Cultivated Slopes Research Articles

Land use, runoff, erosion and their control: a review for southern China

Runoff and soil erosion, based upon plot studies, have been reviewed for southern China. They reveal, with the exception of tree crops, no strong association for a given land use between runoff and erosion. The data support the concept of vegetation as a major control upon runoff and sediment production. Forest and woodland have an average erosion rate of 0·05 t ha−1 year−1; the lowest rate for a given cover. Tree crops experience a slightly higher erosion rate followed by a scrub–grass cover. Cultivated slopes and bare soil, with respective mean erosion rates of 62·4 and 153·0 t ha−1 year−1, experience the greatest erosion. In terms of runoff production the ranking (low to high) goes from forest–woodland, scrub–grass to tree crops and bare to cultivated slopes. Sediment yield and runoff under various ground covers are presented as a ratio to those obtained under forest and this underlines the influence of land use. Further support is given by the use of additional studies from South-east Asia and Tanzania. Variability of sediment production, and to a lesser extent runoff under any given land use or cover, is an important feature of the data. Results from a study in Hong Kong support the importance of ground cover in controlling erosion. For example, sediment yield in splash pans on two plots where vegetation was cut were 2·6 and 3·8 times those of the control. Two plots, which were burnt, had sediment catches 5·4 and 3·1 times those of the control. However, observations of suspended sediment levels in a small stream suggest no great change in sediment levels after burning, which raises the question of sediment delivery from slopes to channels. The erosion rates reported for cultivation raise the question as to how long such rates can continue before productivity is affected. Further consideration needs to be given to economic aspects of erosion and to temporal variability. Copyright © 1998 John Wiley & Sons, Ltd.

Water, nutrients and slope position in on-farm pearl millet cultivation in the Sahel

In the Sahel, short periods of intra-seasonal drought, caused by unfavourable rainfall distribution, often have stronger effect on crop growth than fluctuations in annual rainfall. The interactive effects of nutrient deficiency and water shortage (during panicle initiation, flowering and grain filling) on yield and yield components of pearl millet (Pennisetum glaucum (L.) R. Br.), were studied on-farm along a cultivated slope, during three years with close to average annual rainfall. Grain yield was correlated to plant nutrient availability but not to annual rainfall, which was explained by the capacity of the crop to compensate for damage caused by water shortage during early growth phases. The performance of each yield component was positively correlated to cumulative rainfall during the growth phase when it was formed. Leaf area index (LAI) was very low, and leaf development followed rainfall distribution. Water and nutrients interacted during each growth phase for all fertility levels. Fertilised millet suffered less during water shortage at panicle initiation and at grain filling compared to non-fertilised millet. However, compared to favourable soil water conditions yield components were systematically lower for all treatments, indicating the synergistic effect of water and nutrients. The results suggest that water availability plays an exclusive role during flowering. Grain number dropped significantly due to water shortage and was similar for all treatments. Despite extremely high spatial variability in yields (varying with a factor 46 within the field), a significant slope effect was observed, of progressively increasing yields when moving downslope. Spatial redistribution of surface runoff resulting in higher soil water availability on lower slope positions, contributed to the yield gradient, which was reinforced for fertilised millet. For each drought period, yield components suffered systematically more upslope than downslope. This slope effect was smoothed out for manured millet, which indicates that manure increased soil infiltrability on crusted zones upslope. The slope interaction observed here – indicating that downslope (i) the risk for crop failure during droughts is lower and (ii) the response to fertilisers is greater – suggests that farmers can benefit relatively more from fertilisers applied in lower parts of the watershed. Taking advantage of spatial soil and water variability is an interesting system of low technology precision farming, which combined with water harvesting systems to master droughts, can constitute options for increased crop yields in the Sahel.

Mountain and Ecumene in Japan

The Japanese have not used their mountainland as much as they could have, given Japan's technical level in the sectors of stock-breeding and slope cultivation. Neither is the origin of this neglect to be sought for in natural causes: the mountain in Japan is indeed a harsh environment, but much of it could still be reclaimed. Mental factors account for many difficulties, but in some respects they have, more than in Europe, integrated mountains into man's social life. In fact, it is not in the mountains themselves that one is to seek the reasons why they have been neglected; but in the plains, i.e. in the complex which paddy fields and cities have formed in Japanese history: this complex was conducive, and prone, to high densities, and it has prevented Japanese society from extending its farmland.

