Contour Ridge Research Articles

Soil erosion simulations of land use scenarios for a small Loess Plateau catchment

Several land use scenarios were developed for the 3.5 km 2 Danangou catchment on the Chinese Loess Plateau. These scenarios consist of four groups of three scenarios each: one group is based on the present land use distribution, the other three (alternative land uses) on a redistribution of land use according to slope gradient, soil type, slope aspect and land form. For example, cropland areas are restricted to slope gradients smaller than 25%, 20% and 15%. All groups consist of one scenario that only uses present or alternative land use and two scenarios that apply simple forms of biological conservation practices (mulching, improved fallow) and mechanical conservation practices (contour ridges). The LISEM soil erosion model was used to simulate the effects of these different scenarios on erosion. To do this, a calibrated LISEM-data set for a real storm was used. The results show that the predicted erosion rates for woodland/shrubland are much lower than those for other land uses. According to the simulations, runoff and erosion decrease by about 10% if conservation measures are applied to the present land use, while the predicted decrease for the alternative land uses is much larger at between 40% and 60%. This large decrease can be explained by the fact that one of the main differences in the alternative land uses is that they have much more woodland/shrubland. Differences in predicted erosion rates between the different alternative land uses are caused by conversion of cropland to orchard/cash tree. The present study is one of the first attempts to use soil erosion modelling as a tool for optimising land use and management strategies to reduce runoff and erosion rates on the Chinese Loess Plateau. More research will be needed to validate obtained simulation results with actual field measurements.

Growth Environment of Sloped Millet Field in the Southwestern Niger and Effects of Introducing Contour Ridges

Growth Environment of Sloped Millet Field in the Southwestern Niger and Effects of Introducing Contour Ridges

Site preference in NiAl—determination by thermal conductivity measurement

A contour map of thermal conductivity in a ternary intermetallic phase characterizes the direction of the contour ridge, and the ridge direction has been demonstrated to be a reliable indication of site preference of ternary elements in an intermetallic compound. Site preferences of fifteen kinds of ternary elements in NiAl are determined from the ridge direction of thermal conductivity contours in ternary β phase. It is found that V, Nb, Ta, Mo, Fe, Ru, Co and Pt substitute preferentially for nickel, while Ti, Mn, Ga, Si and Ge for aluminum, and Cr and Cu occupy both nickel and aluminum sites.

The Utilization Prospect of Terrace Slope Land in Purple Rock Area of Middle Sichuan Basin

Terrace-slope land, referring to the side slope of terraces and the ridge of paddyfields is one of the land resources in the Sichuan Basin, China, with favorable sunlight and heat, but a limited amount of water and soil. We investigated the amount and distribution of terrace slopes in the purple rock area of the central part of the Sichuan Basin, and examined the effects of different approaches to ameliorate the soil and water conditions of terrace slopes. The results showed that the total area of terrace slopes accounted for 15% of the basin land, and that for different treatments, decrease in runoff and soil loss was in order: straw mulch > contour ridge > rye grass strip > CK and micro basin gathering.

The need for socio-economic and environmental indicators to monitor degraded ecosystem rehabilitation: a case study from Tanzania

This paper documents the events leading to the imminent collapse of an attempt to rehabilitate a degraded ecosystem in central Tanzania, focusing on the consequences of the failure to systematically monitor socio-economic and environmental indicators. A decision was taken in 1979 to evict all grazing livestock from a 1200 km 2 semi-arid area, the so-called Kondoa Closed Area, in central Tanzania due to their destructive effect on contour ridges and bunds that had been constructed in an attempt to arrest land degradation. Although the closure was successful in that the vegetation quickly regenerated and soil erosion was arrested, the evictions resulted in severe hardship for the agro-pastoralists in the area. As a result, it was decided a decade later to allow the reintroduction of cattle on condition that they were totally confined and were of improved dairy breeds. Although performance and economic data have generally been positive, the top–down approach to the introduction of the cows, the lack of baseline data, followed by the withdrawal of external funding, have resulted in increased illegal free-grazing and the near collapse of the attempt to convert a degraded ecosystem to sustainable use. It is concluded that the probable collapse of the ecosystem in the Kondoa Closed Area is a result of the initial top–down approach to the introduction and implementation of the project, inadequate monitoring of socio-economic and environmental indicators, and ultimately to the withdrawal of donor funding.

