Detailed Explanation of Rice Cultivation Management Techniques and Fertilization Methods and Application Rates

Fertilizer Management in Organic Rice Cultivation

I. Fertilizer management is an important part of rice cultivation, and the fertilizer management in organic cultivation mainly consists of replacing chemical fertilizers with organic fertilizers, but improper application of organic fertilizers often causes poor growth in rice. For example, if the amount of organic fertilizer applied is insufficient, rice will show symptoms of nutrient deficiency, especially nitrogen deficiency: the leaves turn yellow due to low chlorophyll content, the leaves are narrow and small, tillering is reduced, the plants are short, growth is weak, and yield decreases. If the amount of organic fertilizer applied is excessive, rice will show symptoms of nutrient excess, especially when the nitrogen fertilizer level is too high: the leaves become dark green due to high chlorophyll content, but the stems, leaves and branches are weak, making the plants susceptible to rice blast, with many green grains, and both yield and quality are reduced.

        Therefore, proper fertilizer management is one of the requirements for successful organic rice cultivation. In addition, fertilizer management in organic rice cultivation can avoid the accumulation of soil salts and the occurrence of hardening, increase soil aggregate structure, soil aeration, soil fertilizer-holding capacity and water-holding capacity, soil microorganisms and soil buffering capacity, so that under a good aggregate structure the soil becomes a storehouse of various nutrients, various nutrients can be recycled, fertilization efficiency is improved, and soil erosion is reduced.

        In other words, fertilizer management in organic rice cultivation should pay attention to the correct use of organic fertilizers, so as to achieve the recycling of soil nutrients and energy. In natural ecosystems, the decomposition and reduction of organic matter depends on the action of microorganisms, thereby purifying the soil, cultivating healthy soil, and striving to bring into play the greatest production function.

II. Diagnosis of Soil Characteristics

The soil characteristics that affect rice growth include pH, texture, drainage, hardpan, organic matter content, available nutrient content, soil thickness, slope and so on. These should first be investigated and diagnosed, and soil management methods should be adjusted according to their characteristics, rather than only knowing how to use fertilizers, otherwise results are not easily obtained. Taking pH as an example, rice grows well only at a pH value of 5.0~7.0. If this range cannot be reached, lime materials can be applied to adjust it. In this way, not only can the applied fertilizers be effective, but under such an environment rice grows normally and diseases, especially soil-borne ones, are significantly reduced. If the pH is not adjusted and only the three major nutrient fertilizers are emphasized, it is very difficult to achieve the effect of fertilizer management.

III. Selecting Fertilizer Types and Their Application Rates: including organic materials such as livestock waste, industrial waste and the utilization of by-products.

1. Livestock waste:

Cow manure:

The inorganic nutrients in cow manure differ depending on the feed consumed; concentrated feed results in higher levels than green feed. Cow manure has a low carbon content, and applying 10~12 metric tons per hectare provides a source of nitrogen and potassium for the mid and late stages of rice growth.

Pig manure:

Most of the nitrogen in pig manure is organic nitrogen, which must undergo mineralization to become inorganic nitrogen such as ammonium nitrogen and nitrate nitrogen before it can be absorbed by rice. Since its carbon-to-nitrogen ratio is about 8.4, mineralization proceeds quite easily. Applying 8~10 metric tons per hectare, with a medium rate of decomposition and nutrient release, can supply nutrients for absorption during the mid and late stages of rice growth.

Chicken manure:

Chicken manure is very high in nitrogen, phosphorus pentoxide and potassium oxide, so direct application is rather unsuitable. If the ratio of the three major nutrients can be adjusted and it is mixed and processed into a more slow-release organic fertilizer, it will be more beneficial to rice growth. Applying 4~5 metric tons per hectare provides the main source of the three major nutrients for the early and mid stages of rice growth.

2. Utilization of industrial waste and by-products:

Silicate slag:

Silicate mainly improves the leaf morphology of rice to enhance photosynthetic efficiency, promotes the absorption of phosphorus in phosphorus-deficient soils and the translocation of phosphorus within the plant, and strengthens the oxidizing power of rice roots to reduce the harm from organic acids and hydrogen sulfide. In fields where the soil available silicon content is below 40 ppm, applying 2~3 metric tons per hectare, since it contains 23% silicon oxide and 37% calcium oxide, can provide the calcium and silicon elements needed by the rice plant, making the leaves erect, raising the photosynthetic rate, and enhancing the rice plant's resistance to lodging and its resistance to rice blast and bacterial leaf blight.

Oilseed meals:

Oilseed meals are rich in organic matter and nitrogen, and also contain phosphorus pentoxide, potassium oxide and various trace elements. They generally contain 75~85% organic matter, 2~7% nitrogen, 1~3% phosphorus pentoxide and 1~2% potassium oxide. They are a quick-acting organic fertilizer. Applying 300~500 kg per hectare can provide base fertilizer for rice or be piled and fermented with other organic materials containing lignin fibers to make an organic fertilizer for application.

Rice husks:

Rice husks are a by-product of rice mills and are very rich in silicon, with a silicon dioxide content of 15~19%. Applying 15~30 metric tons per hectare to paddy fields can not only loosen the soil and improve soil physical properties, favoring root development, but also increase the silicon content of the rice plant, thereby raising rice yield.

Distillery waste residue:

The inorganic nutrient content of distillery waste residue is quite high, and after piling and fermentation it can become a good organic fertilizer. For example, the distiller's grains sludge from the Yilan Distillery contains 1.5% nitrogen, and applying 8~10 metric tons per hectare has a yield-increasing effect on rice.

IV. Fertilizer Application Timing and Ratio

For the application timing and ratio of organic fertilizer, base fertilizer is 80% and topdressing is 20%; for the application timing and ratio of silicate slag, the entire amount is used as base fertilizer, and after application it should be applied again only after an interval of 1~2 years.

V. Burying Rice Straw

When harvesting the previous rice crop, attach a straw chopping device to the combine harvester to cut the rice straw into 6~9 cm pieces and spread them evenly in the field (estimated at about 4~5 metric tons of rice straw per hectare). After sun-drying for 2~3 days, in the dry field state, plow them into the soil with a rotary plow to increase soil organic matter.

VI. Planting Green Manure

Planting green manure crops during the fallow period of paddy fields is the most economical and effective soil fertilizer management. After the first crop harvest, plant sesbania; after the second crop harvest, plant leguminous green manure (green soybean, black soybean, Chinese milk vetch) or rapeseed. Most green manure crops can coexist symbiotically with soil microorganisms, fixing free nitrogen from the air, and have a low carbon-to-nitrogen ratio when buried. They are a nitrogen source with considerable potential efficiency and are an excellent material consistent with organic rice cultivation management.

VII. Conclusion

Fertilizer management in organic rice cultivation involves nutrient requirements, soil characteristics and the characteristics of organic materials. All nutrients must undergo fermentation and decomposition to be released from complex organic compounds, and the process is affected by the properties of the materials themselves and by the physical, chemical and biological properties of the soil. At the same time, some organic fertilizers contain relatively low amounts of the nutrients needed for rice growth, are bulky, and have higher transportation and application costs. Therefore, selecting appropriate organic fertilizers, planting green manure, and returning crop residues and animal excreta to use, so as to meet the dual goals of economical rice production and waste disposal, is the most appropriate fertilizer management for organic rice cultivation.