Nitrogen Fertilization I: Impact on Crop, Soil, and Environment

*Upendra M. Sainju, Rajan Ghimire and Gautam P. Pradhan*

#### **Abstract**

Nitrogen (N) is a major limiting nutrient to sustain crop yields and quality. As a result, N fertilizer is usually applied in large quantity to increase crop production throughout the world. Application of N fertilizers has increased crop yields and resulted in achievement of self-sufficiency in food production in many developing countries. Excessive application of N fertilizers beyond crops' demand, however, has resulted in undesirable consequences of degradation in soil, water, and air quality. These include soil acidification, N leaching in groundwater, and emissions of nitrous oxide (N2O), a potent greenhouse gas that contributes to global warming. Long-term application of ammonia-based N fertilizers, such as urea, has increased soil acidity which rendered to soil infertility where crops fail to respond with further application of N fertilizers. Another problem is the groundwater contamination of nitrate-N (NO3-N) which can be a health hazard to human and livestock if its concentration goes above 10 mg L<sup>1</sup> in drinking water. The third problem is emissions of N2O gas which is 300 times more powerful than carbon dioxide in terms of global warming potential. This chapter examines the effect of N fertilization on soil and environmental quality and crop yields.

**Keywords:** crop yields, environmental quality, management practices, nitrogen fertilizer, nitrogen-use efficiency, soil quality

#### **1. Introduction**

Nitrogen (N) is a major limiting factor for sustainable and profitable crop production. However, excessive N application through fertilizers and manures can degrade soil and environmental quality by increasing soil acidification, N leaching, and emissions of ammonia (NH3) and nitrogen oxide (NO, N2O, and NO2) gases, out of which N2O is considered a highly potent greenhouse gas that contributes to global warming [1, 2]. Nitrogen application more than crop's need can also result in reduced yield [3]. Additional N inputs include dry and wet (snow and rain) depositions from the atmosphere, biological N fixation, and irrigation water. Because crops can remove about 40–60% of applied N, the soil residual N (nitrate-N [NO3-N] + ammonium-N [NH4-N]) after crop harvest can be lost to the environment through leaching, denitrification, volatilization, surface runoff, soil erosion, and N2O emissions [3, 4]. One option to reduce soil residual N is to increase N-use efficiency. Nitrogen-use efficiency for crops, however, can be lower at high N fertilization rates [5]. Improved management practices can increase N-use efficiency, enhance soil N storage, and reduce N fertilizer application which

reduce N losses to the environment [4]. An account of N inputs, outputs, and retention in the soil provides N balance and helps to identify dominant processes of N flow in the agroecosystem [4].

Economically profitable crop yields could be achieved by recommended N fertilization rates [6]. However, such a yield potential for a crop varies with soil and climatic conditions, crop species, variety, nutrient cycling, and competitions with weeds and pests [6]. Crop production can be optimized and potential for N losses minimized by adjusting N fertilization rates using soil residual and potentially mineralizable N values. Studies show that 1–2% of soil organic N in the 0–30 cm depth is mineralized every year [6]. Measuring the actual amount of N mineralized is a time taking process. A commonly used method for measuring soil available N and determining nitrogen rates for crops in semiarid regions of northern Great Plains, USA is based on testing NO3-N content in soils to a depth of 60 cm after crop harvest in the fall season of the previous year and deduct the value from recommended N rates for the current crop year [7, 8]. In semiarid regions such as Great Plains of USA, N losses to the environment due to N leaching, volatilization, and denitrification during the winter are considered minimal due to cold weather and limited precipitation in the region.

Nitrogen fertilizers are being increasingly applied to crops to enhance their yield and quality in South Asia, where land available for crop production is limited, the proportion of cultivated land to population is low, and the pressure to increase crop yields to meet the demand for growing population is high. Continuous application of N fertilizers to nonlegume crops and excessive application rates in some places have led to undesirable consequences, such as reduced crop yields and degraded soil and environmental quality from soil acidification, N leaching, and greenhouse gas (N2O) emissions. In this chapter, we discuss the consequences of N fertilization to crop yields and soil and environmental quality.

