沟灌侵蚀研究进展English.doc

Research Progress on the Furrow Irrigation Induced ErosionFan Haoming，Zhou Lili, Wu Min, Liu Yanhua(College of Water Conservancy, Shenyang Agriculture University, Shenyang Liaoning, 110161 China)Abstract: Main research achievements in furrow irrigation induced erosion in the world are summarized in this paper. First, the main achievements in furrow irrigation induced erosion affected by the characteristics of irrigation water and the mode of irrigation action are analyzed; second, the prediction model and the prevention and cure technique for furrow irrigation induced erosion are introduced. Finally, the tentative plan on furrow irrigation induced erosion research in china is proposed.Key words: Furrow irrigation induced erosion; Influencing factor; Prediction model; Prevention and cure techniqueFurrow irrigation erosion concerns the phenomenon that soil and nutrients loss and land productivities decrease, which are caused by irrigation waters hitting and eroding forces in the process of irrigation and draining in cropland, vegetable plot, orchard etc. One-sixth of worlds cropland is irrigated, and 90% of the irrigated cropland is surface irrigated 1. Furrow irrigation is one of the most universal surface irrigation forms, and it is also an erosion form which has serious soil erosion amounts under irrigation erosion. China is a large agricultural country, and the statistical data of agricultural department showed that only 42.3% of the total cropland area is effective irrigation cropland in China 2. Actually, the problems of soil erosion, non-point source pollution, water quality impairment etc. which occur extensively in China and the world are closely related to irrigation erosion 3, 4. Berg and Carter reported that annual irrigation soil loss ranging from 98 to 15483 t km-2 in Southern Idaho 5. Koluvel etc. measured from 49 to t km-2 of soil loss per season and 246 to 5407 t km -2 per irrigation in Wyoming 6. Besides, irrigation erosion of agricultural land is a significant factor that affects water quality 7, 8. Westermann etc. reported that the link between phosphorus content and silt content in surface irrigation runoff is strong 9. About over 90% of phosphorus in surface irrigation runoff remove adhering to the silt simultaneously 5. Sojka etc. showed that exposed and transported subsoil caused by irrigation erosion contributes to crusting, sealing, compaction and nutrient deficiencies, ultimately reduces crop quality and yields 10, which are usually neglected. And the matter of ditch, canal and reservoir dredging, water quality impairment etc. caused by irrigation erosion is not emphasized.Irrigation erosion and rain erosion result from very different systematic in duration, spatial relationships, soil properties in erosion, the erosion action mode, eroding water characteristics and irrigated systems. The early researches 11-13 presented that applying modified rain-fed erosion models to estimate erosion from irrigation has not produced satisfied results. Thus only irrigation water quality characteristics are recognized, could the way how irrigation water acts etc, the accurate, stable and feasible irrigation erosion prediction models be developed. 1 Impact of irrigation water quality on furrow irrigation erosionFrom the view of soil surface irrigation water properties, Brown etc. reported that irrigation water commonly contains a substantial sediment or suspended biotic load, the loads change systematically when the stream advances, affecting carrying capacity and surface sealing in furrows 14. Chen Hongsong and Shao Mingan showed that substantial sediments in water contributes to soil surface sealing 15,while rainfall is nearly pure water, and the substantial sediments of rainfall are less than in irrigation water obviously. Rain-fed erosion theories and models concentrate on how the physical properties of raindrops and water streams affect erosion. Laboratory simulations and rainfall simulator studies as well as furrow irrigation studies have demonstrated that EC and SAR influence the water erodibility significantly 16, 17. The early researches commonly showed that high SAR/low EC water is more erosive than low SAR/high EC water. Lentz etc. found that sediment in furrow irrigation runoff more than doubled with SAR 12;EC 0.5 ds m-1 water, compared to SAR 0.7;EC 2.0 ds m-1 water 18.Because the high SAR waters increased aggregate disruption and seal formation in furrows ,infiltration was reduced ,which in return increased runoff, stream velocity and shear. Lentz and Bjorneberg conducted the experiment of the relationship between irrigation water temperature and infiltration rates, finding that soil infiltration rates increased with higher temperatures : infiltration increased by 2% per of water temperature , compared to nature rainfall 19. For the natural rainfall erosion models, soil and water properties are expressed by the soil erodibility. Irrigation water are very different from rainfall, therefore it is difficult to reflect the impact of many chemical materials of irrigation water as well as water temperature on erosion in soil erodibility accurately. The mechanism of soil erosion influenced by irrigation water properties is not clear now; the ration prediction of impact of irrigation water on erosion need to be researched for further advances to occur.2 The impact of the form irrigation water acts on furrow irrigation erosionFor the view of the mode action of soil surface irrigation water, irrigation usually occurs on dry soil quickly and directly, where the transition