NITRATE CONTROL AND QUALITY IN HYDROPONIC LETTUCE BY USING COW DUNG EXTRACT AND NUTRIENT SOLUTION

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.