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Rice plant nutrition and Rice Fertilizer

Author : Miss Yang Date : 7/27/2011 7:58:12 AM
rice fertilizer







Fertilizer Management in Rice Cultivation

Booklet No. 36

Manuers & Fertilizers: MFS-22

Contents

Preface

I.    Introduction

II.   Symptoms of Nutrient Deficiencies in Rice

III. Fertilizer Management in Low Land Condition

IV. Fertilizer Management in Upland Rice

V.   Integrated Nutrient Management.

 

Preface

 

Unscientific approach to fertilizer usage will adversely affect the crop production. A crop like rice is greatly influenced by the soil condition and availability of nutrients from the soil. The proper management of the fertilizers is the only method to make the nutrients available to rice crop.

 

This booklet describes all the aspect of fertilizer management in rice viz. diagnosis of nutrient deficiency, nitrogenous, phosphatic and potassic fertilizer management and fertilizer management of low land and upland rice.

 

Dr. K. T. Chandy Agricultural & Environmental Education

 

I. Introduction

 

Growth and yield of rice crop is the result of its interaction with environmental factors, soil conditions and availability of water and nutrients from the soil. Rice crop needs seventeen essential nutrients. Most important among them are nitrogen, phosphorus: potassium, iron, manganese, zinc and copper. These nutrients are supplied to rice crop through the soil in the form of fertilizers and manures. To provide the required amount of nutrients to rice in time at cheaper rate is of paramount importance and equally important is the proper management of the application practices for economic utilization of fertilizers supplying the important nutrients according to the varietal, soil and agro-climatic factors of low as well as up- land conditions of rice cultivation. Familiarity with the most common visual deficiency symptoms of nutrients in rice crop is also essential for proper fertilizer management.

 

II. Symptoms of Nutrient Deficiencies in Rice

 

Deficiency of a specific element in soil shows some peculiar characteristics of colour and abnormal growth in plants. The visible deficiency symptoms of nitrogen, phosphorus, potassium, iron, manganese, zinc and copper in rice crop are the following.

 

A. Nitrogen

1. Older leaves become orange yellow and die from the tip downwards.

2. The new leaves are thin, short and stiff.

3. Nitrogen deficiency reduces the plant height and number of tillers.

4. Roots are few, thin and elongated.

 

B. Phosphorus

1. The whole plant will become bluish green in colour.

2. In acute deficiency, older leaves die quickly and become purple or pinkish in colour.

3. Sometimes few pinkish spots are observed on the stem.

4. The roots are thin, long and brown.

5. Plant growth will be stunted.

 

C. Potassium

1. The plants look short and droopy.

2. The upper leaves become deep green in colour and wavy.

3. Under prolonged deficiency, yellow coloured portions in between the viens of leaves, called interveinal chlorosis, are observed on the middle leaves and the veins look green in colour.

4. the upper leaves, except the top most, develop dark brown spots.

5. Sometimes scorching or burning of .tips and margins of the leaves is observed.

6. The lower leaves turn dirty yellow in colour and gradually die.

7. If deficiency of potassium occurs during flowering or just before

flowering, the panicle will be longer but thinner than the normal ones.

8. Necrotic spots (dead cells in a lesion) are found on the panicles.

 

D. Iron

Symptoms of iron deficiency are first observed in young leaves soon after the emergence of the second leaf in the seedling i.e. 7 to 10 days after germination.

1. The young leaves appear chlorotic and whitish and wither.

2. If deficiency is prolonged the leaf apex dies.

3. In moderate deficiency, mild and interveinal chlorosis appears.

 

E. Manganese

Manganese deficiency in rice appears soon after the third leaf unrolls.

1. Chlorotic mottling (diversified spots of yellow colour) occurs.

2. A fine patch of green and chlorotic cells appears at some distance away from the basal part of the third leaf.

3. In prolonged deficiency the patches increase in number, spread and coalesce forming large irregular lesions which later form interveinal chlorotic stripping.

4. After 5 to 6 weeks of sowing the chlorotic areas become necrotic and turn reddish brown in colour.

5. The apex and margin of the affected leaves wither and dry.

 

F. Zinc

Zinc deficiency in rice is more serious in low lying portions of fields and affected areas have a. higher water table during the rainy season. The symptoms appear two weeks after transplanting.