from dry soil to excess water and runoff is often virtually instantaneous. In rain events, where the soil surface is hydrated gradually over several minutes after excess water begins collecting on and running off field surfaces that were gradually pre-wet by rain. Guo Yuwen etc. showed that the strong forces produced by irrigation water destroy soil structure and increase soil erodibility 20. Kemper etc. suggested that irrigation water quickly hydrates dry soil in cropland furrows, displacing the air that is in pores and adsorbed on internal soil surface 21. The air forces produced by advancing water in the process of sealing destroy soil structure and increase soil erodibility at last. A small flume study made by Shainberg etc. demonstrated that air-dried soil exhibited great rill erodibility than wet soil, and that erodibility decreased with time went by after wetting 22. Using 24m furrows, Bjorneber etc. showed that erosion from dry furrows in a Portneuf silt loam soil was greater than from gradually pre-wet furrows 23. The mechanism of impacts of irrigation water action mode on soil erodibility is recognized in researches above-mentioned, while the ration relationship has not been made clearly, let long putting it to the irrigation erosion prediction. Besides, from the view of the irrigation water magnitude developing states, water in furrows decreased which was influenced by sustainable infiltration, while rainfall increased gradually with converging events 24. And there is no impact of raindrop striking and disturbing on sheet flow yet. 3 Modeling of furrow irrigation erosionIn the view of modeling of furrow irrigation prediction, although USLE model and RUSLE model are widely validated water erosion prediction models based on statistics in the world, no irrigation erosion data was used in the development of either USLE model or RUSLE model, even documented methods for applying this technology in irrigation erosion prediction are virtually nonexistent. The Idaho NRCS developed the SISL (Surface Irrigation Soil Loss model) model to estimate soil loss from furrow irrigated fields, the SISL equation is as follows： SISL=BSLKAPCCPIPWhere SISL=surface irrigation soil loss from a field SL=the base soil loss rate KA=soil erodibility PC=prior crop factor CP=conservation practice factor IP=respective factor 25Bjorneberg etc. evaluated SISL model and showed that the absolute different between measured and prediction valued were often large, the model application is not accurate and stable enough 26.WEPP model is one of the most comparatively mature and advanced process-based soil erosion models up to now. It contains a separate content for calculating infiltration and runoff from irrigated fields. Furrow irrigation erosion is then calculated by using the same steady state rill erosion algorithms for prediction that are used for rain. A WEPP application research showed that WEPP model over-calculated transport capacity, so sediment deposition was not accurately predicted (Bjorneberg etc.) 11.The author believed that the leading reason of that was no striking and disturbing forces of raindrop to sheet flow in the furrow irrigation erosion process. In addition, WEPP model needs more parameters, which limited the practical application of WEPP in furrow irrigation erosion. In addition, some irrigation flow simulation models such as SRTR (Surface-Irrigation Simulation Model) are modified and added separated contents, and then applied in erosion prediction, all of that had no acceptable results ultimately 27. 4 Prevention and cure research of furrow irrigation erosion International studies on control of furrow irrigation erosion can be divided into three categories, application of polyacrylamide (PAM) to reducing furrow erosion; application of crop residue to reducing erosion, soil conservation tillage and planting pattern adjustment to reducing erosion.Early researches more concerned about the effect of crop residue on furrow irrigation erosion .The Research of Miller showed that when the irrigation rate is greater than 30L/min, add 2mg crop residue in field, the furrow irrigation erosion modulus is 1 Mg / (hm2 d), Compared to greater than 100 Mg / (hm2 d) in bare land. By the way, the furrow of nature crop residue has greater erosion resistance than artificial one 28. The research of Berg showed that the erosion in furrows covered with straw is 30% to 100% less than those without straw. Meanwhile, irrigation infiltration and hydration toward both sides increased in straw covered areas, and the crop yield raise 7% to 16% 29.Conversation tillage play important roles in reducing furrow irrigation. The research of Ashraf etc in Colorado in US showed that Infiltration rates were 24 and 50% higher and advance times were 37 and 25% longer in the CS treatment during 1991 and 1992, respectively, compared with conventional tillage (CV). Furrows in the CV treatment were 8 and 25% wider than those in the CS treatment after the first and sixth irrigations respectively 30.The study about application of PAM to reducing furrow irrigation erosion has attracted more attention since 1990s. The study of Lentz in field showed that 10g/m3 PAM reduced mean sediment load by 97% compared with untreated furrows 31. Other studies also indicated the positive role of PAM in control of furrow irrigation erosion. At present, the application of PAM in furrow irrigation erosion lack study on whether it has other negative effects and economical application of PAM in different regions and conditions.5 Research of furrow irrigation erosion in China The