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  • 1
    Electronic Resource
    Electronic Resource
    Modelling soil organic matter changes in ley–arable rotations in sandy soils of Northeast Thailand (1998)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 49 (1998), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of a 3-year ley-arable rotation (2 years under grass, legume or a grass-legume mixture, followed by 1 year under cassava) on the organic C content of upland sandy soils in Northeast Thailand were evaluated using four field trials (Khon Kaen, Chaiyaphum, Mahasarakham and Udon Thani). At all sites under the existing management system of continuous cassava, soil organic C decreased by 9-20% during the 3-year experiment. The carbon model developed at Rothamsted (RCM-26) predicted that soil organic C would decrease consistently under continuous cassava until it reached very small amounts (0.2–0.3%). This was the case for all sites, except Chaiyaphum, where soil organic C had already declined to 0.1%. Evaluatin the rotations using RCM-26 showed that introducing a ley could increase soil organic C, except at Udon Thani where the organic C exceeded 0.47% before the start of the experiment. The data obtained with the rotations showed that RCM-26 could be used to predict the effects of changes in management on organic C content in the upland sandy soils of Norrtheast Thailand over the 3 years. To compensate for an underestimation of the effects of soil moisture deficit on the decomposition rates of organic matter, we propose that because of the prolonged dry season (from December to the following May) soil moisture deficit and the rate-modifying factor for moisture (Am) should be estimated independently of crop cover. Furthermore, to accommodate the very slow decomposition during this time, (Am) should be allowed to decrease to 0.1. Adopting this simple modification provides a more realistic estimate of the organic C inputs needed to simulate the content of soil organic C measured before trials began.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1998.4930463.x
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  • 2
    Electronic Resource
    Electronic Resource
    Charge relationships of phosphate sorption (1975)
    [s.l.] : Nature Publishing Group
    Nature 255 (1975), S. 51-53 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Study of anion sorption by hydrous metal oxides, as developed by Hingston et #/.6'8 is based primarily on shifts in points of zero charge and on the "adsorption envelope". This approach has been questioned9, and the extrapolation of these concepts, developed using pure components, to soils has not ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/255051a0
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  • 3
    Electronic Resource
    Electronic Resource
    Seasonal responses in microbial biomass carbon, phosphorus and sulphur in soils under pasture (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 421-428 
    Details
    ISSN: 1432-0789
    Keywords: Key words Seasonal responses ; Microbial biomass C ; Microbial biomass P ; Microbial biomass S ; Nutrient cycling ; Pasture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The response of the soil microbial biomass to seasonal changes was investigated in the field under pastures. These studies showed that over a 9-month period, microbial biomass carbon, phosphorus and sulphur (biomass C, P, S), and their ratios (C:P, C:S, and P:S) responded differently to changes in soil moisture and to the input of fresh organic materials. From October to December (1993), when plant residues were largely incorporated into the soils, biomass C and S increased by 150–210%. Biomass P did not increase over this time, having decreased by 22–64% over the dry summer (July to September). There was no obvious correlation between biomass C, P, and S and air temperature. The largest amounts of biomass C and P (2100–2300μg and 150–190μgg–1 soil, respectively) were found in those soils receiving farmyard manure (FYM or FYM+NPK) and P fertilizer, whereas the use of ammonium sulphate decreased biomass C and P. The C:P, C:S, and P:S ratios of the biomass varied considerably (9–276:1; 50–149:1; and 0.3–14:1, respectively) with season and fertilizer regime. This reflected the potential for the biomass to release (when ratios were narrow) or to immobilize (wide ratios) P and S at different times of the year. Thus, seasonal responses in biomass C, P, and S are important in controlling the cycling of C, P, and S in pasture and ultimately in regulating plant availability of P and S. The uptake of P in the pasture was well correlated with the sum of P in the biomass and soil available pools. Thus, the simultaneous measurement of microbial biomass P and available P provide useful information on the potential plant availability of P.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050267
