Relative Agronomic Merit of Fused Calcium Phosphate: III. Forms of Phosphorus in Soils Repeatedly Cropped in Pot Experiments
Titel:
Relative Agronomic Merit of Fused Calcium Phosphate: III. Forms of Phosphorus in Soils Repeatedly Cropped in Pot Experiments
Auteur:
Otabbong, Erasmus Persson, Jan
Verschenen in:
Acta agriculturae Scandinavica. Section B, Soil and plant science
Paginering:
Jaargang 44 (1994) nr. 1 pagina's 2-11
Jaar:
1994-03-01
Inhoud:
Cultivated acid clay, sandy clay, silt loam and sandy loam soils were homogenized with 0, 12, 36 and 108 mg P kg-1 (soil dry wt.), applied as fused calcium phosphate (FP) or single superphosphate (SP), repeatedly cropped in a greenhouse and sampled after harvesting the third and fourth crops to study P disposition. Each soil sample was sequentially extracted with anion exchange resin in the HCO3- form, 0.5 M NaHCO3, 0.1 M NaOH and 1.0 M HCI, whereafter the extracted sample was digested with concentrated p.a. 97% H2SO4 to obtain residual P. The size of the P fractions determined did not vary with the P source. However, they did vary depending on soil type, P rate and whether or not cropping was carried out. Cropping markedly decreased resin-P, NaHCo3-inorganic P and HCI-P levels in all the controls, and decreased NaHCO3-organic P in the clay soil control, compared with initial levels. The FP108 and SP108 treatments enhanced levels of resin-P, NaHCO3-inorganic P, NaOH-organic P and HCI-P in all soils, compared with the controls. NaHCO3-organic P was markedly mineralized in the sandy loam soil. Residual P levels declined in the clay soil and accumulated slightly in the remaining three soils. It was concluded that the P fractions were redistributed in the soils and that they were directly or indirectly involved in plant nutrition regardless of P source. In most cases FP maintained labile P pools (∑ resin-P, NaHCO3-P) better than did SP. The fertilizers were similar in their effects on nonlabile P pools (∑ NaOH-P, HCI-P, resid. P). Based on the results obtained FP seems to be of greater agronomic value than SP.
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