Ingmar Messing

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

Several land use scenarios were developed for the 3.5 km2 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.

Influence of aspect and slope gradient on hydraulic conductivity measured by tension infiltrometer

A tension infiltrometer technique was used to characterize differences in hydraulic conductivity (K) in two rain-fed hillsides (north-facing and south-facing) in central Chile. For the north-facing locations, smaller values of K (at a range of supply water pressure heads ψ) compared with south-facing locations were found, with accentuated differences close to saturation (zero pressure head). The differences were attributed to differences in texture and organic matter contents observed for the two sites. Furthermore, K(ψ) had a tendency to increase with increasing slope gradient. This tendency was to an extent explained by the deviation from requirements of measurements on level ground. The differences found in K(ψ) between different slope gradients were explained by the differences in the vertical and lateral hydraulic conductivity and by the occurrence of surface sealing in low slope plots. Copyright

Soil conditions in a small catchment on the Loess Plateau in China

Abstract This article presents the results from soil surveys carried out within the framework of a soil conservation research project with several components: soil erosion modelling, land evaluation and participatory planning. The study area was a small catchment (3.5 km2), ranging in altitude between 1085 and 1370 m, in the vast Loess Plateau area in northern China. It is continuously affected by soil erosion by water, to a certain extent due to the unprotected slopes resulting from cultivation of subsistence food by the land users. The information on variability of soil properties in the study catchment was required as a basis for development of land use scenarios opting for ecological and economical sustainable production for the land users in the future. Soil profiles to 1-m depth were described, using FAO guidelines, at 17 sites along two transects covering the different facets of the morphology: hilltop, hillslope, valley bottom. Samples were collected from each horizon in the soil profiles for laboratory determination of physical and chemical properties. It was found that the nutrient status of the soils was poor, with ranges in contents of: sand=6.5–30.0%, silt=53.5–74.5%, clay=11.1–29.0%, organic matter=0.11–1.32%, available P=0.1–11 ppm, available N=5–56 ppm. The extremely high pH values, ranging between 8.7 and 9.3, effectively restricted the availability of nutrients. The soils have a high available water storage capacity so that, during years with a good supply of rain water, fair yields of crops can be achieved if the soil is fertilised. However, during dry years, when the soil dries out, the soils are vulnerable to drought and the crops fail. A divide at approximately 1200 to 1225 m above sea level was found between stratified and unstratified loessial soils. Above this altitude, the soils were yellowish, homogeneous silt loams with no or few restrictions for tillage, root penetration or water percolation. Below this altitude, layers that were more reddish (due to soil processes during climatically wetter periods), slightly cemented or higher in clay content, although still having a silt loam texture, were found in the soil profiles. These layers could cause problems at tillage, and could give rise to some restrictions to root penetration and water percolation, thereby increasing the erosion risk. A partitioning into characteristic soil types is proposed, to be used in the other parts of the project: erosion modelling, land evaluation and participatory planning.

Criteria for land suitability evaluation in a small catchment on the Loess Plateau in China

Abstract This article describes some of the results of a land evaluation within the framework of a research project carried out in a small catchment on the Loess Plateau in northern China, which has long been exposed to land degradation from erosion. The project aimed to identify an approach for land use planning, combining participatory (land users) planning, land evaluation and soil erosion modelling. The results from this study were intended to provide the biophysical properties of importance to be used together with results from participatory approach (PA) studies and soil erosion modelling to construct scenarios for a more sustainable use of land. Land properties, which were restricting for agricultural cropping, were defined and values of each property were matched with the requirements for cropping. By defining the spatial distribution of critical properties, they could be combined to achieve compound suitability classes in each land unit for the chosen land use. Information was gathered from measurements and data searches as well as from farmers, using PA methods. Properties for which data and other information were available and which were considered to be relevant for the study included climate, soil water content, slope aspect, soil water storage capacity, rooting environment, tillage constraints, slope gradient, infiltration capacity, soil nutrients and flooding hazard. Each of the properties were discussed in relation to their influence on land suitability, primarily for agricultural crops. Whatever management changes were carried out to improve the productivity and sustainability in the project catchment, restrictions for agricultural production were large. The major constraints were water availability, nutrient availability and erosion hazard. The properties chosen for further use in suitability evaluation and scenario analyses were those having a significant spatial variability in the catchment: soil type, slope gradient and slope aspect. The results from this study are applied in other articles this issue.

Infiltration Rate and Hydraulic Conductivity Measured with Rain Simulator and Disc Permeameter on Sloping Arid Land

The objective of the study was to examine relationships between steady infiltration rates and hydraulic conductivity obtained with drip infiltrometer and disc permeameter on moderately to strongly sloping land. The disc permeameter is generally used for measurements on horizontal or slightly sloping surfaces but is easier to handle in the field than the drip infiltrometer. At two sites on natural prairie in Central Chile, a portable drip infiltrometer was used to measure infiltration rate and simulate rain, including the impact of falling drops, using two strategies: (1) DIH starting with a high application rate and decreasing it until a minimal application rate that generated steady runoff was obtained, and, (2) DIL starting with a low rate and increasing it until steady infiltration rate that did not increase was ensured. In parallel, a disc permeameter was used to determine infiltration rate (PI) and hydraulic conductivity (K) at different supply water pressure heads ( é ). Infiltration rates obtained with the DIL strategy were on average only 46% of those of DIH. Application intensity, particularly at the start of events, was crucial in the impact on structural changes in the soil surface. The drip infiltrometer DIH was larger than or equal to the disc permeameter PI and K at é = -20 mm. The DIL corresponded with PI at é = -40 mm and - 60 mm and K at é = -30 mm. Disc permeameter was shown to be a useful tool as an alternative to drip infiltrometer to determine infiltration rates even on moderately to strongly sloping land, if measurements with the former are carried out at some predefined as é identified in this article.

