GEODERMA

It is now widely recognized that local farmers possess an important body of knowledge concerning soils and their use for agriculture. This article argues that in order for that knowledge to be useful for sustainable development interventions, it is necessary to go beyond the collection of indigenous soil taxonomies and also explore the theories farmers have on soil formation and degradation processes. Based on field research in eastern Burkina Faso, the article demonstrates that farmers' theories of soil go beyond practical rules of thumb and include complex concepts about soil processes and fertility. In this sense they are similar to scientific theories of soil. It is argued that understanding the similarities and differences in soil related concepts, such as that of soil fertility, could do much more to improve communication between farmers, researchers and development workers than only comparing taxonomies. Furthermore, capturing the grammar (theories) rather than the sentences (taxonomies) provides a much clearer insight to how farmers will deal with changing circumstances and new crops than the static way in which local taxonomies are often treated. Finally, local soil theories are a better point of departure in terms of creating the necessary comprehension of farmer practices required for effective collaboration towards sustainable development.

Abstract Forest roads are the most essential projects in forest management. The aim of the present study was to investigate the effects of topographic factors on nutrient transport and degradation areas resulting from forest road construction in the Research and Educational Forest of Tarbiat Modares University in Iran. In this study erosion features around the forest road with a distance of 50 m from the road were documented using a Global Position System (GPS). Work units were determined by using slope, aspect and elevation maps. In addition, physical and chemical soil properties were determined in 19 work units for erosion regions, non-erosion regions and control regions. Results of correlation analysis between regional erosion features with distance to the road and number of erosion features show a significant correlation at the 99 percent level of confidence interval. Furthermore, there is a significant correlation between areal erosion features and elevation classes, slope, road age classes and aspect at the 99, 95, 95 and 95 percent significant level, respectively. Results of analysis of variance (ANOVA) show that areal erosion features at different elevation classes, slope, aspects and road age classes have a significant difference at the five, five, one and five percent level, respectively. Results of ANOVA for physical and chemical soil properties on erosion areas, non-erosion areas and control areas conveyed significant difference in pH, soil organic matter, silt, clay, nitrogen and phosphorus. These findings demonstrate the connectivity of soil properties when they are impacted by human activities.

Soil saturated hydraulic conductivity (Ks) is an important soil physical property. Some laboratory and field methods are expensive, time consuming and labour intensive. Indirect methods such as pedo-transfer functions (PTF) are available. Effective porosity or macroporosity (Øe) is approximately equals to porosity minus volumetric soil water content at the field capacity. According to Kozeny–Carman equation, Ks could be evaluated using Øe. Franzmeier estimated the Ks from Øe based on Ahuja et al. He found a strong relationship between Øe and Ks. This paper presents results of a study to characterize the effective porosity in lowland paddy fields and to show the possibility of using the effective porosity (Øe) in estimating the saturated hydraulic conductivity (Ks). Soil in lowland paddy fields forms its horizon as topsoil, hardpan and subsoil. Soil samples were collected randomly within a 2300-ha rice cultivation area where there are five dominant soil series. A total of 408 soil samples were taken from 136 sampling points and at three depths, namely, the topsoil, hardpan and subsoil. Ks values were measured in the laboratory using the falling head method. Soil bulk density and moisture content at −66 kPa were determined. The Øe was then calculated using the difference of the total porosity (Ø) minus the volumetric moisture content at −66 kPa. The Ks values ranged from 5.35×10−4 to 8.77×10−2 m day−1. The Db varied from 0.62 to 1.91 Mg m−3, and the values of the Dp ranged from 1.10 to 2.89 Mg m−3. The Ø ranged from 0.17 to 0.68 m3 m−3. The results of the Øe of the samples in this study were obtained by calculating the difference of the total porosity and volumetric moisture content at field capacity. For clayey soils, field capacity is taken at the suction of −66 kPa. The Øe varied from 0.05 to 0.55 m3 m−3, with the mean value of 0.24 m3 m−3. The regression equation of a power function shows a highly significant regression coefficient, r2 of 0.50 (n=400). This indicates that there is a strong relationship between Ks and Øe for the lowland paddy soils in the study area.