Problems existing in the utilization of soil resources

The main problems existing in the utilization of soil resources are the increase of non-agricultural construction land area and the return of farmland to lakes, the decrease of cultivated land area and the prominent contradiction between man and land; Unreasonable development or excessive intensity utilization lead to soil quality degradation.

(A) frequent meteorological disasters

1. Frequent floods.

The water level of Poyang Lake is controlled by the incoming water from five rivers, such as Ganjiang River and Yangtze River. Statistics show that floods occur almost every year in Poyang Lake area. During the 30 years from 1954 to 1983, there were 9 times when the flood area exceeded 500,000 mu. From April to July, the water level of the lake fluctuates greatly according to the inflow of rivers, but the water level is not high (generally lower than 20m). From July to September, the Yangtze River entered the main flood season, and the water level of the lake was raised due to the flood jacking or backward flow of the Yangtze River. The water level process changes slowly and remains at a high level for a long time. The years when the measured water level in the estuary is higher than 20m mostly occur from July to September. In the year of abnormal climate, the flood of Poyang Lake system was delayed and the Yangtze River flood came ahead of time, and the Yangtze River flood and Poyang Lake flood immediately met and supported each other to cause the maximum flood peak. For example, in the floods of 1954 and 1998, the high water level in the lakeside area lasted as long as 123d and 94d respectively, which caused heavy losses.

Flood disasters mostly occur from April to early July, which is called the main flood season in meteorology; In some years, there will be spring floods, autumn floods and winter floods. During the main flood season, the catastrophic floods occurred once every three years in the whole province, and the frequency of floods near zhejiang-jiangxi railway, along the river and on the lakeside was higher than that in other areas. According to statistics, the risk frequency of three-level flood disasters in northeast Jiujiang, Anyi County and Fengxin County is above 60%, that is, six years in 10a are three-level flood risk years.

2. The drought is getting worse.

Compared with other areas in Jiangxi Province, Poyang Lake is one of the two drought centers with the highest meteorological drought frequency and the most serious drought degree in Jiangxi Province. The main reason is that the precipitation in Poyang Lake basin and its surrounding areas from August to 10 is usually less than that in other areas of Jiangxi Province. During 2002 1950 ~ 53a, four major droughts occurred in Poyang Lake area, and the most serious drought occurred in 1978 since 1935. Severe drought (collectively referred to as extreme drought and severe drought) 10a average 1 time, 53a average 1 time. The central area of summer drought is in the area of Cinnamomum camphora and Poyang, and the occurrence frequency of Cinnamomum camphora is the highest; Autumn drought in the north is the most serious, mostly in Poyang Lake Plain, with the highest frequency in Poyang County. From the geographical distribution of drought, the valley and plain are heavier, and the hills and mountains are lighter; The time distribution frequency is midsummer drought or autumn drought twice every three years; Severe summer drought occurs once every five years, and autumn drought occurs once every four years. The frequency of drought risk in northern Nanchang, southern Jiujiang and Fengcheng 1 is more than 30%, indicating that the drought-affected area of 10a is larger than that of 1/2, and the drought risk probability of Xinjian, Duchang and Wannian 1 is the highest, reaching 55%.

3. The gale disaster has a great influence.

The gale in Poyang Lake area is obviously more than that in other areas of Jiangxi, and the gale in plain valley basin is more than that in hilly and mountainous areas. According to statistics, the average annual wind speed in Poyang Lake area is above 3.5m/s, and the number of days with average daily wind speed ≥5m/s reaches 99.4d Lushan Mountain has the most gale, with an average of/kloc-0.03 times a year, followed by Xing Zi County at the mouth of Poyang Lake, with an average of 38 times a year. The northern part of Poyang Lake is the gate of cold air invading Jiangxi. The Mufu Mountain in the northwest and Huangshan Mountain in the northeast blocked the cold air from going south, and the cold air could only be injected from Poyang Lake mouth. Because the terrain is flat and the friction coefficient of the wide water surface is small, cold air can drive in directly. Therefore, Poyang Lake Plain is a high incidence area of strong winds in Jiangxi. Gale mainly includes cold air gale, frontal thunderstorm gale and squall line gale, with uncertain wind direction, large wind speed change and short lake time.