research of furrow irrigation erosion in our country is few, but still some achievements were received. Simulated laboratory experiments with holding miniflume were conducted to study the impact of PAM application and irrigation with saline ground water on reducing soil erosion under furrow irrigation .and analyzed the impacts of PAM and interruption time on reduction of soil erosion under influences of slope grade and inflow rate (Lei Tingwu etc) 32. Experiments study of effects of surge irrigation , PAM and irrigation with saline ground water on soil water erosion were carried out in Hetao irrigation district ,inner Mongolia 33.Experiments results showed that there was little influence of methods such as surge irrigation and continuous irrigation on soil water erosion ,while great effects of PAM application on it (Yuan Pujin etc) . Simulated laboratory experiments were conducted to study the impacts of water quality and the field slopes on soil erosion and water infiltration under furrow irrigation with marginal water resources (Zhang Lijun) 34.The results showed that water quality and field slope significantly influenced water infiltration and soil erosion. Simulated laboratory experiments were conducted to study the influenced of marginal water irrigation following PAM application on water infiltration and soil erosion under furrow irrigation. The soil erosion obviously decreases as PAM is applied, however the effects of water quality on the soil erosion is not obvious after PAM application (Dou Chaoying) 35. The domestic researches mainly focus on irrigation methods and the effects of PAM application on erosion, but the research of furrow irrigation erosion mechanism continues to improve and model related to furrow irrigation erosion is not established yet.6 Prospects of furrow irrigation erosion in China The effective irrigation area is 55.03 million hm22 in China, but few research has been conducted in irrigation erosion, therefore it is difficult to evaluate and predict properly the magnitude of soil loss from irrigation erosion and the mechanisms of irrigation erosion is hardly understood, so there were great difficulties to design fields reasonably, establish the right irrigation system for reducing erosion and keep fertility of fields. The erosion prediction models mentioned above continue to improve. It is difficult to apply it in our irrigation production activities in our nation. The author thought that the study on furrow irrigation erosion should focus on the following aspects in the long period from now on:6.1Research on mechanism of irrigation erosion At present, a sound base has been laid for the mechanism of rainfall erosion in China, but the understanding of mechanism of furrow irrigation continues to develop. The author thought that on the basis of previous studies on water erosion, the study on furrow irrigation should explore the unique aspects that different from rainfall run-off, and the unique mechanism of furrow irrigation should be grasped. The mechanism of furrow irrigation erosion in China should focus on the influence of soil dryness on water stable aggregate, the influence of ploughing extent on erosion resistance, the influence of irrigation water quality on infiltration ,the influence of different furrow irrigation methods ,furrow slope ,irrigation quantity on erosion etc for a long time.6.2 Develop furrow irrigation erosion prediction modelAt present, studies on modeling of water erosion prediction are more concentrated in China; although the current models of soil water erosion continue to develop, abundant experiences have been accumulated in the process of water erosion prediction modeling. Then on the basis of previous studies on water erosion prediction, understand characteristics of furrow irrigation effect which are different from rainfall run-off comprehensively, finally develop erosion prediction models that fit the characteristics of furrow irrigation erosion for further researches.6.3 Research on control of furrow irrigation erosion The damage caused by furrow irrigation erosion has become an unavailable issue. It has raised the urgency for the study on the control technologies of furrow irrigation erosion. Currently, the furrow irrigation erosion control should focus on resolving the following issues:(1) The negative effects of PAM in controlling of furrow irrigation erosion, using standard and economic costs problems.(2)The study on irrigation methods are suitable for both water -efficient irrigation and control of furrow irrigation erosion. Being base On evaluating the existing technologies in furrow irrigation erosion thoroughly, seek irrigation technologies parameters fitting for different kinds of regions, soil properties and planting crops, which can take both reducing erosion and ensuring irrigation water qualities well into consideration.(3)For different kinds of soil properties, irrigation water properties and furrow irrigation length (the furrow on plains and rollied areas are long, while on mountains and hilly areas are short)in different regions in China, establish control system and control strategies for different kinds of crops and furrow conditions.7 References1 Food and Agriculture Organization. AQUASTAT. /ag/agl/aglw/aquastat/main/index.stm, 2003.2 中华人民共和国农业部. 中国农业统计资料M. 北京: 中国农业出版社, 2007. (Ministry of Agriculture of the Peoples Republic of China. Chinese agricultural statistics data M. Beijing: China Agriculture Press, 2007)3 张玉斌，郑粉莉，武敏. 土壤侵蚀引起的农业非点源污染研究进展J. 水科学进展， 2007, 18(1): 123-132. 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