The Role of Nitrogen Fertilizer, Why Rice Should Not Be Over-Fertilized, and How to Apply It Efficiently to Vegetables

Nitrogen is one of the three major elements required as nutrients during crop growth. Nitrogen fertilizer is a chemical fertilizer containing the crop nutrient element nitrogen. Applying nitrogen fertilizer can not only increase the yield of agricultural products but also improve their quality. A lack of nitrogen fertilizer affects the synthesis of proteins and amino acids in crops, and also reduces photosynthesis, ultimately leading to lower yield and poorer quality. So, what types of nitrogen fertilizer are there? What specific effects do they have? Why should rice not be over-fertilized? How can nitrogen fertilizer be applied to vegetables for good results? How should nitrogen fertilizer be mixed and applied?

I. Types of nitrogen fertilizer currently available

Nitrogen fertilizers include animal-based nitrogen fertilizers and plant-based nitrogen fertilizers:

1. Human feces and urine, manure from horses, cattle, sheep, and pigs, fish fertilizer, and horse hooves are animal-based nitrogen fertilizers;

2. Sesame residue, soybean cake, rapeseed cake, and cottonseed cake are plant-based nitrogen fertilizers.

Both of the above categories are organic fertilizers.

3. Mineral nitrogen fertilizer, also known as inorganic fertilizer

Ammonium sulfate, ammonium nitrate, urea, and ammonia water are all quick-acting nitrogen fertilizers, usually used for foliar topdressing. If frequently used for root fertilization, they can easily cause soil compaction.  

II. What effects does nitrogen fertilizer have?

The main effects of nitrogen fertilizer are to promote vegetative growth, increase chlorophyll, and make plants thrive with lush branches and leaves, deep green leaf color, larger flowers, and plump seeds. Specifically, it has the following effects:

1. Regulating flower quantity

To overcome the alternate bearing of apple orchards, in an off year, 5-6 weeks after flowering (the critical period for apple flower bud differentiation, when new shoot growth slows or stops and leaf nitrogen content shows a declining trend), spray 0.5% urea solution on the leaves twice in succession. This can increase leaf nitrogen content, speed up new shoot growth, inhibit flower bud differentiation, and bring the flower quantity in an on year to an appropriate level.

2. Flower and fruit thinning

The floral organs of peach trees are relatively sensitive to urea, but the fruit surface response is relatively slow. Therefore, foreign studies used urea to conduct flower and fruit thinning trials on peaches and nectarines. The results showed that flower and fruit thinning of peaches and nectarines requires a relatively high concentration (7.4%) to show good results, with the most suitable concentration being 8%-12%. Within 1—2 weeks after spraying, the purpose of flower and fruit thinning can be achieved. However, the responses under different soil conditions, at different times, and among different varieties still require further testing.

3. Rice seed production

In hybrid rice seed production technology, in order to increase the outcrossing rate of the parents so as to increase hybrid rice seed production or sterile line seed multiplication, gibberellin is generally sprayed on the female parent to reduce the degree of neck enclosure or make it fully emerge; or it is sprayed on both parents to regulate their growth so that their flowering periods are synchronized. Because gibberellin is relatively expensive, using it for seed production costs more. People experimented with urea instead of gibberellin. Using 1.5%-2% urea at the peak booting stage and the initial heading stage (20% heading), the seed multiplication effect was similar to that of gibberellin, and it did not increase plant height.

4. Pest control

Using urea, laundry detergent, and clean water in a 4:1:400 ratio, after stirring and mixing evenly, it can prevent pests such as aphids, red spiders, and cabbage caterpillars on fruit trees, vegetables, and cotton, with a killing effect of more than 90%.

5. Urea iron fertilizer

Urea, in the form of a complex, forms chelated iron with Fe2+. This organic iron fertilizer has a low cost and is very effective in preventing iron deficiency chlorosis. In addition, adding 0.3% urea when spraying 0.3% ferrous sulfate on the leaves gives better chlorosis control than spraying 0.3% ferrous sulfate alone.

III. Why should rice not be over-fertilized?

Nitrogen fertilizer is one of the essential nutrient elements in the rice growth process and plays an important role in increasing crop yield, but excessive application will have the opposite effect. The following 4 hazards are the harmful consequences caused by applying too much nitrogen fertilizer to rice. It is hoped that farmer friends will understand them correctly and apply fertilizer scientifically.

1. Empty grains

If too much nitrogen fertilizer is applied during the rice tillering stage, the aboveground part will grow too quickly while root growth slows down, causing many tillers to become ineffective tillers because they have no roots to supply them, resulting in empty grains.

2. Pests and diseases

During the growth period, applying too much nitrogen fertilizer promotes rapid growth of rice plants, but they are very weak, and the plant shape becomes relatively taller, causing shading of the lower part in the early stage. The humidity and temperature in the lower part are relatively increased, and combined with poor ventilation, it is very easy to trigger pests and diseases, providing favorable conditions for their reproduction.

3. Yield reduction

During the growth period, applying too much nitrogen fertilizer causes large amounts of nitrate nitrogen to accumulate in rice, which can easily cause poisoning. The lower leaves die early, and the root system ages easily. In addition, the stems of ineffective tillers are weak and prone to lodging, so yield reduction is unavoidable.

4. Affecting taste

Applying too much nitrogen fertilizer increases the protein content in rice, thereby affecting quality and taste.

Therefore, in the production and cultivation of rice, nitrogen fertilizer should not be applied in a one-sided way, and even less should excessive nitrogen fertilizer be applied. It is necessary to scientifically increase the application of biological bacterial fertilizer, phosphorus and potassium fertilizers, and organic fertilizers.

