Fate of applied phosphorus in an effluent-irrigated Pinus radiata plantation

Soil Research ◽  
1999 ◽  
Vol 37 (6) ◽  
pp. 1095 ◽  
Author(s):  
R. A. Falkiner ◽  
P. J. Polglase
Keyword(s):  
Pinus Radiata ◽  
Sorption Isotherms ◽  
Average Concentration ◽  
Organic P ◽  
Retention Capacity ◽  
Inorganic P ◽  
Eastern Australia ◽  
Soil Irrigation ◽  
And Migration ◽  
Total P

We examined the fate of applied phosphorus (P) in a young Pinus radiata plantation in south-eastern Australia, spray-irrigated with secondary-treated municipal effluent. Measurements included changes (before irrigation, and after 5 years) in total P, total organic P, total inorganic P, labile P, and sorption and desorption characteristics. During the first 5 years a total of 363 kg/ha of P was applied at an average concentration of 5.4 mg/L. Irrigation changed the forms and distribution of P throughout the profile (0–1 m). Increases in labile inorganic P (membrane-exchangeable, bicarbonate-extractable, and in soil solution) were confined mostly to the 0–0.5 m horizon, and wholly within the 0–0.7 m horizon. In addition, large amounts of organic P (204 kg/ha) were mineralised within the surface 0.7 m, due to stimulation of decomposer activity by increased soil water. Mineralisation, therefore, provided a significant and additional input of inorganic P to soil. Irrigation and P additions changed both the placement and curvature of soil sorption isotherms. Retention capacity (0–0.5 m), calculated from P sorption isotherms, decreased by 180 kg/ha. Desorbable P, determined by sequential extraction with dilute acid, increased by 184 kg/ha. Thus, these 2 independent methods of measuring the changes in exchangeable P gave the same result. Of the total inorganic P added to the soil (in effluent and mineralised), 25% remained in the exchangeable form; the rest was retained unavailable for short-term exchange and migration through soil. After 5 years, fluxes (kg/ha) of P in the 0–0.7 m horizon were: input in effluent less storage in vegetation (323), change in total organic P (–204), change in total inorganic P (517), net change in total P (313). Thus, 97% of the net amount of P added in effluent was recovered in the surface 0.7 m. Results have implications for the way in which P retention capacity is calculated under effluent irrigation.

RESIDUAL PHOSPHORUS SOLUBILITY FOR AN ACID, CLAYEY, FORESTED SOIL IN THE PRESENCE OF OXALATE AND CITRATE

1989 ◽  
Vol 69 (1) ◽  
pp. 111-117 ◽  
Author(s):  
N. B. COMERFORD ◽  
M. F. SKINNER
Keyword(s):  
Key Words ◽  
Pinus Radiata ◽  
Clayey Soil ◽  
Organic Anion ◽  
Sorption Isotherms ◽  
Organic P ◽  
Soil Material ◽  
Residual P ◽  
Residual Phosphorus ◽  
P Sorption

A highly weathered, clayey soil was sampled 14 yr after a Pinus radiata stand was broadcast fertilized with 0, 50 and 200 kg P ha−1 as ordinary superphosphate. Incremental loadings of oxalate and citrate anions from 10 to 100 μmol of anion g−1 soil were evaluated for increased soluble, reactive P (SRP) and soluble, nonreactive (SNP) P. Sorption isotherms were compared to evaluate the effect of the previous fertilization on P sorption by the soil material sampled, and also to measure SNP displacement by orthophosphate-P. A portion of the SNP pool was more readily released than SRP and orthophosphate displaced a significant amount of SNP. After 14 yr the effect of fertilization was still obvious in the sampled soil material. Much of the organic anion-soluble P was in the SRP form. Key words: Citrate, organic P, orthophosphate, oxalate, Pinus radiata, residual P