 

1. Older leaves become reddish brown.

2. The roots become sparse and brown in colour.

3. The base of the actively growing leaves become chlorotic.

4. In mid season crop or in ill-drained fields, mid-rib of the leaf will be bleached and superimposed by bronzing of the leaf. This is called khaira disease.

5. Scattered and dark brown spots which later coalesce and extend over whole leaf are found.

 

G. Copper

1. Leaves become chlorotic near the tip.

2. The chlorosis will extend downward along both sides of the mid-rib, followed by dark brown necrosis of the tip.

3. The new leaves remain rolled and appear needle shaped.

 

III. Fertilizer Management in Low Land Rice

 

Fertilizer management in low land rice is different from upland rice due to continuous submergence of the puddled field. Puddled and submerged condition brings about physical, chemical and biological changes in the soil. Physically, the structure of the soil is changed and water-holding capacity is increased. Chemically, the soil pH shifts more towards neutral. Under water logging condition, ammonium form of nitrogen is more stable and becomes more available to rice plants. Similarly availability of phosphorus, iron, manganese, aluminium and calcium also increases under puddled condition. Soil in puddled rice fields can be divided into two zones based on oxygen concentration: the upper oxidized layer of one centimeter from fresh irrigation water and the lower reduced zone. The former is called aerobic (presence of oxygen) and the latter anaerobic zone (absence of oxygen).

 

When nitrogenous fertilizers are applied in puddled and submerged condition they get oxidised to nitrate in the oxidized zone. But as soon as the nitrate is leached down to the reduced zone it degenerates into gaseous form of nitrogen and is lost into the atmosphere. These losses can be reduced to the minimum by adopting proper management practices of fertilizer application in low land rice cultivation.

 

A. Nitrogen management

 

Nitrogenous fertilizers play a major role in the increase of rice yields. Actually 2 kg of nitrogen is enough to produce 100 kg of rice. However, often we have to apply either more or less than this amount depending on the nitrogen already present in the soil. Experiments show that the minimum required amount of nitrogen to be applied varies from 0.5 kg to 1.5 kg and the maximum amount varies from 2.7 kg to 5.9 kg per 100 kg of rice. However, if we consider the amount already present in the soil and also the required amount of nitrogen to be present in the soil (applied as well as what is already present in the soil) will range from 5.6 kg to 13.7 kg to produce 100 kg rice. Such variations are largely due to the interaction among various factors which influence the nitrogen- use efficiency by rice crop.

 

1. Factors affecting nitrogen-use efficiency

Factors like variety, climatic conditions, soil type, fertility and age of seedlings affect the nitrogen use efficiency.

 

a. Variety

The high yielding dwarf varieties require higher dose of nitrogen than the traditional tall varieties.

b. Climatic conditions

In the cloudy monsoon weather the response of rice to nitrogen application is less because of less photosynthesis due to reduced availability of sunlight. In the rabi season, response is more because of the availability of sunshine resulting in greater photosynthesis.

 

c. Soil type

Leaching is minimum in clay soil and maximum in sandy soil. . Hence nitrogenous fertilizers are applied in maximum number of split doses in sandy soil conditions, whereas this need not be in the case of clay soils. In clay soils nitrogen applied is held securely by clay particles.

 

d. Fertility status

Soils with poor fertility status obviously require higher doses of nitrogen as compared to rich fertile soils.

 

e. Age of seedlings

For seedlings transplanted after 35 days tillering is reduced. This can be compensated to a certain extent by supporting higher rates of nitrogen which enhances quick tillering.

 

2. Sources of nitrogen

Generally, rice prefers ammonical fertilizers such as ammonium sulphate, ammonium chloride and diammonium phosphate (DAP). These are quickly fixed by the clay particles of the soil. Urea can also be used but it is easily dissolved in water and quickly leached down. Compared to ammonical fertilizers, it takes more time (about 48 hours) to convert itself into ammonical form for absorption by the plant. Among the ammonical fertilizers, DAP is better for basal application than all other fertilizers.

 

3. Amount of yield expected

A rice variety which yields 60 quintals of grains and 90 quintals of straw from one hectare, requires 140 kg of nitrogen. Under Indian conditions a good crop of rice can be harvested by applying 80 to 100 kg of 1) nitrogen. The higher the yield expected, the greater will be the requirement of nitrogenous fertilizers.

