Effect of Urease and Nitrification Inhibitors on Nitrogen Transformation and Nitrogen Use Efficiency of Rain-Fed Summer Maize (Zea mays) at Loess Plateau of China

 

Muneer Ahmed1,2,3, Weijia Yu1,2, Ming Lei1,2, Sajjad Raza1,2, Ahmed Salah Elrys1,4,5 and Jianbin Zhou1,3*

1College of Natural Resources and Environment, Northwest Agriculture and Forestry University, Yangling 712100, Shaanxi, China

2Faculty of Agriculture, Lasbela University of Agriculture, Water and Marine Sciences, Uthal 90150, Balochistan, Pakistan

3Key Laboratory of Plant Nutrition and the Agriculture Environment in Northwest China, Ministry of Agriculture, Yangling 712100, Shaanxi, China

4Liebig Centre for Agroecology and Climate Impact Research, Justus Liebig University, Giessen, Germany

5Soil Science Department, Faculty of Agriculture, Zagazig University, Zagazig, Egypt

*For correspondence: jbzhou@nwsuaf.edu.cn

Received 10 May 2023; Accepted 04 September 2023; Published 05 October 2023

 

Abstract

 

Urease and nitrification inhibitors are used to increase N use efficiency (NUE) and decrease N loss. Their efficiencies are dependent on soil properties and climatic conditions. Rain-fed summer maize crop was grown at three different sites (Yangling, Zhouzhi-1 and Zhouzhi-2) in the Loess Plateau of China, having different soil properties and climatic conditions. The study aimed to evaluate the efficiency of urea treatment with N-(n-butyl) thiophosphoric triamide (NBPT) and a mixture of NBPT + dicyandiamide (DCD) on soil N transformation, N uptake and NUE. Control (no N), Urea (220 kg N ha-1), U + NBPT (1.0%) and U+ NBPT + DCD (10%) were applied through the band placement method in two splits (7:3). The application of urea treatment with NBPT alone and a mixture of NBPT + DCD maintained the soil mineral-N content for a longer time, which resulted in more N uptake by the plant, and eventually improved NUE. Urea treatment with inhibitors increased maize grain yield (15–20%) compared to plain urea and (37.7–48%) unfertilized control. The highest plant N uptake was observed in maize fertilized by urea treatment with NBPT + DCD, followed by U + NBPT. Urea treatment with NBPT and NBPT + DCD increased NUE by 13.8–21.6 and 14.3–22.6%, respectively, compared to unfertilized control. The NUE was higher in maize fertilized with urea plus inhibitors, compared to urea alone. Consequently, the application of urea treatment with NBPT and a mixture of NBPT + DCD represented the best approach for improving N uptake, NUE and yield of the maize crop. © 2023 Friends Science Publishers

 

Keywords: Nitrogen accumulation; Nitrogen uptake; Nitrogen management; NBPT; DCD

 


Introduction

 

Nitrogen (N) is a key essential nutrient to maintain a higher crop production and global economic sustainability of agricultural systems (Zhang et al. 2013; Santos et al. 2020). Synthetic N fertilizers have been extensively used in the world (Miao et al. 2015; Santos et al. 2020). Urea is leading among the leading nitrogenous fertilizers, nearly 60% all over the world (Davis et al. 2016). Currently, it is a prominent source of chemical N fertilizer in China, accounting for 50–60% of total N fertilizer consumption and the most common N source for maize (Zea mays L.) crop fertilization (Li et al. 2015, 2017). Due to the complex nature of soil N transformation, accompanied by sub-optimal management practices of N fertilizers, usage of urea generally results in low N use efficiency (30–50%), contributing towards higher economic losses to farmers and hazards to the environment (Cui et al. 2010; Liu et al. 2015). Consequently, farmers are facing dual challenges to decrease N losses and improve N use efficiency (NUE) to sustain crop productivity (Liu et al. 2013; Tan et al. 2017). Enhancement of NUE in crop production is one of the significant ways of addressing the challenges of food security, environmental pollution and climate change (Davidson et al. 2015; Zhang et al. 2015).

Over last three decades, agricultural activities of northern China have relied on the increased use of N fertilizers to maintain the increasing crop yield (Gu et al. 2015). However, the response of N fertilizer varies considerably under different climatic conditions, soil physicochemical properties, fertilization methods, agronomic practices and water regimes, which affect N loss and NUE (Mohanty et al. 1999; Qiao et al. 2015).

