Soil Nitrogen, Phosphorus and Potassium Analyzers to Measure Soil Nutrients in Gansu Province
Gansu Province is located in the northwestern part of China and is located at the intersection of the Loess Plateau, the Qinghai-Tibet Plateau, and the Inner Mongolia Plateau. It is 1655 km long from southeast to northwest and 25 km at the narrowest point in the north and south. It is between the east of 92°13′~108°46′ and the northern latitude of 32°31′~42°7′. The province's land area is 45.4 thousand km2, accounting for 4.73% of the country's land area, ranking seventh in the country. In 1989, the province's soil census resources summarized net arable land area of ​​5,602,200 hm2. In the province, the topography is high in the northwest and low in the southeast, and the elevation is mostly 1000~3000m. The types of landforms are complex, geographical differences are large, and land resources are abundant. The climate is diverse. From the warm temperate zone of the Weinan River valley to the warm temperate zone in the northern part of northern Jiangxi, to the temperate zone in the eastern and middle parts of the Gansu, and to the warm temperate zone in the west of the river, the northwestern part is inland and belongs to arid and semi-arid regions. The southeastern monsoon climate is a humid, semi-humid and semi-arid area. The southwestern part is characterized by high topography and a cold climate. It is a cold and humid area. The latitude and vertical zonality in the province are all obvious. In most areas, the winter is long and cold, and the summer is short and warm. Rain and heat in the same season, mostly concentrated in 7,8,9 months, annual rainfall of 38 ~ 860mm, annual average temperature of 4 ~ 14 °C, the average annual sunshine in 170O ~ 3300 hours, frost-free period is generally 180 ~ 24O days. The bioclimatic conditions and the degree of soil weathering and development have the transition characteristics from north to south of China, and the types of soil parent materials and soil types are diverse. In recent years, with the development of "high-yield, high-quality, high-efficiency" agriculture and the adjustment of crop structure, the output of crops and the amount of nitrogen, phosphorus, and potassium fertilizers have increased dramatically, and the amount of nutrients that crops carry out from the soil has increased year by year. The return of nutrient cycling in the form of farmyard manure, green manure, straw returning, etc. is not optimistic. The imbalance in the amount of fertilization and fertilization results in changes in soil nutrients, either surplus or loss. Therefore, a soil tester was used to evaluate the status of soil nutrients in Northwest China in order to adopt effective fertilization technology measures and management methods from both macroscopic and microscopic perspectives to ensure the sustainable and stable development of agricultural production. This paper mainly introduces the analysis of N, P and K nutrients in soil of Gansu Province by trial soil NPK analyzer, discusses the reasons of soil nutrient changes, and provides basis for comprehensive evaluation of soil fertility and scientific fertilization in the future. 1 Materials and Methods Practical Soil Instrument for Experiment: Soil Moisture Detector Soil Moisture Temperature Analyzer Wireless Public Opinion Monitoring System Sewing Machine,Household Embroidery Machine,Small Embroidery Machine Baolun Computerized Embroidery Machinery Co., Ltd. , http://www.cnembroiderymachine.com
1.1 Soil Nutrient Monitoring Survey In 1998, the Gansu Provincial Agricultural Division Office collected a total of 5,064 soil samples, which were from farmland soils (0-20 cm) of 33 monitoring outlet counties in 12 prefectures and cities in the province. The type of soil collected includes the soil belonging to the main cultivated land in Gansu Province, which is of different nature and has a wide range of representativeness.
1.2 Measurement and Analysis Project The same assay analysis method used in the second soil survey in 1983 was used. Namely: Semi-micro Kjeldahl method for soil total nitrogen; Alkali fusion-molybdenum antimony colorimetric method for soil total phosphorus; Alkali fusion-flame spectrophotometry for soil total potassium; Alkaline solution-diffusion method for soil alkalinity; Soil Olsen method for fast-acting phosphorus; extraction of soil available potassium with ammonium acetate - flame photometric method.