4. Abnormal climate

Abnormal climate includes low temperature and cold damage (late spring cold, small full cold, cold dew wind), high temperature and low humidity, strong wind and winter freezing damage. Late spring cold usually occurs from mid-March to early April, and cold and warm air alternates frequently. After the invasion of cold air, there is often low temperature and rainy weather, which leads to the rot of seeds and seedlings. Xiaomanhan appeared from mid-May to early June, and the average daily temperature was lower than 20℃ for three consecutive days, which was unfavorable to the growth of early rice, cotton and other crops. The cold dew wind mainly appears during the autumnal equinox to the cold dew, and the cold air invades from north to south, which affects the heading and flowering of the second-season late rice and leads to an increase in the empty shell rate.

(2) The quality of forest vegetation coverage is low, and the ability to resist disasters is declining.

In order to comprehensively control the Poyang Lake basin, the Jiangxi provincial government started the development and control project of rivers and lakes in mountainous areas on 1985. Through a series of important measures such as developing economy, cultivating resources and protecting ecological environment, the forest coverage rate has increased by nearly 1 times, but the soil erosion in Poyang Lake basin is still serious. A considerable part of the forest resources in Poyang Lake basin are artificial forests, mainly Chinese fir and pine, and the single tree species are not conducive to soil and water conservation. Because the coniferous forest acidifies the soil, it is difficult for shrub and grass to grow under the forest, and it is impossible to form vegetation conditions for soil and water conservation with trees, shrubs and grass. The forest has less surface coverage and poor soil permeability, so it cannot form a strong water storage and retention capacity. The structural contradiction of forest resources weakens the function of covering factors, which leads to the rapid increase of forest coverage and the decline of forest land quality, which directly leads to the low capacity of soil and water conservation.

The sediment in Poyang Lake mainly comes from five major rivers and Poyang Lake area, and the average amount of sediment entering the lake for many years is 2 1.042Mt, of which the five major rivers account for 87.2% of the total and the interval accounts for 12.8%. Among the five rivers, Ganjiang River is the largest, accounting for 62.80% of the total sediment transport. Followed by Xinjiang, accounting for13.20%; The amount of sediment entering the Poyang Lake is 2.7 million tons, second only to Ganjiang River, accounting for 12.8% of the total sediment entering the lake (Table 5-3). Due to the long-term acceptance of the sediment brought in by the Five Rivers, and the sediment is mainly deposited in the lake beach and grass island near the outlet of the Five Rivers, and the unreasonable reclamation around the lake makes the lake shrink and retreat to the north, and the flood discharge and storage capacity is weakened year by year, and the flood control capacity of the lakeside area is reduced.

Table 5-3 Average sediment discharge of rivers into lakes for many years

(According to Chen Yuehong et al., 2002)

(iii) Soil degradation

Using RS and GIS as technical means, it is proved that the land degradation area in the whole region is 533 1.80 hm2, accounting for about 20% of the total area. It is mainly influenced by natural resources, socio-economic conditions and farmers' concept of land use in Poyang Lake area, among which precipitation, lack of cultivated land, urban land expansion and regional poverty are particularly prominent.

1. Soil erosion

Due to the rapid population growth, the demand for food and fuel is increasing, and the contradiction between man and land is becoming increasingly prominent, which leads to steep slope reclamation, deforestation and extensive farming, serious soil erosion and serious damage to the ecological environment.

According to the remote sensing survey data, the existing soil erosion area in Poyang Lake area is 475,000 hm2, accounting for 30.6% of the total land area, and the mountainous area is 4 1.2% (Figure 5-2). Among them, the light loss area is 6.5438+0.76 million hm2, the moderate loss area is 6.5438+0.54 million hm2, and the loss area of strength and above is 6.5438+0.45 million hm2. From the end of 1980s to 1990s, the area of soil erosion showed a gradual increase trend. Although the controlled area has been increasing and soil erosion has been curbed, the intensity is increasing.

Figure 5-2 Soil and Water Loss and Control in Poyang Lake Area

2. Soil desertification

The parent materials of hills and hills around Poyang Lake are mainly granite, shale and red clay. Due to heavy rainfall intensity, frequent economic activities and unreasonable land use, local land desertification is caused. According to remote sensing survey, there are 38,900 hectares of desertified land in Poyang Lake area, including 67,000 hectares of fixed sand dunes, 65,438+0.36 million hectares of semi-fixed sand dunes and 85,500 hectares of mobile sand dunes. Desertification area accounts for more than 2.2% of the lake area, accounting for more than 30% of the province's desertification area.

(1) Indiscriminate mining of mountains destroys vegetation and leads to land desertification.