Transport of phosphorus through soil in an effluent-irrigated tree plantation

Soil Research ◽  
1997 ◽  
Vol 35 (2) ◽  
pp. 385 ◽  
Author(s):  
R. A. Falkiner ◽  
P. J. Polglase
Keyword(s):  
Sorption Isotherms ◽  
Life Time ◽  
Equilibration Time ◽  
Plantation Establishment ◽  
Water Control ◽  
Tree Plantation ◽  
Retention Capacity ◽  
Soil P ◽  
Eastern Australia ◽  
P Retention

A young plantation of Pinus radiata in south-eastern Australia was irrigated with secondary-treated sewerage effluent for 48 months, when evapotranspiration exceeded rainfall. Concentrations of phosphorus (P) in saturation pastes of soil were measured after 30, 37, 42, and 48 months to monitor vertical transport of P, and results were compared with depth of transport predicted from P sorption isotherms. Standard laboratory isotherms greatly underestimated the capacity of soil to retain P. Thirty months after plantation establishment, 165 kg/ha of P had been applied in effluent, and P in soil solution was predicted from sorption isotherms to be at a concentration of 5 · 7 mg/L to a depth of 0 · 29 m. In comparison, the concentration of P in saturation paste at this time decreased exponentially from 3 · 5 mg/L at 0 · 025 m to 0 · 43 mg/L at 0 · 30 m. Similarly, 48 months after plantation establishment, 318 kg/ha of P had been applied, and P was predicted to be in equilibrium to a depth of 0 · 51 m. At this time, concentration of P in saturation paste was 4 · 7 mg/L at 0 · 25 m but decreased to a concentration of 0 · 11 mg/L at 0 · 45 m. The concentration of P in saturation paste in the bore-water control was low (<0 · 36 mg/L) thoughout the profile. The discrepancy between predicted and observed results was found from subsequent experiments to be due largely to the short (17 h) equilibration time and to the wide solution : soil ratio (10 : 1) used during construction of standard sorption isotherms. In the 0-0 · 1 m layer of soil, P-retention capacity determined in saturation paste and after 21 days incubation was about 9-fold greater than when the standard method was used. Leaching of dissolved P is unlikely to threaten the sustainable life-time of the effluent-irrigated plantation studied.

Forms of phosphorus in virgin and fertilised calcareous soils of Western Australia

Soil Research ◽  
1998 ◽  
Vol 36 (4) ◽  
pp. 585 ◽  
Author(s):  
Abbas Samadi ◽  
R. J. Gilkes
Keyword(s):  
Agricultural Development ◽  
Ammonium Oxalate ◽  
Calcareous Soils ◽  
Organic P ◽  
P Values ◽  
Inorganic P ◽  
Extractable P ◽  
Highly Correlated ◽  
Average Contribution ◽  
Total P

Total phosphorus (P), inorganic P (Pi), organic P, and several Pi fractions were determined for 8 fertilised calcareous soils under agriculture and their virgin analogues under natural bush to ascertain changes due to agricultural development. The relationships between soil properties and forms of P were also determined. In general, agricultural development of soils resulted in increases in total P (average 105% increase), Pi (154%), organic P (49%), Olsen P (200%), Colwell P (100%), and all Pi fractions compared with their virgin analogues. For the virgin soils, the abundance of the Pi fractions was in the order: Al-P>O-P (occluded P)>Fe-P>Ca10-P = Ca2-P>Ca8-P, which changed to Al-P>Ca8-P>Ca2-P>Ca10-P>Fe-P>O-P for fertilised soils. The average contribution of each fraction to the increase in total Pi was Al-P (29%), Ca8-P (26%), Ca2-P (18%), Fe-P (13%), Ca10-P (13%), and O-P (4%). The change in Ca8-P was closely correlated with the content of the active fraction of calcite in the soil (ACCE). The increase in Fe-P associated with agriculture was highly correlated with citrate-dithionite-bicarbonate (CDB) extractable Fe (Fed) and acid-ammonium oxalate extractable Fe (Feo). The increase in Al-P was correlated with the ratio of acid-ammonium oxalate extractable Al (Alo) to Feo. Both Olsen and Colwell NaHCO3-extractable P were highly correlated with Ca2-, Al-, Fe-, and Ca10-P, and total P values. Multiple regression analysis indicated that Ca2-P and Ca10-P were major contributors to available P as determined by the Olsen and Colwell soil tests.