Rainfall harvesting using sand ditches in Jordan

Rainfall harvesting in rain-fed agricultural areas increases water availability for plants during the growing season, thus increasing crop production. Rainfall can be stored directly in the soil for crop production using terraces, rippers, contour ridges, and other types of water collection methods. However, the efficiency of these methods is limited by the infiltration characteristics of soil and climatic conditions. In the rain-fed agricultural areas of Northern Jordan soils are predominantly clay having very low infiltration rates. In such cases the depth of water infiltration is very small and water may remain in the upper layer of the soil profile. With high evaporation rates, collected water is lost to the atmosphere very rapidly and is therefore, unavailable for plants. Field experiments were initiated in Northern Jordan in 1996 to harvest rainfall and store it deeper in the soil profile thereby reducing the effect of evaporation. The experiment consisted of digging experimental trenches 80 cm deep, 5 m long and 1 m wide across the land slope between two rows of olive trees. The trenches were filled up to the original soil level using local deposits of fractured rock and river sand with large infiltration rate. These filled trenches, called sand ditches, were expected to collect rainfall, intercept runoff, and store water in the surrounding soil at greater depths to be used by plants for longer periods of time. It can be a very efficient method since it increases water infiltration and prevents evaporation during the growing season. The efficiency of sand ditches in storing water was assessed by monitoring soil moisture conditions and depth of infiltration in the sand ditch area, a 35 m 2 area located between four olive trees, and at a control area without a sand ditch, using an auger hole. The amount of water stored in the soil was calculated at each time interval and compared with total rainfall. Experimental results indicated that sand ditches increased both the percentage of rainfall stored in the soil matrix and the infiltration depth of water during the two winter seasons from 1996 to 1998. At one of the experimental areas on April 19, 1998 the infiltration depth and water content in the sand ditch area were 100 cm and 28%, respectively compared to only 68 m and 19% in the control area. During the same period, the calculated ratio of depth of water stored in the sand ditch area to rainfall was 73% compared to only 45% in the control area.

Contour Grass Strips and Tillage Affect Corn Production on Philippine Steepland Oxisols

Cultivated steeplands in the humid tropics require better soil management systems to meet increasing food demands. The objective of this 4‐yr study was to evaluate the following four contour soil management systems for corn (Zea mays L.) production: (i) contour moldboard plowing (CP); (ii) ridge tillage (RT); (iii) natural grass barrier strips plus moldboard plowing (GCP); and (iv) grass strips plus ridge tillage (GRT). Eight successive corn crops were grown in limed and fertilized soil from 1992 through 1995. On a total land area basis (cropped area plus the area occupied by the grass strips), the 1995 mean grain yields for RT (10.8 Mg ha−1) and GRT (10.3 Mg ha−1) were significantly greater than yields for CP (10.0 Mg ha−1) and GCP (9.6 Mg ha−1). The corn grain yields for the CP and RT systems before 1995 ranged from 1.3 Mg ha−1 in 1992 to 8.4 Mg ha−1 in 1993, while comparable GCP and GRT yields ranged from 1.4 to 7.6 Mg ha−1. Excluding the area occupied by the grass strips, the GRT system had the highest 4‐yr average corn yield (7.3 Mg ha−1) followed by the GCP (7.2 Mg ha−1), RT (6.9 Mg ha−1) and CP (6.7 Mg ha−1) systems. Yields improved during the 1994 and 1995 growing seasons when the grass was not permitted to grow as tall. The combination of contour ridge tillage and contour grass strips has potential for sustaining crop productivity on highly erodible steepland soils in the humid tropics.

Assessment of tillage erosion rates on steepland Oxisols in the humid tropics using granite rocks

Soil translocation by tillage may be an important factor in land degradation in the humid tropics. The objective of this study was to evaluate tillage-induced soil translocation on an Oxisol with 25% and 36% slopes in Claveria, Philippines for three tillage systems: contour moldboard plowing (CMP), moldboard plowing up and downslope (UMP), and contour ridge tillage (CRT). Small rocks 3–4 cm in “diameter” were used as soil movement detection units (SMDU). The SMDUs were placed at 10 cm intervals in a narrow 5-cm-deep trench near the upper boundary of each plot, the position of each rock recorded, and the trench backfilled. Five tillage operations used to produce one corn crop were performed during a one month period: two moldboard plowing operations for land preparation (except for CRT), one moldboard plowing for corn planting, and two inter-culture (inter-row cultivation) operations. After these operations, over 95% of the SMDU were recovered manually and their exact locations recorded. Mean annual soil flux for the 25% slope was 365 and 306 kg m −1 y −1 for UMP and CMP, respectively. For the 36% slope, comparable values were 481 and 478 kg m −1 y −1. Estimated tillage erosion rates for the 25% slope were 456 and 382 Mg ha −1 y −1 for UMP and CMP, respectively, and increased to 601 and 598 Mg ha −1 y −1, respectively, for the 36% slope. The mean displacement distance, mean annual soil flux, and mean annual tillage-induced soil loss for both slopes were reduced by approximately 70% using CRT compared to CMP and UMP.

