NITROGEN USE AND MANAGEMENT IN ORCHARDS AND VEGETABLE FIELDS IN CHINA: CHALLENGES AND SOLUTIONS

Abstract

● Excessive application of N fertilizers in orchards and vegetable fields (OVFs) in China is particularly common.

● Long-term excessive application of N fertilizers has made OVFs hotspots for N surplus and loss in China.

● Nitrate accumulation in the soil profile is the main fate of N fertilizers in OVF systems.

● Reducing the N surplus is the most effective way to reduce N loss and increase NUE.

China is the largest producer and consumer of fruits and vegetables in the world. Although the annual planting areas of orchards and vegetable fields (OVF) account for 20% of total croplands, they consume more than 30% of the mineral nitrogen fertilizers in China and have become hotspots of reactive N emissions. Excess N fertilization has not only reduced the N use efficiency (NUE) and quality of grown fruits and vegetables but has also led to soil acidification, biodiversity loss and climate change. Studies using ¹⁵N labeling analysis showed that the recovery rate of N fertilizer in OVFs was only 16.6%, and a high proportion of fertilizer N resided in soils (48.3%) or was lost to the environment (35.1%). Nitrate accumulation in the soil of OVFs is the main fate of N fertilizer in northern China, which threatens groundwater quality, while leaching and denitrification are the important N fates of N fertilizer in southern China. Therefore, taking different measures to reduce N loss and increase NUE based on the main pathways of N loss in the various regions is urgent, including rational N fertilization, substituting mineral N fertilizers with organic fertilizers, fertigation, and adding mineral N fertilizers with urease inhibitors and nitrification inhibitors.

Graphical abstract

Keywords

nitrogen fate / nitrogen fertilizer / orchards / vegetable fields

1 INTRODUCTION

The application of nitrogen fertilizer has fed nearly half of the global population^[1]. However, more than 50% of N fertilizer applied to agricultural systems is estimated to be lost to the environment in various ways, resulting in a series of problems, such as low N use efficiency (NUE), soil acidification, eutrophication, climate change and loss of biodiversity^[2,^3]. Clarifying the hotspots of N surplus and fates in an agricultural system is critical for controlling N losses and increasing NUE. China has consumed more than 30% of annual global N fertilizer production^[4]. Compared to cereal crops, excessive application of N fertilizers in orchards and vegetable fields (OVFs) in China is common and is considered a hotspot of N surplus and loss^[5–^7]. Therefore, comprehensively understanding the fates of N fertilization of OVFs in different regions is urgent for optimizing agricultural N management in China.

2 DEVELOPMENT AND N FERTILIZATION OF ORCHARDS AND VEGETABLE FIELDS

The production of fruit and vegetable crops in China has rapidly increased since the late 1980s. The areas of orchards and vegetable crops increased from 1.8 and 3.2 Mha in 1980 to 12.3 and 20.9 Mha in 2019, respectively, accounting for 20% of the total national cropland of China (Fig.1)^[8]. China has become the largest producer and consumer of apples and citrus in the world, and the planting areas of apples and citrus in China are 2.32 and 2.69 Mha, respectively^[4]. The areas and yields of apple in China account for 48% and 54% of the world totals, respectively^[4,^8]. Orchards and vegetables are in second and third ranked in China’s plantation production industry, respectively, and they are of substantial importance for China’s agricultural economy and income of farmers.

The annual application of N fertilizers in China has greatly increased as the OVF area has increased (Fig.1). The areas of OVF in China only account for 20% of the national planting area; however, they have consumed 32% of the annual mineral N fertilizers in China (~10 Tg·yr⁻¹ N; Fig.1)^[9]. The excessive application of N fertilizer in OVFs in China is particularly common^[5,⁶,^10]. For example, the average annual N input in the kiwifruit orchard on the northern slope of the Qinling Mountains in Shaanxi is 1201 kg·ha⁻¹ N, which is 10 times that of the N harvested in fruit and prunings, resulting in a high N surplus^[11–^13]. The averages of N fertilizer application and N surplus in the orchards (including apple orchards, kiwifruit orchards and vineyards) in Shaanxi Province are 1066 and 876 kg·ha⁻¹ N, respectively, and more than 94.8% of these orchards overuse N fertilizers^[13]. The average N input in apple orchards in Shandong Province is 867 kg·ha⁻¹ N, which is 7.2 times the crop N uptake^[7]. High N surplus is also common in orchards in southern China. He et al.^[14] reported that the average N fertilizer rate of mango orchards in Hainan Province is 275 kg·ha⁻¹ N, 3.8 times the N removal by the crop.

The N fertilizer application rates and N surplus of vegetable fields are usually greater than those of orchards in China due to the common use of organic fertilizers and multiple harvests annually (> 2 planting times). A survey in Shandong Province by Ju et al.^[7] found that the average N surplus in vegetable fields is as high as 3327 kg·ha⁻¹·yr⁻¹ N (n = 56). The survey by Fan et al.^[15] in Shaanxi Province showed that the average N surplus in vegetable fields is 1407 kg·ha⁻¹ per season. The average annual N surplus of vegetables in the solar greenhouse of the Guanzhong Plain is 1354 kg·ha⁻¹ N, accounting for 72% of the total N input^[16]. The application rates of N fertilizers in OVFs in China are significantly higher than those recommended by experts^[17]. The average N surplus of China’s OVFs also significantly exceeds the N surplus threshold suggested by the EU Nitrogen Expert Panel (80 kg·ha⁻¹ N)^[18]. The high economic benefits, the lack of knowledge of crop N requirements and N accumulation in soil profile and ignoring the N added by organic fertilizers, N deposition, and irrigation for smallholders are the main reasons for the overuse of N fertilizer.

