Application of Nitrogen Fertilizers

Last updated: June 21, 2025

Forms of Nitrogen Fertilizers

Efficiency of nitrogen fertilizers depends not only on the optimal nutrient regime of the crop during the growing season, but also on the form, timing, and methods of application. Currently in Russia, there is a trend toward an increasing share of urea use.

Urea has a number of advantages: it is well absorbed by the soil, moves little through the soil profile, and in its effect surpasses ammonium nitrate. Its efficiency increases when it is used as the main fertilizer under irrigation and sufficient moisture, especially on light soils, without being inferior to ammonium sulfate. With surface application of urea, for example, when top dressing winter crops in spring, on meadows and pastures, its efficiency is lower than that of ammonium nitrate, which is associated with nitrogen loss.

When applying nitrogen fertilizers, the characteristics of the crops are taken into account. In practice, it is often necessary to combine the application of several fertilizer forms for one crop. For example, to obtain high-quality raw cotton yields, before sowing, 30–50% of the total nitrogen rate is applied in the form of ammonium and amide forms, and the rest as ammonium nitrate in a top dressing. Such a combination is also important in the cultivation of winter and row crops. Or, under irrigation or excessive moisture conditions, slow-release nitrogen fertilizers can be applied as the main fertilizer, while during the growing season nitrogen nutrition can be optimized by top dressings with ammonium nitrate during the growing season.

Liquid nitrogen fertilizers show high efficiency when applied as the main fertilizer for all crops and when top dressing row crops. The most effective is liquid ammonia.

Nitrate forms promote the accumulation of ascorbic acid in plants to a greater extent than ammonium forms.

Application Timing

Under field conditions, the nitrogen use coefficient of mineral fertilizers averages 40–50%. The main part is fixed by the soil in the form of difficult-to-hydrolyze organic compounds that are poorly available to plants, or is lost as a result of denitrification and leaching. The extent of losses depends on the timing and methods of application, the biological characteristics of crops, and soil and climatic conditions. Therefore, for nitrogen fertilizers, application during periods of intensive nitrogen consumption is important.

Thus, the period of active nitrogen consumption by winter crops in spring begins approximately 5–15 days after snowmelt. By this time, fields are free of excess moisture, and the soil warms up sufficiently. The same applies to meadows, which are top dressed 1–3 weeks after snowmelt and the outflow of excess water. Applying nitrogen fertilizers immediately after snowmelt on dryland hayfields with excessive moisture reduces the effectiveness of top dressing due to gaseous nitrogen losses.

Table. Effect of temperature and moisture on the magnitude of gaseous nitrogen losses.

Soil moisture, % FC	Nitrogen losses at temperature
	5º		28º
	NH₄NO₃	(NH₂)₂CO	NH₄NO₃	(NH₂)₂CO
60	8.5	27.0	15.8	31.9
90	20.3	37.0	49.7	61.1

In the forest-steppe, primarily southern, regions and in the steppe zone, the soil dries out quickly in spring, so delaying nitrogen top dressing of winter crops reduces the effectiveness of this practice. In these regions, there is no water flow through the soil profile. Therefore, on level fields, winter crops are top dressed immediately after snowmelt. In the most continental steppe regions with little snow in winter, for example, in the Volga region, the North Caucasus, and Ukraine, on level lands the effect of nitrogen top dressing of winter crops in early spring and late autumn, when stable cooling sets in, and even before winter, is often the same.

All nitrogen forms, under good moisture and optimal temperature, as a result of nitrification pass into the nitrate form, which is not bound by the soil and migrates through the profile together with moisture. Therefore, applying the full rate of nitrogen fertilizers before sowing in winter can lead to significant nitrogen losses with meltwater. However, ammonium forms of nitrogen fertilizers may be applied in autumn, since ammonium is retained by the soil. Nitrate nitrogen is not adsorbed by the soil, so it moves together with the soil solution. Applying nitrate forms in autumn under sufficient moisture, especially on light soils, leads to significant nitrogen losses. For row crops with a well-developed root system, the best effect is achieved by deep incorporation of fertilizers.

Rates of Nitrogen Fertilizers

In the future, the relevance of the nitrogen problem in agriculture and its share in mineral fertilizers will increase, due to its mobility and inability to be fixed in the soil. An increase in the content of other biogenic elements in the soil, its fertility, and its cultivation level leads to nitrogen becoming a limiting factor for yield quantity and quality. This trend is observed in a number of countries where high rates of phosphorus-potassium and other mineral fertilizers have been applied for decades and a sufficient reserve of these elements has been created in the soil.