2 Results and Discussion
2.1 Dynamic Changes of Soil Nitrogen, Phosphorus and Potassium Nutrients Soil nutrients are an important component of soil fertility and the basic conditions for high and stable yields of crops. Under the premise that the conditions of water, heat, and gas are well-coordinated, the soil nutrient content and supply conditions will directly affect the growth and yield of crops and the level of output. Soil nutrient status is also a direct basis for rational fertilization. The results of the second soil survey showed that the soil nutrient status in Gansu Province can be summarized as nitrogen deficiency, low phosphorus, and potassium. After nearly 15 years of soil tillage succession, soil nutrient conditions have changed. Analysis of 5064 plough layer monitoring soil samples in the province showed that the average soil total nitrogen content was 0.92 g kg-1, which was 0.80 g kg in 1983. -1 increased 0.12gkg-1, an increase of 15%. The average soil total phosphorus content was 0. 74g kg-1, which was lower than the threshold value of 0. 8~1. 07g kg-1 of total phosphorus content in the phosphorus supply, which was 0. 70g kg-1 in 1983. Only increased 0. 04g kg-1, the change is not obvious. However, the average content of soil available phosphorus was 11.19mg kg-1, which was 3.83mg kg-1, an increase of 52.0%, compared with 7.36mg kg-1 in 1983. The average content of total potassium and available potassium in soil potassium was 21.77g kg-1 and 195•14mg kg-1, a slight increase from 19.55g kg-1 and 189•50mg kg-1 in 1983, which was 2.22g kg-1. , 5. 62mg kg-1. According to the statistics of national soil nutrient index classification criteria (Table 1), the soil nutrients in the cultivated land in Gansu Province: soil total nitrogen is mainly concentrated in Grade IV and below, accounting for about 72.3% of the total monitoring samples, and the average content of soil alkali dissolved nitrogen is 67 09mg kg-1. The available phosphorus in soil was mainly concentrated in grades III, IV, and accounted for about 82.28%. The soil sample with a grade IV or less phosphorus deficiency accounted for 59.03%. Soil available potassium is mainly concentrated in grades I, II, and III, accounting for 90.47 percent. Approximately 10% of samples lacking or missing potassium below grade IV. It can be seen that the area of ​​nitrogen deficiency and phosphorus deficiency is still very large, and the problem of unbalanced application of nitrogen and phosphorus fertilizers is the key issue. The lack of potassium in soil has already appeared.
The degree of abundance and distribution of soil nutrients is not only related to the parent material of the soil and the type and quantity of minerals, but also related to the geographical location of the soil, the degree of soil maturation, the soil texture, the way of cultivation and utilization, and the degree of fertilization. close relationship. From the perspective of the whole province, the distribution of total soil total nitrogen has a high tendency in the southeast and low in the northwest; soil total phosphorus has a tendency of high in the northwest and low in the southeast. Soil potassium shows changes in the northwest, east and south. The above-mentioned change distribution also includes the variation characteristics of N, P and K nutrient contents in different soil types and cultivated land types. 
2.1.1 Soil Nitrogen Changes Soil nitrogen consists of organic nitrogen and inorganic nitrogen. In the soil surface, organic nitrogen accounts for about 90% of the total soil nitrogen. With the deepening of the soil depth, this ratio rapidly decreases.
Under normal circumstances, soil total nitrogen and alkali-hydrolyzed nitrogen are used as indicators for evaluating soil nitrogen supply capacity and levels in fertilization [2]. According to the monitoring data of 5064 cultivars, the average content of total nitrogen was 0.92 g kg-1±0.51 g kg-1, and the amplitude ranged from 0·09 to 11.14 g kg-1, which ranks the national grading standard. Grade, it can be seen that the arable land soil is relatively lack of nitrogen, and there are large differences among different regions. The average content of alkaline dissolved nitrogen in the soil was 67.09 mg kg-1, with a variation range of 9.00-366. 00 mg kg-1, and 6.06% of the content above 100 mg kg-1; between 50 and 100 mg kg-1. The accounted for 78. 79%; in the 50mg kg-1 accounted for 15.15%. If alkali nitrogen is above 50 mg kg-1, which is the measure of medium supply capacity, the province's arable land will have moderate nitrogen supply capacity in the short term.
