Phosphate fertilizer is suitable for all soil types (acidic, neutral, alkaline, saline), but most effective on non-acidic or less acidic soils …
Read more: >> Phosphorus disorder
1. Types of soil and phosphorus uptake environment of plants
Vietnam's soil is divided into 11 main groups, the ratio of the areas of the soil groups is as follows: Sandy soil 1.70%, alluvial soil 10.81%, saline soil 4.05%, alum soil 5.92%, gray soil 7.47%, valley soil 1.20%, peat soil 0.80%, feralite soil on basic and neutral magma rock 8.53%, other feralite 47.09%, feralite humus on mountain 11, 14%, soil erosion inert stone and gravel 1.29%.
PHKCl value of some major soil groups: Sandy soil 5,5 – 6,5; saline soils 5,5 – 6,5; acid sulfate soil 2,5 – 4,5; alluvial soil 4,5 – 6,0; glay soil 4.0 – 5.0; faded gray soil 4.0 – 5.0; feralite soil 4.0 – 4.5. Most plants grow only well within a certain pHKCl limit; pHKCl < 3 và > 8 will be very limited for many crops; pHKCl = 3 – 4 is moderately limited and pHKCl = 4 – 5,5 is low.
Plants that are sensitive to high pH include cabbage, cotton, sugar beets, sugarcane, etc., which grow well on soil with a pH of 7-8. Group of plants that are sensitive to high pH includes wheat, corn, soybean, peanuts. , sunflower, cucumber, onion … grow best on soil with pH = 6 – 7. Group of plants less sensitive to high pH are tomatoes, carrots, rice, sorghum, cassava, potatoes, sweet potatoes, flax, coffee, pepper, orange, tangerine, longan, watermelon … can grow in the range of pH = 4,5 – 7,5 and most suitable pH = 5,5 – 6,0. The group of plants sensitive to low pH is tea, pineapple, and many green manure crops … best grown on acidic soil pH = 4.5 – 5.5 and adversely affected on neutral and alkaline soils. It is clear that the soil is followed by liming and fertilizing to suit the tree, the soil and the weather.
Except for feralite (on limestone or basalt), alluvial soils of the Red River and the Mekong River have relatively high total phosphorus, most of the remaining soil groups in Vietnam are poor phosphorus. The pH range of the soil is most favorable for phosphorus to be dissolved and the plant is easily absorbed from 5.2 to 6.5. When the pHKCl soil is below 4.5, the soil forms iron phosphate, aluminum phosphate is difficult to dissolve, affecting the efficiency of phosphate fertilizer, so it is necessary to apply lime.
The amount of lime applied to improve the soil depends on the type of plant and the soil composition is light or heavy: very acidic soil pHKCl <3.5 to apply 1.0 - 5.0 tons of CaO / ha, acidic soil is much pHKCl = 3 , 5 - 4.5 applied 0.7 - 2.0 tons, acidic soil pHKCl = 4.5 - 5.5 applied 0.5 - 1.0 tons. The amount of lime contained in the superphosphate or calcined phosphate fertilizer is only meant to provide calcium nutrition to the plants but little to improve the acid soil.
The research results show that phosphorus in Vietnam soil is mainly in the form of iron phosphate 3; This form of wet rice can be used (due to iron removal, phosphorus release), but will be difficult for upland crops. The easiest aspirate is water soluble; Phosphorus adsorption plant H2PO4 – at low pHKCl and HPO42 – at high pHKCl. Phosphorus-absorbing plants are very weak at seedling stage, so they need to be lined with easily soluble phosphate fertilizers such as superphosphate, DAP … to provide plants in time.
2. Advantages and limitations of each type of phosphate
-Supe phosphate provides phosphorus, calcium and sulfur to plants. Chemical formula: Ca (H2PO4) 2.H2O + 2 CaSO4 + 2H2O + free phosphoric acid 2%. Phosphate content 15,0 – 16,5% P2O5, 11 – 12% sulfur (S) and 22 – 23% CaO. Phosphate fertilizer is suitable for all soil types (acidic, neutral, alkaline, saline), but it is most effective on non-acidic or less acidic soils (pH = 5.6 – 6.5) with all type tree; Can be used to fertilize lining, top dressing; Can be applied to soil or mixed with water for irrigation. Due to its water-soluble nature and being quickly absorbed by plants, superphosphate is very suitable for short-term crops such as beans, vegetables, medicinal plants, corn, tobacco … and sulfur-rich plants such as mustard oil, kohlrabi, cabbage, cauliflower, beans …
-Fusing melting slightly soluble in water, soluble in weak acids (citric acid 2%). Theoretical formula: 4 (Ca, Mg) O.P2O5 + 5 (Ca, Mg) O.P2O5.SiO2. Fused phosphate has 15 – 16% P2O5, 15 – 18% MgO, 28 – 34% CaO and 24 – 30% SiO2. Fused phosphorus fertilizer is suitable for acid soil, washed out, hilly, infertile soil, old alluvial soil; with fruit trees, perennial industrial trees, legumes, green manure crops …
Do not apply fused phosphate on slightly alkaline, saline or neutral alluvial soils. Fused phosphate can be applied on acid sulphate soil or alum contaminated, but on this soil, natural phosphorus fertilizer is more beneficial in price and alkaline soil is not lacking in magnesium. Phosphate in molten phosphate can only be converted into soluble form under acidic and organic soils.
In many cases, superphosphate appears to be superior to other types of phosphorus due to the sulfur (S) element in the fertilizer. Even in acid sulphate soils, saline soils also show superiority compared to other types of phosphate thanks to gypsum composition (CaSO4). The advantage of fused phosphate can be masked by sulfur deficiency (S) even when fertilizing on degraded soils of silicon (Si) and magnesium (Mg).
In the process of production, the cultivation industry has formed major commodity areas that are difficult to replace such as rice, maize, peanuts, tea, coffee, pepper, fruit trees, vegetables … because of their adaptability. and comparative advantage in economic efficiency. Therefore, specific fertilizers are suitable for the soil and plants cannot be replaced. Along with some other physiological sour fertilizers such as potassium chloride, potassium sulfate, ammonium sulfate … phosphate superphosphate has been used for decades and still promote good effect.
The long-term use of superphosphate will either acidify soil or fused phosphate will increase soil pH without long-term experiments to prove it on humid tropics in Vietnam. There have been lessons from around the world for the long-term use of sulfur-free phosphorus fertilizers that have led to severe sulfur deficiency for plants, which then adds sulfur to the fertilizer; This is a very unreasonable and expensive job.
3. The method of using phosphorus fertilizers with high efficiency
Phosphate fertilizer of all kinds is precious and needs to be used in order to achieve high efficiency. The problem is to apply the right soil, the right tree and the period of growth and development of the tree, the right dose and the right weather. When applying phosphorus to crops, it is necessary to consider the status of phosphorus in the soil, types of crops, and fertilizers; concentrated fertilization, composting with compost to fertilize; Apply the balanced fertilizer with N and K2O. Based on the season to fertilize, the spring rice dose is higher than the crop; Based on the structure of the crop to fertilize, if the previous crop was legumes, sweet potatoes … have applied a lot of phosphorus, then in the spring rice crop a little amount of fertilizer needs to be reduced. To promote the advantages of two types of phosphate, we should mix these two fertilizers together in a suitable proportion or produce NPK containing both types of phosphorus.
Above are some advice for farmers to use the most effective phosphate fertilizer based on scientific results achieved in our country in the specialties of soil and plant nutrition, crop science …
Source Author group (vaas.org.vn)
Source link