3 FATE OF NITROGEN IN INTENSIVE ORCHARDS AND VEGETABLE FIELDS

The fate of N fertilizer applied in soil and plant systems include crop uptake, soil accumulation and loss. Compared with other methods, the ¹⁵N isotopic labeling method is an accurate way to quantify the fate of N fertilizer^[19,^20]. Given that studies using containerized plants in the OVFs are not representative field conditions, we have summarized the results of the ¹⁵N labeling analyses in microplots in fields of OVFs in China (Tab.1). This showed that the average N recovery rate of the OVFs is 16.6% in the season of application, which is significantly lower than in the principal field crops (25%, 33% and 28% for wheat, corn and rice, respectively) determined by the same method^[19].

3.1 Nitrogen accumulation in the soil profile

¹⁵N labeling analyses showed that the fertilizer N accumulation in the soil of OVFs accounted for an average of 48.3% of the N fertilizer application (Tab.1). Many field studies have provided clear evidence that nitrate accumulation in the soil profile is one of the main forms of residual N fertilizer in OVFs, especially in northern China^[5,¹⁰,^35]. For example, Bai et al.^[5] reported that the nitrate accumulation in the 0–4 m soil profile of vegetable fields is 950–1487 kg·ha⁻¹ N, and that the estimated nitrate accumulation in the 0–4 m profile of vegetable fields in China is 21.1 Tg N, being about 3.7 times the annual N fertilizer input of vegetable fields in China. The average accumulation of nitrate in the 0–6 m soil of apple orchards on the Loess Plateau is 4131–7250 kg·ha⁻¹ N, of which more than 50% of the nitrate nitrogen accumulates in the deep unsaturated zone (2–6 m), which is difficult to reuse for fruit trees^[36]. For the kiwifruit belt of the northern slope of the Qinling Mountains (with irrigation, a shallower vadose zone than apple orchards on the north Loess Plateau), the average nitrate accumulation in the 0−10 m soil profile is 7113 kg·ha⁻¹ N ^[6]. We analyzed the fate of surplus N after land conversion from cereal lands to apple orchards at a county scale on the Loess Plateau and found that soil nitrate accumulation accounted for 52% of the total N input and was the main fate of input N^[10]. A study of the hilly area in southern China also found that orchards (with vadose zone thicknesses > 4 m) have high nitrate accumulation in soil, and the nitrate accumulation increases with the vadose zone thickness ^[37]. Therefore, overuse of N fertilizer, a thick vadose zone, strong soil nitrification and weak denitrification (from low soluble organic carbon content and good aeration) may explain why high nitrate accumulation is found in the vadose zones of intensive planting areas in China^[5,⁶,¹⁰,^38].

Compared with the soils and climates in northern China, the OVFs in the tropical and subtropical regions of southern China have higher rainfall and temperature and shallower vadose zones. N leaching and denitrification losses may be the primary fate of N fertilizer in these agroecosystems (Fig.2). For example, in the OVFs of the Taihu Lake Basin in China (with average annual rainfall of 1344 mm, the vadose zone thickness is usually less than 1–2 m), low nitrate accumulation is found under high N fertilizer input (590–600 kg·ha⁻¹ N) due to the leaching and high denitrification under the anaerobic environment (the dissolved oxygen concentration of groundwater is < 2 mg·L ⁻¹) and the high soluble organic carbon content^[39]. Similar results were found in other intensive agricultural areas with relatively shallow vadose zones around the world, that is, that denitrification is the main fate of N fertilizers. Castaldelli et al.^[40] reported that denitrification is an significant fate of N inputs (37%) in an intensive agricultural watershed in Italy (with wheat and maize the major crops, accounting for 52% of the total; their average N input rate was 194 kg·ha⁻¹ N) due to the simultaneous conditions of hypoxia/anoxia and the availability of nitrate and labile organic carbon. Overall, soil nitrate accumulation in northern China with a thick vadose zone is the main fate of N fertilizer, while N leaching and denitrification loss may be the main fate of OVF in regions with high rainfall and shallow vadose zones in southern China (Fig.2).

3.2 Loss pathways of N fertilizer

The average N loss from OVFs in China is 35.1% (¹⁵N loss rate (%) = 100% − ¹⁵N utilization rate (%) − ¹⁵N residual rate (%)) (Tab.1). It is worth noting when quantifying the N fate based on the ¹⁵N labeling method that most studies only measured ¹⁵N accumulation in the shallow soil layer (less than 100 cm) and ignored ¹⁵N accumulation in the deep soil layer (Tab.1; Fig.2). However, many studies have shown that the nitrate accumulation depth in OVFs may exceed 200 cm^[5,⁶,¹⁰,³⁶,^41]. Therefore, the residual fertilizer N in soil may be underestimated, resulting in the overestimation of the loss of N fertilizer, especially in the regions with a thick vadose zone in northern China.