Ammonia (NH3) emission is considered a principal source of N loss after urea fertilization, especially in alkaline and calcareous soils (Li et al. 2015, 2017). Therefore, it is crucial to decrease N losses, thereby enhancing the NUE. The N-(n-butyl) thiophosphoric triamide (NBPT) is considered as most effective urease inhibitor (UI) and is extensively used in many cropping systems (Sanz-Cobena et al. 2008, 2012; Zaman et al. 2009). NBPT efficiently blocked the urease enzymes thereby effectively delaying urea hydrolysis (Cantarella et al. 2018), resulting in increased N availability for plant uptake (Rose et al. 2018; Meng et al. 2023). Furthermore, the use of NBPT with urea has the potential to be the most appropriate strategy to decrease N loss and enhance NUE, thereby increasing crop productivity (Singh et al. 2013; Martins et al. 2017; Fu et al. 2020).

Generally, nitrate (NO3-) is the most abundant N form in upland soils and prone to highly vulnerable to leaching and denitrification losses, contributing to reduced NUE. A meta-analysis has reported that nitrification inhibitors (NIs) enhanced plant N recovery (34–93%), and subsequently increased grain (6–13%) and straw biomass (12–18%) yield (Qiao et al. 2015). Among the NIs, Dicyandiamide (DCD) has been extensively used in agriculture for agronomic enhancement of N use efficiency (Tian et al. 2015; Raza et al. 2019). Furthermore, the use of DCD with N fertilizers might prolong ammonium (NH4+) in the soil, which enables more plant N uptake (Asing et al. 2008; Li et al. 2009; Meng et al. 2023) and decreased N losses through NO3- leaching and nitrous oxide (N2O) emissions contributing increased NUE (Cahalan et al. 2015; Yang et al. 2016; Montalbán et al. 2021).

Although NIs are effective in improving NUE, however, one drawback of using them is increased NH3 volatilization, which is a significant N loss pathway in arable lands (Soares et al. 2012; Qiao et al. 2015). Some studies reported that the combined use of inhibitors affects the urea hydrolysis by UIs and ammonia oxidation by NIs, thereby enhancing effectiveness of N fertilizer use, is a “win-win” strategy to reduce N losses, increase crop yield and NUE for attaining economic benefits from the agricultural system (Abalos et al. 2016; Martins et al. 2017; Zhao et al. 2017). Furthermore, the use of inhibitors with N fertilizers produced additional revenue of $ 109.49–163 ha-1 Y-1 for maize farms (Qiao et al. 2015; Yang et al. 2016). The urease and nitrification inhibitors are environment-friendly approaches and are not considered harmful to animals or humans (Nugrahaeningtyas et al. 2022).

Some studies reported that the use of DCD with NBPT has no positive effect on N uptake, crop yield and NUE (Ding et al. 2011; Kawakami et al. 2012; Montalbán et al. 2021). It may be related to the differences in soil physicochemical properties (soil pH, soil texture, soil temperature, moisture content, and soil organic matter), climatic factors (precipitation and air temperature) and management factors (time and method of application) (Francisco et al. 2011; Suter et al. 2013; Abalos et al. 2014). Soils with medium to coarse textured and pH ≤ 6 have a positive response to inhibitors in increasing crop production and NUE (Abalos et al. 2014, 2016). The efficiency of NBPT and a mixture of NBPT+DCD are affected by soil moisture and climatic conditions (Sanz-cobena et al. 2012). Furthermore, NIs and UIs immediately decompose within a few days after fertilization and the efficiency becomes lower under high temperatures (>20°C) (Soares et al. 2012; Zhao et al. 2017). However, more studies are needed to evaluate the effectiveness of NBPT and a mixture of NBPT + DCD in different soil and environmental conditions.

In this context, it was hypothesized that different soils and climatic conditions of the Loess Plateau affect the urease and NIs efficiency. Therefore, this field experiment was conducted at three different sites of the Loess Plateau to evaluate the effect of urea treatment with NBPT alone and urea treatment with a mixture of NBPT + DCD. The objectives of the current study were to (1) evaluate the efficiency of NBPT alone and a mixture of NBPT + DCD with urea on soil N transformation; (2) assess the effectiveness of urea treatment with NBPT alone and urea treatment with NBPT+DCD on N uptake, yield and NUE of maize crop in different soil properties under different environmental conditions of Loess Plateau, China.

 

Materials and Methods

 

Research site description

 

The two study sites (Yangling and Zhouzhi) were located at the south of Loess Plateau, Shaanxi, China. This zone has semi-humid continental monsoon climate and almost 65–75% of precipitation happens during June–October. Maize and wheat crop rotation is the principal cropping system of this region. Yangling (34°30′N, 108°02′E) had mean annual precipitation of 600 mm, and air temperature of 12.9°C (1957–2013). The Yangling soil is Eum-Orthic Anthrosol (Udic Haplustalf based on USDA system). Zhouzhi (34°13′N, 108°34′E) had mean annual precipitation of 713 mm, and air temperature of 13.2°C (1957–2013). The Zhouzhi soil is cinnamon (Udic Haplustalf based on USDA system) in nature. The total precipitation at Yangling 349 mm and Zhouzhi 305 mm occurred during current maize growing season (Fig. 1). The major soil physicochemical properties of the top (0–20 cm) surface layer of the selected sites is shown in Table 1.