Increased N fertilization rate can also increase grain quality, such as protein concentration [10, 11]. Increased N fertilization rates increased malt barley grain yield and protein concentration, but reduced kernel plumpness in

*Annualized grain and biomass yields of barley and pea and C content as affected by N fertilization rate in*

Canada [12]. While some studies reported malt barley grain protein concentration of <130 g kg<sup>1</sup> with N rate of 168–200 kg ha<sup>1</sup> (e.g., [13]) others, observed an increase in protein concentration even with N rates <150 kg N ha<sup>1</sup> (e.g., [14]). Grain protein and kernel plumpness are important characteristics of malt barley

fertilization rates are required to malt barley to achieve a balance between optimum

Sainju et al. [16] evaluated the effect of N fertilization on cotton and sorghum yields and N uptake from 2000 to 2002 in central Georgia, USA (**Table 1**). They found that cotton lint, sorghum grain, and cotton and sorghum biomass yields and N uptake increased from 0 to 60–65 kg N ha<sup>1</sup> and then remained either at a similar

fertilization, however, depended on climatic condition, as cotton lint and biomass yields were greater in 2000 than 2002 when the growing season precipitation was below the average. The N fertilizer required for optimizing cotton and sorghum yields varied with the type of tillage and cover crop [16]. Boquet et al. [17] reported that cotton lint yield was lower with no-tillage than surface tillage without applied N, but at optimum N rate, yields were higher with no-tillage. They also found that additional N was required to optimize cotton yield following wheat (*Triticum aestivum* L.) in no-tillage and surface tillage systems without cover cropping, but no N rate was required following hairy vetch cover crop in either tillage practices. Similarly, N fertilization rates to cotton and sorghum can be reduced or eliminated

) for beer production [12]. Therefore, appropriate N

, kernel

. The response of cotton yield to N

that need to be maintained at critical levels (grain protein ≤129 g kg<sup>1</sup>

grain yield, kernel plumpness, and protein concentration [15].

*Nitrogen Fertilization I: Impact on Crop, Soil, and Environment*

*DOI: http://dx.doi.org/10.5772/intechopen.86028*

level or slightly increased at 120–130 kg N ha<sup>1</sup>

plumpness ≥850 g kg<sup>1</sup>

*eastern Montana, USA [9].*

**Figure 1.**

**71**

#### **2. Crop yields, nitrogen uptake, and nitrogen-use efficiency**

Nitrogen fertilization can increase crop yields and N uptake compared with no N fertilization. This has been documented for malt barley (*Hordeum vulgare* L.), cotton (*Gossypium hirsutum* L.), and sorghum (*Sorghum bicolor* [L.] Moench) (**Figures 1** and **2**, **Table 1**) by various researchers in Georgia and Montana, USA [9, 10, 14]. It is not unusual to achieve higher crop yield with increased N fertilization rate due to increased soil N availability [11]. Crop yields, however, can remain at similar level or decline with further increase in N rates after reaching the maximum yield. Sainju [9] observed that annualized grain and biomass yields of barley and pea (*Pisum sativum* L.) and their C content maximized at 80 kg N ha<sup>1</sup> and then declined, as N rate increased to 120 kg N ha<sup>1</sup> (**Figure 1**). Similarly, Sainju et al. [10] reported that malt barley yield and N uptake increased from 0 to 40 kg N ha<sup>1</sup> and then declined with further increase in N rates in no-till and conventional till malt barley-fallow rotation (**Figure 2**). In no-till continuous malt barley and malt barley-pea rotation, they found that increased N rate from 0 to 120 kg N ha<sup>1</sup> continued to increase malt barley yield and N uptake. Increased soil residual N due to fallow as a result of enhanced soil N mineralization from increased soil temperature and water content resulted in a reduced response of malt barley yield and N uptake with N fertilization in no-till and conventional till malt barley-fallow rotation. A study reported a need of 27 kg of total soil and fertilizer N to produce 1 Mg of malt barley grain in irrigated no-till field in Colorado, USA [11].

*Nitrogen Fertilization I: Impact on Crop, Soil, and Environment DOI: http://dx.doi.org/10.5772/intechopen.86028*

reduce N losses to the environment [4]. An account of N inputs, outputs, and retention in the soil provides N balance and helps to identify dominant processes

harvest in the fall season of the previous year and deduct the value from

**2. Crop yields, nitrogen uptake, and nitrogen-use efficiency**

malt barley grain in irrigated no-till field in Colorado, USA [11].

