What Are the Key Fertilization Techniques for Late Rice? A Detailed Explanation
Late rice is generally sown in mid-to-late June and harvested in early-to-mid October. In the same region, after the early rice is harvested, late rice can be planted right away, commonly known as double-cropping rice. The fertilization techniques for late rice have changed greatly from ancient times to the present, and many problems still exist today. Fertilization needs to follow the patterns of rice's demand for fertilizer and grasp the key technical points in order to maximize fertilizer use efficiency.
1. Fertilization methods of China's thousands of years of traditional farming
In the spring of 1909, Franklin H. King, a professor of agricultural physics at the University of Wisconsin in the United States, traveled across the ocean to China, Japan, and Korea, three East Asian countries, going deep into the vast rural countryside to understand why these countries could cultivate crops on very little land, support dense populations, and yet not destroy the natural environment, achieving sustainable development. He wrote the book "Farmers of Forty Centuries."
Through a great deal of visiting and firsthand experience, he discovered that in China's ancient traditional farming civilization, hardworking farmers could always make full use of all recyclable resources in nature, such as river (pond) silt, crop straw, withered plant branches and leaves, weeds and turf, fuel ash, human excrement and urine, barnyard manure from livestock and poultry bedding, animal bones, and so on, as fertilizer inputs, thereby obtaining agricultural products and ensuring the needs of daily life.
2. Current fertilization methods and their consequences
After the 1980s, with the rise of national industry, chemical fertilizers gradually replaced farmyard organic fertilizers as the main fertilizer source due to their advantages of small dosage, fast fertilizer effect, cleanliness and hygiene, and ease of application, making great contributions to China's agricultural yield increases.
Due to biased understanding, farmers gradually abandoned farmyard organic fertilizers and turned to heavy reliance on chemical fertilizers. The long-term, year-after-year use of chemical fertilizers has led to a gradual decline in soil organic matter content, destruction of soil microbial community structure, increased occurrence of pests and diseases, soil acidification or salinization, nutrient imbalance, deterioration of agricultural product quality, poor taste and flavor, and various problems such as water pollution, soil pollution, and heavy metal pollution following one after another.
3. Current problems in rice paddies
(1) Fertilizer application rates are increasing year by year, but yields are increasing slowly or fertilizer increases without yield increase. In the 1980s, 15 jin of urea per mu basically met the fertilizer demand for one season of rice, but now it has increased to 40 jin, yet the yield per mu is still around 1200 jin. This is Teacher Cai's real experience.
(2) Soil water and fertilizer retention capacity has declined, making it prone to fertilizer loss and premature aging. This year, many cases of yellowing leaf tips at the booting stage have appeared. China's fertilizer utilization rate is 30%, while that of developed countries is 50-60%.
(3) Various physiological diseases are showing a trend of frequent occurrence, with nutrient deficiencies, herbicide phytotoxicity, and the like being commonly seen. The reduction in organic matter content increases the risk of herbicide phytotoxicity.
(4) One-sided fertilization is common, with emphasis on nitrogen and neglect of phosphorus and potassium, and insufficient medium and trace element fertilizers.
(5) Emphasis is placed on using the land rather than caring for it. Some large-scale operators sign land contracts on a yearly basis and do not pay attention to the consequences for the next year, making the soil increasingly demanding and increasingly impoverished; plowing is becoming shallower, and mechanical compaction and years of sedimentation are making the plow layer increasingly thin.
4. Fertilizer demand patterns of rice
The approximate demand ratio of rice for the major elements nitrogen, phosphorus, and potassium is about 1:0.5:0.8-1. Rice has 2 peak nutrient uptake periods in its life cycle, namely the tillering stage and the booting stage, and its nutrient demand ratios differ between them. At the tillering stage, nitrogen is dominant, along with phosphorus and potassium fertilizer; at the booting stage, potassium is dominant, followed by nitrogen, and then phosphorus.
(1) Fertilization principles
From the perspective of using and nurturing the land and sustainable soil development, the correct fertilization principle should be based mainly on organic fertilizer, accounting for about 60%, with chemical fertilizer as a supplement, accounting for about 40%.
(2) Increasing fertilizer sources
Under current conditions, feasible measures to increase organic fertilizer sources in rice production include: vigorously developing the planting of green manure during the slack farming season, returning crushed straw to the field, and applying straw decomposing agents or quicklime in combination.
(3) Soil testing and formulated fertilization, balanced fertilization
According to the local soil classification characteristics, targeted soil sampling should be carried out, and fertilization should be reasonably applied according to the rice yield target, soil texture, fertilizer demand characteristics at different growth stages of rice, and the fertilizer demand capacity of the variety, with appropriate supplementation of medium and trace element fertilizers. For early rice in the south after transplanting when temperatures are low, or for cold-waterlogged fields in mountainous areas, and fields showing slow green recovery or stiff seedling phenomena, zinc fertilizer can be appropriately applied as a topdressing to promote seedling growth and prevent stiff seedlings. For some magnesium-deficient fields with strong leaching, about 20 jin of magnesium sulfate per mu should be applied in the base fertilizer or when topdressing the green-recovery and tillering fertilizer.
