Bulgarian Journal of Soil Science

3 - 15

Authors: Rainer Horn

Soils are the most critical life-supporting compartments of the biosphere. They provide numerous ecosystem services such as habitat for biodiversity, water and nutrients, as well as producing food, feed, fiber and energy. Soils undergo intense and irreversible changes due to a non-site adjusted land management and improper application of machinery and techniques in its broadest sense. In combination with the growing population (until 2050 we will have approx. 9 Billion people) the urgent need for a more reliable dataset of soil properties and soil functions gains in importance in order to even prepare more reliable models for various requests. The mechanical strength – the precompression stress - as the result of geo-, pedoand anthropogenic long-term processes - can be defined as the basis for quantifying the rigidity boundary. It distinguishes between the recompression stress (i.e. elastic, rigid properties) and the virgin compression stress range where plastic deformation including irreversible changes of properties and functions occur. The changes in the hydraulic or pneumatic functions like hydraulic or air conductivity, the pore size distribution primarily all occur in the virgin compression stress range, The same is also true for redox reactions and the biological activity (respiration) in soils but also carbon sequestration potential is also linked with the precompression stress value. Thus, a more precise definition and following of sitespecific functionality differences, which may exclude or concentrate certain land use or management forms are needed, in order to optimize yield, soil protection and a sustainable land use management considering the limited site specific resilience at the same moment.

33 - 45

Authors: Patrick S. Michael

Leucaena (Leucaena leucocephala Lam.) trees planted in alley cropping or established on fallowed farms by natural means contribute significantly to soil health and productivity by influencing various soil properties. In this study, the effects of L. leucocephala (Lam.) on sandy loam soil pH, organic matter content, bulk density, water-holding capacity and carbon stock were investigated under humid lowland tropical climatic conditions in Papua New Guinea (PNG). Soil samples were collected from 60 cm deep piths dug out from 1 m and 2 m away from the base of the legume trees. The control soil samples were collected from adjacent grassland dominated by Imperata cylindrica (L.), 10 m away from the legume trees. In all the piths, soil samples were collected from the 0-20, 20-40 and 40-60 cm profiles. The results showed presence of the legume trees acidifies the soil (lowers pH), lowers surface soil organic carbon, improves the water holding capacity within the surface soils and helps improve bulk density, ideal for root growth. Comparatively there was more carbon in the surface soil of the grassland than under the legume trees. In most tropical regions, grasslands are often set a blaze for various land uses and the high carbon content is a potent source of CO2 emission, contributing to the greenhouse gases (GHG) in the atmosphere. The low carbon stock measured under the legume trees means reduced emission of CO2 when burnt and more benefits for the sandy loam soil. This study has implication for management of sandy loam soil using L. leucocephala (Lam.) under humid lowland tropical climatic soil conditions.

55 - 68

Authors: Henry Ahamefule; Ridwan Taiwo; Mathew Amana; Kevin Eifediyi; Betsy Ezuogu; Emmanuel Ihem; Chukwuma Nwokocha; Abdulateef Yusuf; Fatai Fatola; Samuel Adepoju*

Osere River is one of the important rivers that serves as a cheaper and easier disposal alternative to industries and at the same time a less expensive and dependable water supply to farmers for dry season vegetable production in Ilorin, the capital city of Kwara State, Nigeria. The edaphic aftermath of the use of its water for irrigation was investigated using a Randomized Complete Block Design (RCBD) in a two way factorial experiment. Factors comprised of fifty meter distance intervals (50 and 100 m) downstream and a control (50 m upstream) of a soap industry effluent discharge point and irrigation duration (0, 10, 20 and 30 years). River water samples indicated that the activities of the soap industry did not lead to its increased electrical conductivity (which signifies presence of dissolved salts and/or impurities), however soils under prolonged irrigation (up to 10 years) showed signs of salt induced structural deterioration (MWD). Farm soils 50 m downstream showed the lowest structural stability (MWD = 0.77 mm)and highest % silt of 21.2 whereas those located 100 m downstream indicated highest MWD of 1.10 mm. The consequent soil structural degradation was tied to elevated values of sodium adsorption ratio (SAR) following prolonged irrigation.