From 1980 to 2018, spatiotemporal variation characteristics in the soil environment at the Yangtze River Delta.

Variations in N- and P emissions from livestock manure: spatial and temporal variations

Comparison of N and P fertilizer use in the Yangtze River Delta

Although the amount of chemical fertilizers used by the Yangtze River Delta region fluctuated a lot before 2000, the overall trend was still rising and there was a steady downward trend since 2000 (Fig.1). Particularly, the Yangtze River Delta region’s use of chemical fertilizers reached a peak in 1985 at nearly 40 years. It used 1.8710 of these fertilizers.⁹3.3810 and kg of nitrogen fertilizer⁸Kilograms of phosphate fertilizer. It entered the low period in 1990. However, it started to recover slowly. However, since the start of the twenty-first Century, there has been a steady downward trend in fertilizer application. The Yangtze River Delta region saw 7.7910 fertilizer nitrogen, and phosphorus in 2018.⁸kg and 1.3110⁸The weights were 58.28% and 61.28% lower than 1985.

The Yangtze River Delta’s trend toward fewer fertilizers may be due to a combination of changes in cultivated land and national policy. My country has vigorously supported the fertilizer industry since the 1970s.^47,48The 1985 peak was reached by. The market for fertilizer is now relatively chaotic due to the adjustment in agricultural policies around 1990.⁴⁹There are fluctuations in the amount fertilizer used. The area of arable soil is closely tied to the fertilizer application. The area of China’s arable land decreases around 2000. This also affects the amount of fertilization. However, chemical fertilizers still cause serious environmental pollution per unit area. 2015 saw the Ministry of Agriculture issue the Action Plan for Zero Growth of Chemical Pesticide Use by 2020. This provided new guidance for chemical fertilizer application and led to a dramatic reduction.

Over the past 40 years, N and P emissions from manure in Yangtze River Delta have increased and then declined over the past 40 years. Between 1980 and 2005, the Yangtze River Delta’s N-and P emissions showed an increasing trend. Manure N increased from 2.1310⁸From kg in 1980, to 2.6610⁸2005: kg, an increase of 24.77%. Manure P increased from 7.33410⁷kg in 1980 to 1.03310⁸2005: An increase of 40.11% in kg. After reaching a peak of 50.11% in 2005, emissions continued to decline. N and P emissions from organic fertilizer manure were 1.4610 in 2018.⁸5.6810 and kg⁷kg respectively, back to 1980 levels.

Economic development and national policies play a major role in the Yangtze River Delta’s change trend in manure nitrogen, and phosphorus emission. The vigorous economic development promoted the increase in demand for meat, eggs and milk from 1985 to 2005. The growth of animal husbandry⁵⁰There were not many regulations regarding sound manure management in the poultry and livestock farming industries before 2000. The increase in the release of poultry and livestock manure has been caused by a variety of factors. The State Environmental Protection Administration issued a series of normative documents after 2000. These documents effectively slowed the increase in nitrogen and phosphorus emissions from livestock manure.

The spatial and temporal variations in N- and P emissions from livestock manure

There are obvious temporal and spatial variations in N and P emissions from soils in cities throughout the Yangtze River Delta over 40 years (Figs. 2, 3). The trend in N and P emissions from livestock manure was increasing and then decreasing. However, some areas had fluctuating manure nutrient emission trends.

Nantong has always been the geographic center of livestock manure nutrient emission in terms spatial change. Over the past 40 years, Nantong’s average N and P emissions was 3.4710.⁷1.3910⁷kg respectively; the average N and P emissions from Shanghai’s livestock manure over the past 40 years was 2.6710.⁷9.7010⁶kg, respectively. The total N and P emissions from livestock manure in Zhoushan were the lowest over the past 40 years. The average yields of N & P in livestock manure was only 1.1810 between 1980 and 2018.⁶4.3410⁵Zhoushan: kg. The N and P emissions from livestock manure in other places fluctuated at 3.5410⁵3.0110⁷kg and 1.3510⁵Up to 1.1410⁷kg, respectively.