According to conditions of landforms, soils, climate and other factors, Gansu Province is roughly divided into four types of geographical areas. The content and distribution of soil total nitrogen in the four types of areas are higher in the south of Anhui and Hexi than in the whole province and 0.92 kg kg- 1 The average value, Jidong and Yuzhong districts are less than the average of the province.
Hexi District: refers to the west of the Yellow River area, including Jingquan County in Jiuquan, Zhangye, Wuwei, Jiayuguan, Jinchang and Baiyin. The total soil nitrogen content was 0.97g kg-1, varying from 6.60 to 0.09g kg-1 (n=1793), slightly higher than the provincial average. The highest in Tianzhu and Shandan counties were 1.96 g kg-1 and 1.20 g kg-1, respectively, and the lowest in Dunhuang and Minqin counties were 0.64 g kg-1 and 0.62 g kg-1, respectively. , Wuwei, Jiuquan counties between 0. 71~.l 04g kg-1. From the grading point of view, mainly concentrated in III, IV, V grades, accounting for 23. 57%, 31. 75%, 29. 28%. Compared with the results of the census in 1983, grades I, II, and VI decreased by 4.75%, 8.6%, respectively, while grades III, IV, and V increased by 7.5% and 5.9%, respectively.
Yuzhong District: It includes Dingxi, Lanzhou, Baiyin (except Jingtai County), Linxia, ​​Pingliang, and Jingning County. The average content was 0.86g kg-1, ranging from 3.57 to 0.21g kg-1 (n=1337), which was slightly lower than the provincial average. The highest content was 1.21g kg-1 in Laiyuan County, the lowest was 0. 76g kg-1 in Qianxi County, and 0.81~0.83g kg-1 in Dingxi, Suizhong and Jingning Counties. From the grading point of view, mainly concentrated in III, IV, V grade, accounting for 21. 69%, 30. 29%, 34. 55%. Compared with the results of the census in 1983, it has declined, but it is not obvious.
Jidong District: It refers to the Loess Plateau region east of Songshan Mountain, including Qinliang, Wushan, Gangu, Qingshui, and Zhangjiachuan counties in Pingliang (except Jingning and Zhuanglang), Qingyang II, and Tianshui. The average content was 0.88g kg-1, and the amplitude was changed from 11/14 to 0.16g kg-1 (n=1310). The contents were highest in Zhangjiachuan and Wushan counties, which were 1.09g kg-1 and 1.08g kg-1, respectively. Qingyang County, the lowest 0. 68 g kg-1. From the grading level, it mainly focused on the IV and V grades, accounting for 38.09% and 37.33% respectively. Compared with the results of the census in 1983, grades III and IV increased from 26.94% to 49.14%.
Longnan District: It includes the counties in the south of Fujian Province, Zhouqu, Diebu, Lintan, Zhuoni, Xiahe and Qinshui Districts of Qinan and Beidao Districts of Gannan Prefecture. The average content was 1.34 g kg-1 and the variation range was 7.83~0.10g kg-1 (n=624), ranking the first in the province. The highest in Diebu County, the North Road area was 0. 79g kg-1, and the remaining counties were between 0.87~.l 32g kg-1. From the grading, mainly concentrated in III, IV, V grades, respectively 25.0%, 31.0%, 21. 31%, but I, II grade relative to other areas, respectively 9.13% and 9. 94%. Compared with the results of the 1983 soil survey, it is still the highest in Longnan, and the level of Grade III or higher rose from 24.65% to 63.5%, and increased by 38.9 points, an increase of 156%, with an average annual increase rate of 9.9%.
