Scientific registration number: 2524 Symposium n : 29 Presentation: poster A Case Study For Evaluating Sustainable Saline Soil Management Un exemple d évaluation de la gestion d un sol salin en vue d une agriculture durable Fengrong ZHANG and Xuedong TIAN, Dept.of Land Resource Science, Beijing Agricultural University. Beijing, China 100094 In 1993, FAO published FESLM: An International Framework for Evaluating Sustainable Land Management. Quzhou Experimental Zone is selected as a case study of FESLM. LOCATION AND NATURAL CONDITION Quzhou Experimental Zone is located in Hebei province. It is in the middle of North China Plain, with very gentle slop, 1/4000. Soil material comes from the Loess Plateau, so the texture is silty loam dominant. The climate is a typical semihumid monsoon climate. Its annual precipitation is 436 mm, annual evaporation is 1745 mm. There is 64.6% rainfall in summer(june, July and August), 15.4% rainfall in autumn, 6.5% in winter and 13.5% in spring. Before reclamation, it was flooding in summer and autumn, drought in spring. The degree of mineralization of ground water is high, about 4-7g/l. The mineralogical type of ground water is dominated with sodium chloride and sodium sulfate. The depth of ground water is 1.0-1.5m below the surface. With the evapotranspiration of salty ground water, the salts accumulated in the surface of soil, and the soil is saline. The salt content of soil is 0.4-1.0%, Sodium chloride dominated. The ph value of the saline soil is 8.5 or less and the exchangeable sodium percentage is less than 15. Before reclamation the organic matter content of soil is 0.5-0.6%, alkali-n is 30-40 ppm, available-p is 1-3 ppm, Available-K is 79-84 ppm. 1
With drought in spring, flooding in summer and saline, the crop yield was low and unstable before reclamation. RECLAMATION OF SALINE SOIL AND LAND MANAGEMENT Since 1973, farmers have been doing the reclamation of saline soil, guided by soil scientists from Beijing Agricultural University. Establishing Drainage System For Preventing Flooding And Lowering Ground Water Table It is essential in the reclamation process to remove the excess salts from the root zone, and this can only be done by the application of sufficient water to wash them into the lower soil horizons. Unless there is ample drainage, the addition of so much water will raise the water table and enhance lead to increased accumulations of salt in the surface soil instead of to a correction of saline condition. So drainage is the key condition of reclamation of saline soil. Sufficient drainage should be provided to reduce the ground-water level well below the zone of root penetration. Perfect drainage should reduce the water table well below the critical depth of salification. For ding this, drainage system is constructed. The depth of drainage ditches is 2-4 m, corresponding to the grade of drainage ditches. The drainage system effectively drains flooding water, as well as deepens the ground water. Because the ground water table is put down to the critical depth of salification, the salts can not move from ground water to the surface of soil by capillary in dry season. Pumping Salty Water And Lowering Ground Water Table There is a layer of salty water that is 1.0-1.5 m beneath the surface and its thickness is 60-110m. Shallow wells are built for pumping the salty ground water. There are two periods of pumping salty ground water. One is in the early spring. Water evaporation is very strong in spring. Pumping salty water lowers ground water table to the critical depth to stop salts' movement from the low horizon of soil body and ground water to the surface of soil by capillary. In rain season, salty water also is pumped out and drainaged together with flooding water. It is major period of pumping salty water, beginning after two rains. Pumping water effectively lowers ground water table and stops the salification. Leaching Salts Of Soil Body With Fresh Water The basic method of salty soil reclamation is leaching the salts out of soil body. Irrigation system was built up for irrigation against drought, as well as for leaching salts. Irrigation system is made of channel and well. Leaching water must be fresh. Fresh water comes from deep wells that are 250-300 m deep, and also from surface water that is storage of rainfall in drainage ditches. There is a layer of fresh water beneath the surface 60-110 m. Rain is stored in the drainage ditches close to the end of rain season. With the lowdown of ground water, there is good condition of leaching salts. There are three periods of leaching. Spring is dry season, and the crops need irrigation. People pump 2
deep ground water, which is fresh, for leaching, also for irrigation against drought in Spring. Rain also is leaching water in summer and autumn. Summer and autumn are leaching seasons. The drainage ditches are full of fresh water in the end of rain season, the water is pumped and used for leaching also for wheat irrigation at the beginning of winter. Using Slight Salty Water For Irrigation Fresh water is very deficient in Quzhou Experimental Zone, especially in spring. Using slight salty water for irrigation is one way that saves the limited fresh ground water. The mineralization degree of irrigation water must be not more than 5g/l, i.e., using slight salty water for irrigation. There is a layer of slight salty water. The slight salty water is pumped to irrigate the thirsty crops in spring. This also deepens ground water from other side. Fertilizing And Increasing Soil fertility At the beginning of cultivating saline soil, alfalfa is planted for green fertilizer. After two years, the organic content increased from 0.6-0.6% to 0.7-0.8%. In the first period of reclamation, growing grain can only maintain the organic content at 0.8-0.9% level without the application of chemical fertilizer. For