No abstract

Seasonal and fertilizer effects on forms of soil phosphorus and potassium, partially decomposed organic debris and enzyme activities were studied over 2 years on a highly fertile yellow-brown loam (Typic Vitrandept) under grazed pasture. Fertilizer topdressing (potassic superphosphate) increased total inorganic phosphorus, NaHCO3-extractable inorganic phosphorus and NaHCO3- extractable potassium, but did not affect organic forms of phosphorus, microbial biomass potassium and phosphorus, or organic debris. Labile organic phosphorus (extracted by NaHCO3), microbial phosphorus and potassium, and organic debris accumulated over winter and declined in spring. Inter-year differences in climatic factors appeared to influence this basic pattern. Amounts of phosphorus released from labile organic and microbial phosphorus during spring were large (totalling 29 kg P ha-1 in one year) and could contribute substantially to plant P requirements. Mechanisms are proposed to explain the observed seasonal patterns in these soil characteristics. These include changes in the relative amounts of the fungal and bacterial components of the soil biomass during winter, mineralization of labile PI in spring due to increased bacterial growth and activity promoted by plant growth, and the subsequent release of P and K from the microbial biomass as a result of bacterial 'grazing' by protozoa.

No abstract

A strain of Bacillus megaterium isolated from soil has been found to oxidize elemental selenium in laboratory cultures to selenite and a trace of selenate (< 1 percent of the selenite). This observation represents an important but hitherto unreported oxidative step in the biological selenium cycle.

No abstract