The gaseous loss of N from soil includes NH₃ volatilization and N₂O and N₂ emission from nitrification-denitrification. Some studies have reported that the loss by NH₃ volatilization and N₂O for vegetable systems in China are 8.97%–13.6%^[42,^43] and 0.69%–1.41% of the total N fertilizers added^[44,^45], respectively. The total annual losses by NH₃ volatilization and N₂O emissions in vegetable systems in China are estimated to be about 0.63 and 0.085 Tg N, respectively^[43,^46]. The losses of NH₃ volatilization and N₂O for apple orchards were 11% and 0.27%–0.7%^[33,^47], respectively, and the N₂O emission factor is lower than 1% reported by the IPCC (2007)^[48]. Compared with vegetable fields, N fertilizers in orchards are usually more deeply applied (> 25 cm deep), which markedly reduces NH₃ volatilization in orchards^[49].

Production of facility vegetables is a key part vegetable production in China. NH₃ volatilization from the soil surface in the facility system can be absorbed again by the plant canopy or dissolved in greenhouse film water and returned to the soil due to the semiclosed structures. A three-season study found that ammonia volatilization in the entire greenhouse (NH₃ emissions from the venting zone of the solar greenhouse) accounted for only 13.4%–33.7% of the NH₃ volatilization from the soil surface, and the NH₃ emission factor was only 0.46%–1.48%^[50]. If the NH₃ emission factor of the soil surface is used to estimate the NH₃ loss of facility vegetable system, it would overestimate the NH₃ loss in these contexts^[50]. Therefore, newer methods for determining N fertilizer loss pathways require further improvement due to the special environment and different management practices of OVFs in China.

4 CONSEQUENCES OF EXCESSIVE N INPUT TO ORCHARDS AND VEGETABLE FIELDS

OVFs are the hotspots for high N surplus and low NUE in China’s agriculture system due to the long-term overuse of N fertilizer. This not only wastes resources but also affects vegetable and fruit quality. For example, the overuse of N fertilizer negatively affects fruit color, soluble solids, and other quality indicators^[51,^52], decreases the vitamin C content of vegetables and causes nitrate accumulation in leafy vegetables^[53,^54].

The excessive application of N fertilizer in OVFs results in soil salinization and acidification. These effects are more severe in facility vegetable production systems due to the semi-enclosed environment. For example, the soluble salt and EC contents of the surface soil (0−20 cm) in facility vegetable fields are 2.43 g·kg⁻¹ and 630 μS·cm⁻¹, respectively, which are higher than the critical contents of soluble salt (2 g·kg⁻¹) and EC (500 μS·cm⁻¹)^[55]. There is a linear positive correlation between soil EC and nitrate content (R² = 0.84)^[56]. Soil pH significantly decreases and EC content significantly increases with the increase in cultivation years of facility vegetable crops^[16]. Compared with open vegetable fields, the soil pH of facility vegetable fields is lower in the same region; in contrast, the EC in facility vegetable fields (547 μS·cm⁻¹) is three times higher than that in open vegetable fields (157 μS·cm⁻¹)^[15]. This is related to the high H⁺ and basic cations generated by excessive N fertilizer application and nitrification of N fertilizer, and high temperature and strong evaporation lead to the accumulation of base ions in the surface soils. Long-term pear production in southern China has aggravated red soil acidification and has caused severe early defoliation^[57]. Therefore, the overuse of N fertilizer in OVFs causes soil degradation, which in turn will negatively affect crop growth.

A high N surplus in agroecosystems also results in biodiversity loss and climate change^[58]. We will focus on the effect of nitrate accumulation in soil profiles on water quality. Excessive nitrate accumulation in deep soil profiles increase groundwater pollution risk. A recent study in the kiwifruit belt of Shaanxi found that 97% of groundwater samples exceeded the nitrate concentrations of the WHO standard for drinking water (50 mg·L⁻¹)^[59,^60]. The dissolved oxygen concentration (between 3.5 and 8.3 mg·L⁻¹) in the groundwater of the region was > 2 mg·L ^−1[60], indicating that nitrate denitrification in the groundwater in the region is inhibited. Nitrate pollution in the groundwater is also prevalent in other intensive OVF planting regions in northern China^[7]. It is difficult to effectively remove nitrate from groundwater by denitrification^[61]. In addition, the time lag caused by high soil nitrate accumulation and migration brings great challenges for controlling groundwater nitrate pollution. For example, a study on the Mississippi River revealed that more than 50% of the nitrate exported from the watershed is from N fertilizer applied 30 years ago^[62]. Therefore, groundwater is difficult to improve once contaminated, and more attention should be given to regions with high N surpluses, rainfall and irrigation.

5 SUGGESTIONS FOR SUSTAINING N MANAGEMENT IN ORCHARDS AND VEGETABLE PRODUCTION

Quantifying the main fates of applied N fertilizer in OVFs is the key for improving NUE and controlling N loss. However, compared with cereal crops, studies of the fate of N fertilizer in OVFs in China are still far from clear. Given the different climates, soils, and management practices in OVFs in China, more studies are needed to understand the main fates of N fertilizers in these systems. Unlike vegetable crops, fruit trees are perennial crops that have large plant sizes, and N storage in perennial organs (roots, stems and branches) can delay the response of trees to the N added in the year of application. Therefore, more long-term studies are needed. At present, most of the studies on the fate of N fertilizer and N losses in OVFs have focused on the field scale, and few studies have focused on the watershed or at the regional scale. It is difficult to provide decision-making and consulting suggestions for N fertilizer management in the development of the fruit and vegetable industry in China. For example, to prevent pollution of groundwater, it is necessary to clarify nitrate-vulnerable zones or potential vulnerable zones according to nitrate concentration of groundwater, long-term N surplus, water balance, soil texture, vadose zone thickness and topography, similar to the establishment of nitrate-vulnerable zones in the EU^[63], and prioritize the optimization of water and N management in these regions to control N loss and reduce environmental risks. Practical suggestions to reduce N loss and increase NUE are as follows (Fig.3).

