Pond Preparation: Soil Sampling

Part 1: Pond Preparation

• Soil sampling is the first step in pond preparation and involves excavating surface soil for embankment/dikes and analyzing the soil profile.

1. Soil Sampling

• Soil profiles need adequate sampling, which is done using a soil sampler or auger.
• Soil sampling looks at physical properties like soil texture, which is the ratio of sand, silt, and clay.
• It also assesses the load-bearing capacity and permeability.
• Soil texture is determined by either a mechanical method involving percentages of sand, silt, clay, and the use of a soil triangle, or by field identification using the feel method, ball method, or the feel and ball method.
• Soil pH is a chemical property that determines acid-forming substances like pyrite and sulfides.
• To measure the pH of pond bottom soil, dry it in a forced-draft oven at 60°C, pulverize it to pass a 2-mm sieve, mix with distilled water in a 1:1 ratio, stir intermittently for 30 minutes, insert dual electrodes or a combination electrode into the mixture, and measure pH while stirring.
• Organic matter like C, N, P, and K is also a chemical property to analyze.
• Labile organic matter is easily decomposed and improves soil fertility.
• Refractory Organic Matter decays slowly and improves soil structure/stability.
• A 10% OM is acceptable if most OM is refractory but unacceptable if OM is mostly labile.
• Steps for soil moisture and Organic Matter Analysis:
• Record container weight, add sediment sample, record initial weight of sediment, and place wet sediment in a drying oven at 105°C overnight, then transfer the container, cool it in a dessicator to room temperature, and record final constant weight.
• Then % moisture = [(W2 – W3)/ (W3 – W1)] * 100.
• Use a sediment subsample from the moisture test to record the initial dry weight. W1 and W3 from the moisture test is recorded as container weight and initial dry weight, respectively.
• Place dish in a muffle furnace at 450°C for 4–5 hours or overnight, remove with tongs, let cool at room temperature inside the dessicator, and record the weight of the dish with ash W4, then % organic matter = [(W3 – W1) – (W4 – W1)] / (W3 – W1)] * 100
• Organic carbon content affects soil type:

• 15% indicates organic soil

• 3.1 to 15% indicates mineral soil with high organic matter
• 1.0 to 3.0% indicates mineral soil with moderate organic matter and is the best range for aquaculture
• <1% indicates mineral soil with low organic matter

What to do before pond preparation if the pond was previously used

• Vigorously flush the internal drain canals to stir up and remove any accumulated sludge.
• Discharge to the sedimentation pond.
• If the pond bottom cannot be completely dried out, apply nitrates to oxidize the soil and aid organic matter decomposition.

Part 2: Pond Drying

• Ponds need to be dried for 3-5 days until the bottom soil hardens and cracks to eradicate pests, predators, and competitors.
• Drying eliminates obnoxious gases like H2S resulting from organic matter decomposition and hastens the decomposition of organic matter for nutrients to become available for natural fish food; it also kills disease-causing microorganisms.
• Drying is not advised when ponds are infested with burrowing Callianassidae shrimp.
• Do not dry ponds with coastal and river plain soils like "cat's clay" and "mine overburn" because upon exposure to air, pyrite and other sulfur-containing minerals oxidize to form sulfuric acid and iron sulfate compounds (jarosite), which are toxic.

Part 3: Pond Tilling and Leveling

• Tilling the pond brings subsurface nutrients to the surface for natural food growth and eradicates burrowing species while eliminating pond weeds.
• Tilling ensures oxidation of lower layers of anaerobic mud.
• Alternate cycles of tilling and flushing are commonly used to reduce the iron content in acid sulfate soil.
• Leveling the pond makes the pond bottom surface level/sloping towards the gate for the ease of draining and drying.

Part 4: Disinfection

• Disinfecting ponds eradicates all stages (eggs, larvae, juveniles, and adults) of species of fish, crustaceans, insects, and other predatory and competitor species.
• Unwanted organisms in ponds include competitors like tilapia, gobies, snails, and wood-borers.
• Predators include predatory fishes, sea snakes, and birds.
• Aquatic weeds include floating (Eichhornia), Emergent (Nymphaea), Submerged (Hydrilla), and Marginal (Typha) species.
• Prevent the entry of unwanted species by properly screening gates, implementing scare devices and traps for predatory birds/burrowing crustaceans/aquatic snakes, coating wooden structures with preservative paints, and using manual/mechanical/chemical/biological methods to remove aquatic weeds.
• Substances used to disinfect the pond bottom include:
• Tobacco dust, which contains nicotine
• Hydrated lime and ammonium sulfate fertilizer
• Derris root
• Teaseed cake

Soil Conditioning

• Soil conditioning brings undesirable soil to a normal and suitable state with the use of neutralizing or buffering material.