Nantong, Shanghai and other cities have become the geographic focal point for poultry manure emissions. These are due to the following: a) Rapid economic development, abundant population resources and b) high levels of agricultural intensiveification. Aside from this, arable resources are very limited, resulting in a much higher unit arable soil carrying capacity than other cities. Additionally, the dense water network has accelerated the loss nitrogen and phosphorus in livestock dung. Zhoushan is China’s largest seafood producer base. It is also located at the intersection with the golden coastline of east China and the Yangtze River’s golden waterway.

Changes in the manure loads of livestock in Yangtze River Delta between 1980 and 2018

Pattern of N and P loads in livestock manure

The manure N load in soils of the Yangtze River Delta showed a general trend of decreasing and increasing from 1980 to 2018. (Fig.4) Most regions in the study area showed an increase in manure N loads between 1980 and 2010. The average manure N load in 2010 was the highest. The high load area rapidly expanded from the north and middle east to south of the study area. The load center moved from the east to southwest. The manure N load dropped from 2010 to 2018, especially in the middle. The high-load area was transferred to the edge. In 2018, the manure nitrogen load returned to the 1990s level.

Between 1980 and 2010, the average manure nitrogen load increased from 27.46 hm to 50.61 kg hm²This is an 84.30% increase on the maximum manure nitrogen load for the past 40 years. This trend is consistent with the steady increase in nitrogen pollution per unit of arable land in China, as demonstrated by earlier studies.^48,51,52,53. The N load of manure in Zhoushan (located on the eastern coast), Shanghai, Huzhou and Jiaxing, located in the central region, and Hangzhou (located within the southwest region) increased dramatically: Zhoushan saw a significant increase (295.25%), up from 22.04kg hm²1980 to 87.10kg Hm²2010. The price regulation and management of the agricultural materials market affect the livestock breeding industry. On the other hand, production price factors also have an impact on the livestock breeding sector. The main reasons for the rapid rise in manure N loads during this period are the rapid economic development, increased prices, and an increase in the number breeding industries. The average manure load dropped dramatically from 2010 to 2018, decreasing from 50.61 to 30,29kg hm.²This represents a decrease in manure N load of 40.15%. The average N load in Wuxi (Suzhou, Jiaxing, Jiaxing (located centrally) and Zhoushan, (located east coast), showed significant declines. Jiaxing’s load decreased from 100.88 kg hm to 24.60kg.², which is a decrease in 75.62%. Feng et al.⁵⁴Policy is an important factor in standardizing the livestock breeding industry and improving the environment. The policy regulation had a significant impact on the manure N load reduction over this period. Over the past 40 years, Shanghai’s manure N load has remained high, with an average of 50kg hm.²Throughout the period. The Yangzhou manure N load, however, was maintained at a low level for a prolonged time. It was below 30kg hm.²These regional differences are highlighted in the following table. This is due to differences in economic development and urban construction. The demand for livestock products in areas with developed economies is high. However, the area of arable soil is small and has a limited capacity to absorb livestock manure. This results in large manure N/P loads on cultivated land.⁵⁵.

From 1980 to 2018, the manure load center moved from central and northern regions to the northwestern, eastern, and then to southwestern and eastern areas after a peak in manure loads was reached for each city. The maximum livestock manure loads in the 1980s were found in the middle (Jiaxing), and the northern (Wuxi). The center of gravity for N emissions from livestock gradually moved to the east. The gravity center for livestock manure N emissions from livestock was located in the northeastern (Zhenjiang), and eastern (Shanghai). The N load of livestock was relatively high in most cities at the start of the 21st Century. However, the emission centre shifted to the east gradually. The livestock manure N load in 2018 was concentrated in the southwestern region (Hangzhou), and the eastern region, Nantong, Shanghai.

Because there is no set limit on organic fertilizer N in China we used the European Unions farmland standard N to determine the manure load⁵¹. From 1980 to 2018, the manure load N did not exceed the European Unions standard (170kg Hm).²), but still showed an increasing trend. It is evident that the Yangtze River Delta has suffered from the negative effects of livestock manure being discharged in each city.

