Browsing by Subject "Soil science"

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  • Bekele, Abdissa; Kibret, Kibebew; Bedadi, Bobe; Yli-Halla, Markku Juhani; Balemi, Tesfaye (2018)
  • Deressa, Abdenna; Yli-Halla, Markku; Mohamed, Muktar; Wogi, Lemma (2020)
    Ultisols and Alfisols in humid Western Ethiopia are deficient in available phosphorus (P) but respond slightly to P fertilization. The study determined P sorption characteristics of five soils with and without optimum lime rate. Phosphorus sorption was conducted by equilibrating the soils with P solutions. Phosphorus sorption patterns of unlimed soils had no sorption maxima while limed soils had sorption maxima. The sorption data fitted to Langmuir model. The unlimed and limed soils had high P sorption capacity. The net zero equilibrium P concentration (EPC0) ranged from 0.007 to 0.012mg l-1. Standard phosphorus requirement (SPR) ranged from 759 to 831 and 441 to 1164mg kg-1 for soils and lime treatments, respectively. Langmuir adsorption maxima (bmax) ranged from 2072 to 2792 and 2352 to 2367mg kg-1 for soils and lime effect, respectively. Effect of soil types on sorption was not significant while lime significantly decreased SPR from 1164 to 441mg k g-1. The bmax of Alfisols increased while of Ultisols decreased with liming. The study suggested that Alfisols and Ultisols require 39 to 49 kg ha-1 and 63 to 75kg ha-1 to elevate solution P concentration to 0.1 and 0.2mg l-1, respectively. The study indicated that P fertilizer recommendations for most agronomic crops in Ethiopia were lower than SPR. With optimal lime rate, the recommended P fertilizer provides suboptimal SPR to provide 0.1 mg l-1 but require additional P fertilizer to achieve 0.2mg l-1. With optimum lime rate, P fertilizer recommendations should be developed through research for Alfisols and Ultisols of humid Western Ethiopia.
  • Laakso, Johanna Marketta; Uusitalo, Risto; Yli-Halla, Markku Juhani (2016)
    Constructed wetlands and ponds (CWs) are installed to trap suspended material and particulate phosphorus (P) in agricultural runoff. This study investigated whether the P speciation and P sorption capacity of source soils differ from those of CW sediments and whether drying of dredged sediment changes its characteristics. Samples collected from five agricultural CW sites in south-west Finland, two with chemical-aided (aluminium chloride and ferric sulphate) P precipitation and all representing fine-textured mineral soils, were analysed for various P plant availability indices. Clay contents of the CW sediments were much higher than in catchment soils, likely because of selective erosion. All CW sediments were characterised by similar total P content but clearly higher content of anion exchange resin-extractable P in fresh sediments than the source soils. In general, sediment content of NH4F-extractable (aluminium (Al)-associated) P was significantly lower and NaOH-extractable (iron (Fe)-associated) significantly higher than in source soils. Reduced conditions, conducive to mobilisation of Fe-associated P, were observed in all CWs. Accumulation of sulphur (S) in sediments and a pH decline of up to two units upon drying suggested presence of Fe sulphides. Drying also increased oxalate-extractable Al and Fe (hydr)oxide content by 9–47%, resulting in lower degree of P saturation. These results indicate that dredged CW sediments differ greatly in their P retention characteristics from their parent soils. Returning CW sediments to fields is likely to decrease the amount of readily available P for crop uptake.
  • Genetu, Getenesh; Yli-Halla, Markku; Asrat, Mekonnen; Alemayehu, Mihiret (2021)
    The productivity of the faba bean has declined in Ethiopia, owing to poor management practices, such as blanket fertilisation. In 2018, a field experiment was conducted in a Nitisol soil during the main cropping season in Northwestern Ethiopia, to determine the amount of chemical fertiliser and Rhizobium inoculant to be used for the optimum yield within economic feasibility. The experiment consisted of a factorial combination of five rates of blended NPSZnB fertiliser (0, 60, 121, 180 and 240 kg ha(-1)) and three rates of inoculant (0, 500 and 750 g ha(-1)). Sole chemical fertilisation, as well as inoculation, individually produced a seed yield of 2.3-2.5 t ha(-1), about 1.0-1.2 t ha(-1) more than the control. However, the maximum seed yield (3.3 t ha(-1)) was recorded from the combined application of both the chemical fertiliser and the inoculant. The seed yield correlated closely with the number of active nodules (R-2 = 0.78 **), suggesting a substantial contribution of symbiotic N-2 fixation. Inoculation increased the N content of the seed yield by at least 30 kg ha(-1). Chemical fertilisation, containing at least 44 kg ha(-1) of mineral N does not appear to have an adverse effect on N-2 fixation. The combined use of 180 kg ha(-1) blended fertiliser with 750 g ha(-1) inoculant, producing a maximum net profit of 72,918 birr ha(-1) (EUR 2232), is recommended for the study area. This study emphasises that (1) inoculation alone can produce as much seed as the maximum rate of chemical fertilisation, but (2) the maximum yield was produced with a combined use of inoculant and chemical fertiliser, by promoting the vigour of the nodules and N-2 fixation.
  • Deressa, Abdenna; Yli-Halla, Markku; Mohamed, Muktar (2020)
    There is scarcity of scientific information on stocks and retention rate of soil organic carbon (SOC) among mixed farming systems in humid Western Ethiopia. The objectives of study were to determine the SOC stocks and retention rates along a 53-km long toposequence of Didessa watershed. The study was conducted in mixed farming systems (annual arable cropping, grazing, fallow, grassland, coffee agroforestry, eucalyptus agroforestry and mechanized irrigated sugarcane production) within an elevation range of 1273 to 2543 m above sea level. The results revealed that land use types greatly affected SOC stocks and retention rates in the upper 20 cm soil depth. The SOC stocks ranged from 9.27 to 13.5 Mg C ha−1 (0–20 cm) while the retention rates were 0.11, 0.20, 0.28, 0.31 and 1.14 Mg C ha−1 year−1 for coffee agroforestry, fallow, grazing, eucalyptus agroforestry and irrigated sugarcane production systems, respectively. The retention rates demonstrated that the different farming systems are potential source of C sinks. The study indicated that the farming systems are efficient in sequestering SOC and their benefits can be further adopted for their economic values, social significance, restoration of degraded land, and sequestration of carbon (C) in humid tropical Western Ethiopia.
  • Bekele, Abdissa; Kibret, Kibebew; Bedadi, Bobe; Balemi, Tesfaye; Yli-Halla, Markku Juhani (2018)