The disorderly mining of mines, the serious destruction of vegetation and the reverse succession of ecosystems lead to land desertification. For example, the exploitation of granite and porcelain clay in Xing Zi County of Jiujiang City led to obvious land degradation in the low hills adjacent to the southeast of Lushan Mountain. According to the satellite photos of 1980 10.8, the area of degraded land caused by mining is 54. 1km2, accounting for 7.7% of the county's land area. According to the satellite photos of19941.2, the degraded land area is 130.7km2, accounting for 17.7% of the county's land area, with an average annual expansion of 6.38km2.

(2) Water erosion and desertification

Water-eroded desertification soil is mainly produced in Quaternary red clay terraces with loose rocks and easy erosion, as well as on gentle slopes, lakesides and alluvial plains in the lower reaches of rivers, showing a chain of sand ridges or dunes, which tends to expand year by year. Mainly distributed in Poyang Lake, Shang Gang Town of Nanchang County and Houtian Township of Xinjian County, as well as the south bank of the Yangtze River in Hukou and Pengze. Thick aeolian sandy soil is distributed alternately with aeolian sand dunes, sandy wind erosion pits, wavy flaky sandy land, Vitex negundo sand piles and river sand deposition terraces. The content of river sand deposition terraces is more than 76.40%, and the surface layer is as high as 87.78%. Aeolian dunes and wavy flaky sandy land formed on river sand deposition terraces are serious aeolian land.

3. Local soil pollution

The overall situation of soil heavy metal pollution in Poyang Lake area is good, but due to mining and metal smelting, sewage irrigation and municipal waste application, there are heavy metal pollution in some soils.

According to the investigation of Jiangxi Geological Survey Institute, Cd, As, Cu, Pb, Zn and other elements are distributed in the high-value areas along Poyang Lake and the Yangtze River, especially in the high-value areas of Cu along Le 'an River, Raohe River and the south lake of Poyang Lake. Hg mainly forms high-value areas in and around Nanchang and other cities. Therefore, Pb and Cd pollution exists in some soils in Poyang Lake area, among which Cd pollution is more serious. Cd pollution in Poyang Lake lakeside plain is mild, and CD pollution in Hexiuhe alluvial delta plain is moderate. Nanchang, Jiaokeng, Fengcheng and Buhe are slightly to moderately polluted. The pollution of mercury and cadmium in soil of Nanchang City, Zhangshu City and its surrounding areas is mainly caused by urban garbage discharge, sewage irrigation, fertilizer and pesticide application. Jian Minfei et al. (2005) set up sampling points at the entrance of Raohe River in Poyang County, and measured and evaluated the pollution of heavy metal elements Cu, Zn, Pb and Cd in sediments and soil samples. The soil or sediments of Raohe River in Poyang Lake are polluted by heavy metals to varying degrees (Table 5-4).

Table 5-4 Pollution Index of Heavy Metals in Raohe Soil and Sediments in Wet Season and Dry Season

(According to Jian Minfei et al., 2005)

4. The soil fertility of cultivated land decreased and acidification was obvious.

Due to the popularization and application of high-yield crops and the improvement of intensive production, the soil yield of cultivated land has increased greatly, but farmers pay more attention to the cultivation of land, and the investment is insufficient, so the cultivated land can not make ends meet. Poyang Lake area is a traditional green manure producing area. With the popularization of chemical fertilizer, farmers turn to chemical fertilizer to obtain high grain yield, and the output of green manure is greatly reduced. In addition, the low amount of organic fertilizer leads to the decrease of soil organic matter content, effective storage capacity of cultivated soil, soil buffering performance and soil fertility deterioration. The content of total nitrogen in soil decreased, the content of available potassium was low, and the effective content of trace elements decreased obviously.

The comparison between the soil samples collected by Nanjing Institute of Soil Research, Chinese Academy of Sciences in Honghu Township, yujiang county County, Jiangxi Province 1994- 1996 and the data of the second soil survey shows (Table 5-5) that after planting 15a in orange orchards and tea gardens, the contents of organic matter and total nitrogen in the surface soil decreased, while the contents of total phosphorus increased. In dry farming system, due to less input, especially less organic fertilizer, the main evolution characteristics of soil fertility are that organic matter and total nitrogen decrease, total phosphorus increases and nutrient content generally decreases; The input level of high-yield paddy field is high, and the content of soil organic matter and soil nutrients is increased, but the soil acidification is obvious.

