Increasing the fish productivity of ponds through poultry ranging and fertilizer application

Combined duck and common carp grazing in grow-out ponds

Grazing waterfowl in ponds is an effective way to increase natural fish productivity without additional expenditure on artificial feed. Ducks loosen the bottom soil, accelerate the mineralization of organic matter, and enrich the pond with organic elements. This activates the development of the natural food base for the yearling carp.

• Duck stocking density — 230–240 head/ha
• Increase in fish productivity — 37–39%
• Yield of yearling carp — 84–87% of the stocking

The calculation of stocking density consists of two values: the base carp stocking rate and the additional stocking, which is calculated based on the productivity increase from duck grazing. The standards for grow-out ponds with a depth of up to 1 m are provided below.

Mineral fertilizer application regimes and control of the hydrochemical background

In an aquatic environment, mineral fertilizers work differently than on land: higher plants absorb only an insignificant part of them. Nitrogen and phosphorus are consumed by bacteria and microalgae (phytoplankton). This causes mass growth of zooplankton (daphnia, cyclops, rotifers) and benthos, which serve as direct food for the fish. Phosphorus application has a stimulatory effect on daphnia reproduction. In low-productivity ponds, mineral fertilizer allows for increasing fish productivity by 3–3.5 times or more.

Planning the treatment of the water body is always based on a chemical analysis of the water. If the content of mineral nitrogen forms exceeds 2 mg/l, and mineral phosphorus exceeds 0.5 mg/l, fertilizers are not applied. If the indicators are lower, the fertilizer dose (X, kg/ha) is calculated to bring the concentration to target values (A = 2 mg/l N and 0.5 mg/l P), taking into account the actual content of elements (B), the average depth of the pond, and the share of the active ingredient in the preparation.

The procedure and timing of fertilizer application are strictly regulated by the growing season and the type of pond:

1. In nursery ponds, fertilizer application begins 10–15 days before stocking the fish, when the pond is filled to 1/3 of its volume.
2. In grow-out ponds, the first portions are applied when the water warms up to 7–10 °C.
3. In the first half of the growing season, repeat treatments are carried out every 7–10 days.
4. In the second half of the growing season, the interval between applications is increased to 10–15 days.
5. 30–40 days before the final harvesting of fish, fertilizer application is stopped completely. In total, over the season, nursery ponds are fertilized 6–8 times, and grow-out ponds 8–10 times.

Calculate the yearling stocking of carp, the amount of nitrogen and phosphorus fertilizers for fertilizing a grow-out pond with an area of 50 ha and an average depth of 2 m, under the following conditions:

Calculate the yearling stocking considering the increase in fish productivity: B – mass of fish at the end of the period (two-year-olds); b – mass of fish at the beginning of the period (fingerlings);

Calculate the single dose of phosphorus fertilizer application for the entire pond area: Calculate the amount of nitrogen fertilizers for the season: Calculate the single dose of nitrogen fertilizer application for the entire pond area: Calculate the amount of nitrogen fertilizer for the season.

Task. Calculate the stocking of yearling carp, the amount of ammonium nitrate and superphosphate for fertilizing a grow-out pond with an area of ____ ha, an average depth of m, under the following conditions.

Table 11 – Pond farm indicators for calculating the number of carp, as well as fertilizers

1 2 3 4 5 6 7 8 9 Pond area, ha

10 11 12 13 14 14 16 17 18 Natural fish productivity, kg/ha Average mass of yearling carp, g 30 30 33 33 33 34 34 34 34 Average mass of two-year-old carp, g 480 485 485 490 490 490 495 495 495 Yield of two-year-old carp percentage of yearling stocking 85 85 85 85 85 85 85 85 85

Increase in fish productivity 2 3 2 3 2 3 2 3 4 due to applied fertilizers, times Mineral nitrogen content in nitrogen fertilizer, % 35 36 37 35 40 39 35 41 37 Mineral phosphorus content in phosphorus fertilizer, % 10 11 11 12 12 10 12 12 10 Frequency of fertilizer application, times 5 6 7 8 8 7 6 5 6

10 11 12 13 14 15 16 17 18 Pond area, ha 28 20 21 22 23 24 25 26 27 Natural fish productivity, kg/ha 211 211 211 211 215 215 215 215 215 Average weight of year-old carp, g 30 30 33 33 33 34 34 34 34 Average weight of two-year-old carp, g 480 485 485 490 490 490 495 495 495 Survival rate of two-year-old carp as a percentage of yearling stocking 87 87 87 87 87 87 87 87 87 Increase in fish productivity due to fertilizer application, factor 4 4 4 5 5 5 3 3 3 Mineral nitrogen content in nitrogen fertilizer, % 35 35 35 35 35 35 35 35 35 Mineral phosphorus content in phosphorus fertilizer, % 10 10 10 10 10 10 10 10 10 Fertilizer application frequency, times 8 8 7 7 7 6 6 6 6

19 20 21 22 23 24 25 26 27 Pond area, ha 28 29 30 31 32 33 34 35 36 Natural fish productivity, kg/ha 220 225 225 226 257 228 229 201 202 Average weight of year-old carp, g 35 36 34 33 32 31 30 29 28 Average weight of two-year-old carp, g 480 485 485 490 490 490 495 495 495 Survival rate of two-year-old carp as a percentage of yearling stocking 83 83 83 83 83 83 83 83 83 Increase in fish productivity due to fertilizer application, factor 3 4 5 3 4 5 3 4 5 Mineral nitrogen content in nitrogen fertilizer, % 35 35 35 35 35 35 35 35 35 Mineral phosphorus content in phosphorus fertilizer, % 10 10 14 10 12 10 10 10 10 Fertilizer application frequency, times 6 7 6 7 7 7 7 8 8