Bench terraces on loess soil China - 土坎梯田, 梯地 A Terrace is a structural SLM practice with a raised flat platform built on the slope to reduce soil loss and runoff on the slope, increase the rainfall infiltration and yield. A terrace is a leveled section of a hilly cultivated area, designed as a method of soil conservation to slow or prevent the rapid surface runoff and erosion of topsoil. Often such land is formed into multiple terraces, giving a stepped appearance. To change the landform for better agricultural condition of operation of tillage and harvasting, reduction of soil erosion and water loss and finally for higher production. The building of a terrace in the loess plateau takes long because loess is very soft and deep and the severe soil erosion and shortage of water in agriculture hinders the process, as well. Previously, terraces were constructed by hand. These terraces weres narrow and damaged by the great storms. Now, the machinery is used to build wide terrace with high bank size in the loess plateau. The establishment of terrace needs a lot of money but it is a long-term investment. The maintenance of terrace is considerable economic because the major efforts are the annually improvment of terrace bunds. The soil erosion is very severe because of the cohesionless loess soil and very intensive rainfall storms in the summer and autumn that would destroy the land surface into broken hilly area. Terrace is a kind of measure to resolve it combining with crops. The human activities here is very intensive because they must plant on the slopes that would make the soil erosion greater. left: Terrace for crops and cash trees. With the loacl cave dwelling covered with earth. (Photo: Wang Fei) right: Terrace in Mazhuang watershed (Photo: Yangling, Shaanxi Pr) Location: Shaanxi Province Region: Yanhe River Basin Technology area: 253.3 km 2 Conservation measure: structural Stage of intervention: mitigation / reduction of land degradation Origin: Developed through land user`s initiative, traditional (>50 years ago) Land use type: Cropland: Annual cropping Cropland: Tree and shrub cropping Land use: Grazing land: Intensive grazing/ fodder production (before), Cropland: Annual cropping (after) Climate: semi-arid, temperate WOCAT database reference: T_CHN051en Related approach: Bench terraces on loess soil (QACHN52) Compiled by: Wang Fei, Institute of Soil and Water Conservation, CAS and MWR Date: 2009-01-20 Contact person: Fei Wang, Institute of Soil and Water Conservation, CAS and MWR, 0086 29 8701 9829, Classification Land use problems: - Soil and water losses are alarming in this region. The loose loess, steep slopes, and intensive storms in the summer and autumn, accelerates this process. Aditionally, the lack of rainfall negatively impacts agriculture and vegatation. Sediment deposition could increase the river bed and diminish capacity of reservoirs. On one hand side floods occur frequently because of fast and large runoff and on other hand side sedimentation in rivers reduce their water carring capacity. (expert's point of view) The low yield of crops and the low income from land is more important for the local people. It is necessary to improve the agricultural conditions. The land, especially the tableland and gentle slope land could be convert into terrace. (land user's point of view)
Land use Climate Degradation Conservation measure Annual cropping Tree and shrub cropping Grazing land: Intensive grazing/ fodder production (before) Cropland: Annual cropping (after) rainfed semi-arid Soil erosion by water: loss of topsoil / surface erosion Structural: Bench terraces (slope of terrace bed <6%) Stage of intervention Origin Level of technical knowledge Prevention Mitigation / Reduction Rehabilitation ago) Land users initiative: traditional (>50 years Experiments / Research: 10-50 years ago Externally introduced Agricultural advisor Land user Main causes of land degradation: Direct causes - Human induced: deforestation / removal of natural vegetation (incl. forest fires) Direct causes - Natural: Heavy / extreme rainfall (intensity/amounts) Indirect causes: population pressure Main technical functions: - control of concentrated runoff: retain / trap - reduction of slope angle - increase of infiltration Secondary technical functions: - increase / maintain water stored in soil - improvement of water quality, buffering / filtering water - increase of biomass (quantity) Environment Natural Environment Average annual rainfall (mm) Altitude (m a.s.l.) Landform Slope (%) > 4000 mm 3000-4000 mm 2000-3000 mm 1500-2000 mm 1000-1500 mm 750-1000 mm 500-750 mm 250-500 mm < 250 mm > 4000 3000-4000 2500-3000 2000-2500 1500-2000 1000-1500 500-1000 100-500 <100 plateau / plains ridges mountain slopes hill slopes footslopes valley floors flat gentle moderate rolling hilly steep very steep Soil depth (cm) 0-20 20-50 50-80 80-120 >120 Growing season(s): 300 days(march to November), 200 days(april to October) Soil texture: medium (loam) Soil fertility: very low Topsoil organic matter: low (<1%) Soil drainage/infiltration: good Soil water storage capacity: low Ground water table: 5-50 m Availability of surface water: medium, poor / none Water quality: poor drinking water Biodiversity: medium Tolerant of climatic extremes: temperature increase, seasonal rainfall increase, seasonal rainfall decrease, wind storms / dust storms, floods Sensitive to climatic extremes: heavy rainfall events (intensities and amount) If sensitive, what modifications were made / are possible: Loess is very prone to erosion and extreme storms would destory the bank of terrace. In the study site sesonal rainfall increased and the loess terrace could retain more soil water and reduce the runoff.