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  • 4
    Electronic Resource
    Electronic Resource
    Quantifying microbial biomass phosphorus in acid soils (2000)
    Springer
    Biology and fertility of soils 32 (2000), S. 500-507 
    Details
    ISSN: 1432-0789
    Keywords: Keywords Fumigation-extraction techniques ; Microbial biomass P ; Acid soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  This study aimed to validate the fumigation-extraction method for measuring microbial biomass P in acid soils. Extractions with the Olsen (0.5 M NaHCO3, pH 8.5) and Bray-1 (0.03 M NH4F–0.025 M HCl) extractants at two soil:solution ratios (1 : 20 and 1 : 4, w/v) were compared using eight acid soils (pH 3.6–5.9). The data indicated that the flushes (increases following CHCl3-fumigation) of total P (Pt) and inorganic P (Pi) determined by Olsen extraction provided little useful information for estimating the amount of microbial biomass P in the soils. Using the Bray-1 extractant at a soil:solution ratio of 1 : 4, and analysing Pi instead of Pt, improves the reproducibility (statistical significance and CV) of the P flush in these soils. In all the approaches studied, the Pi flush determined using the Bray-1 extractant at 1 : 4 provided the best estimate of soil microbial biomass P. Furthermore, the recovery of cultured bacterial and fungal biomass P added to the soils and extracted using the Bray-1 extractant at 1 : 4 was relatively constant (24.1–36.7% and 15.7–25.7%, respectively) with only one exception, and showed no relationship with soil pH, indicating that it behaved differently from added Pi (recovery decreased from 86% at pH 4.6 to 13% at pH 3.6). Thus, correcting for the incomplete recovery of biomass P using added Pi is inappropriate for acid soils. Although microbial biomass P in soil is generally estimated using the Pi flush and a conversion factor (k P) of 0.4, more reliable estimates require that k P values are best determined independently for each soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740000284
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  • 5
    Electronic Resource
    Electronic Resource
    Single superphosphate-reactive phosphate rock mixtures. 1. Factors affecting chemical composition (1987)
    Springer
    Nutrient cycling in agroecosystems 13 (1987), S. 223-239 
    Details
    ISSN: 1573-0867
    Keywords: exchangeable P ; free acid ; partial acidulation ; superphosphate ; reactive phosphate rock ; X-ray diffraction pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of additon of reactive phosphate rock (RPR — North Carolina) on the degree of acidulation of unreactive phosphate rocks (PRs — Nauru and Christmas Island A) during the manufacture of single superphosphate (SSP) was examined using32P in isotopic dilution studies. Acidulation of unreactive PR during SSP manufacture continued through denning, granulation and drying. Even after 3 hours drying, between 20 and 30% of the total P remained as free phosphoric acid in the reaction mixture. The addition of North Carolina phosphate rock (NCPR) to ex-den SSP reaction mixture (3:7 NCPR:SSP reaction mixture) preferentially consumed the free phosphoric acid remaining in the reaction mixture. This resulted in reduced acidulation of the unreactive PR in the reaction mixture and partial acidulation (10–23%) of the RPR. Hence the SSP-RPR mixture contains more residual, unreactive PR than is present in SSP. The extent of partial acidulation of the RPR when mixed with SSP was determined by the nature of free acid remaining in the SSP reaction mixture, which in turn is affected by the type of unreactive PR used for SSP manufacture. The free acid in the Christmas Island A reaction mixture contained approximately 8 and 12 times as much Fe and Al respectively as that in the Nauru reaction mixture, and was only half as effective at converting the P in RPR to soluble P. Unless made with extended denning times and carefully chosen PR, SSP-RPR mixtures can contain (a) undesirable amounts of unreactive PR residues, and (b) low quality partially acidulated RPR, both of which have low agronomic value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01066446
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  • 6
    Electronic Resource
    Electronic Resource
    Potential losses of fertilizer phosphorus by animal transfer (1987)
    Springer