5.1 Rational N fertilization

Optimizing N input with by the 4R (right source, right rate, right time and right place) method is a basic solution. Given the overuse of N fertilizers is very common in OVFs in China, reducing the N fertilizer rate is the most direct and effective way to reduce N loss^[64–^70]. A seven-year N fertilizer reduction experiment in the northern slope region of the Qinling Mountains showed that, compared with normal N fertilization (900 kg·ha⁻¹·yr⁻¹ N) practiced by farmers, no adverse effects were found on the yield and quality of kiwifruit, with a 25% reduction in the N application rate in 2012–2014 and reaching 45% in 2014–2019; however, it increased economic benefits for farmers and reduced nitrate accumulation in soil ^[71,^72]. Reducing N fertilizer by 40% significantly reduced nitrate accumulation in the 0–1 m of soil and increased NUE in apple planting regions in Bohai Bay^[33]. Obviously, an appropriate reduction in N fertilizer rate in OVFs can still guarantee crop yields while also reducing N fertilizer loss. Although N reduction is the most effective way to reduce N loss in OVFs, the effects of continuous N fertilizer reduction need to be further studied to ensure that production will not decrease.

5.2 Substituting mineral N fertilizers with organic fertilizers

Compared with mineral N fertilizer, partial replacement of mineral N fertilizer with organic fertilizer (30%–60%) significantly reduces N₂O emissions, NH₃ volatilization, and N leaching^[73]. A meta-analysis indicated that reasonable substitution of organic fertilizer for mineral fertilizer (ratio of organic fertilizer less than 70%) increases vegetable yields and reduces reactive N emissions^[42]. There are many kinds of organic fertilizers applied for OVFs in China. Estimations of the N supply characteristics of organic fertilizer effectively and the proportion of different organic fertilizers to mineral N fertilizer in different OVFs are urgently needed.

The separation of cropping and livestock production makes the supply of organic fertilizers to OVFs challenging. Therefore, investigation of how to promote the regional N cycle and reduce N fertilizer application by integrating crop and livestock systems is needed. Other options include planting cover crops in orchards and returning crop straw to OVFs.

5.3 Replacing flood irrigation with fertigation

Commonly-practiced flood irrigation with excessive N fertilizer application is the main cause of N leaching loss in agricultural systems^[74,^75]. Fertigation can match the demand of crops for water and N in the growing season and effectively reduce N accumulation and loss^[76]. Compared with flood irrigation, drip irrigation not only reduces the input of water and N but also significantly reduces nitrate accumulation in soil and the emission of N₂O and N leaching loss and increases NUE^[77–^79]. The key technologies and measures for the comprehensive regulation of water and N in OVFs in the different regions of China need to be studied.

5.4 Developing high efficiency N fertilization systems

Developing high efficiency N fertilization systems that can synchronize fertilizer and soil N supply and plant N demand is another way to increase NUE and reduce its loss, including controlled release fertilizers and mixing N fertilizers with different inhibitors. Urea inhibitors and nitrification inhibitors (Dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP)) can prolong the conversion time of ammonium N to nitrate N, increase the amount of ammonium N and amide N absorbed by crops, inhibit nitrification and nitrate leaching, and ultimately improve NUE and reduce N loss. Compared with urea alone, the application of urease inhibitor decreases NH₃ volatilization, nitrate leaching and N₂O emission^[80,^81]. The application of nitrification inhibition significantly reduces nitrate leaching and N₂O emissions from vegetable fields^[33,⁷⁰,^82]. In addition, the application of DMPP can reduce N runoff loss for sloping orchards by reducing the nitrification of inorganic N^[83]. Notably, the beneficial effect of nitrification inhibitors to mitigate N₂O emission can be undermined by an increase in NH₃ volatilization^[84,^85]. Therefore, the development of high efficiency N fertilization systems could be a key way to decrease N fertilizer losses, but the trade-off of different N loss pathways should be given more attention.

6 CONCLUSIONS

More than 30% of China’s annual N fertilizer application is to OVFs. The long-term excessive application of N fertilizer has led to OVFs as hotspots of both N surplus and N loss. Nitrate accumulation in the soil profile is the main fate of surplus N in OVFs in northern China and has led to increased groundwater pollution. Considering the range of climates, soils and management practices in OVFs in China, more studies are needed to clarify the main fates of N fertilizer in the different systems. Reducing the N rate in fields with excessive application is the most direct and effective way to reduce N loss and increase NUE. Other measures include substituting mineral N fertilizers with organic fertilizers, replacing flood irrigation with fertigation, using a controlled release N fertilizer, and mixing mineral N fertilizers with urease inhibitors and nitrification inhibitors.