The role of wetlands as environmental buffers: comparison of phosphorus retention capacity between hydrosedimentary environments

2020 ◽  
Author(s):  
Jaume Company ◽  
Raquel Vaquer-Sunyer ◽  
Julián García-Comendador ◽  
Josep Fortesa ◽  
Aleix Calsamiglia ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Marine Ecosystems ◽  
Organic P ◽  
Retention Capacity ◽  
Inorganic P ◽  
Depositional Processes ◽  
Coastal Marine ◽  
Accretion Rates ◽  
Coastal Marine Ecosystems ◽  
Artificial Channel

&lt;p&gt;Since the middle of the twentieth century, human societies has quadrupled the environmental flow of phosphorus &amp;#8211;P, dramatically impairing freshwater and coastal marine ecosystems (1). Wetlands act as environmental buffers retaining nutrients and pollutants delivered from upstream parts of river systems. This buffer effect also avoids the conveyance of these pollutants to the marine environment preventing eutrophication of coastal marine ecosystems.&lt;/p&gt;&lt;p&gt;The aim of this research is to assessing P concentrations within the S&amp;#8217;Albufera (1,708 ha), the main wetland of Mallorca (Spain) and protected by the Ramsar list of wetlands of international importance. Since the middle of the ninetieth century, it is an artificial system, in which waters are forced to take the shortest route to the sea (2). The study of accretion rates by using &lt;sup&gt;137&lt;/sup&gt;Cs measurements will be combined with the nutrient retention capacity analysing phosphorus concentrations in fine-grained sediments. Accordingly, 5 integrated sediment cores, composed by two replicas, sectioned at 5-cm intervals were collected in February 2016 in three representative hydrosedimentary environments of S&amp;#8217;Albufera: two at the centre of the main artificial channel, one at the bank of this main channel and two within the lagoon areas. Total, inorganic and organic P were quantified in 532 samples in order to assess the nutrient dynamics into these representative hydrosedimentary environments and depths.&lt;/p&gt;&lt;p&gt;The &lt;sup&gt;137&lt;/sup&gt;Cs measurements depicted how the sediment cores collected in the middle of the artificial channel as well into its banks were mainly characterized by erosional processes due to the lack of &lt;sup&gt;137&lt;/sup&gt;Cs at any depth. On the other side, cores sampled at lagoon areas illustrated depositional processes with mean accretion rates since 1963 between ca. 0.139 g m&lt;sup&gt;-2 &lt;/sup&gt;yr&lt;sup&gt;-1 &lt;/sup&gt;to 0.169 g m&lt;sup&gt;-2&lt;/sup&gt; yr&lt;sup&gt;-1&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;Total P concentrations were significantly higher in lagoon areas (0.082 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment) than in the sediment from banks of the main artificial channel (0.037 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment) or into the middle of this channel (0.03 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment). The same pattern was observed for organic and inorganic P with concentrations within lagoon areas of 0.039 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment and 0.043 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment, respectively. Concentrations for the banks of the main artificial channel were 0.018 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment for inorganic P and 0.019 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment for organic P. At the middle of the artificial channel, concentrations were even lower, with 0.014 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment for inorganic P and 0.016 mg P g&lt;sup&gt;-1&lt;/sup&gt; sediment for organic P.&lt;/p&gt;&lt;p&gt;These results elucidate that the natural maintenance of wetlands is crucial to ensure their optimal functioning as environmental buffers.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;(1) Lane and Autrey, 2017. MFR. DOI: 10.1071/MF16372&lt;/p&gt;&lt;p&gt;(2) Lopez et al., 1996. ECSS. DOI: 10.1006/ecss.1996.0014&lt;/p&gt;&lt;p&gt;This work was supported by the research project CGL2017-88200-R &amp;#8220;Functional hydrological and sediment connectivity at Mediterranean catchments: global change scenarios &amp;#8211;MEDhyCON2&amp;#8221; funded by the Spanish Ministry of Science, Innovation and Universities, the Spanish Agency of Research (AEI) and the European Regional Development Funds (ERDF).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