Ridge tillage and contour natural grass barrier strips reduce tillage erosion

Large amounts of soil are eroded annually from tilled, hilly upland soils in the humid tropics. Awareness has been increasing that much of this erosion may be due to tillage operations rather than water-induced soil movement. This field study estimated soil translocation and tillage erosion for four tillage systems on Oxisols with slope gradients of 16–22% at Claveria, Misamis Oriental, Philippines. Soil movement was estimated using `soil movement tracers' (SMT) which consisted of painted 12-mm hexagonal steel nuts. The SMT were buried in three replicate plots of the following tillage treatments: (1) contour moldboard plowing in the open field (MP-open); (2) contour ridge tillage in the open field (RT-open); (3) contour moldboard plowing plus contour natural grass barrier strips (MP-strip); and (4) contour natural grass barrier strips plus ridge tillage (RT-strip). Two hundred SMT were placed at the 5-cm depth at 5-cm spacings on 10 rows and 20 columns in two microplots within each plot. The microplots were oriented with the boundaries running downslope and along the contour of each 8-m-wide × 38-m-long (downslope) tillage plot. After tilling the land for four successive corn ( Zea mays L.) crops (20 tillage operations), the SMT were manually excavated and their positions recorded. Recovery of SMT ranged from 82% to 85%. Displacement of SMT was directly related to slope length, percent slope, and tillage method. Mean displacement distance of SMT during the four corn growing seasons was 3.3 m for MP-open, 1.8 m for RT-open, 1.5 m for the RT-strip, and 2.2 m for MP-strip. Based on tillage operations associated with two corn crops per year, mean annual soil flux was estimated to be 241, 131, 158 and 112 kg m −1 for MP-open, RT-open MP-strip, and RT-strip, respectively. Compared to the mean annual soil loss for MP-open of 63 Mg ha −1, soil loss was reduced by 30%, 45%, and 53% for the MP-strip, RT-open, and RT-strip systems, respectively. Both ridge tillage and natural grass barrier strips reduced soil displacement, soil translocation flux, and tillage erosion rates.

Variability in ridge and furrow size and shape and maize population density on small subsistence farms in Malawi

Tie-ridging is being promoted in Malawi as an on-field rainwater harvesting technique to reduce drought risk to a maize ( Zea mays L.) crop. Adoption of tie-ridging often requires changes in farmers' tillage and crop practices. To ensure success, there is need to study farmers' current tillage and crop practices. Ridge and furrow sizes and shapes and plant population density were measured in 99 maize fields in four districts of the Central Region of Malawi in January 1997. The majority of farmers in Central Malawi did not follow government extension recommendations on ridge sizes (spacing, height and base width), within-row maize station spacing (maize spacing) and plant population density. Both ridge and maize spacing had a low coefficient of variation (CV<10%), while ridge base width and ridge height had the highest variability (CV>30%). The CV for number of plants per station was between 10% and 14%. The most common ridge shape was hemispherical and the next most common was triangular. Slope along the furrows was close to the zero slope of the contour ridge. Farmers compensated for different ridge spacing by varying the maize spacing and number of plants per station. Maize plant densities 30–50 days after planting were 6–40% higher and not lower than recommended plant density of 3.7 plants m −2 (range 3.9–5.2 plants m −2). There is need to establish the negative impact, if any, of higher maize population densities on yield.

