Control of soil and water losses is the critical issue for black earth conservation
The cultivated area of black earth and its annual grain production respectively account for 1/4 of the national total,while commodity grain accounts for 1/3 of the national total,which is of paramount importance to the national food security.Though this area has been relatively recently developed over a 100-year period since the large-scale agricultural reclamation,it went through highly intensive cultivation and rapid succession processes.The cropping changes and poor management choices,the regional sloping topography coupled with a continental climate have led to soil degradation and water runoff.These processes have caused excessive hillslope and gully erosion,which seriously threatens agricultural production and environmental quality in the region.To effectively conserve and utilize the black earth soils,the national government decreed the First National Black Earth Protection Legislation,and has implemented a series of soil and water conserving projects.However,from the scientific point of view,the key points and critical issues that urgently need to be resolved are not clear.Based on our research group's the long-term scientific research and monitoring of black earth erosion and its impacts on soil quality and grain production,we propose that control of soil and water losses is the priority issue,and several urgent problems needing attention are identified.Water runoff and soil erosion reduce topsoil depth,while decreasing soil fertility and degrading soil structure.From 1982-2002,the annual soil organic matter(SOM)content decline in the typical black earth belt was 0.5％,and was 1.35％in most severely affected areas.Approximate 50 mm rainfall flows out of farmland annually,which is equal to 10％of the average annual precipitation.These soil and water losses simply reduce soil and water resources available for crops aggravating crop water stress frequently observed during the growing season.The loss of each 1 cm topsoil or reduction of 1％SOM lowers the corn yield by 100 kg/ha.If topsoil layer disappears,grain production will be reduced by 30％.Ten million t of grain production is lost annually due to soil and water losses.In addition,over 600000 gullies have been identified in this region;90％of these gullies is active gullies with 70％developed in farmland.Not only do gully processes result in lost soil,gully expansion encroaches on arable land at an annual gully expansion rate of 7.39 km.The estimated loss of farmland from gully erosion is around 333000 ha with an annual grain loss of at least 1.5 million t,while the soil loss by gully erosion accounts for 65％of the total soil loss in the region.Because most soil loss estimates do not include gully erosion,the soil erosion intensity normally reported and grain loss associated with soil and water loss is underestimated.Additionally,gully erosion interferes with operations of agricultural machinery increasing fuel input costs and reducing machinery operation efficiency.Four priority problems are urgently needed to be resolved for the control of soil and water losses.The very first one is to contain sustain or improve of SOM contents.The second is to identify appropriate soil conservation practices and identify implementation bottlenecks.The third is to ecologically rehabilitate existing gullies.The last but not least,is to synergistically control erosion with improved soil fertility.
soil and water losscontrolblack earth conservationcritical issue
张兴义、胡伟、李建业、郭明明、刘晓冰
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中国科学院东北地理与农业生态研究所,哈尔滨 150081
soil and water loss control black earth conservation critical issue
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