 

Experimental design and field management

 

Experimental material: Summer maize (cultivar “Zhengdan 958”) crop was grown (June–October 2018) in three different farmer’s fields (one at Yangling, two at Zhouzhi) at two counties. The crop was sown on June 1st, 2018, by drilling method with space between row to row 60 cm and harvested on October 25th, 2018. The plant population 75,000 plants ha-1 (7.5 plants sq m-1) were maintained. There were four treatments in each site, including control (no N fertilizer), urea (U), U + NBPT and U + NBPT + DCD. The N rate (220 kg ha-1) was same for all fertilized treatments, on the basis of local recommendations (Raza et al. 2019; Wang et al. 2022). The NBPT and DCD rates were 1 and 10% on the w/w basis of applied N, respectively. The NBPT and DCD were manually mixed with urea like coating one day before fertilization. Field trials were organized in randomized complete block design, with three replications. The size of each plot was 5 × 4 (20 m2), with one-meter protection area.

Treatments: Fertilizer treatments were applied in two splits through sub-surface band placement (7 ± 1 cm depth), 70% at 30 days after sowing (V5 leaf growth stage) and 30% at 24 days after first fertilization (V10 leaf growth stage). The experimental fields were plowed with deep plow machine at first, and it was again tilled up to 10–15 cm soil profile using rotavator to homogenize the soil, and properly leveled one week before sowing. The Maize (Zea mays L.) crop (cultivar “Zhengdan 958”) was grown and entirely dependent on natural rainfall. No extra irrigation was applied, same as local farmers’ management.

 

Sample collection and analysis

 

Soil sampling and analysis: Soil profile samples (0–200 cm, 20 cm intervals) were collected from each site before cultivation and after harvesting of the crop, using a stainless steel auger (diameter: 5 cm). The primary physical and chemical properties of soil (0–20 cm) were determined before starting the experiment. Total N was measured by Kjeldahl digestion method and soil organic carbon (SOC) with wet soil digestion with H2SO4-K2Cr2O7 method (Zhang et al. 2017). Available P (Olsen P) and K were determined by extraction with 0.5 mol L-1 NaHCO3 and 1 mol L-1 NH4OAC, respectively (Lu et al. 2016). Soil particles sand, silt and clay distribution were measured by Mastersizer 2000E lasar diffractometer (Malven, UK) as according to Sochan et al. (2012).

For the determination of soil pH, electric conductivity (EC) and mineral-N, soil samples were randomly collected (depth: 0–20 cm) from individual plot at different intervals (2, 6, 10, 14, 20, 26, 30, 34, 40, 46, 60 and 75 days) during maize crop growth season. After each sampling, samples were thoroughly mixed after removing visible roots and litters, sealed immediately in separate marked plastic bags and stored in the freezer until analysis and other air dried for measuring soil pH and EC. A 5 g sub-sample (oven dry equivalent) was extracted with 50 mL of 1 M KCL solution and was used for the analysis of mineral-N by using continuous flow analyzer (Bran and Luebbe AA3, Norderstedt Australia). Soil pH (1:2.5 soil: deionized water ratio) and EC (1:5 soil: water ratio) were measured by using glass electrode Mettler Tloedo 320-S pH meter and DDS-307 EC meter followed by shaking for 30 minutes on a rotary shaker, respectively.

Plant sampling and measurements: The leaf green pigment content of the maize crop was measured by using a portable Minota chlorophyll detector (SPAD-502, Osaka 590-8551, Japan). Approximately, 3–4 leaves of 5 plants randomly were measured in each plot. The chlorophyll contents were measured in four different growth stages i.e., early rapid growth stage (V7), peak vegetative stage (V12), tasseling stage (V15) and maturity stage (VT).

After maturity, whole plots were manually harvested from ground level for the measurement of yield, and fifteen plants were randomly selected from each plot for other analysis. Plant heights were recorded at the time of maturity. The grains from fifteen randomly selected plants were manually separated and weighed. The remaining plant material (leaf and stem) was also detached and weighed. The plant components were thoroughly washed with tap water, followed by rinsing with distilled water and dried up to constant weight at a 65°C for 48 h in an electric oven and reweighed. The plant components were crushed into a fine powder (particle size: 0.15–0.25 mm) with the help of stainless-steel grinder, weighed and digested with H2SO4 and H2O2 for the determination of N concentration. Total N in each plant part was analyzed by the Kjeldahl digestion method and results were used to calculate total N uptake by multiplying the N concentration by dry matter for each treatment. NUE indicators were estimated by using N uptake values. NUE and partial factor productivity (PFP) were calculated by following formulas:

 

NUE (%) =              (1)

 

PFP (kg grain kg-1 N applied) =   (2)

 

Statistical analysis

 

All the experimental data were compiled by using Microsoft Excel 2013 and analyzed by Statistix (version 8.1). Analysis of variance (ANOVA) evaluated data, and the means were compared using least significant difference (LSD) at a P < 0.05 level. Graphs were prepared using OriginPro software (version 2016).

