Study on chemical mineralogical properties and relative agronomic effectiveness of calcined rock phosphate
1992
Pitoon Kitichaichananont
Investigations comprise assessment on phosphorus fertility of various soils, thermal processes for producing calcined phosphates, the relative agronomic effectiveness of the produce as well as quantity and distributions of various inorganic P fractions in the soils. From among 10 soil series employed, severely P deficient soils were Krabin (Kb), Huai Pong (Hp) and Map Ban (Mb) soil series. Moderately P deficient soils comprise Sattahip (Sh), korat (Kt), Satuk (Suk) and Hup Kapong (Hg) soil series whereas Chok Chai (Ci), Pak Chong (Pc) and Takhli (Tk) soil series were not deficient in phosphorus. In the calcination studied, type of additives: activated charcoal (AC), lithium powder (Li), AC+Li exerted significant influence on changes in available P contents of variscite riched-rock and hydroxy apatitic rock. Heating temperatures and heating periods had drastic effects on increasing available P content of the variscite riched-rock but had no impact on hydroxy apatite. In view of economies and practices, the most appropriate calcining treatments were heating the rock at 700 deg C for 1 hour. This resulted in about 5.5 times increase in available P content over the untreated rock i.e. from 3.2 to 17.54 percent of P2O5. The relative agronomic effectiveness of 4 out of 5 calcined phosphates for corn was comparable to that of triple superphosphate in both acid and alkaline soils. Raw and grounded variscite riched-rock also performed well in calcareous Takhli soil series but had no beneficial effect in acidic Huai Pong, Pak Chong and Satuk soil series. For inorganic P fractions, in all 4 soils series (Tk, Pc, Hp, Suk), the main sources of available P in soil were aluminium phosphate and to a lesser extent, calcium phosphate.
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