The need of agriculture for nitrogen fertilizers depending on the natural-economic zones of the country is predicted from data of the Geographic Network of Field Experiments, as well as research institutions. On the basis of these studies, norms of nitrogen fertilizer consumption per increment of crop yield have been developed. Modern computer technologies make it possible to summarize field experiment data, analyze them, and develop programs that allow adjusting optimal nitrogen requirements depending on fertilizer availability, the structure of sown areas, planned yield, weather forecasts, etc.

The optimal solution for determining optimal rates of nitrogen fertilizers for a specific agricultural crop is data from field experiments conducted under local soil and climatic conditions, as well as the results of agrochemical soil analysis for organic matter content, easily hydrolyzable forms of organic nitrogen, soil nitrification capacity, and content of mineral nitrogen forms.

In world agriculture, optimization of nitrogen fertilizer rates depending on the content of mineral (nitrate and ammonium) nitrogen in the soil (the N_MIN method) has become widespread.

Effective nitrogen rates for specific crops depend on zonal characteristics, so methods for diagnosing nitrogen nutrition have their own zonal modifications. There are different approaches to determining nitrogen fertilizer rates based on the content of mineral nitrogen in the soil when using the N_MIN method.

1. Equal consumption by plants of mineral nitrogen from soil and fertilizers is assumed. Knowing the plant requirement for nitrogen for the planned yield and the content of mineral nitrogen in the soil, the difference is compensated by applying nitrogen fertilizer.

This method does not take into account:

residual effect of organic and mineral fertilizers;
mobilization of additional “extra” nitrogen from enhanced mineralization of soil organic matter;
influence of the preceding crop in the crop rotation on the soil nitrogen regime;
soil nitrification capacity;
periodicity of plant nutrition with nitrogen;
depth of soil sampling for agrochemical analysis by crops and in the zonal aspect;
coefficient of use of soil and fertilizer nitrogen depending on the crop, soil properties, and climatic conditions.

Therefore, this method requires refinement.

Table. Rates of nitrogen fertilizer required to obtain planned winter wheat yields depending on the availability of available nitrogen in the soil before sowing (0–60 cm layer) (Nikitichen, 1986).

Planned yield, dt/ha	Average nitrogen removal with the yield, kg/ha	Amount of nitrate and ammonium nitrogen, kg/ha
Planned yield, dt/ha	Average nitrogen removal with the yield, kg/ha	72–96	96–120	120–144	144–168	168–192	192–216
Typical chernozem
40	96	45	20	—	—	—	—
45	112	75	50	25	—	—	—
50	128	100	75	55	30	—	—
55	144	125	100	80	55	> 30	—
60	160	155	130	105	80	60	30
65	176	180	155	130	105	85	50
Gray forest soil
40	111	50	25	—	—	—	—
45	129	75	50	30	20	—	—
50	147	100	75	55	40	25	20
55	164	125	100	80	65	50	40
60	182	150	125	105	90	75	65
65	200	175	150	130	115	100	90

2. The second variant of the N_MIN method consists in determining indices of soil supply with nitrate nitrogen and establishing the crop’s nitrogen requirement and rate. This method is well scientifically substantiated and has found wide practical application in diagnosing crop nitrogen nutrition for the regions of Siberia. Thus, for the regions of Western Siberia, a scale of nitrogen fertilizer requirements for cereal crops has been developed.

To calculate nitrogen fertilizer rates for the planned yield, the following formula is also used:

D_N = \frac { A - \lparen N_{INIT} + N_{TN} \rparen \cdot n } {C},

where

A: — nitrogen removal with the planned yield of main and by-products, kg/ha;
N_INIT: — nitrate nitrogen in the 0–50 cm soil layer before sowing, kg/ha;
N_TN: — nitrogen of current nitrification during the crop growing season, kg/ha;
n: — coefficient of use of soil nitrate nitrogen;
C: — coefficient of use by plants of nitrogen from mineral fertilizers.

It is conventionally assumed that n = 0.8 and C = 0.6; the coefficients differ for each zone.

Table. Need of cereal crops for nitrogen fertilizers depending on N-NO₃ content in the 0–40 cm soil layer in autumn or spring (according to Kochergin).