5. Key points of rice fertilization
On the basis of applying organic fertilizer, apply sufficient base fertilizer. In the short term, because soil organic matter content is low, the effects of organic fertilizer cannot take effect immediately, so the base fertilizer should still be mainly compound fertilizer. Taking current southern soils as an example, apply 50-60 jin per mu of 45% ternary compound fertilizer (3 x 15 balanced type or with an 18-20:10:15-17 ratio), 2 kg of zinc fertilizer (to prevent stiff seedlings and failure to grow after early rice transplanting), and 400-500 g of boron fertilizer (to prevent "dry standing blight") as base fertilizer. For late rice, because of straw return, the carbon-to-nitrogen ratio needs to be adjusted to a standard of 25:1 to meet the nitrogen demand of microorganisms when decomposing straw and avoid competing with the rice seedlings for nitrogen. Therefore, the base fertilizer should also include 10 jin of urea per mu and 2 kg of straw decomposing agent containing 0.5 hundred million/g of bacteria. Later, as organic matter content increases, the amount of chemical fertilizer can be adjusted and appropriately reduced.
(1) Apply tillering fertilizer early
Apply tillering fertilizer as an early topdressing. In double-cropping rice areas, the tillering peak of rice appears 15-20 days after transplanting, and in single-cropping rice areas it appears at 20-25 days. Tillers that appear before this have a high rate of forming productive panicles. Tillers that appear afterward have a lower rate of forming productive panicles, not only competing and wasting nutrients but also creating conditions for later outbreaks of sheath blight and planthoppers. In production, tillering fertilizer should be applied promptly 5-7 days after transplanting early rice (4-5 days after transplanting late rice), with about 20-25 jin of urea per mu plus herbicide.
For shallow sandy fields with poor water and fertilizer retention capacity, in order to prevent fertilizer loss and improve utilization efficiency, it is recommended to apply 15 jin of urea and 20 jin of compound fertilizer per mu.
For fields with insufficient basic seedlings after transplanting, in order to promote early growth and rapid development, the fertilization amount should be appropriately increased, and 30-40 g of 15% paclobutrazol and 1 kg of zinc fertilizer should be added per mu to promote early and abundant tillering.
Because direct-seeded fields have more basic seedlings, the application amount of major element fertilizers should be 20-30% more than that of seedling-throwing fields.
(2) Reasonable field drying
Field drying of rice promotes soil permeability, allows toxic and harmful gases to escape, enhances root activity, promotes new root growth, and controls ineffective tillering. Its tillering control effect is mainly achieved by inhibiting rice's absorption of fertilizer and water. During field drying, nitrogen volatilization and escape inevitably occur, wasting part of the fertilizer, so field drying should be reasonably controlled according to soil texture and rice growth conditions.
For shallow sandy fields and other rice fields with poor water and fertilizer retention that are prone to fertilizer loss and premature aging, as well as direct-seeded fields, field drying should not be too heavy and should be light; for deep mud fields, fields with excessive nitrogen fertilizer, and fields with excessively vigorous growth, heavier field drying can be appropriate.
(3) Skillfully apply panicle fertilizer
After field drying of rice, panicle fertilizer should be applied promptly to promote young panicle development. Panicle fertilizer should preferably be applied from row closure to before jointing, and preferably at stages 1-2 of young panicle differentiation, with about 20 jin of potassium chloride per mu (sandy fields should apply it in 2 split applications to reduce leaching loss), and 8-10 jin of urea (for shallow sandy fields with poor water and fertilizer retention, 20-25 jin of 45% compound fertilizer can be used instead). For fields or varieties prone to lodging, 40-60 g per mu of Zhengzhou Chemical's rice "Xiaopangdun" can be mixed in to dwarf the plants and enhance lodging resistance.
(4) Apply grain fertilizer as conditions warrant.
At 5-7 days before heading, some leaf and panicle green color will fade. If it becomes too pale, this is unfavorable for later grain filling and maintenance of green leaves. At this time, 3-5 jin of urea per mu should be applied to avoid too-rapid premature aging of leaves after heading.
(5) Foliar topdressing
During the jointing to grain-filling stage of rice, in combination with disease prevention and pest control spraying, foliar fertilizer can be mixed in for root-external topdressing. Before heading, 30-50 g of 15% boron fertilizer and 150-200 g of potassium dihydrogen phosphate can be sprayed per mu each time, and once more when 50-80% of heading is reached, for a total of 2 applications. After heading, 150-200 g of potassium dihydrogen phosphate and 250-300 g of urea can be used per mu. Where conditions permit, regulators such as brassinolide, cytokinin, and diethyl aminoethyl hexanoate, as well as silicon-potassium foliar fertilizers, can also be promoted in combination.
Due to differences in soil fertility levels and textures across regions, the fertilizer amounts are for reference only. Each region should reasonably adjust the fertilization amount according to local soil fertility, variety fertilizer demand characteristics, and target yield. There may be errors or inappropriate points in this manuscript; discussion, criticism, and correction are welcome.