Studies on the Phosphorus Retention of Different Soil Types in a Pot Experiment with Perennial Ryegrass

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.