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  • 1
    Electronic Resource
    Electronic Resource
    Soil Phosphorus Fractions in Unfertilized Fallow-Maize Systems on Two Tropical Soils (1999)
    Springer
    Soil Science Society of America journal 63 (1999), S. 320-326 
    Details
    ISSN: 1435-0661
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: i ) and organic P (Po). The land-use systems involved growth of three maizes (Zea mays L.) crops (18 mo total duration) after 17 mo of either (i) Sesbania sesban (L.) Merr. tree growth (sesbania fallow), (ii) natural regrowth of vegetation without cultivation (natural fallow), (iii) three crops of unfertilized maize (maize monoculture), or (iv) bare uncultivated soil (bare fallow). Soil (0-15 cm deep) was collected before post-fallow maize and after the three post-fallow maize crops. Sesbania and natural fallows increased the amount of P in light fraction soil organic matter (OM) (〉 150 μm, 〈 1.13 Mg m-3) and macroorganic matter (250-2000 μm) on each soil and increased chloroform extractable P on the Oxisol. Land-use systems had no effect on extractable Pi (bicarbonate, Bray-1, iron-oxide impregnated paper), except for resin P on the Oxisol. Unfertilized sesbania and natural fallows cycled soil P through plant residues, resulting in increased P in soil microbial biomass immediately after the fallows and increased P in light fraction soil OM for three post-fallow cropping seasons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/
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  • 2
    Electronic Resource
    Electronic Resource
    Soil nitrogen dynamics and relationships with maize yields in a gliricidia–maize intercrop in Malawi (1999)
    Springer
    Plant and soil 211 (1999), S. 155-164 
    Details
    ISSN: 1573-5036
    Keywords: agroforestry ; Gliricidia sepium ; inorganic nitrogen ; maize ; nitrogen mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Many soils of southern Africa are severely N deficient, but inorganic fertilizers are unaffordable for most subsistence farmers. Rotations and intercrops of legumes with crops may alleviate N deficiency through biological N2 fixation and redistribution of subsoil N to the surface. We monitored soil inorganic N dynamics for two seasons in a gliricidia [Gliricidia sepium (Jacq.) Walp.] – maize (Zea mays L.) intercrop in the unimodal rainfall area of southern Malawi. One maize crop per year was grown with or without interplanted gliricidia, in factorial combination with three rates of N (0, 24 or 48 kg N ha-1). Application of gliricidia prunings increased (p 〈 0.001) topsoil (0 to 20 cm) inorganic N at the end of the dry season and during the early rains. Differences between plus and minus gliricidia treatments were less when total inorganic N to 1-m depth was summed. A greater proportion of the total inorganic N to 1-m depth occurred in the topsoil (0 to 20 cm) when gliricidia was present, suggesting that redistribution of subsoil N to the surface accounted for part of the N increase by gliricidia. Gliricidia lowered (p 〈 0.05) subsoil water content during drier periods. Gliricidia plots accumulated more (p 〈 0.01) ammonium-N during the dry season. Nitrate-N remained constant during the dry season but rose rapidly in gliricidia plots after the onset of rains. A 2-factor model including preseason inorganic N and anaerobic N mineralization potential accounted for 84% of the variability in maize yields for the two seasons' data combined. The combination of preseason inorganic N and potential N mineralization appears to provide a good estimate of N supply to maize in systems receiving both organic and inorganic sources of N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004636501488
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  • 3
    Electronic Resource
    Electronic Resource
    Soil phosphorus fractions and adsorption as affected by organic and inorganic sources (1998)
    Springer
    Plant and soil 198 (1998), S. 159-168 
    Details
    ISSN: 1573-5036
    Keywords: maize stover ; microbial biomass ; phosphorus adsorption ; resin P ; triple superphosphate ; Tithonia diversifolia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of organic and inorganic sources of phosphorus (P) on soil P fractions and P adsorption was studied in a field without plant growth on a Kandiudalf in western Kenya. A high-quality organic source, Tithonia diversifolia (Hemsley) A. Gray leaves, and a low-quality source, maize (Zea mays L.) stover, were applied alone or in combination with triple superphosphate (TSP). The P rate was kept constant at 15 kg P ha-1. Soil extractable P (resin, bicarbonate and sodium hydroxide), microbial biomass P and C and P adsorption isotherms were determined during 16 weeks after application of treatments. Application of tithonia either alone or with TSP increased resin P, bicarbonate P, microbial P, and sodium hydroxide inorganic P. Tithonia alone reduced P adsorption at 2–16 weeks. Maize stover had no effect on any of the P fractions or P adsorption. At 8 weeks, the application of tithonia reduced microbial C-to-P ratio (20) as compared to maize stover, TSP and the control (31–34). The reduction in P adsorption by tithonia was accompanied by increases in all measured P fractions, the sum of P in those fractions (resin, bicarbonate and sodium hydroxide) being larger than the P added. The reduction in P adsorption apparently resulted from competition for adsorption sites, probably by organic anions produced during decomposition of the high quality tithonia. Integration of inorganic P (TSP) with organic materials had little added benefit compared to sole application of TSP, except that combination of tithonia with TSP increased microbial biomass. The results indicate that a high quality organic input can be comparable to or more effective than inorganic P in increasing P availability in the soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004389704235
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