Cotton Genomics and Genetics 2016, Vol.7, No.1, 1-7
5
(Nitrogen fixing bacterial fertilizer
Azotobater Chroococcum
consists 5×10
9
CFU/mL), Subtin (
Bacillus Subtilis
consists 1×10
7
CFU/mL) and Fitobisol (consortium of beneficial soil bacteria) were provided by the culture
collection of the Department of Microbiology and Biotechnology, National University of Uzbekistan.
3.3 Study sites
The climate in both sites is continental with a yearly average rainfall of (200
±
36) mm and more than 90% of the
total rain falling between October to May. The average minimum monthly air temperature is 0
°
C in January, the
maximum of 37
°
C in July, and the soil temperature ranges between
−
2
°
C and 35
°
C. The average highest
relative humidity is slightly more than 80% in January and the minimum is less than 45% in June. The combination
of high temperatures and low rainfall under continental climate makes irrigation essential for crop production.
The field experiment was carried out at irrigated agricultural site located in Syrdarya Province
(41°00′N, 64°00′E,) in north-eastern Uzbekistan. In these soils, cotton has been grown for the long
years under a continuous monoculture production system and under flood irrigation without proper
drainage facilities but using a natural flow system. According to the WRB-FAO (2006) classification
(
), the soils of selected fields
were identified as Calcisol (silt loam serozem) having a calcic horizon within 50 cm of the surface. The surface
soil horizon was calcareous saline whereas the deeper soil horizons were only mildly alkaline. The orchic horizon
is low in organic matter. The selected field (0.5 ha each) was categorized salinity levels based on electrical
conductivity (EC): moderately saline ((5.6
±
0.6) dS m
−1
) soils.
The second experiment was carried at the field site of experimental station Tashkent State Agrarian University,
Tashkent region in Uzbekistan. Soil is typical serozem (1% organic matter, 0.6 mg N 100 g
-1
soil; 3.0 mg P 100 g
–
1
;
12 mg K 100 g
–
1
; 6 mg Mg 100 g
–
1
soil; pH 7.4) having a calcic horizon within 50 cm of the surface. The orchic
horizon is low in organic matter. The experiment was in randomized complete-block design. There were 5
treatments including 4 bacterial fertilizers and control variation in 3 replications, 15 plots in total. Each plot was
10 m
2
.
3.4 Soil sampling
So il samp les were coll ec t ed from soil s twe lve convent iona ll y ti ll ed ( (0~40 ) cm depth )
ir ri ga t ed cott on fi e lds bot h saline and non saline conditions. According to the WRB-FAO 2006
(
classification, the soils of all the
selected fields were identified as calcisol (silt loam serozem) and were formed from loess, eluvial, and proluvial
parent materials. The soils have been cropped to cotton monoculture for the last (50~60) years under flood
irrigation without proper drainage facilities using natural flow system.
On average, the soil contained (43
±
9) g sand kg
−1
, (708
±
12) g silt kg
−1
, and (250
±
13) g clay kg
−1
, had the
cation exchange capacity of (23.6
±
1) cmol kg
−1
, with exchangeable Na percentage of 4.41, and Na absorption
ratio of 0.32.
The conventional tillage consisted of moldboard plowing to 30 cm depth after harvest and offset disking, to a
depth of 10 cm, prior to planting in the spring. Soil samples of (0~30) cm depth were taken with a soil corer
(3.5 cm diameter). Samples were collected at the beginning March (spring), and end of the experiments October
(autumn). The cores were pooled; field-moist soils were sieved (<2 mm) directly after collection. The soil
samples were kept in black polyethylene bags and stored at 4°C. These “fresh” field-moist, sieved samples were
used for the incubation study.
3.5 Germination of seeds
The seeds of chickpea were first sorted to eliminate broken, small seeds and then they were surface-sterilized
with a solution of 75 mL chloride
+
25 mL water for (2~3) min, rinsed thoroughly with distilled water.
Surface-sterilized seeds were transferred on paper tissue towels soaked in 0.5 mM CaSO
4
and germinated for 18
