Abstract:
Hydroponic lettuce, like most leafy greens, can accumulate high levels of nitrates
that are often harmful to human health. The accumulation of nitrate closely
related to the amount and composition of the nutrition applied. Therefore, to
minimize the nitrate content on edible parts of lettuce and to access the
production of it, this experiment was conducted by using four different levels of
aerated cow dung extracts (C
1
= cow dung extract 50 g.L
-1
, C
2
= cow dung extract
100 g.L
-1
, C
3
= cow dung extract 150 g.L
-1
, C
4
= cow dung extract 200 g.L
) and
four modified strength of nutrient solution (S
1
= 30% strength of standard
solution, S
2
= 40% strength of standard solution, S
3
= 50% strength of standard
solution, S
4
= 60% strength of standard solution) as a treatments. It was carried
out in completely randomized design (CRD) with three replication in semi-green
house at Horticulture farm of Sher-e-Bangla Agricultural University, during
September 2018 to February 2019. Various growth, physiological and
physicochemical parameters of were estimated in this experiment. In case of cow
dung extract, the highest leaf length (23.54 cm), maximum number leaves plant
1
(17.01) and the highest fresh weight (112.05 g/plant) were recorded from C
3
while the lowest in C
1
. For hydroponic nutrient solution, the highest leaf length
(23.13 cm), maximum number leaves plant
-1
(16.66) and the highest fresh weight
(116.0 g/plant) were recorded from S
4
while the lowest in S
1
. For cow dung
extract, the nitrate content (255.48 mg kg
-1
FW) was statistically higher in C
3
,
which also had a higher ascorbic acid content (45.41 mg/100 g FW), β-carotene
content (239.00 μg/100g) and net assimilation ratio, compared to the lowest in
C
1
. The content of nitrate (281.24 mg kg
-1
FW), ascorbic acid (35.41 mg/100 gm
FW) and β-carotene (226.17 μg/100g), as well as the net assimilation ratio were
the highest for S
4
, the lowest for S
1
in the context of nutrient solution. Therefore,
it can be concluded that among the treatments combination, C
3
S
4
would be much
suitable for lettuce production in hydroponic system with highest yield along
with far less accumulation of nitrate.