 

Results

 

Changes in soil pH and EC

 

The higher soil pH was recorded in urea treatment with NBPT + DCD and control treatments, compared to other fertilized treatments. The soil pH level significantly decreased in urea alone and urea treatment with NBPT after the first week up to 20 days after fertilization (DAF) and also similar trend was observed in second fertilization at all three fields (Fig. 2).

The highest EC was observed in soil amended with urea. Contrarily, NBPT + DCD treated urea decreased soil Table 1: Basic soil physicochemical properties of selected experimental sites

 

Parameter

Yangling

Zhouzhi-1

Zouzhi-2

pH

8.03

7.97

8.02

SOC (g kg-1)

11.8

5.5

6.2

Total N (g kg-1)

0.74

0.36

0.32

NH4+-N (mg kg-1)

5.2

4.2

3.5

NO3--N (mg kg-1)

23.9

12.8

2.6

Olsen P (mg kg-1)

35.6

16.8

17.4

Available K (mg kg-1)

265.9

100.1

114.1

EC (dS m-1)

0.168

0.167

0.134

Texture class

Silt loam

Loam

Silt clay loam

Particle size distribution Sand %

18.4

31.6

15.5

Silt %

56.6

47.9

54.4

Clay %

25.0

20.5

30.1

 

 

Fig. 1: Daily precipitation (mm), Average temperature (°C), relative humidity (%) and wind speed (m/s) during maize crop growing season of different two sites. Dash lines indicate fertilizer application timings.

 

EC throughout the maize growing season. The EC in the urea and U + NBPT treatments gradually increased 10 DAF, reached at peak 20 DAF and subsequently decreased. However, Lower EC was recorded in U + NBPT + DCD at all fields as compared to other fertilized treatments (Fig. 3).

 

Changes in mineral-N in soil

 

The changes in mineral-N were observed in the fertilized soils in all three sites (Yangling, Zhouzhi-1, and Zhouzhi-2) during maize growing season (Figs. 4 and 5). The sharp increase was recorded in soil NH4+-N content, soon after urea application, which reflects rapid urea hydrolysis. At Yangling field, the highest soil NH4+-N was recorded from urea treatment on 10th and 6th day for first and second fertilization, respectively (Fig. 4). However, the maximum soil NH4+-N was observed on 10th day for first and second fertilization at Zhouzhi-1 and Zhouzhi-2 fields. The use of NBPT with urea significantly reduced soil NH4+-N by slowed down hydrolysis as compared to other fertilized treatment throughout growing season at all three fields (P < 0.05). However, the combined use of NBPT + DCD with urea, produced slightly more soil NH4+-N, than U + NBPT (Fig. 4).

Soil NO3--N content increased gradually in urea alone and urea treated with inhibitors as compared to the  control treatment during maize crop growing season (Fig. 5). The highest soil NO3--N was recorded on 14 DAF in all three fields, and afterward gradually decreased. The use of DCD with U + NBPT significantly reduced soil NO3--N throughout the growing season. Urea treated with NBPT + DCD inhibited the urea hydrolysis and nitrification process, thus slightly decreased nitrate leaching (Fig. 6).

Table 2: Yield dry matter, yield increase and different agronomic parameters of maize crop under different treatments after harvesting

 

Sites

Treatment

Yield (DM kg ha-1)

Yield increase (%)

Straw yield

Grain yield

Straw yield

Grain yield

1000 seed weight (g)

Plant height    (cm)

Yangling

Control

4490c

3720c

-

-

287.28b

249.50b

Urea

4790b

4760b

9.82b

27.90b

313.44a

257.20a

U + NBPT

5180a

5500a

15.30ab

47.64ab

317.05a

261.47a

U + NBPT + DCD

5300a

5510a

17.88a

48.03a

323.49a

261.77a

Zhouzhi-1

Control

3360b

2610b

-

-

253.39b

242.90b

Urea

3810a

3250a

13.30a

24.26a

270.31a

260.80a

U + NBPT

4000a

3650a

19.03a

39.48a

273.76a

264.73a

U + NBPT + DCD

4030a

3650a

19.89a

39.53a

272.00a

263.00a

Zhouzhi-2

Control

2990b

2510c

-

-

245.15b

212.80b

Urea

3670a

3070b

22.37a

22.17b

265.15a

249.93a

U + NBPT

3840a

3460a

28.24a

37.66a

269.38a

253.20a

U + NBPT + DCD

3890a

3510a

29.93a

39.81a

269.33a

255.80a

Different letters in a column indicate significant difference at P < 0.05

 