Soil erosion assessment at the Udi-Nsukka Cuesta (southeastern Nigeria)

Biophysical and participatory research methods were combined to examine factors contributing to soil erosion at field plot, village and regional scale on the sandstone dominated Udi-Nsukka Cuesta in southeastern Nigeria. At field plot scale, the properties of seven pedons were related to soil erodibility. Very high infiltration rates measured with a double ring infiltrometer and permeameter, were not in accordance to reported runoff and soil loss. The effect of groundcover and canopy height was incorporated into rainfall erosivity for plots under cashew, oil palm dominated forest and secondary natural vegetation. Cropping systems and field management practices were compared for different positions along a toposequence traversing the plateau and escarpment of the Udi-Nsukka Cuesta. Soil loss, calculated by a modified version of the universal soil loss equation, was 10 to 100 times higher on escarpment than on plateau plots. Farmers are adapting to the problems of interrill and rill erosion through careful crop selection and rotation, and contour ridging. At the village and regional scale, terrain observations were compared to archival research, historical accounts by villagers and geographic analysis of 1962 aerial photographs (1:40 000). Ravine and gully formations seemed influenced by a combination of infrastructure, geohydrology, topography, vegetation and land use. Both community efforts and state measures to combat erosion tend to be crisis managed, and are concentrated on repairing damage to economically important infrastructures. A conceptual diagram has been developed to show the complex interaction between various geophysical, agroecological, socio-economic and political components influencing soil erosion at farm, village and regional scale. Copyright © 1999 John Wiley & Sons, Ltd.

Soil Conservation Effectiveness and Crop Productivity of Forage Legume Intercropping, Contour Grass Barriers and Contour Ridging in Cassava on Andean Hillsides

SUMMARYSoil erosion and the productivity of cassava (Manihot esculenta Crantz) cropping systems, including forage legume intercropping, were monitored under natural rainfall conditions on Inceptisols in southwest Colombia. Trials were conducted over two cropping periods on moderate slopes. The best erosion control and cassava fresh root yields were achieved by sole cropping on contour ridges. Erosion was greater with forage legume intercropping than with cassava sole cropping in the first cropping period but once well established and uniformly distributed, undersown legumes controlled erosion effectively, though yields of cassava were depressed by 40% or more. Dense stands of grass contour barriers decreased erosion to tolerable levels. Lower cassava yields due to reduced cropping area and competition from the grasses could be compensated for by the production of valuable forage and by increasing cassava planting density.

Mechanical soil conservation with contour ridges: Cure for, or cause of, rill erosion?

Based on the results of an erosion damage assessment in Southern Zimbabwe, where mechanical conservation work has been carried out since the 1940s, this paper describes the impact of mechanical conservation systems on processes leading to rill erosion. In a study of a catchment area, it was found that influxes of water from roads and waterways as well as contour ridges that were originally designed to control rill erosion had a major role in the formation of rills. Existing rills and depressions which cause water concentration, siltation of contour drains and overflowing of contour ridges were the main factors leading to excessive rill erosion. The study showed that particularly during a highly erosive year like 1992/93, the damage due to rill erosion can be excessive, causing an abrupt degradation. It is concluded that the present conservation system is insufficient to control rill erosion effectively and is often the cause of this erosion. Effective control of rill erosion is a pre-condition for optimal implementation of land management systems such as conservation tillage. Therefore, an integrated approach to land husbandry must be developed jointly with farmers and promoted in order to improve crop production and sustainable management of natural resources. This should consider improved mechanical conservation as well as agronomic and biological soil and water conservation techniques.

'Water Used to be Scattered in the Landscape': Local Understandings of Soil Erosion and Land Use Planning in Southern Zimbabwe.

Abstract This article presents some local understandings of ecological history in a semiarid area of Zimbabwe as an exploration of how changes in land use that reflect both local initiative and state planning have transformed the hydrology of local catchments of heavy clay ‘mopani soils’ and greatly accelerated soil erosion. Local explanations provide a wide-ranging and challenging analysis of the dynamics of watersheds situated within a complex social and historical context. In conjunction with the spread of ox-ploughing and population growth and redistribution, a range of ill-conceived and authoritarian ‘conservation’ and ‘development’ interventions by the colonial state are argued by local intellectuals to be the major causes of accelerated soil erosion. Particular attention is given to how government imposed the deforestation and intensive use of difficult top land soils, and then transformed that uneven heterogeneous landscape into a smooth bare land connected by contour ridges and paths so that water concentrates, erodes, and then leaves the desiccating land to silt the rivers. The existence of sophisticated ‘indigenous knowledge’ systems in Africa has now been widely accepted, but this case study suggests that their very depth, variability and complexity means that attempts to harness local ecological knowledge for the understanding of – or development action about – environmental change may be more problematic than is often assumed. Researchers, government and conservation and development organisations need to do much more than seek to ‘tap’ such knowledge. Real understandings and ‘sustainable development’ can only flow from new power relationships with rural people and their knowledge

