Technical specification for the production and application of sugar enrichment fertilizer for citrus fruits
Ouyang Xin et al
Funds: Guangzhou Science and Technology Program(2023E04J0191).
Citrus is full of flavor, sweet and sour taste, rich in nutrition, and is deeply loved by the public. In addition, citrus has high economic benefits, fast variety iteration, and broad market prospects. As of 2017, the cultivated area of citrus in mainland China has surpassed apples, reaching 2,533,300 hm 2, and in 2018, the output of citrus in mainland China has caught up with apples, reaching 41.38 million tons. In 2021, the planting area of citrus in mainland China reached about 3 million hm 2, and the output reached 51 million tons, and citrus has become the largest fruit in China. Citrus cultivation in the southern part of the mainland is developing rapidly, and South China is an important area for citrus cultivation in China. However, due to the small temperature difference between day and night, more rain and insufficient sunlight in South China, the citrus produced in South China has problems such as low sugar content, sour taste, less fruit juice and low quality, which seriously affects the planting efficiency of fruit farmers. Therefore, the development of green and efficient sugar-enhancing products and the promotion of sugar-enhancing technology according to local conditions are of great significance for the sugar-enhancing planting of citrus fruits in South China. At present, studies have shown that in addition to nutrients such as nitrogen, phosphorus, and potassium, biostimulants such as humic acid, proteolysate, and seaweed extracts can be applied to plant foliar or rhizosphere to promote the absorption of nutrients by crops, improve fruit quality, and increase fruit sugar content. Based on this, this paper discusses the production and application of citrus fruit sugar-enhancing fertilizer products in South China from the aspects of raw material selection, product formula design, production process exploration, product quality testing, and efficient application and effect, in order to provide scientific sugar-enhancing products and technologies for citrus sugar-enhancing planting in South China.
1 Raw material selection
The raw materials required for the preparation of fruit sugar-enhancing fertilizer products include chemical nutrient raw materials, active functional substances and plant hormones, and the specific raw materials are selected as follows.
1.1 Chemical nutrient raw materials
Chemical nutrient raw materials mainly select raw materials containing phosphorus, potassium, calcium, magnesium, sulfur, zinc, boron, molybdenum and other nutrients. Among them, phosphate fertilizer raw materials mainly include ammonium dihydrogen phosphate, diammonium hydrogen phosphate and potassium dihydrogen phosphate, etc., potash fertilizer raw materials mainly include potassium chloride, potassium sulfate, potassium nitrate and potassium dihydrogen phosphate, etc., calcium fertilizer raw materials are mainly calcium nitrate, calcium ammonium nitrate, calcium chloride and superphosphate, etc., magnesium fertilizer raw materials mainly include magnesium sulfate, magnesium chloride and magnesium nitrate, etc., sulfur fertilizer raw materials are mainly sulfate, sulfite and sulfur element, etc., zinc fertilizer raw materials are mainly zinc sulfate, zinc oxide and nano zinc, boron fertilizer raw materials mainly include boric acid, borax, Sodium octaborate and borate, etc., molybdenum fertilizer raw materials mainly include ammonium molybdate, sodium molybdate and molybdenum trioxide. The raw materials used need to ensure their purity and meet industry standards and requirements.
1.2 Active Functional Substances
Most of the active functional substances are small organic molecules that are easy to decompose and absorb, such as protein hydrolysates, polypeptides, oligopeptides, amino acids, polysaccharides, oligosaccharides, functional microbial metabolites, etc. In recent years, active functional substances, such as humic acid, fulvic acid and seaweed extracts, have been widely used in crop stress resistance and quality improvement. For example, the algae polysaccharides, algae oligosaccharides, algae polyphenols, mannitol, betaine and other active substances contained in seaweed extract have a good sugar-increasing effect. The selection of active functional substances should be in line with the implementation standard "General Requirements for Organic Water-soluble Fertilizers" (NY/T3831-2021). At present, the use of active functional substances to promote fruit sugar is widely used in production practice.
1.3 Plant hormones
Plant hormones mainly include cytokinin, auxin, gibberellic acid, abscisic acid, ethylene and other functional substances, these plant hormones can regulate the color change and maturity of citrus fruits, and reasonable application can significantly increase the sugar-acid ratio in the process of fruit ripening. Table 1 summarizes the applications of various plant hormones to promote fruit sugar and color change.