 

Fig. 3: Changes in soil EC after application of urea and treated urea of three different experimental sites. Vertical bars represent standard error (SE), n = 3. Dash lines indicate fertilizer application timings

 

 

Fig. 2: Changes in soil pH after application of urea and treated urea of three different experimental sites. Vertical bars represent standard error (SE), n = 3. Dash lines indicate fertilizer application timings

 

 

Changes in plant height, seed index and SPAD values

 

Plant height (cm) and seed index (1000 seed weight) were significantly influenced by the application of urea, use of NBPT alone and mixture of NBPT + DCD with urea (Table 2). The increased plant height and higher seed index was recorded in fertilized treatments compared to control at all three fields (P < 0.05). However, no significant difference was noticed between the application of urea alone, U+ NBPT and U + NBPT + DCD.

The temporal variation in SPAD chlorophyll content values were observed during different growth stages at all three fields (Fig. 7). The combined use of NBPT + DCD with urea treatment slightly increased SPAD chlorophyll content at vegetative (V12), tasseling (V15) and maturity (VT) growth stages, as compared to urea treatment. However, the urea treatment with NBPT + DCD significantly enhanced SPAD chlorophyll content, compared to other treatments at tasseling (V15) and maturity (VT) growth stages of Zhouzhi-1 field. All fertilized treatments had significant effects on SPAD chlorophyll during all

 

Fig. 4: Changes in NH4+-N after application of urea and treated urea of three different experimental sites. Vertical bars represent standard error (SE), n = 3. Dash lines indicate fertilizer application timings

 

 

Fig. 5: Changes in NO3--N after application of urea and treated urea of different three experimental sites. Vertical bars represent standard error (SE), n = 3. Dash lines indicate fertilizer application timings

 

growth stages, compared to unfertilized control at all three fields (P < 0.05). Highest SPAD chlorophyll content was observed during peak vegetative growth stage (V12), however, lowest was observed at maturity stage (VT) followed by early growth stage (V7).

 

Changes in plant dry weight and grain yields

 

Grain and straw dry matter were significantly affected by the urea application, and use of NBPT and NBPT + DCD with urea (Table 2). Maximum maize grain and straw yield were recorded in U + NBPT + DCD followed by U+NBPT at all three fields. Moreover, no significant difference was noticed in the U + NBPT and U + NBPT + DCD.

Yield increase percentage was calculated by subtracting control yield form fertilized yield divided by the control yield. The maximum grain yield and straw biomass were found in U + NBPT + DCD, followed by U + NBPT at all three fields. Moreover, the increase in grain yield (15–20%) was observed in NBPT and NBPT + DCD treated urea, as compared to urea alone (Table 2). At Yangling field, the highest grain yield (5510 DM kg ha-1) was recorded with an increase of 37.7–48% in U + NBPT +

 

Fig. 6: Changes in NO3--N accumulation in soil profile after application of urea and treated urea of different three experimental sites. Vertical bars represent standard error (SE), n = 3

 

DCD, followed by U+NBPT as compared to unfertilized control treatment. Moreover, a maximum grain yield increase (20%) was recorded at Yangling field in U + NBPT and U + NBPT + DCD as compared to urea alone treatment (Table 2).

 

Changes in N uptake and N use efficiency

 

The N uptake by different plant organs (stem, leaf, and grain) was significantly affected by the application of urea, urea treatment with NBPT and NBPT + DCD (P < 0.05). Highest N uptake was recorded in U + NBPT + DCD followed by U + NBPT compared to unfertilized control at all three fields. The maximum N uptake was observed in grain and lower in stem across all three fields (Table 3). The temporal variations in above ground biomass, N were taken up by maize crop was observed in all three fields (Table 3). Urea treated with NBPT and NBPT + DCD increased N uptake (79.3–136.1 and 80.1–139.6 N kg ha-1), respectively. The maximum N uptake was recorded in U + NBPT + DCD, followed by U + NBPT at Yangling field.