**70**

recommended N rates for the current crop year [7, 8]. In semiarid regions such as Great Plains of USA, N losses to the environment due to N leaching, volatilization, and denitrification during the winter are considered minimal due to cold weather

Nitrogen fertilizers are being increasingly applied to crops to enhance their yield and quality in South Asia, where land available for crop production is limited, the proportion of cultivated land to population is low, and the pressure to increase crop yields to meet the demand for growing population is high. Continuous application of N fertilizers to nonlegume crops and excessive application rates in some places have led to undesirable consequences, such as reduced crop yields and degraded soil and environmental quality from soil acidification, N leaching, and greenhouse gas (N2O) emissions. In this chapter, we discuss the consequences of N fertilization to

Nitrogen fertilization can increase crop yields and N uptake compared with no N fertilization. This has been documented for malt barley (*Hordeum vulgare* L.), cotton (*Gossypium hirsutum* L.), and sorghum (*Sorghum bicolor* [L.] Moench) (**Figures 1** and **2**, **Table 1**) by various researchers in Georgia and Montana, USA [9, 10, 14]. It is not unusual to achieve higher crop yield with increased N fertilization rate due to increased soil N availability [11]. Crop yields, however, can remain at similar level or decline with further increase in N rates after reaching the maximum yield. Sainju [9] observed that annualized grain and biomass yields of barley and pea (*Pisum sativum* L.) and their C content maximized at 80 kg N ha<sup>1</sup> and then declined, as N rate increased to 120 kg N ha<sup>1</sup> (**Figure 1**). Similarly, Sainju et al. [10] reported that malt barley yield and N uptake increased from 0 to 40 kg N ha<sup>1</sup> and then declined with further increase in N rates in no-till and conventional till malt barley-fallow rotation (**Figure 2**). In no-till continuous malt barley and malt barley-pea rotation, they found that increased N rate from 0 to 120 kg N ha<sup>1</sup> continued to increase malt barley yield and N uptake. Increased soil residual N due to fallow as a result of enhanced soil N mineralization from increased soil temperature and water content resulted in a reduced response of malt barley yield and N uptake with N fertilization in no-till and conventional till malt barley-fallow rotation. A study reported a need of 27 kg of total soil and fertilizer N to produce 1 Mg of

Economically profitable crop yields could be achieved by recommended N fertilization rates [6]. However, such a yield potential for a crop varies with soil and climatic conditions, crop species, variety, nutrient cycling, and competitions with weeds and pests [6]. Crop production can be optimized and potential for N losses minimized by adjusting N fertilization rates using soil residual and potentially mineralizable N values. Studies show that 1–2% of soil organic N in the 0–30 cm depth is mineralized every year [6]. Measuring the actual amount of N mineralized is a time taking process. A commonly used method for measuring soil available N and determining nitrogen rates for crops in semiarid regions of northern Great Plains, USA is based on testing NO3-N content in soils to a depth of 60 cm after crop

of N flow in the agroecosystem [4].

*Nitrogen Fixation*

and limited precipitation in the region.

crop yields and soil and environmental quality.

**Figure 1.** *Annualized grain and biomass yields of barley and pea and C content as affected by N fertilization rate in eastern Montana, USA [9].*

Increased N fertilization rate can also increase grain quality, such as protein concentration [10, 11]. Increased N fertilization rates increased malt barley grain yield and protein concentration, but reduced kernel plumpness in Canada [12]. While some studies reported malt barley grain protein concentration of <130 g kg<sup>1</sup> with N rate of 168–200 kg ha<sup>1</sup> (e.g., [13]) others, observed an increase in protein concentration even with N rates <150 kg N ha<sup>1</sup> (e.g., [14]). Grain protein and kernel plumpness are important characteristics of malt barley that need to be maintained at critical levels (grain protein ≤129 g kg<sup>1</sup> , kernel plumpness ≥850 g kg<sup>1</sup> ) for beer production [12]. Therefore, appropriate N fertilization rates are required to malt barley to achieve a balance between optimum grain yield, kernel plumpness, and protein concentration [15].