2.1.2 Changes in Soil Phosphorus Phosphorus is an important nutrient of crops. It is directly involved in a series of physiological and biochemical reactions such as synthesis and transformation of amino acids, proteins, and fats in plants, and is also an important component of phospholipids and nuclear proteins. The level of soil phosphorus content to some extent reflects the phosphorus storage and supply capacity in the soil. The amount of soil total phosphorus depends on the parent material. The amount of total phosphorus in the farmland is related to the application of phosphate fertilizer, but there is no correlation. Therefore, soil available phosphorus is used as an indicator of the supply level of soil phosphorus [3]. According to the analysis of soil samples monitored by 5064 plough layers in the whole province, the average content of total phosphorus in the province was 0. 74g kg-1±0. 23g kg-1, and the variation range was 0.05 to 7.20g kg-1, which was lower than the second time. The lower limit of 0. 8~1. 07g kg -1 of total phosphorus content in the soil was determined during the general survey of the soil. This indicates that the soil of the plough layer of the farmland in the province is insufficient, and the application of phosphate fertilizer has great potential for yield increase. From the perspective of regional division, the area in Yuzhong District was 0.88 g kg-1, in Hexi District was 0.70 kg kg-1, and that in Minnan and Longdong regions was 0.63 g kg-1. The average content of soil available phosphorus in the province's plough layer was 11.19mg kg-1±10.17mg kg-1, ranging from 1.00 to 188.70mg kg-1, which was the third-level sub-level of national grading standards. Compared with 7.36mg kg-1 in the second soil survey, it increased by 3.83mg kg-1, an increase of 52.00%. This reflects the importance of phosphate fertilizers in recent years, promote the use of formula fertilization, and re-application of phosphate fertilizer. However, due to the differences in soil texture, soil type, climatic conditions, crop types, and farming methods, there is a great deal of variation among regions.
In the four regions, the content of available phosphorus in the Hexi District was the highest, with an average of 12.70mg kg-1, ranging from 188.70 to 1. 00mg kg-1 (n=1793), which was 1.5% higher than the average of the province. Kg-1, compared with 1983's 7.36mg kg-1, an increase of 5.34mgkg-1, an increase of 71.8%, the highest in Tianzhu County, Gaotai County, were 22. 8mg kg-1, 19. 75mg kg -1, Gulang County lowest, 7. 57mg kg-1, Zhangye, Jiuquan, Dunhuang and other counties between 10.11~15. 20mg kg-1. From the grading point of view, they mainly concentrate on grades III and IV, followed by grades II and V, accounting for 33.69%, 33.0%, 12.49%, 12.32%, respectively. Compared with the census results of 1983, only Level III and above increased from 19.29% to 48.49%, basically reflecting the deficiency of phosphorus accounted for one half of each.
Yuzhong District: The average content of soil available phosphorus is the lowest, which is 10. 01mg kg-1, amplitude 107.90~1. 00mg kg-1 (n=1337), 2.48mg kg-1 increase over 1983, an increase 32. 94%, is the lowest increase in all regions, with the highest in Jingning County and Longxi County, respectively 14.83mg kg-1, 14. 04mg kg-1, Wuyuan, Yongjing minimum, respectively 6. 56mg kg -1, 6. 95mg kg-1, the remaining counties were within the range of 7.94~11.40mg kg-1. From the grading point of view, mainly concentrated in the III, IV, V grade, accounting for 26.24%, 37.81%, 20. 84%, compared with the results of the 1983 soil survey, little change.
Jidong District: The average content of soil available phosphorus was 10.89mg kg-1, and the amplitude was 70.40~1. 60mg kg-1 (n=1310), which was 4.91mg kg-1, an increase of 82.11%, compared with 1983. The largest increase. The highest peak was 14.28mg kg-1 in Xifeng City, the lowest was 6.87mg kg-1 in Heshui County, and 12.56~13.06mg kg-1 in other counties. From a grading point of view, they mainly focused on grades III, IV, and V, which were 39. 90%, 35. 65%, and 13.0%, respectively. Compared with 1983, the content of available phosphorus in soil increased from grade III to 42.9%, which was 10 times that of 4.3% in Erpu, and the change was huge.
Taonan District: The average content of soil available phosphorus was 10.21mg kg-1, and the amplitude was 153.60~1. 30mg kg-1 (n=624), which was 4.0% increase than that in 1983, an increase of 64.41%. The areas in Huixian and Beidao districts were 12.17mg kg-1, 10.53mg kg-1 and 6. 7mg kg-1 respectively. The remaining counties are between 8.50~10.20mg kg-1. According to grading standards, the main class is concentrated in grades III, IV, and V, accounting for 13.36%, 29.96%, and 38.87%, respectively. Compared with the results of the 1983 soil survey, soil available phosphorus accounts for less than grade IV. To 72.44%, although it has declined, it still shows that the investment in phosphate fertilizer in the south of Anhui Province is a key issue to be solved urgently.