 

4. Profitability

At per the market rates of 1990, one kg of nitrogen costs Rs. 5.20 and one kg rice sells at Rs. 1.65. To get back the cost of fertilizer, the farmer must get an increase of 5 kg of rice for every kg of nitrogen applied. The cost-benefit ratio should be 1:2 as a criterion to determine the optimum dose, i.e. the farmer should get at least Rs. 2.00 for every rupee spent on fertilizer cost. Under such situations, for every kg of nitrogen applied a return of 10 kg of rice is desirable for economic cultivation. Experiments have shown that for the kharif season crop it is not desirable to apply more than 1120 Kg N/ha, whereas in rabi season it can be raised up to 160 kg N/ha.

 

5. Soil testing

Another ideal practice to apply the correct amount of fertilizers is on the basis of a soil test. According to the availability in soil as determined by soil testing, the required amount of nitrogen is applied (see table 1).

 

6. Number of doses

The application of nitrogen in two or three split doses increases the utilization efficiency as compared with single basal application at transplanting.

 

Table 1: Nitrogen requirement in rice based on soil test and expected yield.

 

Sl. No.

Amount of nitrogen available kg/ha

With yield of 30 q/ha

With yield of 40 q/ha

With yield of 50 q/ha

With yield of 60 q/ha

1

100

83

123

*2

*1

2

200

45

85

125

--

3

300

20

48

88

128

4

400

15

20

50

90

 

1 Such return is not possible beyond certain limits.

2 In less ferule soil maximum yield is not much profitable.

 

7. Time of application

The basal dose is best applied by broadcasting the fertilizer at final puddling followed by ploughing and leveling so that the nitrogen fertilizers get incorporated in to the soil. The first top dressing should be given at tillering stage i.e. about 10-15 days after transplanting for early varieties and 20-25 days after transplanting for medium duration rice varieties. The last top dressing should be given at panicle initiation stage i.e. 20 to 25 days before flowering or 60 to 65 days after transplanting. In relation to dose, half of the nitrogen should be given at the time of transplanting, 1/4th at the time of tillering and remaining 1/4th at panicle initiation stage. In the case of high rainfall areas or areas having sandy soil, nitrogen should be given four split doses i.e. 1/4th at transplanting, 1/4th at tillering, 1/4th at panicle initiation and remaining at head appearance of ears.

 

8. Method of application

Before applying fertilizer as top dressing, water should be drained out from the field. After 24 hours of draining out, the fertilizer should be applied. Application on the moist soil, followed by an interculture operation, helps in mixing the fertilizer with soil and preventing its loss. The water should be refilled after 24 to 48 hours of top dressing. If draining the field before fertilizer application is not possible, fertilizer can be broadcasted in standing water followed by interculture operation. In this case water should not be allowed to go out of the field at least for 24 hours.

 

9. Guidelines for nitrogen application

While applying nitrogenous fertilizer following guidelines should be kept in mind so that maximum efficiency of fertilizer can be obtained.

 

a. Amount of nitrogen for one top dressing should not be more than 20-30 kg/ha at a time.

b. If soil is deficient in nitrogen, apply relatively more nitrogen at planting.

c. If soil is rich in nitrogen, small amount of nitrogen should be applied at transplanting.

d. If soil is permeable, avoid high doses of nitrogen at any time of application.

e. Early application of nitrogenous fertilizers promote tillering.

f. For less tillering rice varieties, more nitrogen at early stage of growth should be applied.

g. For long duration rice varieties, more nitrogen as topdressing  at various stages of growth should be applied.

h. The nitrogenous fertilizer should be incorporated 3-4 cm deep into the soil, so that nitrogen loss can be reduced.

i. Late application does not increase tillering, but increases grain yield by producing heavier panicles.

j. Late and heavy dose of nitrogen at panicle initiation more especially at booting stage, increases the protein content. (Booting stage is the growth stage when panicle with flower is enclosed by the sheath of the uppermost leaf).

K. In case of an incidence of bacterial leaf blight disease, (which is usually related to high dose of nitrogen) it should be given in more split doses and in less amount.

 

10. How to get maximum efficiency from nitrogenous fertilizers?

Nitrogen is an element that is easily lost from the soil in various forms. In warm climate gaseous loss of nitrogenous fertilizers is more common. Therefore, in Indian condition plants get only 30- 40% of total applied nitrogen fertilizer even if it is applied properly. As we know that nitrogen is required by plants up to flowering stage and nitrogen is leached down after it is dissolved in water, we can try to reduce its solubility in water. For this, urea the most commonly used nitrogenous fertilizer, is coated with insoluble materials like neem cake and coal tar. Even soil can be used for this purpose.