Table 1 Effects of plant hormones on fruit glycemic and color change
2. Product formula design
At present, there are three categories of citrus fruit sugar-enhancing fertilizer formulas, which are mainly composed of nutrients and functional substances. The nutrients mainly include phosphorus and potassium, calcium and magnesium and sulfur and potassium, and the functional substances are mainly biostimulants, such as protein hydrolysate, seaweed extract, polypeptides, oligopeptides, polysaccharides, oligosaccharides, amino acids, mannitol and sorbitol. Common citrus fruit sweetener formulations on the market can be broadly divided into the following 3 categories.
1) High phosphorus and potassium sugar-enhancing fertilizers. The contents of P2O5 and K2O can reach 30%~60% or 300~600 g/L, and the trace elements are 1%~5% or 1~50 g/L, and the trace elements usually include Fe, Mn, Cu, Zn, B, Mo, etc. In addition, it contains 1%~20% or 10~200 g/L of functional substances.
2) High calcium and magnesium sugar-enhancing fertilizer. The content of Ca and Mg can reach 10%~20% or 100~200 g/L, and the trace elements are 1%~5% or 1~50 g/L, and the trace elements usually include Fe, Mn, Cu, Zn, B, Mo, etc. In addition, it contains 1%~30% or 10~300 g/L of functional substances.
3) High-sulfur potassium sugar-enhancing fertilizer. The content of S and K2O can reach 10%~50% or 100~200 g/L, and the trace elements are 1%~5% or 1~50 g/L, and the trace elements usually include Fe, Mn, Cu, Zn, B, Mo, etc. In addition, it contains 1%~30% or 10~300 g/L of functional substances.
3. Production process
The production process of citrus fruit sugar-enhancing water-soluble fertilizer is basically the same as that of ordinary organic water-soluble fertilizer. It is important to note that each operation step requires strict temperature control, which is critical to the quality of the sugar enrichment fertilizer product. At the same time, for different types of sugar-enhancing fertilizers, the production process is slightly adjusted, and the general process is as follows.
1) Raw material crushing. The raw materials required for sugar-enhancing fertilizer, such as potassium chloride, potassium sulfate, potassium dihydrogen phosphate, etc., are crushed sequentially, and the particle size after crushing is in the range of 1~2 mm, and then the crushed raw materials are filtered to remove impurities and large particles.
2) Raw material ingredients. The crushed raw materials are accurately measured according to the requirements of the raw material formula, such as high phosphorus and potassium type [50-200-300+5TE (trace element) + 50~300 OM (organic matter)], and the batching is carried out in the automatic batching system to ensure the accuracy of each batch of fertilizer ingredients.
3) Raw material blending. The above-mentioned prepared raw materials are added to the stirring tank or reaction kettle in turn, and mixed thoroughly to form a stable form of fertilizer. For aqueous products, special attention should be paid to reaction temperature, time, pressure, etc.
4) Additive additives. According to the needs of the product, the spreader, emulsifier, suspension agent, penetrant, etc. are added in turn to increase the stability and absorption effect of the water-soluble fertilizer.
5) Defoam and let stand. During the stirring process, bubbles may form and need to be defoamed, and then let sit for a period of time to stabilize sufficiently.
6) Filling, coding, packing. The fertilizer with stable properties is filled into bags or barrels, coded (marked with production information, batch number, etc.), sealed, and sealed to ensure that the product is sealed.
4. Product quality inspection
Quality inspection is a very important part of the product before it is shipped or sold. The product quality testing indicators include chemical nutrient content, organic matter content and functional substance content.
4.1 Chemical nutrient content
Determination of chemical nutrient content contained in the product: nitrogen content is determined by distillation titration method, phosphorus content is determined by quinoline gravimetric method of phosphomolybdate, potassium content is determined by potassium tetraphenylborate gravimetric method, see "Determination of total nitrogen, phosphorus and potassium content of water-soluble fertilizer" (NY/T 1977-2010) for details; calcium, magnesium, sulfur and chlorine content determination reference standard "Water-soluble fertilizer - Determination of calcium, magnesium, sulfur and chlorine content" (NY/T 1117-2010); iron, zinc, boron and molybdenum refer to "Water-soluble fertilizer - Copper, iron, manganese, Determination of zinc, boron and platinum content (NY/T1947-2010) requires the determination.
