Key Points of High-Yield Technology for Integrated Fish-Lotus Culture in Ponds

0. Introduction

The grid-pond fish-lotus integrated culture technology involves partitioning hardened lotus ponds with roof tiles, hard boards, etc. into small grids of 2-4 sq m each, and planting lotus within the grids. On average, each mu of water surface produces 0.5 wan kg of lotus and 400-450 kg of fish, with a net benefit of over 10,000 yuan per mu. This technology can utilize abandoned pits, wasteland, riverbank land, and scattered marginal land to build grid-pond fish-lotus integrated culture systems. It features small investment, low cost, quick results, and high efficiency, making it suitable for widespread development by rural households. It can both increase economic income and improve market supply, enriching the vegetable baskets of urban and rural residents, and therefore has very broad prospects for promotion. Below is an introduction to the technical experience of the Ningyang County Water Affairs Bureau in conducting experimental promotion in 35 villages of Heshan Township.

1. Technical Principles

Dividing the lotus pond into several small grids greatly increases the hard wall surface area within the pond. Since lotus rhizome tuber formation is the result of nutrient accumulation triggered by swelling when the rhizome encounters a hard wall, a greatly increased hard wall area naturally increases lotus yield.

2. Lotus Pond Conditions and Infrastructure

2.1 Selection of Lotus Pond

Wasteland, waterlogged lowland, abandoned kiln pits, and old lotus ponds both inside and outside villages can all be utilized. As far as possible, choose locations with convenient transportation, good water source conditions, unpolluted water quality, convenient irrigation and drainage, and no tall buildings or shade-casting objects around for building lotus ponds.

2.2 Lotus Pond Construction

Lotus pond construction can be divided into several types:

(1) Single-brick running-wall isolation type;

(2) Lime-concrete structure with roof tile isolation type;

(3) Plastic film bottom-lining with roof tile isolation type, as well as plastic thin board and cement board isolation types. Generally, the lotus pond area is 1-3 mu, with 1-1.5 mu being optimal, and a pond depth of 0.8-1.2 m being suitable. After the pond is built, backfill 35-40 cm of fertile soil as the layer for lotus growth, and apply basal fertilizer. Then use roof tiles, cement boards, plastic boards, gypsum asbestos tiles, or other hard boards to partition into small grids of 2-4 sq m. The partition boards should be buried 40 cm into the soil, extend 20 cm above ground level, with a board height of 60-70 cm. Set up inlet and outlet ports at intersecting positions of the lotus pond, install fish-blocking nets, and set up "-" or "+" shaped fish ditches within the pond. The fish ditches should be 1.0 m wide and 0.5-1.0 m deep, accounting for about 15% of the pond area. Practice has proven that large grids produce low lotus yields; although small grids require a larger one-time investment, they produce very high yields.

2.3 Applying Sufficient Basal Fertilizer

Lotus roots favor heavy fertilization. Ample backfilled soil and manure are key to achieving high pond lotus yields. Fertilization should be based primarily on basal fertilizer, supplemented by topdressing; primarily on organic fertilizer, supplemented by chemical fertilizer. Apply about 2000 kg of fully fermented organic fertilizer, 10-15 kg of ammonium sulfate, 5-10 kg of urea, 3-7 kg of potassium nitrate, and 5-10 kg of superphosphate per mu. Chemical fertilizers should be diluted with water and sprinkled, avoiding direct scattering into fish ditches to prevent harm to fish. After applying basal fertilizer, use 50 kg of quicklime per mu, slaked into slurry and evenly sprinkled over the entire pond, to improve the soil, increase calcium fertilizer content, regulate the pH of the pond mud, and simultaneously serve to kill pathogens.

3. Pond Lotus Cultivation

3.1 Selection of Seed Lotus

It is advisable to select fresh, robust, vigorous-budded, fine-noded, disease-free and injury-free high-quality white lotus roots as seed. Each seed lotus plant should preferably have three complete internodes and carry 1-2 daughter lotus roots. Daughter lotus roots can also be used as seed, but they should be robust, with at least 2 fully matured internodes and intact terminal buds. Seed lotus roots can be soaked in 20 mg/kg naphthalene acetic acid for 40 min, propagated by plastic film seedling raising, and transplanted after 15 days, which can bring pond lotus to market earlier and increase yield by over 15%.

