Agriculture Reference
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concentrations of noxious compounds in the biodegraded culture broths of seaweeds were
approximately similar to those concentrations in the fermented broth of fish waste. These
values were known to be lower than those values for commercial fertilizers. Seaweeds were
known to contain significant amounts of essential mineral elements (Yaich et al., 2011), and,
among these elements, heavy metals were regarded as toxic.
Therefore, high concentrations of heavy metals in untreated seaweed leachate and in the
digestate, which was obtained after anaerobic digestion (one of the disposal methods of
seaweed), were of concern (Cecchi et al., 1996; Nkemka & Murto, 2012). Moreover, seaweed
is classified as a toxic waste due to its high Cd content, and the usage of the digestate as a
bio-fertilizer is restricted in Sweden (Nkemka & Murto, 2012). However, the contents of Cd
in the biodegraded culture broths of seaweeds were extremely low. Microbial degradation
may significantly reduce the Cd level.
Hydroponic Culture
The use of the biodegraded culture broths of seaweeds is aimed at elongating the root and
at overall plant growth by improving the uptake of available nutrients in the soil. In this sense,
the fertilizing ability of the culture broths of seaweeds was tested by hydroponic cultures,
which contained kidney bean and barley. In parallel, the fertilizing ability of the mixed broths
(mixture of the culture broths of the three seaweeds, and the mixture culture broths of the
three seaweeds and fish waste) was also tested together with a commercial seaweed fertilizer.
The results of their comparison in a 15-d hydroponic culture are presented in Figure 9 for
kidney bean and in Figure 10 for barley, respectively.
Figure 9. Results of 15-d hydroponic cultures of kidney bean using 4-d culture broths of seaweeds,
mixture of seaweeds, mixture of seaweeds and fish wastes, and commercial seaweed fertilizer.
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