increasing biomass production, chemical fertilizers are applied. With chemical fertilizers, crops grow very well. In the middle period, i.e., since 1980, phosphorus fertilizer was applied with gradual increasement of nitrogen fertilizer. The crop yield greatly increased. In addition to people's fuel need, a lot of straw is left and put back to soil directly. The organic content of soil maintains at the 1.0-1.2% level. This is called that Chemical fertilizer Becomes Organic fertilizer. At the last stage, since 1990, comprehensive agriculture and animal husbandry have been developed. Using extra grain and straw, farmers raise pigs, cattle and chicken. A huge amount of manure is produced and put back to soil. This greatly raises the organic matter content of soil and maintains it at 1.5% level. Developing Animal Husbandry And Increasing Farmer's Income With the soil reclamation, irrigation and fertilization, land productivity is increased, and the risk of crop production is reduced. Grain production not only feeds people themselves, but also there are extra grain left. Selling grain can not bring farmers much money. So scientist helps farmers to develop animal husbandry. This not only increases people's income, but also produces much more manure. Putting the manure back to the field increases soil fertility further. 3
RESULTS OF THE RECLAMATION OF SALINE SOIL AND LAND MANAGEMENT A big change of soil properties and production happened after more than twenty year's soil reclamation and suitable land management. Saline Soil Has Been Reclaimed By leaching the salts, the saline soil has been reclaimed. Saline soil decreased from 878 ha to 447 ha in 10 years. The content of salt reduced greatly, especially the serious saline soil. Table 1 and table 2 show these changes. Table 1. Saline soil area changes(ha) 1973 1984 1986 1989 1994 area (%) area (%) area (%) area (%) area (%) Non-saline soil 289 13 1345 60.5 1591 71.6 1637 73.6 1776 79.9 Saline soil 1934 87 878 39.5 632 28.4 586 26.4 447 20.1 Soil Fertility Is Increased Because of applying fertilizer, both of chemical and organic, soil fertility is increasing. Table 3 shows the changes of soil fertility. Although the pesticides are applied, the soils are not polluted to the critical standard. Land Productivity and Production Stability Are Increased. Because the drainage system is built up, there is not flooding in rain season anymore. With the effective irrigation system, drought is reduced to the least harming crops. Salt harm also is reduced to the least. So the crop yield is greatly raised, and risk of crop production is lowered to the least(table 4). Table 2. Salt content change in 2m depth(ton) --------------------------------------------------------------------------------------------------------- 1984 1986 1989 1994 reduced(1984-1994) ---------------------------------------------------------------------------- ------------------------------ slight saline soil 24218 20325 23209 21089 12.9% medium saline soil 27556 11979 9225 10321 62.5% Serious saline soil 59240 49765 32337 15983 73.0% ---------------------------------------------------------------------------------------------------------- 4
Table 3. Soil fertility Changes ------------------------------------------------------------------------------------------------ Year OM Total-N Alkali-N Available-P Available-K (%) (%) (mg/kg) (mg/kg) (mg/kg) ------------------------------------------------------------------------------------------------ before reclaiming 0.5 0.04 35 2.5 82.0 1980 0.79 0.051 33.3 3.8 131.1 1984 0.94 0.072 40.9 6.4 142.6 1989 1.18 0.071 55.4 9.3 152.4 1994 1.28 0.096 47.7 13.6 163.2 ----------------------------------------------------------------------------------------------- Table 4. Yield's Changes(ton/ha.) ------------------------------------------------------------------------------------------------ Grain(average) Cotton(average) ---------------------------------------------------------------------------------------- 1983 1989 1994 1983 1989 1994 ------------------------------------------------------------------------------------------------------------ First generation of experiment area 8.52 11.12 14.57 0.75 1.21 1.45 ( since 1974) Second generation of experiment area 7.37 10.86 15.04 0.76 1.07 1.32 (since 1978) Third generation of experiment area 5.18 8.21 11.48 0.67 0.94 1.19 (since 1981) ----------------------------------------------------------------------------------------------------------- Water Quantity And Water Quality Because of shortage of surface water and irrigation need, both of shallow and deep ground water are exploited. The water supplement is less than the water exploitation. So, both of the shallow and deep ground waters are deficit (table 5.). The shallow ground water is not only used for irrigation, but also is pumped and drainaged out for deepening water table beneficial to desalification. The shallow ground water is easily replenished with rainfall or irrigation. So it is not always deficit. Because the deep ground water is pressure-bearing water, it is not easily replenished. Because the supplement of the fresh water of deep ground water is less than the usage of it, there is deficit of deep ground water every year, and the fresh ground water is decreasing. 5
