Understanding Nitrogen in Agriculture

Figure 1.

The management of nitrogen is a critical factor in aquaculture. Feeds contain proteins which when uneaten or digested results in ammonia.
Ammonia is water exists as Total Ammonia Nitrogen (TAN) described by the following equation:
NH₄⁺ ↔ NH₃ + H⁺

Feeding rate is a crucial factor in generation of ammonia in an aquaculture pond, and this can be described by


P_TAN = (Daily Feed in Grams) X (%age of Protein Content in Feed) X 0.092

P_TAN is the total ammonia production in grams per day.

In well managed aqua farms, the TAN is consumed by healthy population of plankton, which is then fed by the fishes. This further aids in reduction of Feed Conversion Ratio (FCR). You see, phytoplankton are unicellular chlorophyll containing organisms which take up nitrogen for their photosynthesis. They are a rich source of amino acids and antioxidants, hence as energy source for the fish.

Aquaponics is the science of combining aquaculture and agriculture/horticulture in a single process. The classical indoor method is well known: Separate fish tank where the feed is administered. The nutrient rich aquaculture water is pumped in to a hydroponics unit where vegetables or crops are grown and harvested. The water after getting filtered through the hydroponics unit then recirculates back into the fish tank. This controls the use of fertilizers and optimizes productivity. Not to forget a better utilization of the nitrogen factor.

In aquaponics, the growth of plants from the aquaculture water fed system results in consumption of NH₄⁺ which in turn converts NH₃ to NH₄⁺ for balance as explained in the first equation. Nitrifying bacteria present in the plant grow beds/biofilters convert ammonia to NO3- from which plants take up their nitrogen requirements in aquaponics (Figure 1). 

This process is catalyzed first by Nitrosomonas bacteria by the following equation:
NH₃ + 1½O₂  ↔ NO₂^- + H₂O + H⁺ + 84 kcal mol^-1

Followed by the second step conversion by Nitrobacter bacteria:
NO₂^- + ½O₂  ↔ NO₃^- + 17.8 kcal mol^-1

Hence the stocking density of plants is a crucial factor to balance the nutrient requirements for crop production.

We had constructed a proposed model for a rainwater reservoir pond designed for polyculture of Indian major carps (IMC); Rohu, Catla and Mrigal with freshwater giant prawns or scampi, Macrobrachium rosenbergii. Feed and probiotics get fed in the reservoir pond, while a solar powered motor pumps the nutrient rich pond water in to a vegetation patch via timed sprinklers (Video below). The veggie patch has a specially designed based inclined towards the pond which channels the percolating water towards the reservoir. The sprinklers are programmed to switch off after a certain time by which six inches of top soil is wet. As a back-up for dry seasons, 40 ft. table water pump is operated on solar for a monthly 30% water exchange.

Sustainability is a race to plug the excess flow of nutrients and limit the use of fertilizers. We must respect our environment to reap dividends.

Indian Carp Farming - Best Practices

There are a few simple features which you must ensure prior to carp aquaculture.

1. Pond bottom and water quality

2. Juvenile stocking density and survival

3. Feeding

4. FCR

1. Fertilisation is a crucial feature of aquaculture since it ensure high quality plankton development which aids in carp feed conversion.

A. Ensure the installation of an underground water pump which will assist in 30% water exchange once in 28 days. What is the present source of fresh water? Water should be pumped into the pond from a depth of 40 feet. 

pH of water for carp should be around 6.8 to 7.3

B. Pond area needs to be prepped well prior to addition of water. Fertilizers to be mixed for pond bottom construction been detailed below:

Urea: 9 kg per acre

Single super phosphate: 9 kg per acre

Quick Lime: 360 kg per acre

ZeroTox: 40 kg per acre

AquaCyclo: 5 kg per hectare

After mixing and prep of pond bottom, one must ensure the water height should be a constant 1 meter. First 20% water is filled, then followed by the remaining after 2 days. 

For an existing pond with foreign eggs issue, nothing much can be done at this point. For future, your aqua pond must be dried out once every winter season for preparing. That way to control unwanted seeds.

During pond construction all holes in the pond bottom must be sealed and bleaching powder is recommended to clear out all foreign eggs and disease. Bleaching powder (>33% chlorine) @ 200 kg per acre.

Once all water has been pumped in, allow to stay and fertilize for 10 days. After this, your pond is ready for the carp fingerlings.

2. Juveniles must be a combination of Rahu, Catla and Mrigala. The stocking density of 1/sq.m, 1/sq.m, 0.5/sq.m. The stocking density can be a maximum of 3 times of given values, not exceeding.

Individual fingerlings of body weight 40 to 60 grams recommended.