References

[1] ErismanJ W, SuttonM A, GallowayJ, KlimontZ, WiniwarterW. How a century of ammonia synthesis changed the world. Nature Geoscience , 2008, 1( 10): 636–639

[2] CoskunD, BrittoD T, ShiW, KronzuckerH J. Nitrogen transformations in modern agriculture and the role of biological nitrification inhibition. Nature Plants , 2017, 3( 6): 17074

[3] JankowskiK, NeillC, DavidsonE A, MacedoM N, CostaC Jr, GalfordG L, MaracahipesSantos L, LefebvreP, NunesD, CerriC E P, McHorneyR, O’ConnellC, CoeM T. Deep soils modify environmental consequences of increased nitrogen fertilizer use in intensifying Amazon agriculture. Scientific Reports , 2018, 8( 1): 13478

[4] Foodand Agriculture Organization of the United Nations (FAO). FAOSTAT Statistical Database of FAO Statistical Division. Rome: FAO , 2019. Available at FAO website on January 25, 2022

[5] BaiX, JiangY, MiaoH, XueS, ChenZ, ZhouJ. Intensive vegetable production results in high nitrate accumulation in deep soil profiles in China. Environmental Pollution , 2021, 287 : 117598

[6] GaoJ, WangS, LiZ, Wang L, ChenZ, ZhouJ. High nitrate accumulation in the vadose zone after land-use change from croplands to orchards. Environmental Science & Technology , 2021, 55( 9): 5782–5790

[7] JuX T, KouC L, ZhangF S, ChristieP. Nitrogen balance and groundwater nitrate contamination: comparison among three intensive cropping systems on the North China Plain. Environmental Pollution , 2006, 143( 1): 117–125

[8] NationalBureau of Statistics of China (NBSC). China Statistical Yearbook on National Database. Beijing: China Statistical Press , 2017 ( in Chinese)

[9] HefferP. Assessment of Fertilizer Use by Crop at the Global Level. International Fertilizer Industry Association (IFA), 2014 . Available at IFA website on January 25, 2022

[10] ZhuX, FuW, Kong X, ChenC, LiuZ, ChenZ, ZhouJ. Nitrate accumulation in the soil profile is the main fate of surplus nitrogen after land-use change from cereal cultivation to apple orchards on the Loess Plateau. Agriculture, Ecosystems & Environment , 2021, 319 : 107574

[11] LuY, Chen Z, KangT, ZhangX, BellarbyJ, ZhouJ. Land-use changes from arable crop to kiwi-orchard increased nutrient surpluses and accumulation in soils. Agriculture, Ecosystems & Environment , 2016, 223 : 270–277

[12] GaoJ B, LuY L, ChenZ J, WangL, ZhouJ B. Land-use change from cropland to orchard leads to high nitrate accumulation in the soils of a small catchment. Land Degradation & Development , 2019, 30( 17): 2150–2161

[13] ZhaoZ P, YanS, LiuF, WangX Y, TongY A. Analysis of nitrogen inputs and soil nitrogen loading in different kinds of orchards in Shaanxi Province. Acta Ecologica Sinica , 2014, 34(19): 5642−5649 ( in Chinese)

[14] HeC, Wei Z, ZhangW, ChenY, LiuL, RongQ. Nitrogen budget in the mango orchards in Hainan Island. Chinese Journal of Soil Science , 2020, 51(4): 943−949 ( in Chinese)

[15] FanY, ZhangY, HessF, HuangB, ChenZ. Nutrient balance and soil changes in plastic greenhouse vegetable production. Nutrient Cycling in Agroecosystems , 2020, 117( 1): 77–92

[16] BaiX L, GaoJ J, WangS C, CaiH M, ChenZ J, ZhouJ B. Excessive nutrient balance surpluses in newly built solar greenhouses over five years leads to high nutrient accumulations in soil. Agriculture, Ecosystems & Environment , 2020, 288 : 106717

[17] ZhangF S, ChenX P, ChenQ. Fertilizer application guideline for main crops of China. Beijing: China Agricultural University Press , 2009 ( in Chinese)

[18] EUNitrogen Expert Panel. Nitrogen Use Efficiency (NUE)-An Indicator for the Utilization of Nitrogen in Agriculture and Food Systems. Wageningen: Wageningen University , 2015

[19] QuanZ, ZhangX, FangY, DavidsonE A. Different quantification approaches for nitrogen use efficiency lead to divergent estimates with varying advantages. Nature Food , 2021, 2( 4): 241–245

[20] SmithC J, ChalkP M. The residual value of fertiliser N in crop sequences: an appraisal of 60 years of research using ¹⁵N tracer. Field Crops Research , 2018, 217 : 66–74

[21] ZhuJ H, LiX L, ChristieP, LiJ L. Environmental implications of low nitrogen use efficiency in excessively fertilized hot pepper (Capsicum frutescens L.) cropping systems. Agriculture, Ecosystems & Environment , 2005, 111( 1−4): 70–80

[22] JianH M, ZhangJ F, LiL L, LiS S, ZhangS Q, PanP, GuoJ M, LiuL, YangJ C. Utilization and fate of nitrogen in greenhouse vegetable under optimized nitrogen fertilization. Journal of Plant Nutrition and Fertilizer , 2013, 19(5): 1146–1154 ( in Chinese)

[23] ZhangH Z, TangJ W, YuanS, JiH J, HuangS W. Effect of fertilizer reduction on nitrogen utilization efficiency and fate during overwinter long-season tomato production in greenhouse. Journal of Plant Nutrition and Fertilizers , 2020, 26(7): 1295−1302 (in Chinese)