Liming

• Liming uses lime from limestones and shells containing calcium carbonate.
• Liming raises the pH and alkalinity of acidic waters, increases carbon availability for photosynthesis, and acts as a pond disinfectant.
• Kinds of lime used in aquaculture:
• Agricultural lime (CaCO3)
• Dolomite lime (CaCO3 + MgCO3)
• Burnt limestone / quick lime / unslaked lime (CaO)
• Hydrated lime/slaked lime (Ca(OH)2).
• Lime type is differentiated by examining and analyzing the pH of a slurry of 10-20 parts distilled water and 1 part liming material (10 20:1).
• Agricultural lime- pH will not be more than 10.
• Burnt lime / hydrated lime will exceed pH 12.
• Heavy loam or clay soils and acid sulfate soils require more liming.
• Liming should be done after disinfection & before fertilization.

How Much Lime is Needed:

• Amount of lime needed = (Desired pH - Current pH) / (0.1 x Neutralizing value (decimal)) x Area of pond (ha) x 0.5 ton/ha

Fertilization

• Fertilization is increased by producing natural food organisms.
• Fertilizers can be taken up for storage, assimilation, growth, and reproduction, becoming attached to organic and mineral particles.
• Organic fertilizer includes animal waste byproducts and decaying plants/animal materials.
• In-organic fertilizer is chemically synthesized, provides major elemental nutrients N, P, and K to algae.
• You should establish plankton bloom using fertilizer to maintain neutral or slightly alkaline pond water/soil.
• Nutrient Contents of Animal Manures in Organic Fertilizers:
• Chicken : N (1.15), P2O5 (0.41), K2O (0.37)
• Pig : N (0.49), P2O5 (0.15), K2O (0.53)
• Cattle : N (0.49), P2O5 (0.07), K2O (0.30)
• Single Element: Urea (46-0-0), Ammonium sulfate (21-0-0), Superphosphate (0-20-0)
• Incomplete: Ammonium phosphate (16-20-0), Diammonium phosphate (18-46-0).
• Complete: Triple 14 (14-14-14).
• Use water transparency as a guide to fertilize – Secchi Disc Transparency > 20-40.
• If water transparency is <20cm, prepare for DO problems
• If water transparency is 20–30cm, plankton is too abundant
• If water transparency is 30-45cm, water conditions are ideal
• If water transparency is 45–60cm, plankton is growing scarce
• If water transparency is >60cm, expect aquatic weeds and inadequate plankton
• Fertilize more if the pond is new, is poor in nutrients, and has sandy bottom soil.
• If you are limited in supplies of fertilizer, prioritize the ponds that need it.
• DO NOT fertilize if the species used does not utilize plankton as food, water exchange is high, turbidity is caused by plankton density, and/or the water is murky/muddy.
• Criteria for the use of inorganic fertilizers:
• Phosphate fertilizers are suitable if phosphates are > 0.2 mg/l or Total P > 0.4 mg/l.
• Nitrogen fertilizers are suitable if nitrates are > 2 mg/l or Total N > 1.5-3 mg/l.
• Potassium fertilizers are suitable if potassium is > 1 mg/l.
• P:N must be 1:4 to 1:8, and inorganic fertilizer is advisable for poor water.peaty soil,

Techniques for Fertilizer Application

• Broadcast method
• Bag method
• Spraying/Direct application of Liquid Fertilizer

Relevant Fertilizer Computations:

• To solve for nutrients: Weight of nutrients available = Weight of fertilizers x % of fertilizer nutrient available for use (in decimal)
• To solve for fertilizers: Amounts of fertilizer needed= Dosage of nutrient ÷ % of fertilizer nutrient available for use.

Lab-Lab Method

• "Lab-lab" refers to the algal mat adhering on the pond bottom like a green pasture underwater and is technically known as periphyton.
• The micro-benthic algal species in lablab are diatoms and blue green algae.
• The maximum water depth requirement to grow this benthic mat is 30 cm.