Environmental Engineering Reference
In-Depth Information
other organic acids. The parabolic diffusion equation can better fit the release curve of P,
and the obtained relative diffusion coefficient showed that organic acids can improve the
migration rate of P in the soil, with the improvement effect under the same concentration
presenting the following sequence: citric acid>malic acid>acetic acid>oxalic acid. The
higher the concentration of the organic acids was, the higher the migration rate of P
would be. Given that the P needed by plants basically migrates by means of diffusion,
under the condition of P deficiency of plants, improving the secretion amount of organic
acids can effectively increase the biological utilization rate of P.
Keywords
: Phosphorus, dynamic leaching, organic acids, availability
I
NTRODUCTION
Phosphorus is a key nutrient element for the growth and development of crops (Gerke
1994, Lan et al., 1995, Wang et al., 2011). The phosphorus needed by crops is mainly
absorbed from the soil. However, the phosphorus in the soil can easily be fixed, and
generally, the seasonal utilization rate of phosphorus fertilizer by crops is only 10%~25%
(Liu et al., 2012, Sun et al., 2012), which means that nearly 75%~90% of phosphorus is
accumulated in the soil. Excessive application of phosphorus fertilizer will not only result in
waste of existing phosphorus resource, but also may easily cause environmental problems like
eutrophication of water bodies (Wang et al., 2012, Cheng et al., 2012, Bai et al., 2013,
Chintala et al., 2013, Sarkhot et al., 2013)). With the development of research on rhizosphere
micro ecosystem, the low molecular weight organic acids (such as citric acid, oxalic acid,
formic acid, acetic acid, etc.) of the soil are thought to be able to promote the form
transformation of phosphorus (Ding et al., 2011, Tate 1984, Jones 1998). However, because
the study results can be affected by different soil types and different concentrations of organic
acids, the conclusions reached by researchers are not entirely consistent.
It is held by many researchers that organic acids can exert a positive effect on the release
and availability of phosphorus in the soil. For example, Fox et al., (1990) in his study found
that organic acids such as malic acid, citric acid and oxalic acid could increase the phosphorus
in soil solution by 10~1,000 times. Qu Dong et al., (1994) added citric acid, tartaric acid and
oxalic acid of different concentrations into Lou soil, provided constant temperature incubation
for 96h, and found that the content of available phosphorus increased in all three cases and
that the activation rate of soil phosphorus was in direct proportion to the concentration of the
acid added in. However, there are also researchers who believe that organic acids exert an
inhibitory effect or no effect on the availability of phosphorus. For example, Lyamuremye et
al., (1996) studied the effects of seven types of organic acids on phosphorus composition, and
found that only citric acid showed a significant effect. Traina et al., (1986) found that when
the concentration of citric acid, tartaric acid or formic acid was lower than 0.1mM, adding
them into montmorillonite decreased the solubility of phosphorus; when the concentration of
citric acid was 0.6mM, the solubility of phosphorus gradually recovered to the level detected
when no organic ligand existed. Therefore, the activation effect of organic acids (in particular,
the organic acids with their actual concentrations in soil) needs to be further verified.
Currently the vast majority of the existing research is based on the batch extraction
method or short-term incubation experiment. However, there are some drawbacks with the
