Basic HTML Version
Molecular Soil Biology (online), 2011, Vol. 2 No.1, 1
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8
ISSN1925-2005
http://msb.sophiapublisher.com
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Delta is proposed at Table 6.
Table 6 The classification criteria for the NO
3
-
type SSS in cucumber-based greenhouse in China’s Yangtze River Delta
Soil secondary salinity class
EC1:5, 25
℃
(ds/m)
Effects on tomatoes
Ⅰ
0.89~2.03
Salinity effects negligible or slightly improved with increased
salinity
Ⅱ
2.03~3.76
Plant growth decreased by 0%~15%, yield dropped by10~30%,
Ⅲ
3.76~5.32
Plant growth decreased by 15%~30%, yield dropped by 30%~50%,
Ⅳ
5.32~6.15
Plant growth decreased by 30%~60%, yield dropped by 50%~70%,
Ⅴ
> 6.15
Plant growth decreased by > 60%, yield dropped by >70%
3 Materials and Methods
3.1 Experimental design
The experiments were conducted with four replica-
tions during two successive cropping periods (from
April to July, 2009 and from January to April, 2010) in
Taizhou, Jiangsu Province (32.755°N, 119.891°E).
The greenhouse (200 m × 25 m) was covered with
polyethylene that is penetrable for sunshine. The
experimental plots with 5 m × 3 m located at this
greenhouse. The agrochemical properties of the
experimental soil are presented as follow (Means, n =
4): the soil layer is from 0 cm to 8 cm; nitrate
98.92 mg/kg, available phosphorus 65.40 mg/kg,
available potassium 117.54 mg/kg total nitrogen
2.479 g/kg; sulfate content 79.33 mg/kg; organic
matter 2.253 g/kg; pH (
-
) 6.83 and the electric
conductance 0.89 ds/m. Each experimental plot was
equally divided into 5 rows and cucumber (
Cucumis
sativus
L.
cv
. Dongfangmingzhu) was grown in the
rows. To avoid the exchange of salty and water among
plots, each row was isolated by polyethylene films
(5.0 m × 0.8 m) that were buried at depth of 0.6 m on
both sides of the plots.
The surface soils from 0 to 8 cm in the plots were
treated by adding water soluble magnesium nitrate
(Mg(NO
3
)
2
) and calcium nitrate (Ca(NO
3
)
2
), to make
the initial concentrations of soil salinity at 1.0~3.0 g/kg
for treatment 1 (T1), 3.0~4.0 g/kg for treatment 2 (T2),
4.0~5.0 g/kg for treatment 3 (T3), and 5.0
-
6.0 g/kg for
treatment 4 (T4), respectively. No chemical was added
into the control (ck).
Cucumber (
Cucumis sativus
L.
cv
. Dongfangmingzhu,
mid-tolerant to salinity stress) was used in this
research. The seeds were sanitized with sodium
hypochlorite containing 5% active chloride for 5 min,
and then washed five times prior to immersing in
deionized water for 12 h. The soaked seeds were
raised in well-washed quartz sand and irrigated with
tap water. As long as the second true leaf of cucumber
seedling appeared, the cucumber seedlings were
transplanted to the treated plots in the greenhouse.
During the growth stages the temperature in the
greenhouse was maintained at 25~30 at daytime
℃
and 18~20 at night. All plots were irrigated five
℃
times with river water. The nitrate concentration in the
river water was below 8.0 mg/L.
3.2 Sample and analyses
Soil samples were collected in triplicate on six
occasions (April 14, June 25, July, 30, 2009 and
January 10, February 25, April 2, 2010). Fresh soil (50
mg) was mixed with deionized water (10 mL). The
soil nitrate concentration was determined by spectrop-
hotometer using phenol disulfonic acid (Lu, 2000).
The rest of each fresh soil sample was air-dried and
then sieved through a 1.0 mm mesh, homogenized and
stored in plastic bags at room temperature (from 20
℃
to 25
℃
) until they were required for analysis. Salinity
as expressed by electrical conductivity (EC) was
measured with a DDS
-
320 conductivity meter at 25
℃
after the soil was mixed with water (the ratio of soil to
water in weight is 1:5).
Initial soil available phosphorus (P) was extracted
using 0.5 M NaHCO
3
(pH 8.5) according to the
method of Olsen (Criquet et al., 2007) and the P
concentrations in the extracts were determined using
the molybdenum blue method (Lu, 2000). Soil
available potassium (K) was extracted by 1 M