Thanks Warren  - Manual contains  nice  review of pond fertilisation

 

Hi Chris,

 

Farmers do this by looking at the water colour and fertilising in response to this.  There will tend to be a need to increase fertilisation over time as the fish grow.  A dried pond just filled with go green easily due to good light penetration.  Turbidity reduces light penetration which phytoplankton depend on.  Earthen ponds get more turbid with time.  Soil obviously has a big effect.  Cloudy weather also.  Don't be tempted to keep putting in more fertiliser if the pond doesn't go green, particularly if the weather is very cloudy all day.  As soon as you get a sunny day it will change to pea soup. 

 

The recommended amount found by research at AIT is 4 kg of nitrogen and 1-2 kg of phosphorous per ha per day.  Of course you need to know how much N and P are in any organic ferilisers.  Inorganic fertiliser is easier to calculate.  %N is quoted on the bag, but P is quoted as P2O5 and to calculate how much P in a kg you need to allow of the oxygen.  1 mole of P is 30.974g and a mole of oxygen is 15.999.  So a mole of P2O5 would weigh 109.918.  61.948g of this is P which is equivalent to 56.36%   In 1 kg of16-20-0 fertiliser (N-P-K) you have 160g of N and 200 x 56.36% = 112.7g P.

 

 See this link to a pond rearing manual I put on the website = http://tilapiathai.com/asset/NILE%20TILAPIA%20CULTURE%20IN%20EARTHEN%20PONDS.pdf

 

 If you are using inorganics and are adding N and P only, you might want to try adding K.  For example, we used to use 16-20-0 which we apply at 187 kg/ha/week.  We now use 15-15-15 at the same rate, as we find it gets the pond green better I assume as K is limiting sometimes.  If the pond doesn't go green we can try adding dolomite which contains magnesium. 

 

If you are adding some organics, then you won't have deficiency of elements required in small amounts.

 

Secchi disk measurements will relate not just to phytoplantkton levels, but all suspended solids.  Chlorophyll levels can be measured, but it really isn't difficult to do it by eye.  Remember that any feed going in the pond is also adding N and P.

 

Best

 

Warren

 

On Thu, Oct 22, 2015 at 8:12 PM, William Leschen <william.leschen@stir.ac.uk> wrote:

Dear Chris

Thanks   I will post this up on the sarnissa forum  but am also copying to -  rather than  limnologists – much better in my opinion those who have applied and practiced hands on over many years  -      Peter  (Edwards – you’ve already corresponded with him)  and also Warren Turner  in Thailand as Warren at Namsai has worked out   protocols over the years for optimum fertilisation of his ponds and also maintenance/balance of blooms over longer prod time periods   -   noting also though that as you know  the local pond substrate ,  water quality at inflow  go to make up very specific water chemistry for particular sites – each one different – also   their particular buffering capacity   towards  more stable algal bloom production over time  - I think I realised a while ago on visits to long well established greenwater pond systems  China  exactly how much of a skill and an art this is –   - and something that is very much experience based not just   getting  figures and dose rates   for organic and inorganic from text books.  Ive also copied to Mark Amechi in Ghana as his   pond hatchery site  through a nos of French   origin  site managers has developed greenwater pond systems for them that work over the years  - Also for you might be worth looking  to trial 1-2 ponds from scratch seeding of specific algal species ?If you haven’t already I would  recommend looking at some of Claude Boyds now old but still very valid  publications from Auburn  - books but also plenty of papers

Eg  

http://www.alibris.com/Dynamics-of-Pond-Aquaculture-Claude-E-Boyd/book/1847736

http://www.amazon.com/By-Claude-Boyd-Aquaculture-Management/dp/B008WDSSL0

 

Best wishes Will

 

From: Chris Schnell [mailto:cwschnell@gmail.com]
Sent: 22 October 2015 13:36
To: William Leschen
Subject: Semi-intensive ponds

 

Dear Will,

If you have a limnologist in the forum, he could possibly help me resolve my questions. Or, anyone with experience of growing tilapia in mud ponds would most probably be able to clarify things. Producing tilapia in semi-intensive mud ponds using algae and supplementary feed is not all that easy as it sounds, especially when you start having problems with fertilizing the water.

What is the best way to measure primary production of algae? Does oxygen levels tell the whole story, or does one also look at the green / grey colour of the water? Or are there better methods?

My problem started with overdosing. It seems as if it takes a long time to dilute one’s nutrients and algae once you have a bloom with a reading of less than 15 cm on the Secchi disk. For financial reasons I did not want to remove water from my pond after over dosing, but now I keep on adding more water and the Secchi readings do not go up. I cut down dramatically in adding new fertilizer. This makes me worry that the algae in the pond could be dead or just floating solids and that the primary production, that serves as feed for the tilapia, is not sufficient.

My ponds are around 1 hectare in size and the depth varies between 400mm and 900mm. Temperature is 27°C at the bottom and 29°C at the surface. Oxygen at 12h00 is 12.5 ml/l at the surface and 9.5 ml/l at a depth of 900 mm. I fertilise with dry cow manure, Urea and DAP. Total alkalinity is around 180.

Best regards,

Chris Schnell

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