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Differences in soil properties and among plant species may play an important role in the effectiveness of residual and freshly applied phosphorus fertilizers. However, a limited number of experimental results are available on this subject.  Pot experiments were carried out with soils from 9 sites of the National Long-term Fertilization Trials, varying in their main characteristics, such as pH, soil texture, organic matter content and P status. Soil samples were taken after 20 years from the unfertilized control and from plots annually fertilized with 200 kg P 2 O 5 .ha -1 . Effects of long-term fertilization as well as that of freshly applied phosphorus were studied in the experiments. Perennial ryegrass (Lolium perenne L.) was used as test plant.  The objective of the present study was to develop quantitative relationships between selected soil parameters and the phosphorus retention characteristics of the experimental soils.  Amounts of P removed by plants during 5 cuts were correlated with DM production of plants as well as with the phosphorus amounts extracted at pH 3.7 by ammonium lactate-acetic acid, AL-P mg.kg -1 soil. Phosphorus nutrient balance was calculated from the results to evaluate either P supply or retention characteristics of experimental soils.  Results of the experiments were computed by stepwise regression analyses using the STATGRAPHICS program package.   Soil parameters involved in the study were: humus content, pH values (ranging from 3.9 to 7.4), clay mineralogy, total P contents of soils, P rates applied for 20 years, freshly applied P in the pot experiment.    Based on the results of regression analyses, the importance of soil parameters was evaluated. It was established that several soil parameters significantly influenced the phosphorus retention of soils. Regression coefficients (R²) ranged between 0.619 and 0.285 (n = 86).      Long-term effects of P application, higher pH values and humus content had a favourable influence on the P retention of experimental soils. On the other hand, increasing phosphorus retention could be attributed to higher CEC, vermiculite content as well as to increasing rates of freshly applied phosphorus. It was found that long-term effects of P applications on the P supplying power of soils were related also to the increasing N and K rates, providing a balanced nutrient supply in soils.       Our results may help the broader understanding of phosphorus retention and fixation characteristics under various soil conditions.   

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The phosphorus retention ability of soils depends on several factors and influences the effectiveness of fertilization as well as the release of P from soil to water. In the present study the phosphorus supplying and/or retention ability of soils were estimated by two approaches: biological approach (pot experiments) and modelling (by regression analyses). In the course of the biological approach pot experiments were carried out with soils showing significant differences in total and available P contents. Soil samples were collected from selected plots of 9 sites of the National Long-Term Fertilization Trials (NLFT) after 20 years of fertilization, which represents different agro-ecological regions of Hungary. Site characteristics covered a wide range in pH, carbonate and P content, representing typical soil types of the country. With the statistical approach (modelling), the most important soil properties were included and the role of these factors was evaluated by stepwise regression analyses. From the equations, the contribution of important soil parameters to phosphorus supplying and retention ability could be quantified. The objective of the present study was to find a simple way to compare and evaluate the two approaches in P nutrient turnover of soils. Results of the two approaches were correlated. From these results, a rank correlation was also made from the experimental and calculated results. A very close relationship was observed for the P supply and retention of soils (r value was 0.918 for the N 0 P 0 K 0 unfertilized control and 0.927 for the N 200 P 200 K 100 fertilization level). Values obtained with rank correlation were 0.87 and 0.866, respectively, verifying that both methodologies are reliable for estimating the nutrient dynamics in soils and to predict P dynamics in a diverse range of soils.

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Five soil P-test methods were compared on the soils of the network of unified Hungarian P fertilization long-term field trials. The effect of P application on the soil P-test values was significant on the different P levels and sites. The average effect of the sites varied between 1.5-fold (H 2 O method) and 3.7- fold (AL-method). The amounts of extracted P increased in the order of H 2 O-P < Olsen-P < Pi-P < AERM-P < AL-P < Corrected AL-P. For studying the relationships between the P values extracted by the different methods, acidic, calcareous and all soils groups were taken into account as a basis. A good correlation was found between the Pi- and AERM-methods in each soil group. Within the acidic soil group, pH has a much less expressed effect on AL-P values, presumably this was the reason why the strongest correlation in this soil group was found between the AL- and the Corr. AL-P methods  The next step in our research will be to calibrate these soil-P tests with plant P uptake and yield responses.

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Concentrations of potentially toxic elements were determined in the soil solution of two soils (acidic sandy and slightly acidic clay loam) treated with phosphate rocks having high Cd content in a pot experiment. Relative concentrations characterizing the mobility of metals (expressed as soil solution concentrations in percentage of their “total” amounts in the phosphate rock-treated soil) decreased with increasing phosphate rock rates in the sandy soil. Mn@Sr>Cd@Co were the most, while Pb and Cr the least mobile elements. The relative concentrations in the clay loam soil were much lower than in the sandy soil and they practically remained constant with increasing phosphate rock rates. It was concluded that in the experimental time frame the environmental risk did not increase with the increase of phosphate rock rate. 

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Agrokémia és Talajtan
Authors:
Katalin Sárdi
,
P. Csathó
,
I. Sisák
,
E. Osztoics
,
P. Szűcs
, and
Á. Balázsy
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