THE INFLUENCE OF TOPOGRAPHY ON THE DISTRIBUTION OF ORGANIC AND INORGANIC SOIL PHOSPHORUS ACROSS A NARROW ENVIRONMENTAL GRADIENT

1985 ◽  
Vol 65 (4) ◽  
pp. 651-665 ◽  
Author(s):  
T. L. ROBERTS ◽  
J. W. B. STEWART ◽  
J. R. BETTANY
Keyword(s):  
Environmental Gradient ◽  
Soil Phosphorus ◽  
Regional Distribution ◽  
Extraction Procedure ◽  
Distribution Patterns ◽  
Organic P ◽  
Inorganic P ◽  
Soil P ◽  
Lower Slope ◽  
Total P

A sequential extraction procedure was used to determine phosphorus fractions (resin, bicarbonate, hydroxide, sonicated hydroxide, acid and acid-peroxide digest with separate organic and inorganic P determinations) in surface and subsurface horizons taken from the upper, mid- and lower slope positions of four catenas (representing Brown, Dark Brown and Black Chernozemic soils, and a Luvisolic soil) which encompass a narrow environmental gradient of climate (annual precipitation: 300–475 mm) and vegetation. Trends in the local distribution of organic and inorganic soil P between upper and lower slope positions in any one catena were similar to the regional distribution patterns across all soil zones. Concentration of organic P, in both the surface and subsurface horizons, increased from the upper to the lower slope positions and from the Brown to the Black soils, while inorganic P decreased. The largest single organic fraction (hydroxide extractable) accounted for up to 22 and 17% of the total P (surface and subsurface horizons, respectively). Acid extractable P dominated the inorganic fractions, accounting for 40–63% of the total P (surface and subsurface horizons, respectively). The distribution of organic P along the catenas and among the soil zones was related to the transformations of inorganic P caused by differences in weathering intensity between slope positions and across the Province. Key words: Catena, climo-toposequence, sequential P extraction

Influence of long-term irrigation on the distribution and availability of soil phosphorus under permanent pasture

Soil Research ◽  
2006 ◽  
Vol 44 (2) ◽  
pp. 127 ◽  
Author(s):  
L. M. Condron ◽  
S. Sinaj ◽  
R. W. McDowell ◽  
J. Dudler-Guela ◽  
J. T. Scott ◽  
...  
Keyword(s):  
Soil Phosphorus ◽  
Soil Layer ◽  
P Availability ◽  
Organic P ◽  
Retention Capacity ◽  
Pasture Production ◽  
Inorganic P ◽  
Permanent Pasture ◽  
P Movement

This study examined the influence of irrigation on soil phosphorus (P) distribution and availability under permanent pasture in New Zealand. Soil samples (0–0.075, 0.075–0.15, 0.15–0.25 m) were taken from a long-term field experiment, which included a dryland and 2 irrigation treatments (irrigated at 10% and 20% soil moisture) that had received 25 kg P/ha annually as superphosphate for 52 years. Corresponding data for soil from an adjacent ‘wilderness’ site that had not been used for agriculture for 54 years were included for comparison. Analyses included total P, organic P, and inorganic P; isotopic exchange kinetics (IEK) was used to determine soil inorganic P pools of differing plant availability. Concentrations of total and inorganic P were greater in soil taken from the dryland treatment than the irrigated treatments at all depths. This was attributed to a combination of decreased pasture growth and P transfer in drainage and off-farm produce. Concentrations of organic P were greater in the irrigated treatments (e.g. 0–0.075 m: 672–709 mg P/kg) than in the dryland treatment (e.g. 0–0.075 m: 574 mg P/kg) as a consequence of increased pasture production and soil biological activity. Inorganic P availability (Cp and E1min) was also greater in the dryland treatment than the irrigated treatments. Furthermore, concentrations of inorganic P in the recalcitrant IEK pool (E>3m = E3m–1y + E>1y) in the 0–0.075 m soil from the dryland treatment (479 mg P/kg) were significantly greater than the 10% irrigated (346 mg P/kg) and 20% irrigated (159 mg P/kg) treatments, which was mainly attributed to physico-chemical reactions that decreased the exchangeability of accumulated inorganic P with time. Despite increased P retention capacity at depth (R/r1, 0.15–0.25 m: dryland 6.6, 10% irrigated 10.2, 20% irrigated 12.8), concentrations of total inorganic P in the 0.15–0.25 m soil layer were lower under irrigation (195–266 mg P/kg) than dryland (354 mg P/kg), which indicated that long-term flood irrigation increased P transfer by leaching. The findings of this study revealed that while irrigation improved the utilisation of applied fertiliser P it also resulted in increased P movement to depth in the soil profile.