[24] XuJ Y, MinJ, ShiW M. Effects of nitrification inhibitor on nitrogen fate of labeled ¹⁵N-urea in tomato cultivation under greenhouse condition . Journal of Nuclear Agricultural Sciences , 2020, 34(12): 2793−2799 (in Chinese)

[25] SunW T, ZhangY L, LouC R, YuL H, WangC X, GongL. Effects of irrigation techniques on ¹⁵N-urea utilization by tomato in greenhouse . Journal of Nuclear Agricultural Sciences , 2007, (3): 295−298 ( in Chinese)

[26] ChengY Z. Study on utilization and fate of nitrogen fertilizer under different irrigation and nitrogen conditions in solar greenhouse. Dissertation for the Master’s Degree. Yangling: Northwest A&F University , 2019 ( in Chinese)

[27] DuH Y, JiH J, XuA G, ZhangR L, ChengB, ZhangW L. Study on the utilization of nitrogen fertilizer under greenhouse vegetable by ¹⁵N tracer Chinese . Journal of Soil Science , 2011, 42(6): 1446−1450 ( in Chinese)

[28] CaoB, HeF, Xu Q, CaiG. Use efficiency and fate of fertilizer N in tomato field of Nanjing suburb. Chinese Journal of Applied Ecology , 2006, 17(10): 1839–1844 ( in Chinese)

[29] CaoB, HeF Y, XuQ M, CaiG X. Nitrogen use efficiency and fate of N fertilizers applied to open field vegetables. Journal of Nuclear Agricultural Sciences , 2008, (3): 343−347 ( in Chinese)

[30] JuS R, WangW B, GengJ M. Effects of optimized fertilization on yield of line pepper and utilization of nitrogen in latosols in Hainan. Chinese Journal of Tropical Crops , 2019, 40(5): 864−868 ( in Chinese)

[31] HanP Y, JiaoX Y, WangL G, DongE W, WangJ S. Use efficiency and fate of applied nitrogen in long-term tomato districts of Taiyuan. Chinese Journal of Eco-Agriculture , 2010, 18(3): 482−485 ( in Chinese)

[32] DuL F, JiH J, ZhangH Z, ZhangR L, ZhangW L. The fate of nitrogen fertilizer in three fertility level vegetable fields. Journal of Agro-Environment Science , 2010, 29(S1): 162−166 ( in Chinese)

[33] WangF, GeS, Lyu M, LiuJ, LiM, Jiang Y, XuX, XingY, CaoH, ZhuZ, JiangY. DMPP reduces nitrogen fertilizer application rate, improves fruit quality, and reduces environmental cost of intensive apple production in China. Science of the Total Environment , 2022, 802 : 149813

[34] JiaC. Study on nitrogen direction of wine grape fertilizer under different water and nitrogen regulation. Dissertation for the Master’s Degree. Baoding: Hebei Agricultural University , 2020 ( in Chinese)

[35] ZhouJ, GuB, Schlesinger W H, JuX. Significant accumulation of nitrate in Chinese semi-humid croplands. Scientific Reports , 2016, 6( 1): 25088

[36] LiuZ J, MaP Y, ZhaiB N, ZhouJ B. Soil moisture decline and residual nitrate accumulation after converting cropland to apple orchard in a semiarid region: evidence from the Loess Plateau. Catena , 2019, 181 : 104080

[37] YangS, WuH, Dong Y, ZhaoX, SongX, YangJ, HallettP D, ZhangG L. Deep nitrate accumulation in a highly weathered subtropical critical zone depends on the regolith structure and planting year. Environmental Science & Technology , 2020, 54( 21): 13739–13747

[38] JiaX, ZhuY, HuangL, WeiX, FangY, WuL, Binley A, ShaoM. Mineral N stock and nitrate accumulation in the 50 to 200m profile on the Loess Plateau. Science of the Total Environment , 2018, 633 : 999–1006

[39] ZhouW, MaY, Well R, WangH, YanX. Denitrification in shallow groundwater below different arable land systems in a high nitrogen-loading region. Journal of Geophysical Research. Biogeosciences , 2018, 123( 3): 991–1004

[40] CastaldelliG, VincenziF, FanoE A, SoanaE. In search for the missing nitrogen: closing the budget to assess the role of denitrification in agricultural watersheds. Applied Sciences , 2020, 10( 6): 2136

[41] ZhouJ B, ChenZ J, LiuX J, ZhaiB N, PowlsonD S. Nitrate accumulation in soil profiles under seasonally open ‘sunlight greenhouses’ in northwest China and potential for leaching loss during summer fallow. Soil Use and Management , 2010, 26( 3): 332–339

[42] LiuB, WangX, MaL, Chadwick D, ChenX. Combined applications of organic and synthetic nitrogen fertilizers for improving crop yield and reducing reactive nitrogen losses from China’s vegetable systems: a meta-analysis. Environmental Pollution , 2021, 269 : 116143

[43] MaR, Zou J, HanZ, YuK, Wu S, LiZ, LiuS, NiuS, HorwathW R, Zhu-BarkerX. Global soil-derived ammonia emissions from agricultural nitrogen fertilizer application: a refinement based on regional and crop-specific emission factors. Global Change Biology , 2021, 27( 4): 855–867