    Nutrient cycling in agroecosystems 14 (1987), S. 125-134 
    Details
    ISSN: 1573-0867
    Keywords: single and triple superphosphate ; Sechura phosphate rock ; Chatham Rise phosphorite ; legume growth ; pasture phosphorus concentration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Pasture production, phosphorus (P) concentration, and P uptake by mixed pasture following addition in the autumn of 50 and 100 kgP ha−1 as single superphosphate (SSP), triple superphosphate (TSP) and Sechura phosphate rock (SPR), and of 50 kgP ha−1 of Chatham Rise phosphorite (CRP) were measured for one year on a Wainui silt loam (Typic Dystrochrept) and Tokomaru silt loam (Typic Fragiaqualf). A sharp increase was measured in the P concentration of mixed pasture immediately following the application of 50 and 100 kg P ha−1 as either SSP or TSP at both sites. However, this increase was not accompanied by an increase in pasture production. In contrast, the application of 50 kgP ha−1 as either SPR or CRP resulted in only small initial increases in the P concentration of mixed pasture, as did the addition of 100 kgP ha−1 as SPR at both sites. The potential P losses by animal transfer in dung, which could result from the use of these four P fertilisers, were calculated using a P cycle constructed for intensively grazed, steep hill country pasture. Potential losses of fertilizer P, calculated as a percentage of fertilizer P added, were 7–14% for SSP and TSP, and 4–5% for SPR and CRP in the first year at the two sites. The implications of these results to the efficiency of P fertilizer use are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01066605
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of liming on phosphate extracted by two soil-testing procedures (1987)
    Springer
    Nutrient cycling in agroecosystems 14 (1987), S. 143-152 
    Details
    ISSN: 1573-0867
    Keywords: lime ; soil testing ; Olsen P ; Mehlich P ; coprecipitation ; constant pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Lime and phosphate (P) additions had a variable effect on Olsen- and Mehlich-extractable P in 4 acid soils from Fiji. Olsen-extractable P was at a minimum between pH values of 5.5–6.0, on either side of which it increased, particularly in soils which received large amounts of added P. The initial decrease in Olsen-extractable P is attributed to the removal of P from solution by precipitation during the Olsen extraction. The increase at higher pH values is thought to be due to the slow release of P from precipitated Ca-P compounds. There was a consistent decrease in Mehlich-extractable P with increasing soil pH. When the pH of the Mehlich reagent was kept constant, using an autotitrator, there was no decrease in Mehlich-extractable P, suggesting that in the absence of pH control the decrease in extractable P was largely due to the neutralizing effect of lime on the Mehlich reagent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01066607
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  • 8
    Electronic Resource
    Electronic Resource
    Characterizing the dissolution of phosphate rock materials by electro-ultrafiltration (1987)
    Springer
    Nutrient cycling in agroecosystems 14 (1987), S. 161-171 
    Details
    ISSN: 1573-0867
    Keywords: Electro-ultrafiltration ; chemical reactivity ; dissolution rate ; ionic strength ; North Carolina phosphate rock ; Sechura phosphate rock ; Chatham Rise phosphorite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Electro-ultrafiltration (EUF) was evaluated as a potential technique for characterizing the dissolution and assessing the chemical reactivity of contrasting phosphate rock (PR) materials. The types of rock used were: three reactive rocks, Sechura phosphate rock (SPR), North Carolina phosphate rock (NCPR), and Chatham Rise phosphorite (CRP), which contains significant amounts of calcium carbonate; one unreactive rock, Tennessee phosphate rock (TPR); and one iron and aluminium phosphate, calcined Christmas Island “C” grade phosphate rock (Calciphos). Dissolution of SPR increased as the solution:solid ratio increased to 250:1, the voltage was increased from 0 to 400 V, and the ionic strength of the extracting solution was increased. The neutralizing effect of any CaCO3 present in PR materials, which is a major limitation with single chemical extraction procedures, does not appear to be a problem with EUF. A limitation of using de-ionized water as the extracting solution with EUF is the small amounts (1 to 6%) of total of P extracted. Addition of NaCl to the extracting solution increased the dissolution of all PR materials, although this varied with the PR. With both de-ionized water and NaCl as the extracting solution, EUF was inferior to 2% formic acid for assessing agronomic effectiveness of the PR materials. EUF appears to be of limited value in assessing the chemical reactivity of PR materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01066609