Elution of inorganic and organic phosphorus from surface applied organic amendments

2008 ◽  
Vol 88 (5) ◽  
pp. 709-718
Author(s):  
M K Idowu ◽  
D V Ige ◽  
O O Akinremi
Keyword(s):  
Beef Cattle ◽  
Agricultural Soils ◽  
Organic Phosphorus ◽  
Organic Amendments ◽  
Inorganic Phosphorus ◽  
Cattle Manure ◽  
Organic P ◽  
Retention Capacity ◽  
Hog Manure ◽  
Total P

Understanding the effects of organic amendments on the movement of organic and inorganic phosphorus (P) in soils is important for effective P management in agricultural soils. Thus, the effects of beef cattle manure, hog manure and biosolids on the downward movement of organic (Porg) and inorganic (Pi) P in Lakeland and Osborne soils were investigated. The amendments were added to the soils at the rate of 0, 200, 400 and 800 kg P ha-1 by mixing with the top 1 cm of soil in a column. The column was eluted with 20 pore volumes (PV) of 0.01 M CaCl2. The amount of total P (PT), Porg and Pi in the effluent was determined. The concentrations of Porg and Pi in the effluent increased as the rate of amendment application increased. A greater percentage of PT was lost as Pi in the soils amended with hog manure and biosolids, while in the soil amended with beef cattle manure, Porg constituted a greater portion of the total P eluted. As much as 63% of total P eluted from the Lakeland soil at the highest rate of beef cattle manure was in the form of Porg. Lakeland soil retained more Pi than the Osborne soil due to its greater P retention capacity. Organic P was lost within the 2nd and the 4th PV in the two soils, which illustrated the ease of Porg movement through the soil. In conclusion, both organic and inorganic P can move through the soil in organically amended soils and the risk of losing organic P by leaching is greater in soils amended with high rates of beef cattle manure. Key words: Biosolids, hog manure, beef cattle manure, elution, organic phosphorus, inorganic phosphorus

Phosphorus in virgin peat soils

1956 ◽  
Vol 28 (1) ◽  
pp. 142-167
Author(s):  
Armi Kaila
Keyword(s):  
Correlation Coefficient ◽  
Partial Correlation ◽  
The Other ◽  
Organic P ◽  
Peat Soils ◽  
Inorganic P ◽  
Total Correlation ◽  
P Content ◽  
Total P ◽  
Partial Correlation Coefficient