With much more fertilizers' application, the nitrate content of ground water is increasing. At present, only few sites sampled, the nitrate content of shallow ground reaches 20 mg/kg and gets over the national standard of drinking water. Because people do not drink shallow water, it is not a problem. The nitrate content of deep ground water is less than 10 mg/kg in all of sites sampled. Now, people drink deep ground water that is fresh water. Although there is pesticide application, it does not cause pollution up to now. Table 5. Ground water exploitation ------------------------------------------------------------------------------------------------------ Shallow ground water Deep ground water --------------------------------------------------------------------------------------- Exploitable Exploited Deficit Exploitable Exploited Deficit ---------------------------------------------------------------------------------------------------- 1980 3775 5332-1653 30.7 2370-2339 1982 3819 2970 +849 30.7 2240-2209 1984 4855 2976 +1897 30.7 2799-2768 1986 3268 3684-415 30.7 3106-3075 1989 4624 5421-1797 30.7 4550-4519 ---------------------------------------------------------------------------------------------------- Social and Economical Changes With the reclamation of saline soil and farmland construction, crop production has been increasing, and the social-economical situation also changed. Since 1973, people's income has been increasing. The life of starvation has gone forever and the living standard has been rising. But one thing may be an obstacle, that is population explosion. Because of the population growth rapidly, the farmland per capita is decreasing(table 6). Because only small arable land is left, the exploiting of farmland is getting harder and harder. There is another problem that is the occupation of farmland by house building. Table 6. Social-economical changes Year Population Total Farmland Total Grain Total Cotton Net Income (ha) (ton) (ton) (RMB) 1980 9990 1945 3189 79 175 1994 13083 1946 9412 660 1026 ----------------------------------------------------------------------------------------------------------- 6
CONCLUSION AND DISCUSSION 1. Because of soil reclamation, fertilizing and farmland construction, the land productivity has increased. Crop's yield has been increasing since 1973. In 1972, the average grain yield was 2.63 ton/ha. In 1996, the average grain yield reached 10.5 ton/ha. This meets the demand of maintaining or enhancing production of SLM. 2. The farmland construction, including drainage system and irrigation system built, has increased the land production stability in addition to soil reclamation. Higher and more stable yield can be gained whether it is drought year or waterlogging year. This illustrates that the production risk is reduced. The Security objective of SLM is reached. 3. Because of the crops yield increasing and animal husbandry developing, people's income also has been greatly increasing from 1980 to 1994. This fits the economical viable requirement of SLM. 4. The result of dynamic analysis on sample site indicates that soil fertility has increased significantly. The salt content within 2 m depth of soil body has decreased. There is no soil pollution. Soil quality is rising. The dynamic monitoring of ground water indicates that the table of ground water is maintained at about 3 m because of drainage and well irrigation. This benefits to salt washing and stops salification. Although, the nitrate content of shallow ground reaches 20 mg/kg and gets over the national standard of drinking water in few sites, it is not a problem. People do not drink shallow water. They drink deep ground water. The deep ground water quality remains at the national standard of drinking water, i.e., it is not polluted. The monitoring of soil and water illustrates that the land management benefits to protect the potential of natural resources and prevent degradation of soil and water quality(protection). 5. With the increase of income and rising of living standard, farmers like this kind of land management, and the experience of land management is spreading outside of the experimental zone. This illustrates that the land management is social acceptable. Generally saying, the land management is sustainable within the concepts of FESLM in Quzhou Experimental Zone. But people should pay attention to the following things: 1. Table 5 shows that the exploitation, both of shallow and deep ground waters, is more than the supplement. The water deficit is the major factor of system's unsustainability in long term. Water-saving irrigation technique should be taken. The soil should be fill up water as possible as people can at the end of raining season. This can decrease the amount of 7
irrigation in dry spring season. In this case, irrigation water is not the restrictive factor of agricultural production at least in 20 years. Balancing fertilization method should be taken for preventing ground water from nitrate pollution. 2. Family planning should be taken for slowing down the speed of population growth. If this could not be done, the local production of agriculture could not satisfy increasing people's food needs. 3. For maintaining and enhancing the crop production, the tendency of farmland decreasing should be retarded too. With the first measures above, the land manages is sustainable. If people take family planning and prevent farmland from occupying, their food need can be satisfied in the future. Reference 1. FAO, 1993. FESLM: An International Framework for Evaluating Sustainable Land Management. World Soil Resources Report No.73, pp.7-8. 2. Shi Yuanchun, et al, 1986. The Water and Salts Movement of Saline Soils. Beijing Agricultural University Publishing House, pp. 17-21. 3. Xin Dehui, et al, 1990. Comprehensive Managing and Developing of Saline and Low Yield Area in North China Plain. Beijing Agricultural University Publishing House, pp. 2-17, 32-37, 42-83, 93-94, 387-403. 4. Xin Dehui, et al, 1995. Comprehensive Agricultural Developing of Saline Reclaiming Area in North China Plain. China Agricultural Scientific and technical Publishing House. 5. Tian Xuedong, 1996. The Theory and Practice for Evaluating Sustainable Land Management. Msc. Thesis, Beijing Agricultural University, pp. 25-75. Key words : saline soil, sustainable management, drainage, irrigation, China Mots clés : sols salés, aménagement durable, drainage, irrigation, Chine 8