Optimization of inter-seasonal nitrogen allocation increases yield and resource-use efficiency in a water-limited wheat–maize cropping system in the North China Plain

Abstract

Winter wheat–summer maize cropping system in the North China Plain often experiences droughtinduced yield reduction in the wheat season and rainwater and nitrogen (N) fertilizer losses in the maize season. This study aimed to identify an optimal interseasonal water- and N-management strategy to alleviate these losses. Four ratios of allocation of 360 kg N ha-1 between the wheat and maize seasons under one-time presowing root-zone irrigation (W0) and additional jointing and anthesis irrigation (W2) in wheat and one irrigation after maize sowing were set as follows: N1 (120:240), N2 (180:180), N3 (240:120) and N4 (300:60). The results showed that under W0, the N3 treatment produced the highest annual yield, crop water productivity (WPC), and nitrogen partial factor productivity (PFPN). Increased N allocation in wheat under W0 improved wheat yield without affecting maize yield, as surplus nitrate after wheat harvest was retained in the topsoil layers and available for the subsequent maize. Under W2, annual yield was largest in the N2 treatment. The risk of nitrate leaching increased in W2 when N application rate in wheat exceeded that of the N2 treatment, especially in the wet year. Compared to W2N2, the W0N3 maintained 95.2% grain yield over two years. The WPC was higher in the W0 treatment than in the W2 treatment. Therefore, following limited total N rate, an appropriate fertilizer N transfer from maize to wheat season had the potential of a "triple win" for high annual yield, WPC and PFPN in a water-limited wheat–maize cropping system.

Headnote

ABSTRACT

Winter wheat–summer maize cropping system in the North China Plain often experiences droughtinduced yield reduction in the wheat season and rainwater and nitrogen (N) fertilizer losses in the maize season. This study aimed to identify an optimal interseasonal water- and N-management strategy to alleviate these losses. Four ratios of allocation of 360 kg N ha-1 between the wheat and maize seasons under one-time presowing root-zone irrigation (W0) and additional jointing and anthesis irrigation (W2) in wheat and one irrigation after maize sowing were set as follows: N1 (120:240), N2 (180:180), N3 (240:120) and N4 (300:60). The results showed that under W0, the N3 treatment produced the highest annual yield, crop water productivity (WPC), and nitrogen partial factor productivity (PFPN). Increased N allocation in wheat under W0 improved wheat yield without affecting maize yield, as surplus nitrate after wheat harvest was retained in the topsoil layers and available for the subsequent maize. Under W2, annual yield was largest in the N2 treatment. The risk of nitrate leaching increased in W2 when N application rate in wheat exceeded that of the N2 treatment, especially in the wet year. Compared to W2N2, the W0N3 maintained 95.2% grain yield over two years. The WPC was higher in the W0 treatment than in the W2 treatment. Therefore, following limited total N rate, an appropriate fertilizer N transfer from maize to wheat season had the potential of a "triple win" for high annual yield, WPC and PFPN in a water-limited wheat–maize cropping system.

Keywords:

Cropping system

Water-saving irrigation

North China Plain

Nitrogen optimization

Sustainable intensification

(ProQuest: ... denotes formulae omitted.)

1. Introduction

The wheat–maize cropping system in the North China Plain (NCP) faces the simultaneous challenges of water conservation, yield improvement, and high nitrogen (N) fertilization efficiency. In recent decades, groundwater irrigation has been widely used in the NCP to achieve high yields owing to the disparity between crop water requirements and rainfall [1,2], exacerbating groundwater depletion [3]. Conventional agricultural practices have also employed large N inputs (often exceeding 210 kg N ha-1 season-1 ), regardless of soil fertility and target yield [4,5]. As a result, excessive irrigation has driven large amounts of residual soil nitrate downwards, leading to groundwater pollution [6].

Optimization of N management under limited irrigation conditions in the NCP is desirable. Promoting water-saving irrigation is a strategic measure to reduce irrigation water and improve crop water productivity (WPC) in the wheat–maize cropping system [7–9]. To date, irrigation frequency has been reduced to 1–3 times for wheat and 1–2 times for maize [10–12]. The double cropping system has achieved high WPC in past decades [13,14]. In particular, a new water-saving irrigation technique of one-time presowing root-zone irrigation, consisting of applying full irrigation before wheat sowing with no subsequent supplemental irrigation, and only one irrigation after maize sowing in the wheat–maize cropping system, reduced groundwater depletion without much yield loss [11,15,16]. Qin et al. [17] showed that the optimal N application rate should be determined based on the target yield, which depends mainly on cropland water resource availability. Water-saving irrigation strategies are now being implemented in water-scarce areas in the NCP, leading to a need to determine optimal N management in these strategies.