From 1980 to 2018, the spatiotemporal pattern of livestock manure in soils was very close to that of manureN load. There was a general trend of first increasing then declining (Fig.5). The trend for the livestock manure load in soils was to increase from 1980 to 2010. In 2010, the livestock manure load had reached its highest level in 40 years. The central area had high livestock manure loads. They spread to the surrounding areas, then radiated out to the regions around the load center. Between 2010 and 2018, the livestock manure loading decreased significantly. Areas with high manure loads migrated from central to the southwestern margin region and the northeastern coastline cities.

The average livestock manure load in the Yangtze River Delta rose from 9.36 to 19.47kg hm between 1980 and 2010.²The average growth rate was 108.02%. The average manure P load in Zhoushan and Ningbo (located along the eastern coast), Jiaxing and Hangzhou (located in central and southern regions) saw significant increases of 347.66% and 323.28%, respectively. The average livestock manure P load dropped from 19.47 kg hm to 11.74 kg hm from 2010 to 2018.²This represents a decrease of 39.71%. Zhoushan, located in the eastern coast area, Jiaxing, and Suzhou (located centrally) saw the largest declines of 73.26% and 72.49%, respectively. Additionally, the average manure load content was higher than 20kg hm²In the central region (Huzhou Jiaxing, Shanghai), and in the southwestern area (Hangzhou), but less than 15kg hm²In the southeastern region of Taizhou (Tai), and in the northwestern region of Yangzhou, Taizhou.

The center of the livestock manure phosphate P load moved from the northern and central regions of the study area to eastern and northwestern regions. After reaching peak P loading in each of these regions, it then moved to the northeastern or southwestern regions. In the 1980s, the majority of the livestock manure load was concentrated in the middle (Jiaxing), the northern region (Wuxi), and then in the 1990s the center moved to the east (Shanghai), and then to the northwest (Zhenjiang). At the beginning of this century, the livestock dung P load remained high in most cities. In 2018, the center P load of livestock manure had accumulated towards the Yangtze River Delta. It was concentrated mainly in the northeastern region (Nantong), as well as the southwestern regions of (Hangzhou).

It is generally believed that manure should not be applied to the soil for more than 35kg per year.²⁵⁶Excessive P can lead to soil P leaching and eutrophication. Jinxing’s livestock manure concentration exceeded this limit in 2010, causing a significant negative effect on the local environment. It is imperative to rationally treat and utilize livestock manure.⁵⁷.

The Yangtze River Deltas livestock manure has increased and then declined over the past 40 years. Its significant rise in the past 40 years is due to rapid economic development and urban construction. The manure spreads to surrounding areas. Urban development has led to a significant reduction in agricultural land and a relative decrease in the area that contains livestock manure nutrient. This has resulted in an increase in the Yangtze River Delta’s manure N- and P loads. The subsequent introduction and implementation of environmental policies for livestock breeding in various cities and provinces may have contributed to the decrease in manure N and phosphorous loads in the Yangtze River Delta. The state has strengthened macro-control of the livestock breeding sector since the 2010 promulgation the Pollution Prevention and Control Technology Policy to Livestock and Poultry Breeding Industry. The Yangtze River Delta was designated as a restricted development area, and the industrial structure has been optimized and adjusted. This has resulted in a decrease of the Yangtze River Delta’s manure N- and P loads. Year after year, the manure P and N load has been decreasing. This trend is consistent with policy measures. It shows that current poultry and livestock pollution prevention and control measures have had remarkable results.⁵⁸.