IV. How can nitrogen fertilizer be applied to vegetables for good results?

The macroelement nitrogen is a component of amino acids and chlorophyll in plants and plays an important role in the growth of crop plants, with leafy vegetables having the greatest demand throughout the entire growth period. So how can nitrogen fertilizer be applied to vegetables for good results?

According to surveys, the way farmers habitually apply nitrogen fertilizer (taking urea as an example) is mostly broadcasting on the soil surface followed by watering, or flushing with water. Farmers often think that this application method helps crops absorb nutrients quickly and improves fertilizer use efficiency.

In fact, this is not the case. With this fertilization method, the seasonal utilization rate of nitrogen fertilizer is only 30%-40%, and the remaining 60%-70% of nitrogen is wasted through volatilization, leaching, and other forms. Increasing the amount of nitrogen fertilizer year after year not only fails to meet the crop's demand for nitrogen during its peak nitrogen requirement period, but also damages soil structure and increases fertilization costs.

Effective ways to improve the nitrogen fertilizer utilization rate of vegetables:

1. Deep application followed by soil covering

A depth of 7-10 cm is appropriate, and after application, cover firmly with soil. Deep application with soil covering can effectively extend the fertilizer effect by nearly double and can effectively improve utilization rate. Deep application of base fertilizer, deep application of seed fertilizer, and deep application of topdressing.

2. Apply less each time and more often, and apply in appropriate amounts

Because the effective period of nitrogen fertilizer is relatively short, it is necessary to apply different amounts of nitrogen fertilizer each time according to the different growth stages of different crops. Never apply it all at once, to avoid unnecessary loss and waste of nitrogen fertilizer and excessive plant growth.

3. Apply according to the soil

According to the nature of the land, choose different nitrogen fertilizers for different farmlands, and for farmlands with different soil textures, choose different amounts and frequencies of use. For example, paddy fields can use ammonium bicarbonate. Sandy soil loses water seriously, so a smaller amount should be used each time and applied more times. Urea needs to be applied 3-10 days in advance. Depending on the season and temperature, the higher the temperature, the shorter the time. Apply about 7 days in advance, and only after transformation can it be absorbed by plants. Therefore, it is not advisable to water immediately after application.

In addition, there is basically no difference in urea, and it is also very difficult to adulterate. The main things to look at are the uniformity of the urea granules, that there is not a lot of powder, and that it has not been soaked in water or become damp in the bag. The use effect of urea from various manufacturers is basically no different; the only difference in price comes from different freight, labor, and sales policies among manufacturers. Therefore, it is recommended that farmers use cheaper urea and spend less money unnecessarily.

4. Apply slow-release nitrogen fertilizer

Slow-release nitrogen fertilizer can effectively extend the effective period of nitrogen fertilizer, but slow-release nitrogen fertilizer is generally more expensive, and the slow-release nitrogen fertilizer market is mixed with good and bad products. Under the drive of profit, many slow-release nitrogen fertilizers are concept fertilizers and do not play a true slow-release role. It is recommended to use slow-release nitrogen fertilizers from large manufacturers or with actual effects, and not to seek cheapness.

V. How should nitrogen fertilizer be mixed and applied?

1. Add an ammonium bicarbonate additive. Add the chemical assistant ammonium bicarbonate additive to ammonium bicarbonate in proportion and apply them together. This can effectively inhibit the decomposition and volatilization of nitrogen, thereby increasing the fertilizer efficiency utilization rate of ammonium bicarbonate by 3-4 times.

2. Mix in a nitrogen-fixing agent. Mix a nitrogen-fixing agent into nitrogen fertilizer in proportion and apply it deeply. The amount of nitrogen fixed can be increased by 1.5-2.0 times, and the nitrogen utilization rate can be increased by 10-30%.

3. Mix and apply urea with borax. Mix and apply urea and borax in a ratio of (400-500):1. This can significantly reduce ammonia volatilization loss, improve nitrogen utilization rate, and effectively prevent phenomena such as wheat grains not being plump, rapeseed flowering without setting seed, and cotton buds not opening.

4. Mix and apply urea with oxalic acid. For cotton base fertilizer, if a formula of 200 kg nitrogen fertilizer, 140 kg phosphorus fertilizer, 40 kg potassium fertilizer, and 5 kg oxalic acid is used, the nitrogen fertilizer utilization rate increases by 17.3%, and the nitrogen loss rate decreases by 25%.

The “four cannots” of mixing chemical fertilizers:

① Superphosphate cannot be mixed with alkaline fertilizers such as plant ash, lime nitrogen, and lime, otherwise the effectiveness of phosphorus will be reduced; sparingly soluble phosphate fertilizers such as phosphate rock powder and bone meal also cannot be mixed with alkaline fertilizers such as plant ash, lime nitrogen, and lime, otherwise because the organic acids in the soil are neutralized, the sparingly soluble phosphate fertilizer becomes even more difficult to dissolve, and crops cannot absorb and use it.

② Alkaline fertilizers such as calcium magnesium phosphate fertilizer cannot be mixed and applied with ammonium nitrogen fertilizers, because if alkaline fertilizers are mixed and applied with ammonium nitrogen fertilizers, ammonia volatilization will increase and losses will increase.

③ Chemical fertilizers cannot be mixed with bacterial fertilizers, because chemical fertilizers have strong water absorption, corrosiveness, and volatility. If mixed with bacterial microorganisms such as rhizobia, they will kill or inhibit living bacteria, making the bacterial fertilizer ineffective.

④ Undecomposed farmyard manure cannot be mixed and applied with ammonium nitrate. If mixed and applied with ammonium nitrate, the nitrogen in the undecomposed farmyard manure will be lost during the decomposition and rotting process; otherwise, the nitrogen in both will be damaged, reducing fertilizer efficiency.