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Fluid Journal : Fluid Journal 1999-2001
0 20 40 60 CLARION SOIL Temperature (F ) 506886 0 20 40 60 WEBSTER SOIL 0 20 40 60 MUSCATINE SOIL 0 20 40 60 CANISTEO SOIL P2 P3 P5 P15 P25 P35 P65 TMP POLYPHOSPHATE-P HYDROLYZED (%) Table 1. Half-life values (days) for solid and liquid APP in different soils under aerobic and anaerobic conditions. Solid APP Liquid APP Aerobic Anaerobic Aerobic Anaerobic Alluvial 27.0 9.2 8.7 2.0 Sodic 15.0 7.0 5.4 1.8 Laterite 12.5 3.9 5.2 1.6 Figure 1. Effect of temperature on hydrolysis of polyphosphates in soils incubated for seven days. polyphosphate. There are likely only subtle differences between ammonium and sodium phosphate reactions in soils (Mnkeni and Mackenzi, 1987). Hashimoto et al. (1969) reported that APP hydrolysis increased with greater microbial activity and indicated that the catalytic influence of soil minerals was less with higher APP concentrations. Sample et al. (1979) reported that diammonium phosphate (DAP), triammonium pyrophosphate (TPP), and APP fertilizer additions behave essentially as salts. The NH4+ moved along with the phosphate ions in the form of salt diffusion. High concentrations caused the NH4+ to displace calcium on the exchange complex. Displaced calcium precipitated phosphates. Ortho and polyphosphates influenced soil aluminum (Al) and calcium (Ca) by releasing into soil solution and subsequent reprecipitation. Both elements appeared to be reprecipitated in place with added DAP. Sequestration by TPP and APP moved the cations slightly before complex ion reactions caused precipitation back to insoluble forms. Virtually all movement was in the ortho form (Sample et al., 1979) probably due to the high hydrolysis rate. Hydrolysis was occurring faster than diffusion through the soil column. They calculated hydrolysis half-lives for the first two weeks as 8.8 days and for the second two weeks as 15.6 days. Venugopalan and Prasad (1989) also showed that hydrolysis rate was rapid in the beginning and slowed down with incubation time, regardless of soil type. They further demonstrated that liquid APP hydrolyzed faster than solid APP and that anaerobic conditions (caused by subsequent flooding) accelerated hydrolysis (Table 1). Plant uptake Polyhosphates are widely distributed among bacteria, blue-green algae, fungi, and algae. Meta- and linear polyphosphates with chain lengths as long as 500 have been isolated from microorganisms. Plant available phosphate is mainly controlled by hydrolysis reactions because most P is taken up as orthophosphate. Small amounts may be used as pyrophosphate. Dick and Tabatabai (1986) found that hydrolysis rates were Fall 2001 Fluid Journal
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