[44] WangX, ZouC, GaoX, GuanX, ZhangW, ZhangY, ShiX, ChenX. Nitrous oxide emissions in Chinese vegetable systems: A meta-analysis. Environmental Pollution , 2018, 239: 375–383

[45] YangT, LiF, Zhou X, XuC, FengJ, FangF. Impact of nitrogen fertilizer, greenhouse, and crop species on yield-scaled nitrous oxide emission from vegetable crops: a meta-analysis. Ecological Indicators , 2019, 105 : 717–726

[46] LiuQ, QinY, ZouJ, GuoY, GaoZ. Annual nitrous oxide emissions from open-air and greenhouse vegetable cropping systems in China. Plant and Soil , 2013, 370( 1−2): 223–233

[47] ZhuZ, YangL, FengT, TongY. Characteristics of N₂O emissions from different fertilization treatments in Weibei dryland apple orchard . Agricultural Research in the Arid Areas , 2020, 38(1): 59−65 ( in Chinese)

[48] IPCC. Climate change: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. UK: Cambridge University Press , 2007

[49] ZhuZ J. Effects of fertilization system on ammonia volatilization and greenhouse gas emission in Weibei apple orchard. Dissertation for the Master’s Degree. Yangling: Northwest A&F University , 2019 ( in Chinese)

[50] ZhangZ B, LuoW, BaiX L, ChengY Z, ChenZ J, ZhouJ B. Comparative study on ammonia volatilization from soil surface and whole shed in solar greenhouse. Acta Pedologica Sinica , 2021 ( in Chinese)

[51] XiaoY, PengF, ZhangY, WangJ, ZhugeY, ZhangS, GaoH. Effect of bag-controlled release fertilizer on nitrogen loss, greenhouse gas emissions, and nitrogen applied amount in peach production. Journal of Cleaner Production , 2019, 234 : 258–274

[52] ZhangQ Y, GuK D, ChengL, WangJ H, YuJ Q, WangX F, YouC X, HuD G, HaoY J. BTB-TAZ domain protein MdBT2 modulates malate accumulation and vacuolar acidification in response to nitrate. Plant Physiology , 2020, 183( 2): 750–764

[53] AlbornozF. Crop responses to nitrogen overfertilization: a review. Scientia Horticulturae , 2016, 205 : 79–83

[54] LiH, Liu H, GongX, LiS, Pang J, ChenZ, SunJ. Optimizing irrigation and nitrogen management strategy to trade off yield, crop water productivity, nitrogen use efficiency and fruit quality of greenhouse grown tomato. Agricultural Water Management , 2021, 245 : 106570

[55] ZhangZ, SunD, TangY, ZhuR, LiX, Gruda N, DongJ, DuanZ. Plastic shed soil salinity in China: current status and next steps. Journal of Cleaner Production , 2021, 296 : 126453

[56] ShiW M, YaoJ, YanF. Vegetable cultivation under greenhouse conditions leads to rapid accumulation of nutrients, acidification and salinity of soils and groundwater contamination in South-Eastern China. Nutrient Cycling in Agroecosystems , 2009, 83( 1): 73–84

[57] KangY, YangH, ZengS, JiangS, XieC, WangZ, DongC, XuY, Shen Q. Mitigation of soil acidification in orchards: a case study to alleviate early defoliation in pear (Pyrus pyrifolia) trees. Rhizosphere , 2021, 20 : 100445

[58] SteffenW, RichardsonK, RockströmJ, CornellS E, FetzerI, BennettE M, BiggsR, CarpenterS R, deVries W, deWit C A, FolkeC, GertenD, HeinkeJ, MaceG M, PerssonL M, RamanathanV, ReyersB, SörlinS. Planetary boundaries: guiding human development on a changing planet. Science , 2015, 347( 6223): 1259855

[59] WorldHealth Organization (WHO). Guidelines for Drinking-water Quality. 3rd ed. Geneva: WHO , 2006

[60] GaoJ, LiZ, Chen Z, ZhouY, LiuW, WangL, ZhouJ. Deterioration of groundwater quality along an increasing intensive land use pattern in a small catchment. Agricultural Water Management , 2021, 253 : 106953

[61] RivettM O, BussS R, MorganP, SmithJ W, BemmentC D. Nitrate attenuation in groundwater: a review of biogeochemical controlling processes. Water Research , 2008, 42( 16): 4215–4232

[62] VanMeter K J, VanCappellen P, BasuN B. Legacy nitrogen may prevent achievement of water quality goals in the Gulf of Mexico. Science , 2018, 360( 6387): 427–430

[63] CameiraM R, RolimJ, ValenteF, MesquitaM, DragositsU, CordovilC M S. Translating the agricultural N surplus hazard into groundwater pollution risk: implications for effectiveness of mitigation measures in nitrate vulnerable zones. Agriculture, Ecosystems & Environment , 2021, 306 : 107204

[64] MinJ, ZhangH, ShiW. Optimizing nitrogen input to reduce nitrate leaching loss in greenhouse vegetable production. Agricultural Water Management , 2012, 111 : 53–59

[65] LuoW, ChengY Z, ChenZ J, ZhouJ B. Ammonia volatilization under different nitrogen and water treatments of tomato-watermelon rotation system in solar greenhouse in Losses Plateau, China. Chinese Journal of Applied Ecology , 2019, 30(4): 1278–1286 ( in Chinese)