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  • 9
    Electronic Resource
    Electronic Resource
    An evaluation of water extraction as a soil-testing procedure for phosphorus II. Factors affecting the amounts of water-extractable phosphorus in field soils (1988)
    Springer
    Nutrient cycling in agroecosystems 15 (1988), S. 225-236 
    Details
    ISSN: 1573-0867
    Keywords: Soil P test ; water extraction ; seasonal variation ; sampling depth ; fertilizer P addition ; microbial biomass P
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects of seasonal variation, sampling depth, and fertilizer P addition on water-extractable P values were investigated in two field experiments, involving soils of contrasting P retention capacity (Ramiha and Tokomaru) under permanent pasture over 12 months. The effects of the same parameters on Olsen-extractable P were also evaluated. The amounts of water-extractable P in soil were always lower than those of Olsen-extractable P. Over the 12-month period, the average value of water-extractable P in the unfertilized Ramiha soil (0–7.5 cm depth) was 1.8µg g−1 soil compared to an Olsen-extractable P value of 12.6µg g−1. The variability associated with water-extractable P at each sampling time was comparable with that for Olsen-extractable P. However, the relative seasonal variation over 12 months was larger for water-extractable P than for Olsen-extractable P. The results obtained with both extractants showed a seasonal fluctuation which was closely related to the pattern of pasture P uptake. The amounts of water- and Olsen-extractable P were higher in samples taken from the 0–4.0 cm than the 0–7.5 cm sampling depth. Fertilizer P addition resulted in larger increases in water-extractable P in the 0–4.0 cm sampling depth than in the 0–7.5 cm depth. The relative increase in water-extractable P following fertilizer P addition was larger than that of Olsen-extractable P. Seasonal changes in the soil microbial biomass P were not related to changes in either water-extractable P or plant uptake of P. Microbial biomass P may be a less sensitive index of soil P availability than is commonly thought.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01051344
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  • 10
    Electronic Resource
    Electronic Resource
    Application strategies for Sechura phosphate rock use on permanent pasture (1988)
    Springer
    Nutrient cycling in agroecosystems 17 (1988), S. 219-234 
    Details
    ISSN: 1573-0867
    Keywords: Phosphate response ; legume growth ; pasture production ; single superphosphate ; reactive phosphate rock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract At two phosphate (P) responsive sites in hill country the effectiveness of Sechura phosphate rock (SPR) as a direct application P fertilizer for permanent pasture was evaluated. Sechura was applied at two rates, in three different application strategies. The treatments were 16.7 and 50 kgP ha−1 annually, 25 and 75 kgP ha−1 biennially, and 50 and 150 kgP ha−1 triennially giving a total of 50 and 150 kgP ha−1, respectively, over three years. Single superphosphate (SSP) served as the standard P fertilizer. A comparison was also made between SPR and Chatham Rise phosphorite (CRP), another reactive PR. Total pasture and legume production and P uptake by pasture was measured with all fertilizer treatments over a three year period. In the year of application, SPR was as effective as SSP in stimulating total pasture and legume production and P uptake by pasture. This reflects the very reactive nature of this PR. In the second and third years of measurement, SPR did not show superior residual efffects to SSP. The ability of CRP to stimulate legume growth more than SPR in the second year following application demonstrates the danger of generalizing about the residual effects of reactive PR materials. Of the application strategies evaluated, a biennial appplication of 25 kgP ha−1 as SPR maintained legume growth at a higher level than a smaller (16.7 kgP ha−1) annual dressing. The biennial strategy also increased total pasture yield, in addition to legume production to a greater extent in the second and third years than a single (50 kgP ha−1) triennial application.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01049579
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