Table 5-5 Fertility Changes of Red Soil Topsoil (0 ~ 20 cm)

According to the results of agricultural geological survey in Poyang Lake area of Jiangxi Geological Survey Institute, compared with the data of the second soil survey, the soil pH value decreased by 1 ~ 1.5 units. The main factors leading to soil acidification are acid precipitation and unreasonable use of a large amount of nitrogen fertilizer. Nanchang is one of the areas with serious acid rain, and the frequency of acid rain is as high as 87%. With the acceleration of industrialization, the intensity of acid rain has increased. According to the positioning measurement results of the Red Soil Ecological Experimental Station of China Academy of Sciences, more than 80% of the rainfall is acid rain pH.

5. Secondary culture of soil

In the depression of Poyang Lake area, the groundwater level is close to the surface for many years, and the soil particles are highly dispersed, which leads to serious hatching. The mountain streams and valleys near the lake are short of light, and they are often irrigated by spring water or cold spring water. The water temperature and ground temperature are low, so there are large areas of cold-soaked fields. In plain areas, continuous cropping of fertilizer rice or double cropping rice is idle in winter, long-term flooding and improper drainage, short alternation time of soil wetting and drying, and serious secondary incubation of soil lead to the increase of reducing toxic substances in soil and the deterioration of nutrient availability. The secondary potential fertility of waterlogged low-yield fields in Poyang Lake Plain is 65,438+800,000 hm2, accounting for 50% ~ 60%.

(d) the area of cultivated land has decreased.

1. The rigidity of cultivated land is reduced.

Since 1980s, due to the increase of construction land in the process of industrialization and urbanization exceeding the increase of newly-added cultivated land, cultivated land occupied by ecological returning farmland, cultivated land occupied by agricultural structure adjustment and cultivated land damaged by disasters, the area of cultivated land has been decreasing year by year.

According to the statistical annual report, the cultivated land area in Poyang Lake began to decrease gradually from 1999 (Figure 5-3), and the cultivated land area decreased from 65438+880500 hm2 in 0992 to 8 1.7 1000 hm2 in 2003. In 2004, due to land consolidation, the cultivated land area rebounded slightly. However, in areas with high degree of urbanization, due to urban expansion and the need of construction land in development zones, the cultivated land area has obviously decreased.

Figure 5-3 Changes of Cultivated Land Area in Poyang Lake Area

Taking Nanchang as an example, the cultivated land area in Nanchang decreased from 22 1.7 million hm2 in 2000 to 207,800 hm2 in 2004, which actually decreased by 1.44 million hm2 (Figure 5-4), and both paddy fields and dry land declined. The population increased from 4,283,900 in 2000 to 4,557,800 in 2004, and the contradiction between man and land became increasingly prominent.

2. Hidden loss of cultivated land

The current cultivated land protection policy pays attention to the dynamic balance of the total cultivated land, unilaterally emphasizes the regional cultivated land quantity balance and ignores the quality balance. It is difficult to guarantee the quality of supplementary cultivated land, which leads to the decline of the overall level of cultivated land quality and the hidden loss of quantity.

Figure 5-4 Change Map of Cultivated Land (Paddy Field and Dry Land) in Nanchang City

At present, most of the cultivated land occupied by local construction is concentrated on the fertile land around the town, which ensures the harvest in drought and flood. The main ways to increase cultivated land are the development and utilization of unused land (mainly barren hills, slopes and grasslands), the consolidation of rural settlements, the consolidation of cultivated land and the reclamation and utilization of abandoned industrial and mining land. Generally, the unused land has poor soil fertility and water resources conditions, and even if it is developed and utilized, it is difficult to achieve high and stable yield. The reclamation of abandoned industrial and mining land, due to the destruction of soil physical and chemical structure and soil fertility factors, as well as possible soil pollution, is difficult to achieve the goal without necessary engineering measures and years of bioremediation.

Taking Nanchang as an example, according to the statistical data, in 2004, through land reclamation and land consolidation, 7 174hm2 of cultivated land was added in that year, and the cultivated land area was reduced by 8089hm2 due to national construction and other infrastructure occupation, which made up the difference and reduced by 9 15 hm2. Under normal circumstances, the cultivated land of more than 3 ~ 4hm2 can make up the production capacity of the existing cultivated land 1hm2. From this calculation, Nanchang should reclaim at least 24267hm2 of land in that year, so as to ensure the productivity decline caused by the decrease of cultivated land in that year.