In the present paper the total and organic P content of virgin peat soils is studied on the basis of 217 peat samples mostly collected from Northern Finland and consisting of 32 Sp, 34 CSp, 62 SCp, 12 EuSCp, 36 BCp, and 41 Cp samples. The material was found to be satisfactorily typical for a study of Finnish peat soils as to the pH, ash and N contents. Only the BCp samples were, in some respect, of a poorer quality than in general. The total P content of the 217 samples ranged from 190 to 2350 ppm or from 30 to 2440 kg/ha. In the Sp and BCp groups the mean P content was equal, 580 ± 80 ppm and 560 ± 90 ppm resp., and significantly lower than the corresponding value in all the other groups which was 950 ±120 ppm in the Cp-group, 980 ± 290 in the EuSCp-group, 800 ± 60 in the SCp-group, and 800 ± 120 ppm in the CSp-group. A low but significant correlation was found to exist between the degree of land quality estimated on the basis of the surface vegetation and the P content of the surface samples: r = 0.361***. When the BCp samples were excluded an even closer correlation was detected: r = 0.481***. The correlation coefficient between the total P content and the degree of humification was r = 0.317***, that between the total P and the ash contents r = 0.289**, and that between the total P and N contents r = 0.206*. The organic P content of the 217 samples ranged from 130 to 1950 ppm with an average of 600 ± 40 ppm. The Sp and BCp groups showed significantly lower means, 430 ± 60 ppm and 440 ±7O ppm resp., than the other groups with averages of 630 ± 120 ppm in the CSp-group, 620 ± 50 ppm in the SCp-group, 770 ± 100 ppm in the Cp-group and 820 ± 280 in the EuSCp-group. The organic P content was very closely correlated with the total P content; the total correlation coefficient was r = 0.934***. The connection with the degree of humification was not distinct: the total correlation coefficient was r = 0.336***, but the partial correlation coefficient after the elimination of the effects of total P and N contents was only r = 0.136. No significant correlation existed between the organic P content and the N content, r = 0.184. The organic P content of the 217 samples expressed as a percentage of the total P content ranged from 55 to 95 per cent with an average of 78 ± 1 per cent. The proportion of organic P of total P was correlated with the degree of humification, the total correlation coefficient was r = 0.504***, the partial correlation coefficient after the elimination of the effect of the sampling depth was r = 0.427***. No correlation with the sampling depth existed after the elimination of the effect of the degree of humification: the partial correlation coefficient was r = 0.159, whereas the total correlation coefficient was r = 0.334***. A low correlation existed between the percentage of organic P of total P and the pH value even after the elimination of the effect of the degree of humification, r = 0.228*, but the connection with the total P content appeared to be only indirect and arised from the effect of the degree of humification, the total correlation coefficient was r = 0.222*, the partial correlation coefficient r = 0.076. The amount of organic P expressed as a percentage of the organic dry matter ranged from 0.01 to 0.25 per cent with an average of 0.07 ± 0.004. The ratio of N/org.P ranged from 12 to 133 with an average of 45 ± 3. Owing to the low P content of the BCp-group its mean ratio was significantly higher than that of the other groups. The degree of humification did not show any correlation with the ratio of N/org.P. The solubility of inorganic P in 0.5 N acetic acid and in 0.2 N sulphuric acid was highest in the Sp-group. On the average approximately from 15 to 30 per cent of total inorganic P was extracted by the latter solution. The acetic acid extracted only about 2 per cent of the inorganic P in the Cp-group but about 15 per cent in the Sp-group. The phosphorus conditions in virgin peat soils was discussed and it was attempted to explain the results obtained on the basis of the supposition that phosphorus is a minimum factor in the metabolism of peat.

Long-term phosphorus trends in Vertisols under continuous cereal cropping

Soil Research ◽  
1997 ◽  
Vol 35 (2) ◽  
pp. 327 ◽  
Author(s):  
R. C. Dalal
Keyword(s):  
Size Fraction ◽  
Available P ◽  
Organic P ◽  
Organic C ◽  
Inorganic P ◽  
P Loss ◽  
Clay Size Fraction ◽  
Extractable P ◽  
Total P ◽  
Sand Size