 

a. Neem cake coated urea

For 100 kg urea, 30 kg well-powdered neem cake and about 1 litre of kerosene oil is required. First, wet this urea with kerosene oil and spread neem cake powder over the heap of urea. Mix thoroughly all these ingredients so that neem cake powder adhere to urea granules. Neem coated urea should be applied to the field as early as possible before transplanting the rice. The whole amount is given only once in the field as a basal dose. No other split dose is required for the crop. This coated urea dissolves slowly and becomes available to plant in all the growth stages continuously.

 

b. Coal tar coated urea

For 100 kg urea, about 5 kg of coal tar and one and a half litre of kerosene is required. First of all coal tar is melted and allowed to cool down. Then it is mixed with kerosene oil thoroughly. Urea is spread in a thin layer. The mixture of coal tar and kerosene oil is sprinkled. Mix them till urea granules are covered by fine layer of coal tar. Afterward apply it like neem coated urea.

 

c. Soil urea mixture

Urea and slightly moist soil are mixed in the proportion of 1:6 and kept for 48 hours. Spread this mixture in the field before transplanting rice. Soil of this mixture serves in slow release of nitrogen. .

 

B. Phophorus management

There are two peak stages of absorption of phosphorus by rice plant: one is during vegetative stage and the other at reproductive stage (flowering stage). In vegetative stage phosphorus is absorbed during tillering stage. It is true that Indian soils are medium to rich in phosphorus content, but now the intensive cropping round the year has deprived the soil of its phosphorus reserves. It is therefore, now considered that phosphorus is a major constraint for successful rice production in India.

 

1. Sources of phophorus

Phosphatic fertilisers containing water soluble phosphorus such as single and double superphosphate are more efficient than other sources in all types of soil. The single superphosphate is used more widely as it is cheap and easily available. In acidic soils single superphosphate gets fixed rapidly and becomes unavailable to the plant In such cases finely ground rock phosphate should be applied which is also much cheaper than single super-phosphate.

 

2. Amount of phosphorus

Generally. phosphorus is applied at the rate of half of the nitrogen dose. The maximum phosphorus which can be applied to rice crop is 60 kg/ha. If the level of nitrogen is 80 kg/ha the phosphorus level may be kept 40 kg/ha. Now crop production, especially rice production, is no longer only for subsistence. Other basic needs of small farmer are also to be fulfilled from the same field where he has grown rice. Therefore, for getting more profit, it is necessary to get the soil tested and according to the availability of phosphorus in the soil, remaining amount can be added through fertilizers. The recommendation of amount of phosphorus application to the rice crop is given in table 2.

 

Table 2: Phosphorus application based on soil text and expected yield.

 

Sl.

No.

Phosphorus available in soil as Dete-

cted in soil testing kg/ha

Yield 30

 q/ha

Yield 40

 q/ha

Yield 50

 q/ha

Yield 60

 q/ha

1

5

82

117

--

--

2

10

64

99

132

--

3

20

23

57

92

126

4

30

20

33

53

87

5

40

15

20

30

46

 

 

Note: In poor fertile soil, going for maximum yield is not profitable.

 

3. Time and method of application

Phosphatic fertilisers are usually applied as basal dose just before transplanting. Phosphorus absorbed after tillering is not used by plant for increasing grain production. However, phosphorus absorbed during tillering stage is most efficiently utilised for grain production. Split application is beneficial because of the high mobility of phosphorus from old leaves to the new leaves. As phosphorus does not move in the soil, it should be applied near the root zone of plant. By nature, maximum amount of phosphorus can be fixed in the soil which will be released gradually. Therefore, the whole amount of recommended phosphorus is given to crops either at final phoughing or mixed with the seed which is to be used for sowing. Better results are obtained if phosphorus is applied a little below the seed in the soil. The emerging roots will be able to use this phosphorus easily.