Optimizing interseasonal N allocation in the wheat–maize cropping system under limited irrigation conditions is promising to further increase yield and N-use efficiency. Previous studies [5,17–19] of the wheat–maize cropping system in the NCP have focused mainly on the effects of intra-seasonal N optimization on yield improvement and N use efficiency, including N fertilizer type, amount, timing, and placement. However, optimization of N allocation between crop seasons is still in its infancy. Agricultural N use is associated with field water resource availability in regions where water is scarce [4,6]. Under full irrigation conditions, soil reservoir capacity after the wheat harvest was too low to accommodate the excess rainfall in the maize season, resulting in rainwater drainage and nitrate leaching [15,20]. In contrast, limited irrigation in wheat reduced deep drainage, nitrate leaching, and nitrous oxide (N2O) emissions throughout the growing season and even into the following summer maize season, thereby improving maize yields [6,11].

We hypothesized that given a fixed total N application in the wheat–maize cropping system, increasing the N allocated to the wheat crop would increase wheat yield under limited irrigation, reduce N loss to stabilize maize yield, and thus increase annual yield and water- and N-use efficiency. N cycling in a cropping system is subject to rainfall and temperature variation [4,6]. In the hot and rainy maize growing season in the NCP, N losses from nitrate leaching and N2O emissions were greater than in the wheat season [11,21], indicating the need to reduce N application rates as much as possible. In contrast, an increase in N fertilizer rate in wheat under limited irrigation conditions increased seedling growth, soil water utilization, and grain yield and protein content [22,23].

This study aimed to identify an N-allocation and watermanagement regime that would maximize crop yield and waterand N-use efficiency in the wheat–maize cropping system. The experimental approach was to evaluate these target traits in four treatment combinations of annual N allocation with two irrigation regimes.

2. Materials and methods

2.1. Study site

Field experiments were conducted in 2017–2019 at the Experimental Station of China Agricultural University (37.63N, 116.44E) in Wuqiao county, China. Seasonal precipitation was 191.5 mm in 2017–2018 and 62.3 mm in 2018–2019 in the wheat season, and 484.7 mm in 2018 and 287.9 mm in 2019 in the maize season (Fig. S1). Mean temperatures in the wheat and maize seasons were 7.8 and 26.0 C in 2017–2018, and 7.7 and 26.1 C in 2018–2019, respectively. In the 0–20 cm soil layer prior to the experiment in 2017, organic matter was 12.6 g kg-1 , total N was 1.1 g kg-1 , and available P and K were 45.5 mg kg-1 and 163.9 mg kg-1 , respectively.

2.2. Experiment design

A split-plot experiment was conducted in two seasons. The main plots were two irrigation regimes: application of a onetime root-zone (0–200 cm) irrigation before wheat sowing to reach 85%–90% of field capacity (W0) with an additional irrigation at the jointing and anthesis stage (W2) (Table S2). Each irrigation of wheat was of 75 mm. Irrigation after maize sowing was applied at 75 mm in 2018 and 90 mm in 2019. The subplots consisted of four N regimes: based on a total N rate of 360 kg ha-1 , the N allocation ratios between wheat and maize seasons were 120:240 (N1), 180:180 (N2), 240:120 (N3) and 300:60 (N4). Each treatment was replicated in three plots of 66 m2 (6 11 m). Winter wheat (cultivar Nongda 399) was sown in mid-October and harvested in the following June. Summer maize (cultivar Zhengdan 958) was then sown in early June. All fertilizers were applied before sowing. The P2O5 fertilizer application rates were 135 and 90 kg ha-1 for wheat and maize, respectively. The K2O rate was 112.5 kg ha-1 in each plot. Other field practices are detailed in Liu et al. [11].

A microplot experiment was performed to quantify maize plant N uptake from fertilizer N applied in the wheat season in 20182019. Each microplot was of 1.5 2 m and surrounded by a 0.35-m deep Zn-coated iron frame to separate it from the field soil. Prior to wheat sowing in 2018, the W0N2 and W0N4 treatments received N fertilization with 15N-labeled urea with 10.2% abundance and 46.8% N concentration. In the subsequent maize season, the two treatments received normal urea. Other management practices followed local standards.

