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  • 1
    Electronic Resource
    Electronic Resource
    Phosphorus status and cycling in native savanna and improved pastures on an acid low-P Colombian Oxisol (1999)
    Springer
    Nutrient cycling in agroecosystems 55 (1999), S. 77-88 
    Details
    ISSN: 1573-0867
    Keywords: acid low-P soils ; improved pastures ; P budget ; P cycling ; soil P fertility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract On acid low-phosphorus (P) Colombian Oxisols, improved pastures with acid-soil-tolerant grass and legume varieties have increased beef production by a factor of 10 to 15 with only modest P fertilizer inputs. This indicates that the efficiency of P fertilization could be greater than is commonly expected on such strongly P-sorbing soils. To understand the effect of improved pastures on P cycling and availability, we estimated P budgets, and characterized soil P by sequential fractionation, isotopic exchange and biological activity measurements on soil samples from unfertilized native savanna, and fertilized improved grass-only (Brachiaria decumbens cv. Basilisk) and grass-legume (B. decumbens + Pueraria phaseoloides, Kudzu) pastures established in 1978 on a medium-textured isohyperthermic, tropeptic haplustox. Comparison of calculated P budgets, based on inputs and exports, with total soil P contents showed that fertilization, as part of the improved pasture management, had resulted in a measurable increase of total P in the surface 0–20 cm soil layer of nearly 30 mg kg-1 or about 20% over the savanna level. Sequential soil P fractionation of different seasonal samplings indicated that grass-legume maintained higher organic and available inorganic P levels with less temporal variation than the two other types. The linkage of organic P and available P was also reflected in soil biological activity. Estimates of P in microbial biomass and phosphatase activity were significantly higher in grass-legume than grass-only and savanna. The improvement in soil P availability, as measured by solution P concentration, P sorption and exchangeable P, was much greater in grass-legume than in grass-only. With comparable fertilizer inputs and greater product exports, improved P availability in grass-legume cannot be due to differences in budgets but can be attributed to changes in the overall biological activity in the soil-plant system caused by the presence of legumes in the vegetation cover. Total C, organic P content and macrofaunal activity were all significantly higher in grass-legume soils. Greater turnover of organic litter in grass-legume may provide for steadier organic P inputs and, therefore, higher P cycling and availability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009813008445
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Is the isotopically exchangeable phosphate of a loamy soil the plant-available P? (1994)
    Springer
    Plant and soil 158 (1994), S. 287-297 
    Details
    ISSN: 1573-5036
    Keywords: arbuscular mycorrhizae ; available P ; barley ; Glomus intraradices ; soil solution ; 32P uptake ; P uptake ; soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This study compared the validity of using the isotopically exchangeable phosphorus (P) as an accurate measurement of plant available P by comparing the specific activity of P, i.e. the 32P/31P ratio, in soil solution (Ss) against the specific activity of P in plants (Sp) growing in a loamy soil after applying a 32P-labelled fertilizer (NaH2PO42H2O) at different rates (F) and specific activities (Sf). Non-mycorrhizal and mycorrhizal (Glomus intraradices) plants of two species (soybean and barley) were grown in greenhouse experiments. Ss values were determined on 1:10 soil suspension after periods of incubation ranged from 1 min to 35 d. At a given rate of P application, the Sp values of both non-mycorrhizal and mycorrhizal soybean and barley did not show significant difference although the plant P uptake varied 18 fold for all the (crop species × mycorrhizal infection) treatments over soil solution P values ranging from 0.02 to 5.46 mg P L-1 (0.6–176 μM). Ss values decreased with time and reached a steady state after 35 d of equilibration period. Both Sp/Sf and Ss/Sf increased with applied P and there is a 1:1 correspondence between Sp/Sf and Ss/Sf values. The identity between the isotopic composition of both P in soil solution and in plant indicates that the isotopically exchangeable P (E=F(Sf/Ss−1)) is the only source of phosphate in solid soil phase which replenishes P of the soil solution after P has been removed by the plant, i.e. the only source of P which participates in plant nutrition. The isotopically exchangeable P of a loamy soil is the P available to growing plants and mycorrhizal fungi increases the P uptake giving plants wider access to isotopically exchangeable P in soil, and not making previously non-exchangeable P available. An immediate application of the 1:1 correspondence between a soil parameter (Ss/Sf) and a plant parameter (Sp/Sf) concerns the agronomic evaluation of P fertilizers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009502
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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