Is your pond producing less than it should? Well, one of the common causes can be insufficient nutrients to support fish growth, especially in semi intensive and extensive pond systems. Pond preparation is a key element in any pond production system.

Pond preparation involves liming and fertilisation to provide an ideal environment for tilapia to grow.

Drain

The first step in pond preparation is to drain your pond after harvest, removing any sludge from the pond bottom along with any mortalities that may have occurred. Thereafter, you should let the pond dry for 10 to 14 days.

Lime

The second step is liming your pond. Liming will help improve pond soil quality, provides CO₂ for photosynthetic organisms and will help combat parasites within the pond. One common practice is to use agricultural lime which is relatively cheap and abundant. The agricultural lime or calcium carbonate should be applied at a rate of approximately 50 to 200 g per square meter of pond area.

Alternatively, you could use slaked or quick lime which can be applied at approximately 20 to 50 g per square meter of pond area. The lime should be applied evenly across the whole bottom. It is not necessary to disc the lime into the soil, however this will improve its effectiveness. The liming process will remove the majority of unwanted organisms from the pond and improve the effectiveness of fertilisation. After the lime has been applied, you can fill your pond to approximately half to two-thirds. Thereafter, fertilisation can begin.

Fertilise

Fertilisation is the third step in preparing your pond. It provides nutrients to the water, which stimulate the growth of algae and other organisms, such as insects that provide a nutrient source for your fish. When fertilising your pond, you can use either inorganic or organic fertilisers. These fertilisers should be applied at the optimum of 20 kg N and 5 kg P per hectare per week. Tables 1 and 2 can be used to determine how much fertiliser is needed.

Table 1: Average NPK values for some common organic fertilisers

Organic fertilizer	N (% by weight)	P (% by weight)	K (% by weight)
	N	eq. P2O5	eq. K2O
Swine manure	0,93	1,12	0,68
Dairy manure	0,72	0,46	0,73
Cattle manure	0,92	0,76	0,79
Chicken manure	2,71	3,02	1,74
Horse manure	0,50	0,34	0,52
Sheep manure	0,87	0,78	0,91
Composted, all types	1,09	0,78	1,00
Chicken litter	3,10	3,43	3,00
Cottonseed meal	6,34	2,31	1,88
Rice bran	1,98	3,16	2,09
Lucerne	0,74	0,14	0,64
Soya bean meal	7,31	1,47	2,30
Meat and bone scrap	7,79	15,09	-

Table adapted from FAO, 2019

Table 2: Average NPK values for some common inorganic fertilisers

Inorganic fertilizer	N (% by weight)	P (% by weight)	K (% by weight)
	N	eq. P2O5	eq. K2O
Basic slag	-	16-20	-
Super phosphate	-	14-20	-
Triple phosphate	-	44-54	-
Ammonium nitrate	33-35	-	-
Ammonium phosphate	18-21	48-52	-
Ammonium sulphate	20-22	-	-
Di-ammonium phosphate (DAP)	18-21	48-52	-
Calcium nitrate	15-16	-	-
Sodium nitrate	15-16	-	-
Urea	42-47	-	-
Potassium nitrate	13-14	-	44-46
Potassium sulphate	-	-	45-54
Potassium chloride	-	-	50-62

Table adapted from FAO, 2019

For example, if you were to use a combination of high-grade urea (47-0-0) and DAP (21-52-0) to fertilise your 1 ha pond to the optimum of 20 kg N and 5 kg P per hectare per week, you would need 38,3 kg of urea and 9,6 kg DAP as seen in Calculation 1

Calculation 1: Example of calculating fertilisation quantities

Urea 38,3 kg x (47%, 0%, 0%)
= 18 kg N, 0 kg P and 0 kg K

DAP 9,6 kg x (21%, 52%, 0%)
= 2 kg N, 5 kg P and 0 kg K

Total (38,3 kg urea + 9,6 kg DAP)
= 20 kg N, 5 kg P and 0 kg K

You can test if there is sufficient phytoplankton in the pond by placing your arm into the pond up to your elbow. If your hand is barely visible it means that your pond is ready to be filled and stocked.

Fertilising should proceed once or twice a week for 3 to 4 weeks after the fish have been transferred. Fertilisation can be gradually reduced as soon as the fingerlings start eating the newly introduced artificial feed. As soon as the fish have been weaned onto artificial feed alone, feed must be available as often as possible. The fertilisation of semi-intensive pond systems can allow for the growth of fingerlings to around 100 g per fish, depending on stocking density, after which supplementary feed should be provided for optimal growth.