Methods to Estimate Lettuce Evapotranspiration in Greenhouse Conditions in the Central Zone of Chile

This study evaluates five methods to estimate crop evapotranspiration in greenhouse conditions. It compares their performance in relation to the evapotranspiration directly determined from water balance measurements (ETlys) in an irrigated lettuce (Lactuca sativa L.) crop during 9 weeks. Daily values of the reference evapotranspiration (ETo) from Class A pan (CAP), Piche atmometers (ATM), Andersson evaporimeters (ANE), FAO-Radiation (FRE) and FAO-Penman-Monteith (PME) equations were compared. The methods showed similar temporal variations but at different ranges as follows: ANE < CAP < FRE < PME < ATM. Furthemore, ETo had a clear correlation with solar radiation. Crop coefficients (Kc = ET lys/ETo) varied somewhat amongst the methods, but trends were identified for two periods: in the first week, the overall mean Kc was 0.3 (± 0.1) and in weeks 2 to 9 on average 0.6 (± 0.3). The greenhouse values of Kc were lower than those generally adopted for lettuce in field conditions. In terms of irrigation design, crop evapotranspiration can be estimated by the methods in this study, on the condition that the appropriate crop coefficients are applied. The fact that ANE showed values closest to those of ET lys, along with cost and management convenience, makes it an advantageous alternative as compared to the other methods.

Influence of root mass on saturated hydraulic conductivity in arid soils of central Tunisia

Abstract Saturated hydraulic conductivity, Kfs,measured with the inversed auger hole method was related to root mass (living and dead roots) in the uppermost 30 cm of the soil. The studies were carried out in mountain, piedmont and plain areas. Acacia cyanophylla, Eucalyptus occidentals, Pinus halepensis, Atriplex numularia and Opuntia ficus‐indica as well as irrigated and non‐irrigated almond and olive orchards were included in the study. In older stands with well developed root systems, a significant positive linear relationship between Kfs and root mass was obtained. The regression coefficients, i.e., influence of root mass on Kfs, were generally higher in non‐aggregated than in aggregrated soil. In younger plantations (2–3 years old) the relationship was weaker and negative, probably owing to the lower proportion of dead roots and channels formed after root death. Measurements of Kfs with a double ring infiltrometer were compared to those obtained with the inversed auger hole method. Two‐to three‐fold...

Influence of shelterbelt type on potential evaporation in an arid environment

The results from three studies in central Tunisia are presented, the first and second in November‐December of two consecutive years and the third in April‐May. The spatial variation in reductions of potential evaporation behind the shelterbelts, measured with the Andersson evaporimeter, is reported. The types of shelterbelt systems were a mechanical shelter of porous nylon netting on the open plain, a cactus Opuntia ficus indica shelter with very low porosity, a nursery with an Acacia cyanophylla shelter within a system of rows of tall Eucalyptus camaldulensis situated 40 to >170 m from the shelter, and an orchard of dispersed young fruit trees sheltered by young plantations of Acacia cyanophylla and Casuarina equisetifolia shelterbelts. The mechanical shelter reduced potential evaporation similarly in the three studies. The cactus shelter was inefficient owing to its low porosity. In the nursery the tall eucalyptus trees reduced potential evaporation at distances >20H (H is distance in terms of height of...

A comparison of near-saturated hydraulic properties measured in small cores and large monoliths in a clay soil

Abstract The effect of measurement scale on hydraulic properties close to saturation was investigated in a clay soil. Results from measurements on undisturbed “standard” small soil core samples were compared with results from three large intact soil monolith samples which were assumed to reflect natural soil hydraulic behaviour. An intermediate sample size, which was used to characterize soil water retention relations (θ(ψ)) in each layer in the intact monoliths, was obtained by cutting the intact monoliths in three layers. The small cores were subsequently sampled from the cut monoliths so that all measurements were made on the same soil material. Measurements of θ(ψ) and saturated hydraulic conductivity ( K s ) were compared, as well as the exponential relationships between K s and macroporosity ( ϕ ma ), the latter derived from the θ(ψ) data for small cores and from specific yields for intact monoliths. Between soil water pressure heads of −60 cm and −15 cm the small core data and the cut monolith data showed similar θ(ψ) relations, whereas they diverged closer to saturation. When comparing K s and ϕ ma , small core data were correlated with the intact monolith data although the small cores had smaller values. Thus, the “standard” small cores can satisfactorily predict the investigated soil hydraulic properties for a natural soil at pressure heads equal or less than −15 cm, but they may be in error, especially in soils with macropores, in the pressure head range −15 cm to saturation, i.e. in the largest macropores.

Agricultural land needs protection

Abstract Since 1960, the amount of arable land per capita in the world has decreased from 0.41 to 0.21 ha. During recent decades, there has also been a significant increase in the impact of soil degradation. It is estimated that 5–10 million ha of agricultural land are abandoned every year as a result of soil degradation and the construction of buildings and infrastructure. The Nordic and Baltic countries have on average more arable land per capita and larger water resources than many other areas of the world. Land and water resources are expected to become gradually more critical, and Northern European arable land is likely to increase in importance in contributing to our basic food and bioenergy demands. It is important that these land resources are protected for future generations. Therefore, soil degradation and exploitation of arable land needs more attention from individuals, society and governments.