[66] LuoQ, ChenZ J, YanB, LeiJ F, ZhangX M, BaiX L, ZhouJ B. Effects of reducing water and fertilizer rates on soil moisture and yield and quality of tomato in solar greenhouse. Journal of Plant Nutrition and Fertilizers , 2015, 21( 2): 449–457

[67] WangS C, BaiX L, ZhouJ B, ChenZ J. Reducing nutrient and irrigation rates in solar greenhouse without compromising tomato yield. HortScience , 2019, 54( 9): 1593–1599

[68] WangD Y, GuoL P, ZhengL, ZhangY G, YangR Q, LiM, Ma F, ZhangX Y, LiY C. Effects of nitrogen fertilizer and water management practices on nitrogen leaching from a typical open field used for vegetable planting in northern China. Agricultural Water Management , 2019, 213 : 913–921

[69] ZhangJ, HeP, Ding W, UllahS, AbbasT, LiM, Ai C, ZhouW. Identifying the critical nitrogen fertilizer rate for optimum yield and minimum nitrate leaching in a typical field radish cropping system in China. Environmental Pollution , 2021, 268(Pt B): 115004

[70] ZhangJ, LiH, Deng J, WangL G. Assessing impacts of nitrogen management on nitrous oxide emissions and nitrate leaching from greenhouse vegetable systems using a biogeochemical model. Geoderma , 2021, 382 : 114701

[71] LuY L, KangT T, GaoJ B, ChenZ J, ZhouJ B. Reducing nitrogen fertilization of intensive kiwifruit orchards decreases nitrate accumulation in soil without compromising crop production. Journal of Integrative Agriculture , 2018, 17( 6): 1421–1431

[72] GaoJ B. Impact of land use change on soil nitrogen accumulation and loss in the northern slope region of Qinling Mountains. Dissertation for the Doctoral Degree. Yangling: Northwest A&F University , 2020 ( in Chinese)

[73] ZhouJ, LiB, Xia L L, FanC H, XiongZ Q. Organic-substitute strategies reduced carbon and reactive nitrogen footprints and gained net ecosystem economic benefit for intensive vegetable production. Journal of Cleaner Production , 2019, 225 : 984–994

[74] FanZ B, LinS, ZhangX M, JiangZ M, YangK C, JianD D, ChenY Z, LiJ L, ChenQ, WangJ G. Conventional flooding irrigation causes an overuse of nitrogen fertilizer and low nitrogen use efficiency in intensively used solar greenhouse vegetable production. Agricultural Water Management , 2014, 144 : 11–19

[75] LvH F, ZhouW W, DongJ, HeS P, ChenF, BiM H, WangQ Y, LiJ L, LiangB. Irrigation amount dominates soil mineral nitrogen leaching in plastic shed vegetable production systems. Agriculture, Ecosystems & Environment , 2021, 317 : 107474

[76] TeiF, DeNeve S, deHaan J, KristensenH L. Nitrogen management of vegetable crops. Agricultural Water Management , 2020, 240 : 106316

[77] PhogatV, SkewesM A, CoxJ W, SandersonG, AlamJ, ŠimůnekJ. Seasonal simulation of water, salinity and nitrate dynamics under drip irrigated mandarin (Citrus reticulata) and assessing management options for drainage and nitrate leaching. Journal of Hydrology , 2014, 513 : 504–516

[78] GaoJ B. Accumulation of nitrate in soil and nutrient and water managements in kiwifruit orchards in the northern slope region of Qinling Mountains. Dissertation for the Master’s Degree. Yangling: Northwest A&F University , 2016 ( in Chinese)

[79] ZhaoY, LvH, Qasim W, WanL, WangY, LianX, LiuY, HuJ, Wang Z, LiG, WangJ, LinS, Butterbach-BahlK. Drip fertigation with straw incorporation significantly reduces N₂O emission and N leaching while maintaining high vegetable yields in solar greenhouse production. Environmental Pollution , 2021, 273 : 116521

[80] CantarellaH, OttoR, SoaresJ R, SilvaA G B. Agronomic efficiency of NBPT as a urease inhibitor: a review. Journal of Advanced Research , 2018, 13 : 19–27

[81] SouzaE F C, RosenC J, VentereaR T. Co-application of DMPSA and NBPT with urea mitigates both nitrous oxide emissions and nitrate leaching during irrigated potato production. Environmental Pollution , 2021, 284 : 117124

[82] KouY P, WeiK, ChenG X, WangZ Y, XuH. Effects of 3,4-dimethylpyrazole phosphate and dicyandiamide on nitrous oxide emission in a greenhouse vegetable soil. Plant, Soil and Environment , 2015, 61( 1): 29–35

[83] YuQ G, FuJ R, MaJ W, YeJ, Ye X Z. Effect of DMPP on inorganic nitrogen runoff loss from vegetable soil. Environmental Sciences , 2009, 30( 3): 870–874

[84] LamS K, SuterH, MosierA R, ChenD. Using nitrification inhibitors to mitigate agricultural N₂ O emission: a double-edged sword. Global Change Biology , 2017, 23( 2): 485–489

[85] WuD, Zhang Y, DongG, DuZ, Wu W, ChadwickD, BolR. The importance of ammonia volatilization in estimating the efficacy of nitrification inhibitors to reduce N₂O emissions: a global meta-analysis. Environmental Pollution , 2021, 271 : 116365

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