- The Federal Water Pollution Control Act Amendments of 1972
prohibits the discharge of seafood processing solid wastes into
navigable waters after July 1, 1977. Oregon shrimp and crab processors
must use other methods of disposal for the 15 to 30 million
pounds of solid waste generated annually. The application of shrimp
and crab wastes to nearby agricultural land can consume the wastes
generated at major processing ports.
As they came from the processing plant, shrimp and crab solid
wastes contained 1.3% to 1.6% N, 0.47% to 0.54% P, other nutrients,
7% to 14% CaCO₃
equivalent, and 64% to 78% water.
A greenhouse experiment was established to determine the
effects of 1) grinding the wastes, 2) surface vs. incorporated waste
applications, and 3) waste applications vs. inorganic N applied at
equivalent N rates (56, 168, and 336 kg N/ha) with applications of
P, S, and lime supplied with the inorganic N only. The fertilizer
materials were applied on two coastal soils, and two pasture crops were
grown. Forage yields and the P concentration in 'Potomac' orchard
grass (Dactylis glomerata L.) were significantly higher with incorporated
waste applications than with surface waste applications.
Application method did not affect the P concentration in New Zealand
white clover (Trifolium repens L. ). The difference in crop response
between application methods would assumably be less under field
conditions than was measured in the greenhouse. Grinding crab waste
significantly increased forage yields when the waste was surface
applied, but not when incorporated with the soil. Unground shrimp
waste gave significantly higher forage yields than ground shrimp waste.
No significant difference occurred in the forage yields, the N uptake
by orchardgrass, or the P concentrations in orchardgrass and white
clover among applications of shrimp waste, crab waste, and inorganic
nutrients with lime. Applications of shrimp and crab wastes increased
white clover yields over the control by a factor of more than 3.5 on
Knappa silt loam (pH 4.9 - 5.0) but did not measurably increase the
soil pH. It was assumed that the wastes, in the immediate area of the
shell material, increased the availability of Ca, P, S, and Mo,
decreased soluble soil Al, and allowed effective rhizobial nodulation
and N fixation. Increasing application rates of shrimp and crab
wastes to Knappa and Nehalem silt loams significantly increased the
extractable soil P and Ca, and significantly decreased the extractable
soil K after 28 weeks of orchardgrass growth. No consistent
effect on soil pH was measured.
In a second greenhouse experiment, N rates of 165 and 330
kg/ha and P rates of 61 and 122 kg/ha were supplied by shrimp waste
and by inorganic sources to a limed coastal soil in a 2 x 2 x 2 complete
factorial arrangement. Applications of shrimp waste resulted in
significantly higher orchardgrass yields and P uptake than applications
of the inorganic nutrients, but no significant difference occurred
in the N uptake.
In an irrigated coastal pasture, fresh shrimp waste was applied
at 6,726, 17,936, and 35,872 kg/ha and ammonium phosphate
(16-20-0 15 S) was applied at 224 and 448 kg/ha and a stand of orchardgrass
was established. Forage yields were higher with shrimp waste
than with ammonium phosphate. Shrimp waste applications beyond
17,936 kg/ha did not further increase the forage yield or P uptake.
Shrimp waste applications increased extractable soil P, SO₄ -S,
soluble salts, and NO₃ -N, but resulted in a depletion of soil K when
measured at the end of the growing season.
Shrimp and crab processing wastes are effective sources of
N and P for crop plants and should be applied at rates necessary to
supply the recommended rates of N.