Effect of some modification of extraction technique on extractable p in soils of South West Nigeria

Publisher Website
Google Scholar
Abstract
In Nigeria and in some other tropical countries routine soil testing is at its infancy, therefore research into handling and processing techniques is very essential. For the investigation being reported, thirty surface (0–15cm) soils having different cropping histories and variable levels of P were collected from different ecological zones of South Western Nigeria and the following techniques using Bray's P1 and NH4F.HF solutions were investigated; shaking time, type of shaker, length of shaking, positioning of bottles in the shaker, lag period before filtering after shaking and time lag after colour development before P reading. The extractable P from all these techniques were correlated with P uptake in the greenhouse. The results indicated that 5 minutes shaking gave the best correlation with uptake (r= 0.91**) for Bray's P1 and 1 minute for NH4F.HF (r= 0.88**). Neither vertical nor horizontal placement affected the extractable P, but stirring gave a non‐significantly lower correlation. Lag period before filtering was dependent on type of extractant and P status of the sample. For Bray's P1 extractant, 5 minutes lag period after the addition of colour developer gave the lowest reading. There was no significant difference between the correlation at 15 minutes lag period (r = 0.55*), and 30 minutes lag period (r = 0.56*). Colour development was much faster in the case of NH4F.HF extractant and 5 minutes lag period gave the best correlation. It was concluded that shaking should be done for 1 minute for both extractants but for routine soil analysis involving processing of large number of samples, stirring should be preferred. Filtering of Bray's P1 should be done between 5 and 15 minutes after shaking but with NH4F.HF filtering should be done not later than 5 minutes and time allowed for colour development in the case of Bray's P1 extractant should be between 15 and 30 minutes, while that of NH4F.HF should be 5 minutes. In routine soil analysis either Bray's P1 or NH4F.HF could be used, but NH4F.HF might be preferred because some time is saved.