2.3. Measurements and calculation

2.3.1. Yield and dry matter accumulation

Grain yield (GY) was determined using three 3-m2 plots for wheat and three 12-m2 sampling plots for maize at harvest stage. Plants from two 50-cm inner rows in each plot were sampled to count spike number, kernels per spike, and thousand-kernel weight at wheat maturity stage. All wheat plants from three 0.18-m2 plots (four 0.3-m rows) and nine maize plants were collected to determine aboveground dry matter accumulation at the anthesis (DMA) and maturity (DMM) stages. Harvest index (HI) was calculated as the ratio of grain weight to DMM.

2.3.2. Nitrogen and water utilization characteristics

.3.2. Nitrogen and water utilization characteristics At sowing and maturity stage, soil samples were taken at 0.2-m intervals to determine soil nitrate content of the 2-m soil profile by ultraviolet spectrophotometry and soil water content by the drying method following Liu et al. [11]. Soil mineral nitrogen (kg ha-1 ) was calculated as follows:

... (1)

where B is bulk density (g cm-3 ), H is soil depth (cm), SNC is soil nitrate content (mg kg-1 ).

Crop water productivity (WPC, kg m-3 ) was calculated as follows:

... (2)

where GY and ET are grain yield (kg ha-1 ) and evapotranspiration (mm), respectively.

... (3)

where I is irrigation (mm), P is rainfall (mm), SWD is the difference between initial and final soil water storage from a depth of 0200 cm (mm), and D is drainage amount (mm). The D during the experiment in 2017–2019 was estimated using a local modified DSSAT model following Liu et al. [11].

N partial factor productivity (PFPN, kg kg-1 ) is a measure of crop yield per kilogram of nitrogen applied.

... (4)

where NF is N application rate (kg ha-1 )

Plant and soil samples were collected at the end of the wheat and maize seasons in 2019 and measured for total N concentration and 15N enrichment using an elemental analyzer (Elementar, Bremen, Germany) and mass spectrometer (Vario EL, Elementar). Plant N uptake derived from 15N-labeled urea was calculated following Yao et al. [24].

2.4. Statistics

Two-way analysis of variance (ANOVA) was used to test treatment differences (LSD, P < 0.05) in yield and its components with SPSS 26.0 (IBM Corp, Armonk, NY, USA). Figures were plotted with Origin 2021 (OriginLab Corporation, Northampton, MA, USA).

3. Results

3.1. Yield and nitrogen partial factor productivity

Irrigation, N and their interaction affected grain yields, while only N had no effect on maize yield (Table 1). Appropriate N fertilizer transfer from maize to wheat season under W0 would increase yield of the wheat-maize cropping system. Over the two growing seasons, annual yield followed the order N3 N4 > N2 > N1 under W0. The W0N3 treatment resulted in higher annual yield than in W0N2 and W0N1, but did not differ from W0N4. In both seasons, wheat yield was higher in W0N3 than in W0N2 and W0N1, with an average increase of 7.6% and 20.7%, respectively. Likewise, wheat spike number and thousand kernel weight increased from W0N1 to W0N2 and from W0N2 to W0N3 (Fig. 1). Dry matter accumulation at wheat maturity stage was higher in W0N3 than in W0N1 and W0N2, while harvest index did not different between N regimes. In the two seasons, maize yield did not differ between N regimes under W0.

In the W2 treatments, an equal N application ratio between the wheat and maize seasons achieved the highest yield (Table 1). Across two growing seasons, annual yield was the largest in N2 under W2, but did not differ from N3. Under the same N regime, annual yield was slightly lower in W0 than in W2. The W0N3 achieved 90.5% of the annual yield of W2N2 in 2017–2018, but did not differ from W2N2 in 2018–2019. Compared to W2N2, the W0N3 maintained a relatively high wheat yield averaging 6545 kg ha-1 , and improved maize yield by 6.0% over two growing seasons.

The PFPN was influenced by N, irrigation, and their interaction (Table S3). Based on the total N rate, increased N allocation in wheat under limited irrigation increased annual PFPN. Annual PFPN was the largest in the N3 treatment under W0 across both years. Compared to W0N2 and W0N1, the W0N3 had higher annual PFPN, with an average increase of 4.1% and 8.4%, respectively, but did not differ from W0N4. In the wheat seasons, the W0N3 treatment resulted in respectively 18.3%–20.4% and 37.9%–41.4% lower PFPN for winter wheat compared with W0N2 and W0N1, and 49.3%–56.7% and 101.2%–103.8% higher PFPN for summer maize. Under W2, the PFPN of wheat-maize system was the largest in N2, but did not differ from N3. At the same N regime, the PFPN was often lower in W0 compared to W2.