N-NO₃		Supply of plants with soil nitrogen	Need for nitrogen fertilizers	Approximate rates of nitrogen fertilizers, kg/ha a.i.
mg/kg soil	kg/ha	Supply of plants with soil nitrogen	Need for nitrogen fertilizers	Approximate rates of nitrogen fertilizers, kg/ha a.i.
At low and medium phosphorus supply to plants (up to 100 mg P₂O₅ per 1 kg soil, according to Frantsesson)
0–5	0–25	Very low	Very strong	60
5–10	25–50	Low	Strong	45
10–15	50–75	Medium	Medium	30
> 15	> 75	High	Absent	0
At high phosphorus supply to plants (150–200 mg P₂O₅ per 1 kg soil, according to Frantsesson)
0–10	0–50	Very low	Very strong	80
10–15	50–75	Low	Strong	60
15–20	75–100	Medium	Medium	45
> 20	> 100	High	Absent	0

Table. Content of mobile nitrogen in the 0–40 cm soil layer before sowing winter crops and the need for nitrogen fertilizers on chernozems.

N-NO₃, mg/kg soil		Need for nitrogen fertilizers	Approximate fertilizer rates, kg/ha
Initial nitrate content	Nitrate content after 7-day composting (nitrification capacity)	Need for nitrogen fertilizers	N	P
< 5	< 15^*	strong	90	40
5–10	15–25	medium	60	40
10–15	25–30	weak	20–30	60
> 15	> 30	absent	30^**	60–90

Notes.

^* Nitrification capacity without subtracting the initial nitrate content.

^** Only as a top dressing.

3. Determination of the need for nitrogen fertilizers and approximate rates for specific crops can be carried out by the content of mineral nitrogen in the soil and the value of nitrification capacity. The method was developed for the Volga region and Orenburg oblast and recommended for wide application in agricultural practice.

In various modifications, these diagnostic methods are used in other regions of Russia.

Calculations of nitrogen fertilizer rates can be carried out by the balance method. In our country, A. V. Sokolov, Z. I. Zhurbitsky, I. S. Shatilov, and N. K. Boldyrev contributed to the development and improvement of these methods.

The calculation of the amount of effective nitrogen (N_EFF), which enters plants from the soil itself during the growing season, based on the N_MIN content at the beginning of the growing season, is determined by the formula:

N_{EFF}(kg/ha) = \frac {N_{MIN} \cdot d \cdot h \cdot CUS_{N_{MIN}}} {10 \cdot 100} ,

and the calculation of the nitrogen rate for the planned yield or its increase is determined by the formula:

D_N(kg/ha) = \frac {(B - N_{EFF}) \cdot 100} {CUF(\%)}

where

D_N: — nitrogen rate for the planned yield, kg/ha;
B: — nitrogen removal with the planned yield, kg/ha;
N_MIN: — content of mineral (nitrate and ammonium) nitrogen in soil, mg/kg;
N_EFF: (kg/ha) — amount of effective nitrogen that plants obtain from the soil (of a given layer), taking into account current nitrification capacity, determined by the CUS indicator, %;
CUS_{N MIN}: — coefficient of use of soil mineral nitrogen, % (for nitrate nitrogen in the 0–30 cm layer of chernozem soil it is 200%);
CUF: — coefficient of use of nitrogen from mineral fertilizers;
d: — bulk density of 1 cm³;
h: — depth of the soil layer (cm);
dh/10: — mass of the soil layer, million kg, for converting soil mineral nitrogen from mg/kg to kg/ha;
100: — conversion of percentages of CUS and CUF, %.

Example.

Calculation of nitrogen fertilizer rates by the balance method: nitrate nitrogen content in the 0–30 cm layer of ordinary chernozem is 10 mg/kg, h = 30 cm, d = 1.2 g/cm³; CUS~NMIN~ = 200%, CUF N = 60%, B — nitrogen removal at a grain yield of 40 dt/ha is 120 kg/ha.

Then by the formula:

Y = \frac {N_{EFF}} {N_y},

where

N_y: — nitrogen content in grain, kg/dt.

The wheat yield (Y) due to soil nitrogen will be:

\frac {72 (kg/ha)} {3 (kg/dt)} = 24\ dt/ha.

The nitrogen rate by the balance method will be:

D_N = \frac { (120 - 72) \cdot 100} {60} = 80\ kg/ha.

Of the 80 kg of nitrogen applied to wheat, plants use 60%, i.e. 48 kg, which will provide a yield increase equal to:

\frac {48 (kg/ha)} {3 (kg/dt)} = 16\ dt/ha.