Application of U+NBPT and U+NBPT+DCD had significantly improved N use efficiency compared to urea alone (P < 0.05), while no significant difference was observed between U + NBPT and U + NBPT + DCD (Table 3). The highest N use efficiency was recorded in U + NBPT + DCD (14.3–22.6%), followed by U + NBPT (13.8–21.6%). However, lowest N use efficiency (9–15.5%) was recorded in urea alone as compared to unfertilized control treatment across all fields. Urea treatment with NBPT and NBPT + DCD produced higher N use efficiency at Zhouzhi-2 field, followed by the Yangling. However, lower N use efficiency was observed at Zhouzhi-1 field for all fertilized treatments (Table 3).

Higher partial factor productivity (PFP) was recorded in U + NBPT and U + NBPT + DCD, compared to unfertilized control (Table 3). Application of urea treatment with NBPT + DCD increased PFP (15.97–25.1 kg grain kg-1 N applied), followed by U + NBPT (15.7–24.99 kg grain kg-1 N applied). The maximum PFP was increased by the application of urea treatment with NBPT + DCD and U + NBPT at Yangling field. However, minimum PFP was observed at Zhouzhi-2 for all fertilized treatments, contrast with Yangling and Zhouzhi-1 (Table 3).

 

Discussion

 

Application of NBPT significantly affected soil N transformation, thereby increased N uptake, crop yield, and ultimately improved NUE. The change in soil pH during first week of fertilization was due to the production of NH4+-N in the soil, afterward gradually decreased, because of the nitrification of the NH4+-N by soil microbes. A short-term rise in soil pH always happens after urea application due to urea hydrolysis (Zaman et al. 2009; Zaman and Nguyen 2012). The application of NBPT with urea inhibited urea hydrolysis, resulting in decreased NH4+-N content and low rise of soil pH throughout the maize growing season (Sanz-Cobena et al. 2008; Zaman et al. 2009; Meng et al. 2023), which is associated with release of hydroxyl (OH-) ions (Singh et al. 2013). Observations of other studies confirm these results that application of urea treatment with NBPT decreased NH4+-N content (Zaman et al. 2009, 2013; Suter et al. 2013; Montalbán et al. 2021).

The use of NBPT increased EC and NO3--N content throughout maize growing season, compared to U+NBPT+DCD (Figs. 3 and 5). There is a close relationship between NO3--N content and EC of the soil under aerobic conditions. The gradual decrease in NH4+-N and increase in NO3--N concentrations, demonstrate the happening of nitrification after urea hydrolysis (Martins et al. 2017; Lan et al. 2018).

Table 3: N uptake by different plant parts, above ground biomass, Nitrogen use efficiency and partial factor productivity of maize crop under different treatments in three different experimental sites after harvesting

 

N uptake (N kg ha-1)

Sites

Treatment

Leaf

Stem

Grain

Above ground biomass

NUE (%)

PFP (N kg kg-1)

Yangling

Control

22.30c

21.21c

51.50c

95.00c

-

-

N-220

25.41b

23.72b

68.52b

117.65b

10.30b

21.65b

N + NBPT

29.00a

26.44a

80.62a

136.06a

18.66a

24.99ab

N + NBPT + DCD

29.72a

28.37a

81.53a

139.63a

20.28a

25.06a

Zhouzhi-1

Control

11.27b

7.758b

29.85c

48.881b

-

-

N-220

16.42ab

10.73ab

41.56b

68.71a

9.01a

14.76a

N + NBPT

18.03a

12.53a

48.72a

79.29a

13.82a

16.57a

N + NBPT + DCD

18.40a

12.24a

49.63a

80.27a

14.27a

16.57a

Zhouzhi-2

Control

7.64b

6.34c

23.68c

37.663c

-

-

N-220

18.73a

14.46b

38.62b

71.80b

15.52b

13.97b

N + NBPT

20.14a

17.81a

47.32a

85.27a

21.64a

15.73a

N + NBPT + DCD

20.70a

18.21a

48.39a

87.30a

22.56a

15.97a

Different letters in a column indicate significant difference at P < 0.05.

 

 

Fig. 7: SPAD chlorophyll values after application of urea and treated urea of three different experimental sites. Values followed be same letters in each column do not differ significant differently. Vertical bars represent standard error (SE), n = 3

 

Plant growth and yield were significantly influenced by the use of NBPT with urea. N is one of the major components of chlorophyll, and the chlorophyll content depends on increase and decrease of plant N uptake (Makino and Osmond 1991). The application of urea treatment with NBPT was significantly increased SPAD chlorophyll content throughout all growth stages across all fields (Fig. 7). Our results are confirmed by other studies, reported that the addition of NBPT with urea had increased leaf chlorophyll content (Kawakami et al. 2012; Zuki et al. 2020).

