|
The low stocking and low feeding envisaged under the present system does not lead to accumulation of organic matter at the pond bottom. However, for better growth and survival of the shrimps, the soil needs to be conditioned. The best way to improve the pond bottom conditions is to dry the pond wherever possible and till the surface layer. This process shall enhance the mineralisation of organic load at the bottom.
Application of lime is useful in correcting the pH of the soil. It is a disinfectant; it also increases the mineralisation process. If the PH of the soil is not below 7.5, a basal dose of 300-500 Kg/ha can be applied. However, in acid soils, where the soil PH is low, the quantity of lime to be applied should be calculated on the basis of the PH and the type of lime used. The following dosages of quick lime/slaked lime are advocated for low PH soils.
|
Soil pH
|
Quick lime *
(tonnes/ha)
|
Slaked lime **
(tonnes/ha)
|
|
5.0
|
9.2
|
17.0
|
|
5.5
|
6.9
|
12.7
|
|
6.0
|
4.6
|
8.5
|
|
6.5
|
2.3
|
4.2
|
*During pond Preparation ** During culture
The cultured species largely depend on the natural feed. To achieve sustained production, it is essential that supplementary additions of fertilizers should be resorted to. Both organic manures and inorganic fertilizers are generally used for the purpose. The dosage of organic manure to be applied is dependent on the organic carbon content of the soil. The following basal doses are prescribed.
Dosage of manures in relation to organic carbon content of soil
|
Organic carbon in soil (%)
|
Prescribed basal dose
Raw cow dung (Kg/ha)
|
Dry chicken manure
(Kg /ha)
|
|
1
|
500
|
175
|
|
0.5
|
1000
|
350
|
|
0.25
|
2000
|
700
|
Similarly, application of inorganic fertilizers should be based on the nitrogen and phosphorous content of the soil which is detailed below.
Application of urea in relation to available N
|
Organic carbon in soil (%)
|
Prescribed basal dose
Raw cow dung (Kg/ha)
|
Dry chicken manure
(Kg /ha)
|
|
1
|
500
|
175
|
|
0.5
|
1000
|
350
|
|
0.25
|
2000
|
700
|
|
Available P in soil
(mg/100 g soil)
|
Super phosphate to be applied
(Kg/ha)
|
|
1.5
|
100
|
|
3.0
|
50
|
|
6.0
|
25
|
While using inorganic fertilizers, care should be taken to avoid over-fertilization. The fertilization dosage given may not hold good for all the waters. The best way to regulate the fertilization schedule is through monitoring the algal bloom conditions based on the colour or transparency of the water.
Application of super phosphate in relation to available phosphorus
|
Available P in soil
(mg/100 g soil)
|
Super phosphate to be applied
(Kg/ha)
|
|
1.5
|
100
|
|
3.0
|
50
|
|
6.0
|
25
|
While using inorganic fertilizers, care should be taken to avoid over-fertilization. The fertilization dosage given may not hold good for all the waters. The best way to regulate the fertilization schedule is through monitoring the algal bloom conditions based on the colour or transparency of the water.
|