As a result, the planned yield is provided by soil nitrogen (24 dt/ha) and fertilizer nitrogen (16 dt/ha).

Experimental data allow some researchers not to take into account CUS and CUF for nitrogen. In this case, the formula for calculating nitrogen rates takes the form:

D = B - \frac {N_{MIN}dh} {10}

The disadvantage of the balance method is the need for optimal values of the parameters included in the above equation.

Modifications of the N_MIN methods or the balance method make it possible to determine quite accurately the nitrogen fertilizer rate for obtaining the planned winter wheat yield. The plant diagnostic method makes it possible to control the level of plant nitrogen nutrition and timely adjust spring and late nitrogen top dressings of crops. The combination of soil and plant diagnostics makes it possible to purposefully regulate the level of nitrogen nutrition of winter wheat taking into account soil-climatic and agrotechnical factors.

In Czechoslovakia, a system for monitoring the nutrition conditions of cereal crops was developed based on plant analysis data. For this, at the booting phase (5 leaves), plant samples are taken and the content of nitrogen, phosphorus, potassium, and other elements is determined. From the ratio of these elements, the need of cereal crops for fertilizers and optimal rates for top dressing are determined.

Table. Optimization of nitrogen fertilizer rates for top dressing winter wheat at the booting phase based on chemical analysis of plants (according to Bayer).

Criterion and plant analysis data			Degree of plant need for nitrogen	Optimal nitrogen rates for top dressing at the beginning of booting (at yield > 40 dt/ha), kg/ha
P, %	N : P	(100·K)/N	Degree of plant need for nitrogen
> 0.30	< 7.5	—	very high	80–100
	7.5–8.5	> 100 100 and below	medium high	60–80 80–100
	8.6–10.0	> 100	weak	40–60
	10.1–12.5	100 and below > 100	medium very weak	60–80 30–40
	> 12.5	100 and below > 100	weak plants supplied	40–60 top dressing not needed
< 0.30	10.0 and below	100 and below > 100	very weak very weak	30–40 30–40
	10.1–12.5	100 and below > 100	weak plants supplied	40–60 top dressing not needed
	> 12.5	100 and below	very weak	30–40

Determination of Nitrogen Fertilizer Rates

Long-term studies (Chernenok 1993, 1997) identified 4 main factors of nitrogen fertilizer efficiency: nitrate content in the 0–40 cm layer, mobile phosphorus content, their ratio, and moisture conditions. A quantitative relationship was established between these factors, which makes it possible to determine the need of crops for fertilizers and ensure their effectiveness.

Taking these factors into account, a zonal scale of soil supply with nitrogen and phosphorus was developed.

Table. Classification of nitrogen supply to cereal crops by N-NO₃ content, mg/kg soil, in the 0–40 cm layer (Chernenok V. G.).

Supply class	P₂O₅ supply		Need for N fertilizers	Recommended N rate, kg a.i./ha	Standard yield increase
Supply class	Very low — medium	Medium — high	Need for N fertilizers	Recommended N rate, kg a.i./ha	dt/ha	%
Very low	Up to 4	Up to 6	Very high	60	3–5	30 and >
Low	4–8	6–9	High	45	2–3	20–30
Medium	8–12	9–12	Medium	30	1–2	10–20
Elevated (optimal)	12–15	12–15	Low	—	<1	<10
High	>15	>15	Absent	—	—	0

To calculate the nitrogen fertilizer rate, it is necessary to determine the nitrate nitrogen content in the soil in the 0–40 cm layer. If the content of hydrolyzable nitrogen is known (according to Tyurin-Kononova), the indicator must be converted to nitrate nitrogen (N-NO₃) by multiplying by a coefficient of 0.26. For subsequent crops after fallow, the N-NO₃ content according to long-term average data decreases by 30%.

More accurately, the nitrogen deficit in the soil and the need for nitrogen fertilizers are calculated by a formula that takes into account the biological characteristics of the crop, requirements for nitrogen nutrition conditions, and soil nitrogen content N-NO₃ mg/kg in the 0–40 cm layer (Chernenok V. G.):

D_N = (N_{opt} - N_{fact}) \cdot K \cdot MC_{moist},

where

D_N: — rate of nitrogen fertilizers, kg/ha a.i.;
N_opt: — optimal nitrate nitrogen content in soil, mg/kg in the 0–40 cm layer;
N_fact: — actual N-NO₃ content, mg/kg in the 0–40 cm layer;
K: — equivalent of kg a.i. of fertilizers per 1 mg N-NO₃ of soil, equal to 7.5 kg (the amount of kg N fertilizers that must be applied to increase N-NO₃ content in soil by 1 mg/kg).

