同灌溉条件下,施加有机肥处理可以显著提高土壤有机质含量、净初级生产力和籽粒碳输出并降低土壤碳排放。其中,滴灌灌水下限-20 kPa与褐煤碳基有机肥用量4.5 t/hm^(2)(W1LBF)相结合的处理有效促进了作物生长,并获得了最高的净初级生产力以及较低的土壤碳排放量,最终获得了最高的生态系统碳汇能力。此外,净初级生产力、土壤有机质和土壤碳排放等指标的变化影响了生态系统服价值。与MCK处理相比,W1LBF处理能够显著提升农产品供给功能价值、积累有机质功能价值和气体调节价值,增幅分别为8004.20、923.9和2094.70元/hm^(2)。综上所述,该研究发现在河套灌区向日葵盐碱农田中,采用滴灌-20 kPa灌水下限结合4.5 t/hm^(2)褐煤碳基有机肥可以增加作物初级净生产力、提高盐碱农田系统的碳汇能力和生态系统服务功能价值。该研究可为干旱半干旱地区盐碱向日葵农田固碳减排和生态系统可持续发展提供科学依据。

Inappropriate irrigation and fertilization have led to high carbon(C)emissions and degradation of ecosystem services in the saline-alkali sunflower farmland in the arid upper Yellow River basin of Northwest China.This study aims to determine the rational irrigation and fertilization strategy for the sustainable production of saline-alkali sunflower farmland in this area.A field experiment was carried out to investigate the effects of organic fertilizer application on the net ecosystem carbon budget(NECB)and ecosystem service values of saline-alkali farmland under drip irrigation in 2021 and 2022.Two factors were considered,including the lower limit of irrigation and the fertilization mode.Among them,the lower limit of irrigation(drip irrigation)was divided into two soil matric potential thresholds(SMPT)(W1:−20 kPa SMPT and W2:−30 kPa SMPT).Three fertilization modes were selected(CK:Chemical fertilizer,LBF:Lignite C-based organic fertilizer 4.5 t/hm^(2),SMF:Sheep manure compost 5 t/hm^(2))under each SMPT using a completely random block design.In addition,the border irrigation combined with chemical fertilizer was set as the control treatment(MCK),corresponding to the local farmer practices.A comparison was performed on the NECB of different ecosystems and the components,as well as three ecosystem service values(supply function value of agricultural products,accumulated functional value of organic matter,and gas regulation value)among different treatments.Results indicated that the LBF and SMF treatments effectively promoted crop growth and biomass accumulation,compared with the CK.There was also an increase in the soil moisture content and soil organic matter(SOM)content under the drip irrigation.Among all treatments,better performance was achieved in drip irrigation with−20 kPa SMPT combined with 4.5 t/hm^(2) lignite C-based organic fertilizer application treatment(W1LBF).The highest aboveground biomass and yield also increased by 32.30%and 44.13%,respectively,compared with the MCK.These soil and crop indicators depended mainly on the NECB.The net primary productivity(NPP)and grain C output were the main components of the carbon sink and carbon source in the farmland system,respectively.NPP,SOM content,grain C output,and soil C emission in the drip irrigation treatment were higher than those in the surface under the same fertilization,where the values of these indicators increased with the increase of SMPT.Moreover,the organic fertilizer application(LBF and SMF)also significantly improved NPP,SOM content,and grain C output under the same irrigation,but reduced the soil C emissions,compared with the chemical fertilizer application(CK).The W1LBF treatment obtained the highest NPP and lower soil C emissions,thus achieving the highest NECB.Compared with the W1CK and MCK treatments,the W1LBF treatment increased NECB by 26.24%-159.98%and 151.74%,respectively.In addition,the changes in NPP,SOM,and soil carbon emissions also significantly affected the ecosystem service value.W1LBF treatment increased the supply function value of agricultural products,SOM accumulation,and gas regulation by 8004.20,923.90,and 2094.70 Chinese Yuan/hm^(2),respectively,compared with the MCK.In conclusion,the drip irrigation with−20 kPa soil matric potential thresholds combined with 4.5 t/hm^(2) lignite C-based organic fertilizer application can effectively increase the C sink and service values from the saline-alkali sunflower farmland ecosystem in the arid upper Yellow River basin of Northwest China.The research can provide the scientific basis for the saline-alkali farmland C sequestration and ecosystem service value,while greenhouse gas emission reduction in the arid and semi-arid areas.