4.2 Organic matter content
The potassium dichromate volume method was used to determine the organic matter content in fertilizers, and the specific steps are described in the implementation standard "Determination of Organic Matter Content of Water-soluble Fertilizers" (NY/T 1976-2010).
4.3 Content of functional substances
Functional substances include amino acids, humic acids, alginic acid, sugar alcohols, etc. The amino acid content is determined by the amino acid automatic analyzer method, see the implementation standard "Determination of Free Amino Acid Content of Water-soluble Fertilizers" (NY/T 1975-2010). Humic acid was determined by redox titration after sulfuric acid precipitation, and the detailed steps are described in "Determination of Humic Acid Content in Water-soluble Fertilizers" (NY/T 1971-2010). The content of alginic acid was determined by carbazole sulfate spectrophotometry or m-hydroxybiphenyl spectrophotometry, and the specific steps refer to the implementation standard "Determination of Alginic Acid Content in Water-soluble Fertilizers" (NY/T3174-2017).
5 Product application and effect
The application methods of citrus fruit sugar-enhancing fertilizer products are mainly drip irrigation, flushing, spraying or drone application, which can be applied alone or mixed with other fertilizers, additives or pesticides. The application time is generally in the late flowering stage of citrus, the expansion stage of young fruits and the early stage of fruit veraison. When mixing, take a small amount for the test first, if no precipitation or odor occurs, it can be mixed according to the principle of dilution one by one and sequential addition.
Generally speaking, when the sugar-enhancing fertilizer product is drenched, the dilution factor is 300~500 times, and the root application can be carried out on fruit trees of different ages. For 1~3-year-old fruit trees, the amount of diluent is 3~5 L/plant, for 3~5-year-old fruit trees, the amount of diluent is 8~10 L/plant, for 5~10-year-old fruit trees, the amount of diluent is 13~15 L/plant, and for fruit trees over 10 years, the amount of diluent is 15~20 L/plant. Drip irrigation is usually applied at a dosage of 2~8 kg/hm 2. The dilution factor is 500~1 000 times when spraying with a sprayer, and 5~20 times when spraying with a drone. Spraying principle: the sugar-increasing fertilizer is fully sprayed to the front and back of the citrus fruit surface and leaves, so that the leaf surface is fully moistened, but there is no water droplets; special attention should be paid to spraying the leaves and fruits in the middle of the citrus canopy to ensure that the spraying is uniform, so as to achieve a better fruit sugar effect.
In this laboratory, three sugar-enhancing fertilizers (high-phosphorus and potassium-type sugar-enhancing fertilizers, high-calcium and magnesium-type sugar-enhancing fertilizers, and high-sulfur potassium sugar-enhancing fertilizers) were selected to carry out the application effect test of ordinary compound fertilizers on sugar oranges in Zhengguo Town, Zengcheng District, Guangzhou City. The results showed (Table 2) that compared with the common compound fertilizer treatment, the three sugar-enhancing fertilizer treatments could significantly increase the soluble solids, soluble sugar, vitamin C content and sugar-acid ratio in sugar orange fruits, but there was no significant difference in the titratable acid content in the fruits. Among the three kinds of sugar-enhancing fertilizers, the effect of high-phosphorus-potassium and high-sulfur-potassium sugar-enhancing fertilizers was more obvious, and the sugar-acid ratio was significantly higher than that of ordinary compound fertilizer treatment and high-calcium and magnesium sugar-enhancing fertilizer treatment, which had a better taste. The results can provide a scientific basis for the further promotion of citrus sugar-enhancing fertilizers. Subsequently, sugar-enhancing fertilizers can be applied to other citrus varieties and other crops such as tomatoes and grapes to further explore their sugar-enhancing effects in different crops.
Table 2 Effects of different fertilizer treatments on fruit quality of sugar orange
Note: Different lowercase letters in the same column indicate significant differences (P<0.05).