Sainju et al. [16] evaluated the effect of N fertilization on cotton and sorghum yields and N uptake from 2000 to 2002 in central Georgia, USA (**Table 1**). They found that cotton lint, sorghum grain, and cotton and sorghum biomass yields and N uptake increased from 0 to 60–65 kg N ha<sup>1</sup> and then remained either at a similar level or slightly increased at 120–130 kg N ha<sup>1</sup> . The response of cotton yield to N fertilization, however, depended on climatic condition, as cotton lint and biomass yields were greater in 2000 than 2002 when the growing season precipitation was below the average. The N fertilizer required for optimizing cotton and sorghum yields varied with the type of tillage and cover crop [16]. Boquet et al. [17] reported that cotton lint yield was lower with no-tillage than surface tillage without applied N, but at optimum N rate, yields were higher with no-tillage. They also found that additional N was required to optimize cotton yield following wheat (*Triticum aestivum* L.) in no-tillage and surface tillage systems without cover cropping, but no N rate was required following hairy vetch cover crop in either tillage practices. Similarly, N fertilization rates to cotton and sorghum can be reduced or eliminated

#### **Figure 2.**

*Effects of cropping sequence and N fertilization rate on malt barley grain yield, N uptake, and N-use efficiency in eastern Montana, USA. CTB-F denotes conventional-till malt barley-fallow; NTB-F, no-till malt barleyfallow; NTB-P, no-till malt barley-pea; and NTCB, no-till continuous malt barley. Vertical bar with LSD (0.05) is the least significant difference between treatments at P = 0.05 [10].*

by using legume cover crops, such as red clover (*Trifolium incarnatum* L.) and hairy vetch (*Vicia villosa* Roth), regardless of tillage practices [18]. The high rate of N fertilization can produce excessive vegetative growth that delays maturity and harvest and reduces cotton lint yield and N uptake [19].

Nitrogen-use efficiency, defined as crop yield or N uptake per unit applied N fertilizer, is a useful measurement of the efficiency of N fertilization to crop yields [5]. Enhancing N-use efficiency can maximize crop yield and N uptake with limited use of fertilizer N while reducing N rate and sustaining the environment [3]. Nitrogen-use efficiency, however, can decrease with increased N fertilization rate due to the inability of crops to utilize N efficiently [5]. Sainju et al. [10] found that N-use efficiency by malt barley decreased curvilinearly with increased N fertilization rate (**Figure 2**). Varvel and Peterson [5] reported that N removed by corn and sorghum grain was 50% of the applied N at low N rates and at least 20–30% at high N rates.

**2000 cotton lint**

**73**

**2000 cotton biomass**

**2001 sorghum grain**

**2001 sorghum biomass**

**2002 cotton lint**

**2002 cotton biomass**

> **(kg ha1**

**)**

**(kg ha1**

**)**

**(kg ha1**

**)**

**(kg ha1**

**)**

**(kg ha1**

**Treatment**

Cover cropa

WW

R HV HV/R

N fertilization

0 60–65

120–130

*aCover crops are HV, hairy vetch; HV/R, hairy vetch/rye; R, rye; and WW, winter weeds.*

*bNumbers followed by the same letters within a column in a set are not significantly*

**Table 1.** *Effect of cover crop and N fertilization*

 *rate on yield and N uptake by cotton lint, sorghum grain, and their biomass (stems + leaves) from 2000 to 2002 in central Georgia, USA [16].*

 689a

 11a

 7600a

 209a

 3700a

 *different at P ≤ 0.05.*

 57a

 13,300a

 152a

 587b

 11b

 4000a

 97a

 783a

 13a

 7000a

 178b

 3100b

 46b

 12,400ab

 135a

 980a

 16a

 3900a

 86b

736a

 12a

 5700b

 135c

 2800b

 41b

 11,600b

 108b

 1021a

 17a

 3700a

 80b

 rate (kg N ha1

)

 706b

 12b

 7300ab

 194a

 4000a

 58a

 14,100a

 138ab

 711b

 14a

 4233a

 102a

660b

 11b

 8200a

 239a

 3500ab

 60a

 14,100a

 175a

 708b

 13a

 4067a

 98a

879a

 15a

 6300bc

 138b

 2300c

 32b

 9400b

 81b

 940ab

 15a

 3567a

 77a

 699bb

11b

 5200c

 124b

 2800bc

 43ab

 12,000ab

 133ab

 1091a

 16a

 3667a

 74a

*Nitrogen Fertilization I: Impact on Crop, Soil, and Environment*

 **Yield**

 **N uptake**

 **Yield**

 **N uptake**

 **Yield**

 **N uptake**

 **Yield**

 **N uptake**

 **Yield**

 **N uptake**

 **Yield**

 **N uptake**

*DOI: http://dx.doi.org/10.5772/intechopen.86028*

**)**

**(kg ha1**

**)**