2.1.3 Changes in Soil Potassium Potassium is an important nutrient for plants.
Soil potassium supply capacity is closely related to total potassium content [4, 5]. Therefore, understanding the status of total potassium in the soil is of great significance for the rational application of potassium fertilizer. From the perspective of plant nutrition, potassium in the soil is divided into three parts: 1 soil-insoluble potassium, 2 soil-reduced potassium, and 3 soil-efficient potassium, and there is a reversible dynamic balance between the latter two. Under normal circumstances, soil total potassium content and available potassium content are used as indicators of soil abundance. According to the statistical analysis of 5064 plough soil samples, the total potassium content of arable land in the province was between 7.50~130.00g kg-1±5.50g kg-1, with an average content of 21.77g kg-1. The soil total potassium in the county is between 18.78~33.24g kg-1, which is distributed in grade III or above of the national soil nutrient content classification standard. It is a moderate area with a balanced potassium content. The average content of soil available potassium 195. 14mg kg-1, amplitude 35. 00 ~ 1198. 00mg kg-1. The average content of soil available potassium is distributed in the national soil nutrient classification standard level II, which belongs to the potassium-rich region. However, due to differences in conditions such as climate, soil, and farming systems among different counties and counties, the test values ​​differ greatly.
In addition to the type and amount of potassium-bearing minerals in the soil, the extent and distribution of potassium in the soil are related to the geographical location of the soil, the soil parent material, the degree of soil development, the soil texture and the way of use, and the degree of fertilization. There is a close relationship. Judging from the division of the whole province, the total potassium content in the four regions of Hexi, Langzhong, Jidong, and Minnan are all above 20g kg-1. The soil available potassium is quite different. The average available potassium content in the province is 195.14mg kg-1, which is higher than 189.50mg kg-1 in 1983, an increase of 5.62mg kg-1, a slight increase. According to the national soil nutrient grading standard, the province's soil available potassium levels changed: Level I arable land with a soil available potassium content of >200 mg kg-1 was increased from 33.29% in 1983 soil to 36.6%, an increase of 3.31 percent. Percentage; Grade II cultivated land of 150~200mg kg-1 decreased from 30.22% to 26.09%, decreased by 4.13%; Grade III cultivated land of 100~150mg kg-1 decreased to 28.86%. 78%, a decrease of 1.08 percentage points; 50 to 100 mg kg-1 of Grade IV arable land increased from 6.90% to 9.19%, an increase of 2.29 percentage points; ≤ 50 mg kg-1 or less of Grade V, VI Cultivated land fell from 1.17% to 0.35%, a decrease of 0.82%. The cultivated land below Grade IV increased from 7.63% to 9.53%, an increase of 1.90 percentage points, suggesting that there is a potential upward trend in the area of ​​arable land where potassium is lacking. Soil available potassium changes in four sub-regions:
Hexi District: The average content of soil available potassium is 211. 88mg kg-1, and the amplitude is 1000. 00~43. 00mg kg-1 (n=1793), which is 27.27mg kg-1 higher than that in 1983, and the increase rate is 14.7%. . The highest in Tianzhu and Gaotai County were 348.48mg kg-1, 279.86mg kg-1, and the lowest was 151.52mg kg-1 in Jiuquan City. The rest of the counties were in the range of 190. 56 to 271.63 mg kg-1. With reference to grading standards, they were mainly distributed in grades I, II, and III, accounting for 44.46%, 27.5%, 21.1%, respectively.
Yuzhong District: The average content of soil available potassium is 182.96mg kg-1, which varies by 1198. 00~56. 00mg kg-1 (n=1337), which is 16.64mg kg-1 lower than that in the 1983 soil survey. The amplitude was 8.34%. The highest Dingxi County 339. 48mgkg-1, Qingshui County, the lowest 140. 07mgkg-1, the remaining counties in the range of 152. 76 ~ 205. 69mg kg-1, mainly in I, II, III accounted for 30. 25% , 26. 40%, 34. 60%, IV only accounted for 8.75%.