 

C. Potassium management

Potash prevents lodging by providing mechanical strength to the plant and strengthens the defence mechanism of the plant against certain diseases. The prevalence of Helminthosporium disease in potash deficient rice crop serves as an example. In general, Indian soils are high in potash content. Still some amount of potash is to be applied for getting good yield as only 1-2% of total potash is readily available. Sometimes due to some reasons it will not become available to the plant even if it is sufficiently available in the soil. Compared with local and traditional varieties, high yielding varieties of rice remove 2 to 2.5 times more potash from soil. The main sources of potash used in India are muriate of potash and sulphate of potash only.

 

1. Amount of potash

Like phosphorus, potash is also applied at the rote of about half the dose of nitrogen. Dose exceeding 60 kg/ha will not prove more profitable. (See Table 3)

 

2. Time and method of application

Potash is applied as a basal dose in rice crop. Whole amount , of potash and phosphorus with half to one-fourth dose of nitrogen are applied together during [mal puddling.

 

 

Table 3: Recommended dose of K according to soil test and targeted yield.

(kg per ha)

Sl.No.

Potash availa

ble in soil as detected in soil testing (kg/ha)

With Yield of 30 q/ha

With Yield of 40 q/ha

With Yield of 50 q/ha

With Yield of 60 q/ha

1

100

43

63

--

--

2

200

27

47

67

--

3

300

20

30

50

70

4

400

15

27

47

67

5

500

10

15

33

54

 

Note: In poor fertile soil it is advisable that roe does not go for maximum yield.

 

D. Balanced nutrient management

One flower does not make a garland and, as such, only one nutrient cannot give a good yield. Therefore, application of a balanced combination of various essential nutrients is necessary for optimum yield. Experiments have revealed that application of nitrogen alone can double the yields but a combination of nitrogen, phosphorus and potash has greater effect than nitrogen alone. In general, phosphorus and potash are recommended to be half of the nitrogen dose. A combination of 100 kg nitrogen + 50 kg phosphorus and 50 kg potassium per hectare is believed to be optimum for the transplanted low land rice.

 

E. Micro-nutrient management

Intensive cropping, application of soil amendments in problematic soils and heavy dose of major nutrients particularly phosphorus have resulted in deficiency of several micro-nutrients, especially zinc, in rice fields. Application of lime corrects the acid soil but makes zinc unavailable to the rice plant. Generally rice plant shows the deficiencies of zinc, iron, manganese and copper.

 

For correcting the zinc deficiency, 25-30 kg/ha sulphate is mixed with 25-30 kg of fine soil and broadcast in the whole field at the time of final ploughing. In standing crop, if plants show deficiency, it can be corrected by spraying a mixture of zinc sulphate and lime. One kilogram of zinc sulphate and one kilogram of lime are dissolved in 5 litres of water, each in separate containers. After filtering, the solutions are mixed and 240 litres of water is added. This solution is sufficient for spraying one hectare crop. If results are not positive enough, the treatment may be repeated after IS days. Similarly, iron, manganese and copper can also be applied in the soil during final ploughing, if their deficiency is observed. These nutrients are applied in the form of, iron sulphate, manganese sulphate and copper sulphate, respectively @ 15-20 kg/ha. However, to mitigate the deficiency in standing crops foliar spray of 1% of iron or manganese or copper sulphate solution (i.e. 10 gms in one litre of water) is effective. If results are not favourable, treatment can be repeated 3 times at 10-15.

 

F. Implements for applying fertilizer

At present, majority of farmers apply fertilizer to the crop by hand. But this method is unscientific as distribution in the whole field cannot be uniform. Moreover, as these are spread on the soil surface, gaseous loss due to photodecomposition (decomposition of nutrient due to sun light) will be greater. Therefore, for efficient use, drilling of fertilizer in lines at plough depth (6 inches) is recommended. A bullock drawn fertilizer drill can be used for fertilizer drilling (designed by the Central Rice Research Institute, Cuttack, Orissa). This drill is supported on a wooden float having alternate ridges and depressions at the bottom. As the implement moves in the puddled field, a series of alternate ridges and depressions are formed behind the first float which pushes the water ahead and keeps the depressions free from water for a few seconds. The fertilizer is dropped into the depressions and instantenously covered up by soft puddle due to ploughing action of the second float, following the first immediately after the placement of fertilizers. A float type leveler following the second float makes the field leveled and allows the water to flow backward. The drill can place fertilizer at a depth of 8 cm from the surface of the puddled soil and can cover 0.3 hectare area in one hour time.