3. Feed optimization is a crucial step. Start the culture with 10% of total biomass, divided equally into 4 portions fed daily. To ensure proper feeding, use floating feeds, 32% protein, 1 mm pellet size. Construct a netted nylon tent with an open bottom. The bottom part of the net should be dipped 6 inches to 1 foot below water surface. The top send needs to be constructed on a bamboo to create a conical or cylindrical shape. The net must be installed near the bank of the pond by fastening it to a bamboo horizontal pole which is in turn tied to a vertical pole on the dyke. You must add the feed into this feeding net. Since the bottom of the net is submerged in water, feed cannot float away. And you can monitor how much feed is actually been consumed. Carp feeding time is 30 mins. For eg. if the total fish biomass in the pond is 100 kg. Then you need to feed 10 kg feed per day. This is 2.5 kg per feeding time. So you add the 2.5 kg in to the feeding tray and observe how much is being actually consumed. If you see they are actually eating 2 kg in 30 mins, then next time to give them 2 kg. Floating feed helps you to monitor the volume of feed being consumed. Remove feed not consumed from the feeding net after 30 mins.

You should change the feeding programme once every 2 weeks after checking length and weight of at least 25 fishes once a fortnight. The philosophy is to gradually reduce feed quantity with time. Feed should always be used as supplement, since carp will feed on plankton. Contact us for more info on this feature.

We recommend you to use Matsya360 at 1.5 lites per acre, once in 3 weeks, 30 days from culture start. This should be combined with AquaCyclo used at 1 kg per hectare once in 3 weeks. These are probiotics which will ensure proper cycling of ammonia and sulphides along with plankton balance, reduced FCR, increased D.O. with pond bottom quality.

Natural Alternatives in Aquaculture

Intensive fish farming has spread of several bacterial diseases over the years and as a solution more antimicrobials (antibiotics and drugs) are used. The negative consequences of antibiotic use on public health have encouraged the development of strict regulations controlling the use of antibiotics and other drugs. The high numbers of antibiotic-resistant bacteria because of antibiotic usage provides a threat to aquaculture as they become the source of the antibiotic resistant gene that stays in the culture.

Bacterial antibiotic resistance and antibiotic residues has become a matter of concern across the globe, there is a need to develop alternatives to deal with for bacterial pathogens in aquaculture.

Several alternatives to the use of antibiotics have been used successfully in aquaculture. The use of probiotics or friendly bacteria to avoid pathogenic infections in aquatic organisms has been tested in aquaculture.

Several microorganisms has been tested and used as probiotics in aquaculture research. The most studied are species of lactic acid bacteria , Bacillus, Pseudomonas, Aeromonas, yeasts, Acinobacter… These probiotics have been used in different aquatic organisms and have been shown to be successful, not only for their ability to prevent disease, but also for improving digestion and growth. Many of these applications have been targeted at the early stages of development of the aquatic organisms, such as the larval stages, because these stages are more susceptible to infections.

Some of the proposed mechanisms that provide protection against pathogens involve the production of inhibitory compounds, competition for essential nutrients and adhesion sites, the enhancement of disease resistance and the modulation of host immune responses.

Another alternative treatment is using natural essential oils and herbal extracts, which are natural components from plants that are generally recognized as safe substances (GRAS). Due to their antimicrobial properties, these natural products may constitute alternative prophylactic and therapeutic agents in aquaculture.

There is still a lot of research going on and huge scope of development in the area of natural substitutes to increase productivity with sustainable environment for Aquaculture. To reduce antibiotic use in aquaculture best practices are to minimize the level of stress on the fish and reduce the chance of infections requiring antibiotics treatment.

Herbal Extracts in Aquaculture

Medicinal herbs and plants have strong antibacterial effects and this knowledge is used in Ayurveda in India since primitive times. 

Phenolics, polysaccharides, proteoglycans and flavonoids that are part of herbal extracts can help in preventing and controlling infections in Aquaculture. Several plant products found to have potent antiviral activity against fish and shrimp viruses.

With use of Antibioics and other drugs more the pathogens are becoming resistant to the drug and it also harms the environment.Use of antibiotics and drugs are now banned in most scientifically forward countries. 

Natural plant products are an extremely viable and ecofriendly alternative to antibiotics or other drugs which are not safe for the fish, the environment and people who are eating it. Use of herbal and natural remedies in aquaculture should be encouraged in India to boost production with sustainability.

Herbal extracts can be used as remedies, growth promoters, stress resistance boosters and prevention of infections. The use of herbal extract as feed additives can significantly benefit not only aquaculture but also poultry and animal feeds.

Aquaculture and Sustainability

Fish Farming or Aquaculture means human intervention to enhance production by stocking the fish, feeding them, providing protection from predators and so on. The farmer also needs to take complete of the fish that is being cultivated and the place where it is cultivated. The Aquaculture process vary from place to place from Marine Aquaculture processes like Sea Ranching, lines, racks etc to Freshwater fish farms.

The proper management and conservation of natural resources in Aquaculture, can help in meeting human needs today and also the needs of future generations. In aquaculture, sustainable development needs to be practiced to conserve land, water, plant and animal genetic resources and be environmentally friendly, technically bettered and economically viable to the population.

FAO defines food security as physical and economic access by all members of a population at all times to sufficient, safe and nutritious food in order to meet dietary needs and allow an active and healthy life. Aquaculture has enormous potential to better Food Security for the global population.