Jidong District: The average content of soil available potassium is 203.72mg kg-1, which varies by 731. 00~54. 00mg kg-1 (n=1310), which is 19.62mg kg-1 higher than that in the 1983 soil survey. 10. 66%. The highest concentration was 219.45mgkg-1 in Lingtai County, and the lowest was 166.63mgkg-1 in Heshui County. The remaining counties were in the range of 210.00~218.55mg kg-1, mainly in Class I, II, and III, respectively. 63%, 27. 67%, 23. 26%.
Taonan District: The lowest average content of soil available potassium is 122. 05mg kg-1, amplitude 887. 0~35. 00mg kg-1 (n=624), 73.09mg kg-1 lower than the average of the province, which may be related to In southern Yunnan, there is a large amount of rainfall and a strong leaching effect. Potassium is "inaccessible". Compared with the soil survey in 1983, it decreased by 12.55 mg kg-1, a decrease of 9.32%. The highest level was 282.12mgkg-1 in Diebu County and 104.30mgkg-1 in Kangxian, and the remaining counties were in the range of 105.70-198.04mg kg-1, mainly distributed in Grades III and IV, respectively. 32%, 45.34%; Class I and II accounted for only 8.91% and 12.96% respectively.
2.2 Characteristics of Nitrogen, Phosphorus and Potassium Content in Main Farmland and Cultivated Land Types
2.2.1 Soil Nitrogen There are 37 soil types in Gansu Province, of which the soil for cultivation is mainly loessial soil, black loessial soil, irrigated desert soil, chernozem, cinnamon soil, chestnut-calcium, red clay, irrigation silt, tide Soil, gray soil, etc. [1]. The nitrogen status of these major soils directly affects the province's agricultural production. Among the 24 soil types monitored, the total soil nitrogen content was still the highest in meadow swamp soil, chernozem soil and black soil, which were 1.92 g kg-1, 1.91 g kg-1, and 1.79 g kg-1, respectively. Saline soil, aeolian sandy soil and grey desert soil were the lowest, only 0. 47g kg-1, 0. 65g kg-1 and 0. 65g kg-1, respectively; there were 11 soil types with total nitrogen content of 1. Above 0g kg-1. The total nitrogen contents of the nine main tillage soils were as follows (Table 2): chestnut soil 1. 49g kg-1, cinnamon 1.37g kg-1, gray cinnamon soil 1. 28g kg-1, irrigated desert soil 0 97g kg-1, 0. 97g kg-1 of red clay, 0. 94g kg-1 of fluvo-aquic soil, 91g kg-1 of black loess, 0. 76g kg of loess soil, 0.7g of kg 1. Among them, soils of 7 soil types are ranked below Class IV of national grading standards. The average content of alkaline dissolved nitrogen in the nine cultivated soils was 56.54-97.47mg kg-1, indicating that the short-term soil nitrogen supply capacity was moderate.
The average total nitrogen content of each cultivated land type was: 1.24 g kg-1 for the dry floodplain, 1.23 g kg-1 for the irrigated paddy field, 1.16 g kg-1 for the dry sand land, and 1.16 g kg-1 for the grassland. 1. 00g kg-1 in land, 0.99 g kg-1 in dry land, 0.97 g kg-1 in slope dry land, 0.89 g kg-1 in water terraces, 0. 87 g kg-1 in dry terraces, and 0 in other irrigated lands. 85g kg-1. The average content of alkaline dissolved nitrogen was between 63.0 mg kg-1 and 124 mg kg-1, which was higher than 50 mg kg-1, indicating that the short-term nitrogen supply capacity of various types of cultivated land was better.