From 1980 to 2018, changes in N and P loads of livestock manure

The spatial variability in manure N- and P loads between 1980 and 2018 was significant (Fig. 6). Changes in animal husbandry space have been promoted due to the influence of government guidelines, large demand for production land and environmental protection pressure.^59,60,61. The northwestern and central regions of livestock manure N, and P loads have seen a significant decrease in their respective levels. However, the manure P and N loads in the surrounding areas have increased to varying degree, indicating a shift from central to the surrounding regions. Particularly, the manure P and N loads in Nanjing (Wuxi), Suzhou, Jiaxing and Suzhou showed a decreasing trend in 2018. The manure N load declined by 41.55%, 48.26% and 44.49% respectively, compared to 1980. Comparing with 1980, the manure N load dropped by 21.63% and 43.08% respectively, while the manure P load fell by 43.47%, 43.47%, 17.98%, and 47.77%, respectively. The central region saw a decrease in manure N and P levels due to policies of livestock pollution prevention that were successively implemented in the Tai Lake area.^32,33,62. The relevant departments have optimized animal husbandry in their regions and made extensive use of livestock manure to reduce the pollution. The manure N and P loads of all 11 cities, including Yangzhou, Zhenjiang and Changzhou, Nantong and Shanghai, Huzhou and Tai, increased in different ways. Hangzhou saw the greatest increase. Hangzhou’s 2018 manure N load and P load increased by 76.72%, 112.58%, and respectively, 1980 and 1980. The manure N, and P loads in the 10 remaining cities have increased less than 100 percent. Small-scale factors may explain the increases in N and P loads.^63,64Lack of awareness and distribution of local farms and a scattered distribution^65,66.

Identification of high-risk areas for soil pollution from livestock manure

Manure N and particulate N were most prevalent in high-risk areas in 2018. These were located in the Yangtze River Delta’s northwestern and south regions (Fig.7). Manure N and particulate N emissions in northern cities could not meet the nutrient needs of the local soil. Manure N, and P emissions in Changzhou reached 215.60%, 334.54%, respectively, while those in Nanjing reached 102.18%, 71.02%, and respectively, lands absorption capacities of Nanjing. It is possible to reduce the number of breeding and increase the quantity of planting. This may lead to greater environmental pollution of poultry and livestock.^67,68. Wuxi and Hangzhou had close to the maximum soil absorption capacity for livestock nutrients. This indicated that there was an equal supply and demand for plant and animal breeding. The use of local organic fertilizers can therefore be increased to reduce the need for chemical fertilizers and reduce the risk of pollution from the enrichment of manure nutrients.^69,70. The discharge of livestock manure from the northern region of Yangzhou, Taizhou and Nantong was only 020% of the land absorb capacity. This indicates that the livestock manure nutrient cannot be used to meet the nutritional needs of local crops. Additional nutrients are needed to support the normal growth and development of local crops.⁷¹.

Selection of common models and main control points based on long-term N and P emissions

Analysis of manure N and E emissions by systematic clustering

Based on the similarity between manure N- and P emissions in cities, we performed variable analysis based upon the Ward minimum variance methodology⁷². Based on the Yangtze River Delta change trend of manure N emission, four categories were drawn for the cities.⁷³ (Fig.8a). Class I: Yangzhou, Tai, Wuxi, Suzhou, Shaoxing, Ningbo, Zhoushan, Hangzhou; class II: Nantong, Taizhou, Changzhou; class III: Huzhou, Jiaxing; class IV: Nanjing, Shanghai, Zhenjiang.

Similar to the manure N classification method cities were divided into four groups based on the trend in manure P emissions in Yangtze River Delta (Fig.8b). Class I: Nantong, Taizhou, Changzhou, Yangzhou, Tai, Shaoxing, Ningbo, Zhoushan, Hangzhou; class II: Huzhou, Jiaxing; class III: Wuxi, Suzhou; class IV: Nanjing, Shanghai, Zhenjiang.

Principal component analysis of manure N & P emissions

Based on the results from systematic clustering, the typical cities were extracted in order to establish a model of manure N/P emissions. The main control variables were also selected⁷⁴. Yangzhou and Nantong were selected from Class I to Class II, Class III and Class IV respectively for manure N emission. Combining these with the risingandfallingtrend characteristics of manure N emissions over the long study period, we established four typical models of manure N emissions as up-down-down model, down-up-up model, down-up-down model, and up-up-down model. Based on the clustering results for manure P emissions, Hangzhou and Jiaxing were selected from Classes I, II, III, and IV, respectively. Based on the rising or falling trend characteristics of manure nitrogen emissions over a long study period, four models of manure P emission were developed.

Analyse on the main factors that control N emissions from manure

The total variance of Yangzhou’s two principal components was 85% (Fig.9a); Nantong was described as a typical up-up/down model city with 82% variance (Fig.9b); Huzhou was a typical up-up/down model city with 82% variance (Fig.9c); the sum of the variances from the two main components was 96% in the up/down model for Shanghai (Fig.9d).