In our study, the addition of NBPT with urea significantly increased the crop yield, N uptake and NUE, compared to urea and control treatments (P < 0.05). Application of NBPT delayed urea hydrolysis for both fertilization, that enables to plant uptake N in NH4+-N form, which is more efficient than uptake in the form of NO3--N, as less energy consumed to convert NH4+-N into plant proteins, compared to NO3--N (Zaman et al. 2009). The use of NBPT with urea intensely reduced ammonia (NH3) volatilization ranged 80–93% in the Chinese Loess Plateau (Ahmed et al. 2018), thereby increased N uptake and NUE (Kawakami et al. 2012; Singh et al. 2013). The increase in N uptake could be related to reduced N losses, which conserve N in the soil (Zaman et al. 2013; Rose et al. 2018). The N conservation in the soil ultimately increased NUE and crop yield (Abalos et al. 2014; Ramalingappa et al. 2023).

Application of urea treatment with NBPT was resulted in significant increase in maize grain yield (37.7–47.6, 15–19.7%), compared to control and urea treatments, respectively (Table 2). Almost same results were obtained with the application of NBPT treated urea increased (10–15%) maize grain yield compared to urea (Ding et al. 2011; Martins et al. 2017; Montalbán et al. 2021). Furthermore, different meta-analysis have been reported that the use of NBPT with urea significantly increased crop yield (10%) and NUE (12%) (Abalos et al. 2014; Silva et al. 2017; Meng et al. 2023). The other studies described that the use of NBPT with urea have potential to increase N uptake and crop yield (Ding et al. 2015; Zhao et al. 2017; Fu et al. 2020). In addition, NBPT treated urea demonstrated higher N uptake than urea alone (Singh et al. 2013; Ramalingappa et al. 2023).

The use of NBPT with urea significantly increased N uptake (33%), N recovery efficiency (48–61%) and crop yield (27–38%) (Dawar et al. 2011), which resulted in 1.8 times more NUE than urea alone (Hube et al. 2016). Moreover, the use of NBPT with urea has potential to increase uptake (17–22%) and improve NUE (29–41%) as compared to urea treatment (Kawakami et al. 2012, 2013; Sanz-Cobena et al. 2012; Ding et al. 2015; Fu et al. 2020). Application of Limus (75% NBPT + 25% NPPT) with urea increased N recovery efficiency ranged 11–17%, compared to urea alone (Li et al. 2015, 2017). The results of the present study stated that use of NBPT with urea could be an appropriate approach for increasing yield, N uptake and improving NUE of the maize crop.

The combined use of NBPT + DCD with urea delayed urea hydrolysis and nitrification process, result in increased soil pH, which is due to the presence of NH4+-N in the soil (Zaman et al. 2009). In addition, the inclusion of DCD with U + NBPT retained high soil NH4+-N concentration and pH for a long time (Soares et al. 2012). Our results are agreed with other studies, reported that the high NH4+-N content remained in the soil for a longer time by the use of DCD with U + NBPT (Zaman and Nguyen, 2012; Montalbán et al. 2021), possibly due to nitrification (Lan et al. 2018).

Generally, the trend of EC was more or less similar pattern to changes in soil NO3--N. The changes in soil EC associated with NO3--N, probably due to nitrification. The soil NO3--N was significantly lower in the urea treatment with NBPT + DCD across all fields, due to NI reduced nitrification (Lan et al. 2018). The results of the current study are agreed with the observations of previous studies (Ding et al. 2011; Rose et al. 2018). Application of NBPT+DCD with urea had slow down the nitrification and decreased soil NO3--N on the surface, thereby influenced the nitrate leaching (Zaman and Nguyen, 2012; Montalbán et al. 2021). Addition of DCD with U+NBPT affected nitrate accumulation in the soil profile (Zaman et al. 2009, 2013). Although, in our study, nitrate leaching was not significantly observed, might be due to the short duration and less precipitation.