 

IV. Fertilizer Management in Upland Rice

Farmers growing rice in upland seldom use fertilizers because in uplands the fertilizers applied are not used by plants efficiently due to low moisture supply and poor water holding capacity of these soils. Adopting certain practices for conserving moisture and following different methods of fertiliser application in dry land area, one can harvest a better crop than the crops without the use of fertilizer. The dose of all three nutrients is less than what is recommended for the low land. Generally 60 kg nitrogen, 40 kg phosphorus and 25-30 kg potash per hectare is recommended.

 

The whole amount of phosphorus and potash and three-fourth of nitrogen should be either mixed in soil during final ploughing or drilled below the seed placement zone (4 inches below soil surface). Applying fertilizers mixed with seeds and then sowing does not show as much response as it is obtained when they are drilled below the seed. The remaining one fourth of nitrogen is given at tillering stage (25-30 after germination). If soil moisture remains less for a longer time half of the recommended nitrogen dose is applied during sowing time, one fourth at tillering and remaining one fourth can be added during panicle initiation stage (about 60 days after germination). The sources of fertilizers are the same as described earlier.

 

Foliar application of fertilizers is yet another means to increase the fertiliser use efficiency in rice crop. It is a very easy and effective method of applying urea under dry land conditions. Urea is preferred because it has a high nitrogen content easily soluble in water, easily available and is less costly compared with other nitrogenous fertilisers and does not leave any adverse effect on plant leaves. Generally 3-4% (i.e. 30-40 gm in one litre of water) concentration of urea solution is used for foliar application.

 

For one hectare of rice crop, 600 litres of solution is sufficient. As this solution is very dilute, the droplets do not stick to leaves bur drop down to the soil. This can be prevented by mixing 0.02% Teepol, det or surf in the urea solution. If needed, repeat the spray after 10 days. During flowering time spraying will not be much effective. Spraying on a bright sunny day enhances absorption of nutrient by plant leaves.

 

V. Integrated Nutrient Management

Owing to continuing energy crisis and high prices of chemical fertilizers, use of organic manure has become inevitable. The proper blend of organic and chemical fertilizers not only helps exploit the full potential of high yielding varieties but also maintains soil health.

 

Application of compost or farmyard manure is most desirable particularly under upland rice, to maintain physical condition of soil and to increase water absorbing and holding capacity. Well rotten farmyard manure or compost can be applied at the rate of 6-10 tonnes per hectare, one to one and half months before sowing. In no case, manure should be kept in field in heaps exposed to sun for long period as exposure to sunlight degrades the nutrient content of manure. Since availability of organic manure in huge quantity is difficult to obtain, it can be applied once in three years.

 

Green manures (green leaves of leguminous and non-leguminous plants) are other organic manures which can be applied to rice. But in areas receiving annual rainfall less than 25 inches, green manuring is not recommended. Addition of dhaincha, sunnhemp or subabul as green manure (6-10 tonnes biomass per hectare) with 50% of the recommended chemical fertiliser dose 50:25:25 NPK (50:25:25: NPK) gives as much yield as a full recommended dose (100:50:50: NPK). If adequate moisture is available (rain or irrigation) green manure crop is raised by broadcasting 18-20 kg/ha seed of dhaincha or 20-25 kg/ha seed of sunnhemp two months before sowing or transplanting the rice. A 45-day old crop can produce a biomass of 20-25 tonnes in one hectare and can provide 100 kg of nitrogen. Green manure crop should be incorporated into the soil when it is around 50 days old, at least one week before transplanting of rice. To grow dhaincha or any other green manure crop, at least 6 irrigations or equivalent number of rains are required during its 50-60 days growth period.

 

Oil cakes are also quick acting organic manures which provide nutrients to the plants in a week or ten days after application. But from the economic point of view, use of oil cakes is not advisable in rice cultivation.

 

As in integrated nutrient management, 6 to 10 tonnes/ha organic manure along with NPK at the rate of 60, 40, and 20 kg per hectare is the most efficient form of manuring practice for paddy. Organic manure should be applied and incorporated into the soil at least one month before sowing or transplanting. The whole amount of phosphorus and potash should be mixed in the soil after puddling. In uplands, they can be drilled below the seeds in rows. The amount of nitrogen can be applied in two split doses. One half can be given at maximum tillering stage (around 60 days after sowing or 45 days after transplanting) and remaining half after panicle initiation stage (75 days after sowing or 60 days after transplanting).