Paysage, milieu physique et anthropisme (Landscape, physical environment and anthropism)

Abstract. - From two rural landscapes (granitic middle mountain and Grands Causses) the study presents two farmer societies. After showing the elementary units (geomorphology and soil) and their utilization, it has been shown how the agricultural erosion has changed the cultivated slopes as to remodel them ; new physical conditions are so different as before that a new settlement must consider them.

Soil erosion and sedimentation indicated by caesium 137: Jackmoor Brook catchment, Devon, England

The tracer caesium-137 was used to study the status of soil erosion and sedimentation in the Jackmoor Brook catchment, Devon, U.K. It was postulated that (1) sites at the top of a cultivated slope should be most depleted of caesium-137, (2) sites at the base of a slope should contain greater amounts of caesium-137 and have a distinctive depth profile, (3) hillslope erosion indicated by caesium-137 levels should be related to slope length and angle, and (4) caesium-137 levels should discriminate between the chief source of sediment transferred to the stream (cultivated soils) and uncultivated soils (under pasture, orchards and woodland). These hypotheses were tested in two contrasting physiographic areas of the basin. Depletion of caesium-137 levels at the top of slopes indicated soil erosion, and deeper-than-plough-depth caesium-137 profiles at the base of slopes indicated sedimentation. These characteristics were most marked in the steeper, Upper Jackmoor, portion of the catchment. Slope-length effects on soil movement were more difficult to ascertain from the caesium-137 levels, but soil sampling of contrasting land-uses showed that cultivated soils had significantly less caesium-137, probably as a result of soil erosion. In general, the hypotheses were supported and the utility of the caesium-137 technique was confirmed.

Tracing movements of topsoil by magnetic measurements: two case studies

An array of magnetic measurements is used to trace the occurrence of magnetically enhanced topsoil in two different environmental settings. The first is a cultivated slope section where the results confirm that movements of topsoil have occurred, but that identification of specific erosional processes is problematic. The second is a lake-catchment system where measurements on soils and sediments allow a partial reconstruction of soil movements from different sources over the last 200 y. The study highlights both the need to analyse the magnetic mineralogies of different particle size fractions and the difficulties that may be encountered in trying to discriminate between topsoil and subsoil material on the basis of demagnetization parameters alone.

A survey of the fauna of streams on Mount Elgon, East Africa, with special reference to the Simuliidae (Diptera)

SummaryThe stream fauna of Mt Elgon is described from collections taken during a 6‐week visit. Collections were mainly made on the cultivated slopes below the belt of montane forest, and although stations were concentrated on the western sides of the mountain sufficient were worked elsewhere to show that there was little or no geographical variation of the fauna.The streams are physically diverse but faunistically rather uniform, with a few genera dominating the fauna throughout the entire range of altitude investigated. Most of the other taxa showed evidence of altitudinal limitation which may be attri‐buted to the pronounced temperature gradients of the mountain's streams.As the species of Simuliidae and adult Elminthidae could be reliably distinguished their distributions were studied in greater detail. The Simuliidae showed a pronounced zonation of species, the majority being confined to narrow ranges of altitude below the forest margin. Factors considered to influence their distribution were principally altitude (temperature), current speed and, to a lesser extent, stream size. The influence of these factors on the distribution of adult Elminthids was less marked, although all species showed at least an upper or a lower limit of altitude, and more than half the commoner species a preference for a particular stream type.Taxonomic knowledge of African freshwater faunas allows few groups to be identified beyond the genus, and with this limitation the Elgon stream fauna is found to differ in only minor respects from the faunas of other highland areas in Central Africa.

The choking of pore‐space in the soil and its relation to runoff and erosion

The identification and evaluation of all factors influencing runoff and erosion on the erosive lands of the nation are manifestly studies of the most fundamental importance, especially in so far as they may be made to yield definite information upon methods of control over this insidious tendency upon cultivated lands.Investigations in progress at our Soil Erosion Experiment Stations have rather clearly shown that we may divide the factors that are mainly responsible for preventing or provoking erosion into two broad categories, namely: (1) The protective effects of dense covers of vegetation of one kind or another, and (2) the almost certain destruction that follows the exposure of cultivated slopes to natural conditions of rainfall. Thus it is a fact that increasing the slope on Kirvin fine sandy loam‐soil— which is the most extensive and probably the most erosive soil‐type in the East Texas—Louisiana‐Arkansas sandy‐land region served by the Erosion Station at Tyler, Texas—from 8 3/4 per cent to 16 1/2 per cent does not appreciably affect the almost perfect erosion‐control provided by the use of a dense Bermuda sod. However, under conditions of clean cultivation, as with cotton, the same change in slope on the same soil greatly increases the soil‐loss which already is excessive under such conditions on slopes of more than six or seven per cent.