The slow release of NH4+-N and NO3--N in the soil, less susceptible to N loss and provide greater opportunity for more N uptake by plant, thereby improving NUE and crop yield (Zaman et al. 2009; Zaman and Nguyen, 2012; Rose et al. 2018). Urea treatment with NBPT+ DCD also increased SPAD chlorophyll content throughout all growth stages across all fields (Fig. 7). Our results are agreed, that the combined use of NBPT + DCD with urea increased chlorophyll content (Kawakami et al. 2013). Moreover, application of UIs and NIs with N fertilizer significantly enhanced chlorophyll content (Zuki et al. 2020; Meng et al. 2023). Reduction in nitrification is possible to protect N against denitrification and NO3--N leaching and provide more chance to plant N uptake (Zaman and Nguyen, 2012; Montalbán et al. 2021). Our results are confirmed, that combined use of NBPT + DCD with urea slightly increased crop yield, N uptake and NUE compared to use of NBPT (Ding et al. 2015; Rose et al. 2018). Furthermore, observations of other studies revealed that use of DCD with U + NBPT did not significantly increase crop yield, compared to U + NBPT (Ding et al. 2011; Fu et al. 2020). Furthermore, combined use of UIs and NIs with N fertilizer significantly increased crop yield compared to single use of N fertilizer (Zuki et al. 2020; Meng et al. 2023). The inclusion of NBPT with DCD considerably decreased 75–90% NH3 volatilization in different soils under different climatic conditions (Ahmed et al. 2018), thus improving the bioavailability of N, thereby increasing 8–13% plant dry matter, then urea alone (Zaman and Nguyen 2012). Furthermore, Sanz-Cobena et al. (2012), also reported that combination of NBPT + DCD with urea increased N uptake of maize crop 38.5 and 18% compared to control (no fertilization) and urea treatments, respectively. In addition, a meta-analysis reported that mixture of NBPT + DCD with urea increased 14.7% NUE (Abalos et al. 2014). Application of inhibitors (UI + NI) also increased grain yield (23–30%), N uptake (47%) and N recovery efficiency (30%) of maize crop (Martins et al. 2017; Meng et al. 2023). In addition, the combined use of UI and NI along with urea demonstrate higher NUE of maize crop (22 and 37%) compared to urea and control treatment, respectively (Zhao et al. 2017; Montalbán et al. 2021). Such increase in crop yield, N uptake and NUE can be attributed to combined use of inhibitors (Meng et al. 2023), probably delayed urea hydrolysis and nitrification (Zaman et al. 2009), provide chance for efficient N uptake by plants with the conversion of N into proteins (Rose et al. 2018). The combined application of NI and UI with urea also represented the best strategy tended to enhancement in crop production (Abalos et al. 2014, 2016; Zuki et al. 2020).

The highest crop yield and N uptake were recorded at Yangling field which might be due to high soil fertility status, such as high residual NPK content and more amount of precipitation. These results agree with previous observations, that yield response was intensely influenced by residual fertility status and soil water content (Cui et al. 2008; Abalos et al. 2016). In addition, it was reported that high crop yield is correlated with residual soil NO3--N (Li et al. 2015; Miao et al. 2015). Moreover, the difference in precipitation (44 mm) could be the other reason, which plays a vital role in increasing crop yield and NUE (Zhao et al. 2017).

The positive response of inhibitors in terms of increased crop production, N uptake and NUE were mainly differentiated by the soil texture and soil moisture content. In our study, soils with high soil clay and silt, and low sand contents resulted in more effectiveness of inhibitors, compared to high sand content. This efficiency is probably related to the ability of clay and silt content to retain NH4+-N fixation in the soil and reduce N loss. The soil clay content keeps NH4+-N concentration long time in the soil matrix by water coming through precipitation, resulting in more N uptake by plants, thereby increasing crop yield and NUE (Francisco et al. 2011; Li et al. 2017). In addition, UIs and NIs are effective in fine-textured soils, and probably lower N losses through leaching (Abalos et al. 2014).

The current study demonstrated that soil properties such as basic fertility status and climatic factors (precipitation, air temperature) could have effects on increasing yield and NUE of the maize crop. Overall, these findings indicate that the application of NBPT alone and the combination of NBPT + DCD with urea could be an integrated strategy to increase crop yield, N uptake and NUE of maize crops in different soil properties under various environmental factors.

 

Conclusion

 

Application of urea treatment with NBPT and a mixture of NBPT + DCD increased urea N retention, in different edaphic and environmental circumstances conducive to N loss. The sole application of NBPT with urea increased nitrate leaching compared to U + NBPT + DCD. However, the combined application of NBPT + DCD with urea delayed urea hydrolysis and nitrification processes, thereby alleviating N losses by NO3--N leaching and gas emission. In this manner N remained in the soil for a long time, providing an opportunity to more plant N uptake, resulting in improved NUE and crop yield. This integrated strategy had increased above-ground dry matter, N uptake and NUE of the maize crop, and could be helpful for more economic benefits to growers and the environmental performance of the agricultural system. The current study concluded that the combination of NBPT + DCD with urea would be the more reasonable approach to overcome N losses, thereby enhancing NUE and crop yield.

 

Acknowledgments

 

This research work was supported by the National Natural Science Foundation of China (41671295) and National Key Research and Development Prog of China (2017YFD0200106).

 

Author Contributions

 

MA and JZ planned experiment, WY and M L interpreted results, M A, SR and ASE made the write up, MA statistically analyzed the data and SR made illustrations.

 

Conflicts of Interest

 

All authors have read and approved the final manuscript and declare no conflict of interest.

 

Data Availability

 

Data presented in this study will be available on a fair request to the corresponding authors.

 

Ethics Approval

 

Not applicabe to this paper

 

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