Die Bodenkultur - Journal for Land Management, Food and Environment
TAYE BEKELE and W. HÖFNER:
The effects of various N-sources on the availability of phosphate from rock phosphate and mono-calcium phosphate
The effects of (NH4)2SO4, CO(NH2)2, Ca(NO3)2 and blood meal on the amount of available P relwased to barley (Hordeum vulgare L.) and maize (Zea mays L.) from Marocco rock phosphate (RP) and monocalcium phosphate (MCP), applied to slightly acid soils from Holetta, Jima (Ethiopia) and Pettenbrunn (Germany) were studied under greenhouse conditions. When the sparsely soluble P-source (RP) P-uptake. When the soluble P-source (MCP) was used, no significant effect of Nform on P-uptake or dry matter yield of plants was observed, although (NH4)2S04 and CO(NH2)2 applications decreased the pH of the soils as when applied with RP. The increased P-uptake due to (NH4)2S04 application appears to have resulted both from soil acidification and increased plant growth.
When N was applied as (NH4)2S04 together with either RP or MCP remarkable pH decreases on all the soils were observed. Although not so pronounced as (NH4)2S04, CO(NH2)2 and blood meal when applied with either P-sources had also a pH decreasing effect on all the three soils. Unlike to the other N-sources, Ca(N03)2 increased the pH of each of the soils when applied with either Psources.
The residual P including root residues had no effect on the dry matter yield and P-uptake of maize (second crop), except on Pettenbrunn soil, which contained less P-fixing components (Fe- and Al-oxides) as compared with that of Holetta or Jima.
Fractionation of phosphorus carried out at the end of the experiment showed that the major part of the applied phosphorus, that was not taken up by the plant, was transformed to a larger extent to difficultly soluble Fe- and AI-P and to a smaller extent to Ca-P forms.