There was a positive correlation between changes of manure N emissions in Yangzhou and the proportion of the Primary Industry in Yangzhou. This suggests that Class I’s up/down-down model is primarily influenced by the Primary Industry. The Pollution Prevention and Control Plan for Livestock Breeding Industry (Yangzhou) proposes to regulate livestock breeding, limit prohibited and restricted areas, and reduce the amount of pollutant emissions from livestock breeding. Accordingly, Yangzhou’s livestock breeding has been less extensive and the total manure (N) has shown a decrease in Yangzhou. This is consistent in line with the interannual changes of the primary sector. This class’s primary industry is mainly agriculture and animal-handling; therefore, the main factor controlling the total manure is the percentage of primary industry.

Nantong’s total manure N decreased, then increased, before finally becoming flat over the course of the study. There was a clear relationship between Nantong’s manure N emission changes and animal husbandry’s total output value. This suggests that Class II is dominated primarily by these two factors. The Class II livestock breeding industry is relatively advanced^75,76, and meat output showed a consistent trend along with total manure N.

The trend in total manure N in Huzhou was decreasing, increasing, then decreasing, and finally declining. Manure N emissions changes and meat output showed a strong positive correlation. This suggests that Class III is mainly affected meat production and has little correlation to factors such as GDP. This is consistent with the changing trend in meat product. Huzhou’s agriculture is dominated mainly by fishing and planting.⁷⁷Because animal husbandry has a minimal impact on cities, meat production is the main factor that has the greatest impact.

Over the study period, Shanghai’s total manure N began to rise in accordance with changes in meat output. There was a strong correlation between manure N emissions and meat production. This suggests that Class IV is greatly affected in terms of arable land. Shanghai adopted relevant measures to regulate livestock breeding after that, including the Shanghai Livestock a Breeding management Measures. Due to a decrease in farmland, meat production fell and manure N showed an upward trend.⁷⁸. Both total manure N and meat production in Shanghai increased initially, and then declined. In such cities, meat production is the most important.

Selection of key control factors for manure emissions

The total variance of Hangzhou’s two principal components accounted 91% in the up-up down model (Fig.10a); in a typical down -up-down, the total variance in Jiaxing accounted 88% (Fig.10b); Suzhou was a typical flat-down model and the sum of both principal components accounted 95% (Fig.10c); in the up-down down model, the variance in Shanghai accounted 96% (Fig.10d).

Hangzhou’s manure P first increased, then decreased. This is essentially the same trend as Hangzhou’s meat production. There was a strong correlation between manure P emissions and Yangzhou’s total meat output. This indicates that Class I’s up/down model is mainly affected. Hangzhou is suffering from severe pollution from livestock and poultry.⁷⁹Relevant policies have been adopted to reduce the number of livestock breeding and thus reduce meat production.

Manure P in Jiaxing showed an initial decline, then a rise, and finally a decline. There was a strong positive correlation between changes to manure P emissions in Jiaxing and meat production, which indicates that Class II’s down-up/down model is mainly influenced by meat production. Class II is dominated both by agriculture and animal husbandry.^34,35The breeding industry is highly developed. These industries also change the meat production, and their inter-annual variation is consistent to that of manure P.

Suzhou’s manure P showed a downward trend consistent with inter-annual changes to the area of arable. Changes in manure P emissions and the area of arable land showed a significant positive correlation, indicating that the Class III cities with a decrease-level-decrease model were mainly affected by the area of arable land and the proportion of the primary industry. Suzhou is an important industrial development base. The local economic development is quite rapid⁸⁰As such, its arable area is continually decreasing⁸¹.

Shanghai’s livestock manure increased in Shanghai at first and then dropped, which is consistent in relation to inter-annual changes of meat production. In 2002, Shanghai Municipal Peoples Government outlined a special plan for animal husbandry. It prohibited breeding areas, controlled breeding areas, and allowed moderate breeding. The city saw a decline in total poultry and livestock production, as well as a decrease in meat production.⁸². There was a strong positive correlation in the changes in livestock manure emissions and meat production. This indicates that Class IV’s up-down-down model is primarily affected by meat production.