Author: C. K, Tseng, K. Y. Sun and C. Y. Wu
J Integr Plant Biol 1955, 4 (4): -.
Cultivation of haitai (Laminaria japonica Aresch.) in North China, to date, has been confined to Tsingtao,
Chefoo and Dairen, and in these places, conducted only in heavily polluted harbours, in bays where sewage
disposal takes place and in their immediate vicinities, in these places, haitai grows very fast and in a single
growing season (from November to June of the next year), the thallus may grow to 3-4 meters long, 25-30
cm broad and 2-3 mm thick, weighing as much as 1 kilogr am and showing a healthy chestnut brown color.
In other places along the North China coast, however, growth of the haitai is very poor, and within a growth
season, the thallus rarely reaches more than one meter in length, usually only 50-60 cm long, the color is of a
pale yellowish brown, and the product is not of commercial value. In such places, therefore, commercial
cultivation of the haitai is not carried on. Evidently, the difference in the growth of haitai in these two types
of localities is a matter of the fertility of the waters, sea water temperature and light not being the limiting
facters. Thus, it is of great importance to our haitai cultivation industry, if ways and means could be
devised by which the fertility of a selected body of sea water can be raised effectively and, of even greater
Gross et al (1944) had conducted experiments in an enclosed sea loch for observing the effect of fertilizer
application on the growth of phytoplanktons, zooplanktons, benthic animals and ultimately flatfishes. Later,
experiments were conducked by Gross et al (1946) in an open sea loch for the same purposes. In both cases,
the results were encouraging. Gross et al, however, had not made the studies from the economic point of
view and had not investigated into the production of flatfishes so that calculation could be made on the
amount of fertilizer required to yield a kilogram of the fish. It has been an established fact for ages that
increasing the fertility of the soil by the addition of fertilizers will lead to an increase in the production of
crops. Even in aquiculture, the addition of fertilizer to a body of water to increase fish production has long
been a practice in many places. No one will even question if pouring tons of fertilizer into open bays would
increase the production of phytoplanktons and benthic plants. Rather, the question is: will the resulting
increase in production be worth the amount of fertilizer thus consumed? Owing to the ceaseless movement of
sea water, fertilizers if artificially added to open bays will mostly be lost to the sea outside, although Gross et
al (1946) estimated that the loss is not serious. The amount of loss will depend, of course, on the
configuration of the bay. Ways and means must therefore be sought to decrease the amount of loss due to
water movement in order that the methods of fertilizer application could be of practical value.
Haitai and other seaweeds grow only in a certain layer of the sea water and in the cultivation of haitai, these
plants grow on racks which are several meters apart from each other. Evidently, fertilization of the entire
body of water, as in the experiments of Gross et al, is not necessary. Whatever practical method of fertilizer
application is to be successful in seaweed cultivation, it must be one in which fertilizer application is limited to
selected spots, thus minimizing loss of the fertilizer to the places where the particular seaweed does not occur.
The method which we have devised takes advantage of the porous nature of earthen-wares. Fertilizers were
added into specially made elongated earthen bottles, which were then filled with sea water, rubber-stoppered,
sealed, and horizontally tied in specially made elongated bamboo baskets suspended horizontally in the one
meter layer below the sea surface. Thalli of the haitai, 30 cm long, were twisted in ropes, and the ropes tied
laterally on the baskets (cf. the illustrations). The kinds of fertilizers used were: sodium nitrate and ammonium
nitrate as source of nitrogen and trisodium phosphate, apatite and apatite powder as sources of phosphorus.
Porosity of the earthen-wares admits the gradual outflow of the enclosed fertilizer in solution. In our
experiments, the amount of the dissolved salts diffused out into the sea was, on the average, about 50 grams per
bottle per day. The results were very encouraging and in one experiment (Experiment V), within a growth
period of 94 days, the thalli grew to over 2 meters in length, and was in every respect of commercial value. In
this particular experiment, the average airdried weight of the thalli was 33.2 gram and daily increase 353.2 mg
as aginst 7.9 grams and 84.0 mg respectively for the control, representing an increase of 320% in weight. In
another experiment (Experiment Ⅰ), the growth period of the thalli was 196 days, and when harvested, the
air-dried weight of the thalli was 40.6 grams against 12.8 grams for the control, representing an increase of
220% in weight.
From the economic point of view, this method of fertilizer application yields equally encouraging results,
although the amount of fertilizers applied was still very high. In Experiment V mentioned above, m produce
1 kilogram of the haitai required 1.01 kilogram of the nitrogen fertilizer. In view of the great difference
between the value of the produce and the cost of the fertilizer, the margin was still very broad. There is no
doubt in our minds, that the methods could be improved and the results would be better.
Unit area production based on the above experiments has been calculated and comparison made with the
cultivation of wheat crops in the Tsingtao region. It was estimated that 209-265 kilograms of air-dried haitai
could be harvested in one mow, or about 300-400 grams per square meter of the sea surface. Therefore, in
both the quantity and the value of the produce, haitai cultivation yields better returns than local wheat
growing, mow for mow.