Human Environment Cropland per household (ha) <0.5 0.5-1 1-2 2-5 5-15 15-50 50-100 100-500 500-1,000 1,000-10,000 >10,000 Land user: Individual / household, Small scale land users, common / average land users, men and women Population density: 50-100 persons/km2 Annual population growth: < 0.5% Land ownership: state Land use rights: individual Water use rights: open access (unorganised) (Like other rural area in China.) Relative level of wealth: average, which represents 80% of the land users; Importance of off-farm income: 10-50% of all income: The yield of terrace is much high and stable. Access to service and infrastructure: low: drinking water and sanitation, financial services; moderate: health, employment (eg off-farm); high: education, roads & transport Market orientation: mixed (subsistence and commercial) Technical drawing The brief structure of terrace in the Yanhe River Basin. (Wang Fei) Implementation activities, inputs and costs Establishment activities - Built the platform and bank with soil digged - Backcover the topsoil on the surface of platform - Check and accept the terrace - Survey and design - Move the topsoil to other place Establishment inputs and costs per ha Inputs Costs (US$) % met by land user Labour 395.30 100% Equipment - machine use 1428.00 100% TOTAL 1823.30 100.00% Maintenance/recurrent activities - Reinforce the bank - Build the edge in some terraces - Fill the erosion hole of the landform - Reinforce the bank - Build the edge in some terraces - Fill the erosion hole of the landform Maintenance/recurrent inputs and costs per ha per year Inputs Costs (US$) % met by land user Labour 263.50 100% TOTAL 263.50 100.00% Remarks: The terrace on the steep slope need more input for more soil and earth should be moved. It is the most important factor.the soil depth is not so important for the deep soil layer here.the cost of labour increases greatly in the last several years and the cost of construction of terrace increased. In general condition, slope and soil, in the middle reaches of Yan River Basin. The prices of labour-day and Machine-hour are around 2005. Assessment
Impacts of the Technology Production and socio-economic benefits increased crop yield increased product diversification increased farm income reduced risk of production failure decreased labour constraints decreased workload Socio-cultural benefits improved conservation / erosion knowledge improved food security / self sufficiency Ecological benefits reduced surface runoff reduced soil loss reduced hazard towards adverse events improved harvesting / collection of water increased soil moisture improved soil cover increased biomass above ground C Off-site benefits reduced downstream flooding reduced downstream siltation improved buffering / filtering capacity reduced wind transported sediments reduced damage on public / private infrastructure reduced damage on neighbours fields Contribution to human well-being / livelihoods Production and socio-economic disadvantages reduced animal production Evaporation form the wall of terrace decreased drinking water availability / quality Socio-cultural disadvantages Ecological disadvantages Off-site disadvantages reduced river flows The contribution of agriculture is very limited, but in some watershed, the imcome of apple has already improve the human-being. Benefits /costs according to land user Benefits compared with costs short-term: long-term: Establishment slightly positive positive Maintenance / recurrent slightly positive very positive The yield of terrace is stable and relative higher. The income from terrace is high and the maintain cost is low. Acceptance / adoption: 90% of land user families (95 families; 95% of area) have implemented the technology with external material support. Most land farmers have some terrace. I do not know the exact number of land user families who adopted the technology. 10% of land user families (5 families; 5% of area) have implemented the technology voluntary. the old narrow terraces, now a very small area left, are build voluntarily. There is strong trend towards (growing) spontaneous adoption of the technology. Nearly all the people know the benefit of terrace. the benefits of terraces are very good for crops and orchards are high enough in this region.
Concluding statements Strengths and how to sustain/improve Weaknesses and how to overcome Reduce soil erosion on the slope. The loess soil is prone to erosion because of its loose character induced by fine sand content and low soil organic matter. The plain flat makes the dispersion and transportation of soil particls difficult. Reduce runoff and increase the soil moisture The runoff generation is smaller on the plain than on the slope. Slow movement of surface water lead to more soil infiltration. Increase yield. Water is the limit factor in the loess plateau. The yield would increase if there is enough water available. Decrease flood risk. It is a kind of off-site benefits because less runoff generation and gentle process of runoff decrease flooding. Reduction of sediment also diminish flood risk because the drainage capacity of channel and adjusting capacity of reservior increase when sedimentation decrease. There is possible damage of terraces because the loess is very loosen and prone to collapse. Keep upmaintaining the bank and land well. Decrease runoff of lower stream. No way to overcome it, but it also could decrease the risk of floods. The output is also low in contrast with other industries. way to overcome it. The total and net income is too low because the area of terrace per capita is very small. The income is relative compared with other industries. No way to overcome it. The net income is low because the labour costs are increasing, and the total income because labour cost and very small area of terrace per capita. No Increase yield and income. If the terrace is maintained well, the water condition would be better than that on the slope land even in dry year with low precipitation. Convenient to till and harvest Tillage and harvesting is much easier on the plain flat land than on the slope. The maintainance of terrace is important. Copyright (c) WOCAT (2018)