3.2. Temporal and spatial distribution of soil nitrate content

Surplus nitrate after wheat harvest was retained mainly in the topsoil layers under W0 (Fig. 2). After wheat harvest in 2018, soil nitrate content from a depth of 0–60 cm generally followed the order N4 > N3 > N2 > N1 in the W0 treatments (Fig. 2). Under the same N regime, the 0–60-cm soil nitrate content was higher in W0 than in W2 after wheat harvest in 2018. In contrast, the 60–200-cm soil nitrate content was often lower in W0 than in W2 in 2018. Similarly, soil nitrate content from a depth of 040 cm after wheat harvest increased with N rate under W0 in 2019. At the identical N regime, the W0 treatment had higher 040-cm soil nitrate content after wheat harvest in 2019 compared to W2, with no difference in the 40–200 cm soil profile.

Nitrate leaching from a depth of 0–120 cm decreased under W0 during the maize season. After maize harvest in 2018, soil nitrate content at 0–100 cm depth generally followed the order N1 > N2 > N4 N3 in the two irrigation regimes, but did not differ in the 100–200 cm soil profile. Under the same N regime, soil nitrate content at soil depths of 0–200 cm after maize harvest in 2018 was often higher in W0 compared to W2. In the dry year in 2019, soil nitrate content did not differ between N regimes at soil depths of 0–200 cm after maize harvest, regardless of the irrigation regime.

3.3. Effect of diverse nitrogen management in wheat on nitrogen uptake of subsequent maize under limited irrigation

The residual topsoil nitrate after wheat harvest was available for the subsequent maize (Fig. 3). After wheat harvest in 2019, residual fertilizer 15N was distributed mainly in the 0–40 cm soil profile. With increased fertilizer 15N rates, the residual fertilizer 15N after wheat harvest increased and was available for the subsequent maize crop (Table 2). In particular, the maize plant N uptake from fertilizer 15N applied in wheat was approximately two times higher in W0N4 than in W0N2. Total maize plant N uptake did not differ between W0N4 and W0N2. As a result, the proportion of maize plant N uptake from fertilizer 15N in wheat was 75.4% higher in W0N4 than in W0N2. At the end of the maize season, fertilizer 15N was observed only at soil depths of 0–140 cm.

3.4. Soil water dynamics and crop water productivity

Irrigation, N and their interaction affected WPC, whereas only N had no effect on WPC in the maize season (Table 1). In the W0 treatments, appropriate N fertilizer transfer from maize to wheat season improved annual WPC. Annual WPC generally followed the order N3 N4 > N2 > N1 in the W0 treatment. The W0N3 treatment resulted in 1.6%–8.6% and 6.0%–10.0% higher annual WPC compared to W0N2 and W0N1, while did not differ from W0N4.

In the wheat seasons, the WPC was higher in W0N3 than in W0N2 and W0N1, with an average increase of 8.5% and 17.5%, respectively. In the maize seasons, the WPC did not differ between N regimes under W0. Annual WPC did not differ between N regimes in the W2 treatment. Under the identical fertilization regime, WPC was often higher in W0 compared to W2.

Limited irrigation in wheat increased 2-m soil water depletion, then the enlarged soil reservoir capacity after wheat harvest accommodated more rainfall and reduced deep drainage in the maize season (Fig. 4). After wheat harvest in 2018, soil water content of the 200-cm soil profile generally followed the order N1 > N2 > N3 > N4 in the W0 treatment (Fig. S2). In 2019, the 0200-cm soil water content after wheat harvest showed no significant difference between N regimes. Across the two wheat seasons, soil water depletion after wheat harvest was lower in W2 than in W0, while drainage was higher in the wetter year in 2018. By the time of the subsequent maize in both years, there was no difference in soil water content at 0–200 cm depth between N regimes. Drainage was greater in W2 than in W0 during the maize seasons in 2018.