2.2. Soil Phosphorus There are significant differences in available phosphorus content in different soils. The soil available phosphorus content in the monitored 24 types of soils ranged from 4.61 (yellow brown earth) to 18.34 (new soil) mg kg-1, of which 16 available soils contained more than 10% available phosphorus. 0mg kg-1, accounting for 66.7%. The order of the available soil phosphorus content from top to bottom in the first 7 soils was (Table 2): fluvo-aquic soil (15. 82mg kg-1), chestnut soil (15·15mg kg-1), and irrigated desert soil (14.03mg kg-). 1, 9.90 mg kg-1 of black earthworm soil, 9. 93 mg kg-1 of gray cinnamon soil, 9. 84 mg kg-1 of red clay, 9.01 mg kg-1 of cinnamon soil. The top three soil types are mainly distributed in the Hexi area, while the last one is mainly distributed in the Minnan area.
According to the type of cultivated land, the contents of available phosphorus and total phosphorus in the 10 kinds of cultivated land were as follows: irrigation field 46.93 mg kg-1, 0. 67g kg-1, vegetable field 43.30mg kg-1, 1.27g kg-1. , Water terraces 14. 49mg kg-1, 0 · 81g kg-1, other irrigated land 13. 34g kg-1, 0. 70g kg-1, dry land terraces 11. 23mg kg-1, 0. 75g kg-1 , 11.75 mg kg-1, 0.78 g kg-1 for the dry floodplain, 10. 61 mg kg-1 for the dry land, 0.73 g kg-1 for the dry land, and 9.86 mg kg-1 for the dry land on the hillside, 0.72 g kg -1, 8.49 mg kg-1, 0. 69 g kg-1 of dry land, 7.79 mg kg-1, 0-76 g kg-1 of dry land. It can be seen that the content of available phosphorus in dry land is generally lower than that of irrigated land, indicating that the application amount of phosphate fertilizer in dry land, especially in mountain dry land, is still very small. In the 10 types of arable land, the available phosphorus content is quite different. The first place is 6 times of the 10th place. It highlights the imbalance of rural economic conditions in Gansu Province, and also reflects the problem of insufficient input of phosphate fertilizers in agricultural production in a considerable part of the province. 2.2.3 Soil potassium In the 24 soil types monitored in the province, the soil available potassium content was highest in swamp soil and chernozem, which were 333 mg kg-1 and 307.7 mg kg-1, respectively. The lowest was only 78.23 mg kg-1, and most of the remaining soils were more than 150 mg kg-1. The available potassium content in the 10 main cultivated soils ranged from 163.79 to 268.86 mg kg-1, both of which were above the national nutrient classification grade II. The order from high to low is (Table 2): chestnut soil 268. 86 mg kg-1, fluvo-aquic soil 240. 14 mg kg-1, irrigated desert soil 214. 04 mg kg-1, irrigation silt soil 205·17 Mg kg-1, Red clay 199. 23mg kg-1, Calcium-cemented soil 198・83 mg kg-1, Black loessial soil 188. 13mg kg-1, Loose soil 186·61 mg kg-1, Cinnamon 164·85mg kg -1, 165.79mg kg-1 of grey cinnamon soil, the top three are still mainly distributed in the Hexi area. According to the type of cultivated land, the total potassium content of the ten types of cultivated land was above 20g kg-1, and the available potassium content was between 160.50 and 31. 00mg kg-1. The order was 315 mg kg-1 vegetable field, 263 33 mg kg-1 irrigation field, 234.89 mg kg-1 floodplain, 220.62 mg kg-1 dry sand, and 210.70 mg other irrigated land. Kg-1, Arid land 209. 51mg kg-1, 184.07 mg kg-1 in dry terraces, 180.78mg kg-1 in dry slopes, 180.30mg kg-1 in dry land, and 160.50mg kg-1 in water terraces. . 
