The fertilization strategy of crab-raising paddy field

I. Misunderstandings

Recently, I talked to a farmer on the phone several times to answer some of his questions about fertilizing after big eyes in paddy field farming, and found that some farmers still have some misunderstandings in the issue of fertilizing crab paddy fields, and some operations still rely on so-called experience or The experience of some successful people is more accidental and more risky, which is not conducive to the healthy development of the rice field crab breeding business. Through consulting the data and the test results over the years, it is concluded that it is a relatively feasible and safe fertilization strategy for crab-raising paddy fields, which is hoped to be helpful to farmers.

II. Fertilization strategy

In order to ensure a certain amount of rice production, a certain amount of fertilizer must be used in the rice field. At present, the most common ones are solid organic fertilizer and inorganic fertilizer applied to the soil and liquid fertilizer sprayed on the surface of the rice plant. The harm mainly comes from nitrogen in inorganic fertilizers.

Nitrogen is an essential nutrient element for rice growth. It exists in three forms in water bodies: molecular nitrogen (such as N2), inorganic nitrogen (such as NH3, NH4+, NO2-, NO3-) and organic matter (such as urea, amino acids, proteins). Among them, ammonia nitrogen (NH3) and nitrite (NO2-) in inorganic nitrogen are the main factors that increase rapidly after fertilization and cause harm to river crabs.

The experimental results of Wang Yuheng et al. from the College of Animal Husbandry and Veterinary Medicine of Jiangsu Agriculture and Forestry Vocational and Technical College show that the safe concentration of NH3 for river crabs is 0.20 mg/L under normal dissolved oxygen content (6.0-7.0 mg/L), and in supersaturated oxygen (10.0-7.0 mg/L) Under the condition of 12.0mg/L), the safe concentration of NH3 to river crab is 0.32mg/L. The results of Shi Junyan, Liaoning Institute of Freshwater Research, etc. showed that the safe concentration of NH3 on the Larva of the river crab is 0.185mg/L. According to our experience, the traditional fertilization method of throwing chemical fertilizers into the water will lead to the rapid increase of ammonia nitrogen in the water. For example, applying 20 catties/mu of urea will increase the ammonia nitrogen to 20mg/L the next day, and reduce the dosage to about 5 catties/mu. It will also rise to more than 2mg/L. If it is fertilizers such as ammonium bicarbonate and diammonium, ammonia nitrogen will rise higher and faster.

Therefore, experienced farmers put an end to the operation of applying chemical fertilizers after the crabs are put into the fields. According to our experience in recent years and the feedback from farmers, the use of slow-release fertilizers as the base fertilizer fertilization method, the ammonia nitrogen in the paddy field water is always below 0.1mg/L after the rice turns green. Of course, the source of ammonia nitrogen in the water body is not only one way of fertilization. Ammonia nitrogen is the main component in the metabolites of river crabs. At the same time, the ammoniation of residual bait and nitrogen-containing organic matter in feces by microorganisms will also produce ammonia nitrogen. Thunderstorm weather will also increase the content of ammonia nitrogen. However, these are relatively slow and mild processes and are mostly local high and global low states, which gives the crabs sufficient time to escape from the high ammonia nitrogen area.

To sum up, we believe that under the current state of the art, the fertilization strategy for crab-raising paddy fields should be combined with the rotation of the ground to evenly put enough slow-release fertilizer into the paddy field at one time, and no top-dressing is required in the later stage. Topdressing urea in a small amount and several times, the dosage should be controlled within 4-5 jin/mu, and the maximum should not exceed 10 jin/mu, and the changes of ammonia nitrogen should be monitored to pay attention to the reaction of crabs.

R&D Center: Zheng Yan

Guanghe crab rice home

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