Tillage systems for root and tuber crops in the tropics

Although limited information is available on tillage practices for root crops, published results show that tillage methods vary widely depending upon the specific root crop, the soil type, the previous vegetation, as well as the socio-economic conditions of farmers. These aspects are discussed in this review. In general terms, it has been found that root and tuber crops are sensitive to soil compaction, inadequate aeration or poor drainage and therefore respond favorably to intensive tillage, followed by ridging or mounding. However, large differences exist between crops, with potato, sweet potato and yam requiring more intensive cultivation than cassava and taro. On light-textured soils, cassava can be grown without or with minimum tillage as long as weeds are controlled; in heavy or compacted soil cassava responds favorably to tillage and yields tend to increase when grown on ridges. In order to reduce erosion as well as production costs, cassava should be grown with as little tillage as possible as long as high yield can be maintained. Contour ridging and mulching are other practices that not only tend to increase yields but also reduce erosion losses. Organized data for use in a classification of the tillage requirements of different soils for the various root crops is lacking. We suggest that research efforts should be directed towards the characterization of the physico-chemical and biological factors which determine the tillage requirements of a given soil for a given root crop.

Limitations of determining density or magnetic boundaries from the horizontal gradient of gravity or pseudogravity data

The horizontal‐gradient method has been used since 1982 to locate density or magnetic boundaries from gravity data (Cordell, 1979) or pseudogravity data (Cordell and Grauch, 1985). The method is based on the principle that a near‐vertical, fault‐like boundary produces a gravity anomaly whose horizontal gradient is largest directly over the top edge of the boundary. Magnetic data can be transformed to pseudogravity data using Fourier techniques (e.g., Hildenbrand, 1983) so that they behave like gravity data; thus the horizontal gradient of pseudogravity also has maximum magnitude directly over the boundary. The method normally is applied to gridded data rather than to profiles. The horizontal‐gradient magnitude is contoured and lines are drawn or calculated (Blakely and Simpson, 1986) along the contour ridges. These lines presumably mark the top edges of magnetic or density boundaries. However, horizontal‐gradient magnitude maxima (gradient maxima) can be offset from a position directly over the boundary for several reasons. Offsets occur when boundaries are not near‐vertical, or when several boundaries are close together. This note predicts these offsets. Many other factors also cause offsets, but they are less straightforward and usually are only significant in local studies; we discuss these factors only briefly.

Progradation on the Portuguese continental margin: Interpretation of seismic facies

Using seismic profiles, an inventory of the prograding sedimentary sequences from the Neogene and Quaternary periods is presented. The prograding layers are located at three levels on the Portuguese continental margin. The inner shelf in front of river mouths is covered by Holocene deltas, the outer shelf is built out by progradation associated with paleovalleys, and finally, the Algarve upper continental slope is overlain by contour ridges. On the shelf, progradation may be easily explained by the supposition of a stability level H at which sedimentary particles come to rest. If H is supposed to be stable, the sigmoid or oblique configuration of the prograding layers is related to the subsidence of the margin. Discontinuities between prograding sequences are determined by changes in water depth. The particular role of each one of these factors is determined by interpreting prograding seismic facies and their associations.

Studies on the Cultivation and Control of Erosion

The crumbling action caused by a slight cultivation helps erosion control. Its effect is very remarkable in Hokkaido, where we have a heavy precipitation in a short time. Further, this effect depends upon the time cultivation is performed. It is effective for reducing erosion to cultivate after the first excessive rain-fall. But cultivating tends to reduce the effect when it is done to much. However, the erosion in the contour ridge is heavier than in the up and down hill when it is left after the ridge is fallen. It is necessary for keeping the effect of contour lister that we repair fallen ridge by cultivation as soon as they are fallen.

Synoptic Models of Thickness and Isotherms

Models of daily thickness patterns were developed for the layers 500–300 mb, 300–200 mb and 200–100 mb. Isotherm models are also given for the 300-, 200-, and 100-mb levels. The models apply to an idealized wave-pattern and show the substantial difference between conditions over contour troughs and those over contour ridges. Tropospheric-type patterns (cold troughs, warm ridges) are predominant in the 500–300-mb layer while stratospheric patterns (warm troughs, cold ridges) prevail in the 200–100-mb layer. The 300–200-mb layer shows a mixed tropospheric and stratospheric type. The presented models are only tentative as limited data were available for their construction. The use of models in analysis and forecasting is discussed.