Environmental Engineering Reference
In-Depth Information
short-term extraction experiment; for example, the excessively high water-soil ratio and high-
intensity mechanical oscillation are far different from the actual soil environment. Compared
with the batch extraction method, the soil column leaching method (flow method) has many
advantages such as relatively low water-soil ratio, continuous secretion of organic acids by
simulating the plant root system and ceaseless absorption of nutrients by the root system.
Therefore, employing the soil column leaching method can better promote the studies on the
process and degrees of soil phosphorus release under the continuous effect of organic acids
and more faithfully reflect the changes of soil phosphorus and the effectual degrees of
different influencing factors in the presence of organic acids. In this study, the dynamic
process of the activation of soil phosphorus by organic acids under the continuous leaching
condition was studied using the soil column simulation experiment, and the effects of various
organic acids in different concentrations on phosphorus activation were discussed to reveal
the degree and rule of activation of soil phosphorus by low molecular weight organic acids
under the continuous leaching condition.
1.
M
ATERIALS AND
M
ETHOD
1.1. Experimental Materials
The experimental soil was the surface soil (0~20cm) collected from the Yellow River
Delta in Dongying, Shandong Province. This type of soil is alluvial loess parent material,
which mainly consists of silts, and the plants growing on it are mainly saline-alkaline tolerant
suaeda salsa and tamarix chinensis. The specific physical and chemical properties of the soil
are listed in Table 1. The low molecular weight organic acids used in the experiment were
citric acid, oxalic acid, malic acid and acetic acid.
Table 1. Characteristics of the soil samples
clay
(%)
silt
(%)
sand
(%)
TOC (mg
Kg
-1
)
TP
(mg kg
-1
)
Fe-P
(%)
Al-P
(%)
Ca-P
(%)
Soil
pH
Fluvo-aquic
soil
8.1
4.7
83.5
11.8
6710
748
2.5
3.8
74.7
1.2. Leaching Experiment Devices and Method
In the leaching experiment an organic glass tube (7cm in length, 3cm in inner diameter)
was used, with two pieces of qualitative filter paper placed at the bottom.
A layer of quartz sand (1.5cm in thickness) was placed on the paper, and then cover by
another filter paper. After that, three layers of soil (45g in total) was added into the tube to
form a soil column with a length of about 4cm, and each layer was compacted to ensure a soil
bulk density of around 1.5g cm
-3
, which was similar to its bulk density in natural state.
A piece of filter paper was place on the soil column, followed by a layer of quartz sand
(1.5cm in thickness) that had been soaked by salpeter solution. The inner side of the soil