3 Conclusion
3.1 The soil nitrogen content of farmland in Gansu Province has increased significantly.
Since 1983, the amount of nitrogen fertilizers has been increasing year by year, and the input of organic fertilizers has increased, which has greatly increased total nitrogen in soils, laying a foundation for future increase in crop yields. In 1998, the total content of total soil nitrogen was 0.92g kg-1, which was 0.12g kg-1, an increase of 15%, compared with 0.80g kg-1 in the second soil survey in 1983. The average content of soil alkaline nitrogen was 67.09. Mg kg-1, if the alkali hydrolysis of nitrogen above 50 mg kg-1 is a measure of medium-term nitrogen supply capacity, the province's arable land will have moderate nitrogen supply capacity in the short term. From the aspect of soil total nitrogen content and distribution characteristics, the height in South Jiangxi was 1.34g kg-1, Hexi 0.97g kg-1, which was larger than the average in the province; the two regions in the east and middle of Anhui were smaller than the average of the province, respectively 0・86g kg-1, 0.88g kg-1. From the grading point of view, the proportion of the proportion of the proportion of all showed an upward trend
3.2 The soil available phosphorus content has increased significantly in the past 15 years.
The average soil total phosphorus content in 1998 was 0.74 g kg-1, which was lower than the lower limit of 0.8-1.07 g kg-1 in total phosphorus content in the soil, which was higher than that in 1983 when it was 0.70 g kg-1. 0.04g kg-1. However, the average content of soil available phosphorus was 11.19mg kg-1, which was 3.83mg kg-1 higher than that of 1983, an increase of 52.0%. From the perspective of regional division, the highest average phosphorus content in the west of the river is 12.70mg kg-1, and the lowest is 10.01mg kg-1, while in the east and south of Anhui is 10.89mgkg-1 and 10.21mgkg-1, respectively; this is the increase compared with 1983. They were 71.85%, 32.94%, 82.11% and 64.41%, respectively. Judging from the grading level, the proportions at all levels have been increased except in southern Jiangxi Province. The reason for the analysis is the result of popularizing "prepared fertilization and re-application of phosphate fertilizer" in the 1980s.
3.3 The overall evaluation of the province's soil K content slightly increased, and the local decline was significant.
In 1998, the average content of total potassium and available potassium in soil was 21.77 g kg-1, 195.14 mg kg-1, which was only 2.22 g kg-1, 5.62 mg kg-1 more than in 1983. From the grading point of view, the soil available potassium was more In 1983, the results of grades I and IV increased by 3.31% and 2.29%, respectively. Grades II, III, and V+VI decreased by 4.13%, 1.8%, and 0.35%, respectively. In the four districts, the available potassium content in Hexi and Longdong was 211.88 mg kg-1 and 203.72 mg kg-1, respectively, which was 27.27 mg kg-1 and 19.62 mg kg-1 higher than that in 1983; 182 in Minzhong and Longnan respectively. 96 mg kg-1, 122. 05 mg kg-1, which was 16.64 mg kg-1 and 12.55 mg kg-1 compared with 1983. With the increase in the yield per unit area of ​​the crop, the consumption of potassium in the soil will expand, and the amount of carry-in will be greater than the input. The problem of potash fertilizer application must be taken seriously, otherwise it may become a limiting factor affecting the crop yield and the quality of agricultural products.
3.4 The main cultivated soil and cultivated land types have large differences in nitrogen, phosphorus and potassium contents.
Nine main tillage soil total nitrogen contents chestnut soil (1.49 g kg-1)> cinnamon soil> gray cinnamon soil> irrigated desert soil> red clay> fluvo-aquic soil> black soil> Loessal soil> irrigation and silting soil (0.74 g) Kg-1), the average content of alkaline dissolved nitrogen in soil was 56.54-97.47mg kg-1; the average total nitrogen content of all types of cultivated land was higher than that of irrigated land, and the average level of soil alkali hydrolysis nitrogen was 63.0-124 mg kg-1. between. 7 main tillage soils available phosphorus content Chao soil (15.47mg kg-1)> chestnut soil> irrigated desert soil> black soil> gray cinnamon soil> red clay> cinnamon soil (9.01mg kg-1); 10 species The available phosphorus content of arable land is generally 6.0 times lower than that of irrigated land. The order of available potassium content in 10 species of cultivated soil: chestnut soil (268.86mg kg-1)> fluvo-aquic soil> irrigated soil> irrigated silt> red clay> sierozem> black loess> loessial soil> cinnamon soil> Cinnamon soil (163.79mg kg-1); Soil available potassium is highest in vegetable land and irrigation land, and low in drought and flood land and water terraces.