The formula assumes bringing phosphorus content to the optimal level. If the P₂O₅ content in soil remains below optimal even after applying phosphorus fertilizers, which can be determined by dividing the applied fertilizer rate by 10 (the equivalent cost of kg a.i. of fertilizers to increase soil phosphorus by 1 mg/kg, taking into account the actual soil phosphorus content):

P (mg/kg) = P_{fact} + \frac {D_P} {10},

where

D_P: — applied phosphorus rate.

In this case, the nitrogen fertilizer rate is calculated by the formula:

D_N = (1/3P_{fact} - N_{fact}) \cdot K \cdot MC_{moist},

where (1/3 P_fact) is the N-NO₃ level, mg/kg, to which nitrogen should be brought, ensuring an optimal P:N ratio of 2.5–3.

Example.

The soil contains 15 mg P₂O₅/kg soil. 120 kg a.i. were applied; the P₂O₅ content increased to 27 mg (15 + 120/10). The optimal phosphorus level has not been reached, so nitrogen should not be brought to 12 or 15 mg. For 27 mg P₂O₅, the optimal N-NO₃ content will be 27:3 = 9 mg.

This allows, with a phosphorus deficiency in the soil, maintaining the optimal phosphorus-to-nitrogen ratio for plants. This makes it possible to save fertilizers and money, since phosphorus deficiency will not allow the full nitrogen rate calculated to bring it to the optimum to be realized.

MC_moist — moisture correction coefficient, calculated by the formula:

MC_{moist} = \frac{O_f} {275},

where

O_f: — actual (forecast) precipitation for the year;
275: — standard precipitation, a constant equal to the long-term average for the study period.

Actual (forecast) precipitation is calculated on the basis of precipitation actually fallen from September to May plus forecast precipitation for the growing season. If in June precipitation is expected within the norm, the long-term average is added; if above, 1.5 of the norm is added; if below, 0.5 of the norm.

MC_moist makes it possible to adjust the standard indicators and calculate the rate and yield increase from nitrogen fertilizers for any year in terms of moisture within the zonal variation of precipitation. The data in the table are applicable to all soils.

Table. Rates of nitrogen fertilizers and yield increases (dt/ha) depending on N-NO₃ content in soil and moisture MC.

Precipitation per agr. year, mm	MC_moist	Nitrogen supply
		Very low		Low		Medium
		N rate, kg a.i./ha	Yield increase	N rate, kg a.i./ha	Yield increase	N rate, kg a.i./ha	Yield increase
200	0.7	42	2.1–3.5	32	1.4–2.1	21	0.7–1.4
225	0.8	48	2.4–4.0	36	1.6–2.4	24	0.8–1.6
250	0.9	54	2.7–4.5	40	1.8–2.7	27	0.9–1.8
275	1.0	60	3.0–5.0	45	2.0–3.0	30	1.0–2.0
300	1.1	66	3.3–5.5	50	2.2–3.3	33	1.1–2.2
325	1.2	72	3.6–6.0	54	2.4–3.6	36	1.2–2.4
350	1.3	78	3.9–6.5	58	2.6–3.9	40	1.3–2.8
375	1.36	82	4.2–6.8	61	2.7–4.1	41	1.4–2.7

More accurately, the yield increase is determined by the formula:

YI_N = 1.24 - 0.14N-NO_3 + 1.62 MC_{moist} + 0.06 \frac{P}{N} ,

where

YI_N: — yield increase from nitrogen fertilizers;
N-NO₃: — content in soil, mg/kg in the 0–40 cm layer;
P/N: — ratio of actual P₂O₅ content, mg/kg soil in the 0–20 cm layer to N-NO₃, mg/kg in the 0–40 cm layer.

In market conditions, it is important to know the possible yield increase so that, even before applying fertilizers, based on prevailing prices, one can determine how economically justified this practice will be.

Correlation analysis showed high reliability (r = 0.93) of the forecast of nitrogen fertilizer efficiency calculated by the above method taking into account all 4 factors determining efficiency.

References

Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Edited by B. A. Yagodin. Moscow: Kolos.
Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Edited by Mineev V. G. Moscow: Publishing House of VNIIA named after D. N. Pryanishnikov.
Evtefeev Yu. V., Kazantsev G. M. (2013). Fundamentals of Agronomy: A Textbook. Moscow: FORUM.