Evaluation of iron oxide impregnated filter paper method for predicting available phosphorus in selected paddy soils of Tanzania
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Date
1999
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Publisher
Sokoine University of Agriculture
Abstract
Experiments were conducted to evaluate the suitability of iron oxide impregnated filter paper (Pi) method for predicting available phosphorus in selected paddy soils of Tanzania. Two versions of the Pi method, namely; directly embedding Pi strips in moist soil or flooded soil (designated as PiPe) and shaking Pi strips with soil suspensions in the laboratory (designated as Pi-P) were evaluated. These methods were compared with Bray-I and Olsen methods which arc used routinely for assessing available P in Tanzania. Ten soil samples from selected rice growing areas were used for a pot experiment and one of those sites was used for a field experiment. The studies included laboratory analyses to characterise the selected experimental soils and assess the levels of P and its availability to rice in the selected soils. Pot and field experiments were conducted to assess the effect of flooding on P availability and the response of rice (Oryza saliva L) variety Super to P application. In addition, these parameters were related to extractable P by the methods evaluated under aerobic and anacrobic/flooded conditions. Good correlations were found between extractable P by pairs of the extracting procedures tested with the correlation between Pi-P from air dry soils and PiPe from Pi strips directly embedded in moist soils designated as PiPem (r = 0.98**) being among the highest. The same correlation coefficient was also obtained between Pi-Pf (P extracted from soil sample after flooding) and PiPef (P extracted by Pi strips directly imbedded into flooded soils). Olsen P and Bray-I P gave an r value of 0.99 (P < 0.01). Phosphorus application significantly increased dry matter yield in six soils out of ten tested under glasshouse conditions. Rice response to P was best correlated to Pi-Pf (r = 0.76**) followed by PiPef (r = 0.71*). Correlation between the two variables for the rest of the P tests were nonsignificant. The Pi-Pf and rice growth data were used to estimate the critical P concentration in soils and gave a critical level of 22 mg P /kg. A field experiment conducted on one site of the soils which responded to P in the glasshouse study confirmed the need for P fertilizer on this soil and also indicated the Pi-Pf data to be well correlated with grain yield. It is recommended that Pi-Pf be one of the tests for assessing P availability in paddy soils in Tanzania and that PiPef be evaluated further since it was a close second in all the parameters measured.
Description
Dissertation
Keywords
Iron oxide impregnated, Predicting available phosphorus, Paddy soils, Tanzania