Vertisols originally carrying brigalow vegetation (Acacia harpophylla F. Muell. ex Benth.) and cultivated for cereal cropping for up to 45 years were examined for trends in available phosphorus (P) [sodium bicarbonate extractable P (bicarb. P) and dilute acid extractable P (acid P)], organic P, inorganic P, and total P. The soils (0-0 · 1 m depth) in their virgin state contained 60 mg/kg of bicarb. P, 168 mg/kg of acid P, 239 mg/kg of organic P, and 330 mg/kg of inorganic P. All fractions of soil P declined following first-order decay with the period of cereal cropping; the rates of bicarb. P and acid P (available P) decline were 0 · 047 and 0 · 08/year. The organic P, inorganic P, and total P declined more slowly than available P; the respective rates were 0 · 026, 0 · 019, and 0 · 021/year. The rates of loss of total P and inorganic P were much higher from the clay-size fraction than the silt-size or sand-size fraction, with the t½ value of inorganic P in the sand-size fraction being almost 20 times greater than any other fraction. On the other hand, organic P loss from the clay-size fraction was much less; presumably, clay provides physical protection to soil organic matter and hence to organic P from decomposition. On average, bicarb. P and acid P declined at the rate of 1 · 3±0 · 3 and 4 · 6±1 · 4 mg P/kg soil · year. The declines in organic P and inorganic P were 3 · 0±0.4 and 4 · 1±1 · 2 mg P/kg soil · year, with a loss in total P of 7 · 2±1 · 3 mg P/kg soil · year. There was no significant shift in the ratio organic P: total P (38±7%) with the period of cultivation and cereal cropping. Organic P was closely correlated with organic C and total N in these soils. The mean amounts of P contained in the grain and the dry matter of each cereal crop from 1981 and 1984 were 7 · 6±1 · 8 and 8 · 3±2 · 4 kg P/ha, respectively. Thus, most of the soil total P loss could be accounted for by crop removal, of which organic P contributed about 40%. However, the continuous decline in available P, especially below 15 mg P/kg soil, warrants remedial measures to arrest the decline in the yields of crops grown on these Vertisols.

Evaluation of the phosphorus status of some coconut-growing soils of Sri Lanka

1982 ◽  
Vol 99 (1) ◽  
pp. 25-33 ◽  
Author(s):  
P. Loganathan ◽  
P. M. N. Dayaratne ◽  
R. T. Shanmuganathan
Keyword(s):  
Sri Lanka ◽  
Sandy Soils ◽  
Available P ◽  
Organic P ◽  
Inorganic P ◽  
P Concentration ◽  
Phosphorus Status ◽  
Almost All ◽  
Leaf P ◽  
Total P

SUMMARYThe phosphorus status of 58 soil samples representing 15 soil series and four soil Orders (Ultisol, Entisol, Alfisol and Oxisol) in the major coconut-growing regions of Sri Lanka was evaluated by determining the available P extracted by the methods of Olsen, Bray & Kurtz No. 1, Bray & Kurtz No. 2 and NH4OAc (pH 4·8) and the various P forms. Total P in the soils ranged from 37 to 338 mg/kg with organic P and active P constituting only about 20 and 50% of the total P respectively. In general the sandy soils of the Entisols and Oxisols had lower total and organic P but higher active and available P than the rest. The relative abundance of the various inorganic P forms was generally in the decreasing order of inactive P, Fe-P, Al-P and Ca-P. Al-P and Ca-P were positively correlated with percentage sand and negatively correlated with percentage silt and percentage clay whereas total P and organic P had the opposite trend. Available P extracted by the four methods was very low in almost all soils except some of the sandy soils (Entisols) which had marginal to moderate P contents. They were positively correlated with Al-P, Ca-P, percentage sand and negatively correlated with percentages of silt, clay and organic carbon.Phosphorus concentrations (0·074–0·116%) in the 14th leaf of coconut at the soil sites were all lower than the critical leaf-P concentration (0·120%). Leaf-P correlations with Bray & Kurtz No. 2-P and NH40Ac-P were significant (P < 0·05) and with Al-P and Ca-P were close to significant.The study revealed that the coconut-growing soils of Sri Lanka were deficient in total as well as the active and available forms of P except perhaps some of the sandy soils of the Entisol. This was confirmed by coconut leaf P analysis.

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