3.2 Planting Time

Plant when air temperature rises above 12°C-15°C. Too early and low soil temperature can cause seed lotus to rot; too late and buds grow long and are easily broken. In Shandong Province, planting around Qingming is generally suitable.

3.3 Method and Quantity

First, plow and harrow the soil and manure in the lotus pond evenly and finely, then plant the lotus. Plant 1 seed lotus root or 2 daughter lotus roots per 2 sq m in the pond, with a general seed quantity of 320-380 kg per mu. When planting, the bud end of the seed lotus should be slightly lower and the rear part slightly raised, at a 20-30 degree angle, 5-8 cm from the ground level, which is exactly the depth of the first water filling.

4. Fish Stocking

4.1 Stocking Time

Generally, stocking can begin when water temperature stabilizes at 8°C-10°C. When stocking Clarias leather carp (walking catfish) fingerlings, stocking should only begin after water temperature stabilizes above 15°C.

4.2 Stocking Species

Generally speaking, any fish that can be cultured in ponds can be cultured in lotus fields, mainly including grass carp, silver carp, bighead carp, common carp, crucian carp, and bream. In addition, faster-growing fish such as Clarias leather carp and Pengze crucian carp are good choices for lotus field culture. Monoculture of Clarias leather carp is preferred. Since the water surface in lotus fields has poor light and lower temperatures, with fewer plankton in the water body, filter-feeding silver carp and bighead carp should not be selected as the main species. Omnivorous fish should be the main species, with filter-feeding fish as supplementary.

4.3 Stocking Density

This should be determined based on fish species, stocking size, water quality and water source conditions, and management level. Generally, stock 200-300 large-size fingerlings per mu, or 600-800 Clarias leather carp fingerlings per mu.

4.4 Mixing Ratio

The general fish stocking ratio is 70% grass carp, 15% common carp, 5% silver carp and bighead carp, and 10% others; or 70% common carp, 15% grass carp, 10% silver carp, and 5% bighead carp. Clarias leather carp and Pengze crucian carp are suitable for monoculture. It is worth noting that before the lotus grows two standing leaves, large-size grass carp fingerlings should not be stocked, to prevent grass carp from eating lotus leaves.

5. Management Techniques

5.1 Water Level Regulation

In spring, to increase water temperature and soil temperature, the water should be kept shallow, at around 10 cm. Later, as water temperature rises, gradually deepen it, with fish ditch water depth reaching 0.8-1.0 m. When adding water, use the method of small amounts but frequent additions to maintain good water quality.

5.2 Reasonable Topdressing

When lotus leaves have fully grown, apply 10-15 kg of ammonium sulfate or 5-10 kg of urea per mu. When terminal leaves appear, apply 5-10 kg of urea, 10 kg of superphosphate, or 20 kg of potassium fertilizer per mu.

5.3 Weeding and Leaf Removal

During the growth process of lotus roots, especially in the early growth stage, there are many weeds that need to be removed promptly. In the mid-management period, leaves should also be regularly thinned and excess flower buds broken off to allow sunlight to penetrate into the water.

5.4 Feed Feeding

To enable rapid fish growth and achieve higher yields, artificial compound feed must be fed reasonably. When culturing Clarias leather carp, animal offal such as chicken intestines should be fed to ensure fish can promptly eat fresh, high-quality, and sufficient feed.

5.5 Disease and Pest Control

Main lotus root diseases include rot disease, leaf blight, and brown spot disease. Rot disease: applying an appropriate amount of quicklime into the pond before cultivation can serve as prevention, or directly spray 600-800 times solution of 80% zineb wettable powder. Leaf blight: spray 800 times solution of 50% thiophanate in the early stage of disease, for 2-3 consecutive times. Brown spot disease: prevention and treatment are the same as leaf blight. Main pests include aphids, prodenia litura, and root maggots. For prodenia litura, spray 1000 times solution of 90% crystalline trichlorfon at night.