4. Discussion

4.1. Optimal inter-seasonal nitrogen fertilizer allocation for annual yield improvement

Optimizing inter-seasonal N allocation is an efficient strategy to further improve yield in the wheat–maize cropping system. Groundwater crisis and nitrate contamination are increasingly threatening agricultural sustainable development all over the world [5,25]. As a case study, we considered the water-scarce areas in the NCP, where a series of water-saving irrigation strategies and alternative cropping systems have been proposed [11,16,26]. Alternative cropping systems are not accepted by most farmers and policy makers due to high yield penalty. In terms of the doubling cropping system, under conventional irrigation (W2), this study confirmed that an equal N application ratio between the wheat and maize seasons achieved the highest yield, in accordance with local N management [27]. Under limited irrigation (W0), increased N application rate improved wheat yield, which was attributed to an increase in the soil water use, photosynthetic rate, and drought resistance [22,28]. Residual topsoil nitrate after wheat harvest has the same efficacy as that of N fertilizer applied throughout the maize growing season [29–31], which explains the stable maize yield under W0 (Fig. 5). Overall, based on limited total N rate, an appropriate N transfer from summer maize to winter wheat season under limited irrigation increased wheat yield, and the residual topsoil nitrate after wheat harvest helped to maintain the subsequent maize yield, contributing to annual yield improvement.

4.2. Synergy effect of inter-seasonal water and nitrogen management to improve resource use efficiency

This study highlighted the synergy of inter-seasonal water and N management and provided a practical application case study for high water- and N-use efficiency. Precipitation, irrigation and soil moisture served as the main physical drivers of cropland N use, cycles and losses [32,33]. Exploiting the synergistic effect of water and N management helped to improve crop productivity and resource use efficiency [34]. The study confirmed that limited irrigation in wheat increased soil water depletion and prevented topsoil nitrate from moving downwards, in line with previous studies [11,30]. As a result, the wheat yield increased with increasing N rates under W0, whereas there were often no significant differences under W2 (Table 1). Therefore, the intra-seasonal N allocation differed between the irrigation regimes. All the N applied as base fertilizer became feasible under limited irrigation, while postponing top dressing N application was necessary to balance N supply under conventional irrigation [35,36]. Furthermore, limited irrigation altered cropland N use in wheat–maize cropping system. The improved N retention potential in wheat under limited irrigation was maintained in the subsequent maize season (Fig. 3). Zhou et al. [29] also gave an example of how deep-rooted wheat could capture the residual nitrate after maize harvest. Notably, a reduction in N and water inputs may simulate soil organic N mineralization and decrease soil organic carbon stock [37]. In this study, the W0N3 achieved 95% of the GY and guaranteed straw returning amount compared with W2N2 (Fig. 1). Liu et al. [11] conducted a similar irrigation experiment and reported that the reduction in straw carbon input was less than the carbon loss from soil CO2 emissions. Therefore, the W0N3 could maintain or improve the soil organic carbon/N stocks. Above all, compared with conventional irrigation, the reduction in nitrate leaching under limited irrigation lowered N fertilizer requirement, and the reduced N rate would in turn further reduce N loss.

4.3. Prospects for sustainable agricultural production

To produce more grain with lower water and N inputs, this study considered wheat-maize cropping system as a whole and optimized inter-annual N allocation based on integrated watersaving cultivation practices: 1) late planting controlled wheat flourish before wintering and built proper wheat population structure, 2) an appropriate increase in N application ratio in the wheat season promoted early growth and compensated for the adverse effects of water deficit on spike number, 3) no seasonal irrigation reduced topsoil fertilizer N leaching and increased deep soil water use for late-season grain development. As in many world regions, developing integrated cultivation management is becoming increasingly important for sustainable agricultural intensification [11,38–40]. The N fertilization and irrigation were key factors controlling carbon footprint of crop production [41]. Limited irrigation significantly lowered carbon footprint by reducing power use for irrigation and soil N2O emissions in the wheat-maize cropping system [11,21]. Soil N2O emissions were positively correlated with N application rate [42]. Compared to the wheat season, most of the soil N2O emissions occurred in the maize season due to higher soil moisture and temperature [43]. In this study, transferring the N fertilizer from summer maize to winter wheat placed fertilizer N in the deeper layer layers in advance (Fig. 2), and lower N applications in the maize season might have the potential for negative emissions from soil N2O emissions. Today, aging is a threat to agricultural development [44]. Conventional N-saving strategies have been poorly accepted by farmers due to their complicated implementation and high economic costs [4]. In recent years, the onetime presowing root-zone irrigation has been adopted in severe ground funnel regions due to its effective results and easy implementation. Transfer of N fertilizer from summer maize to winter wheat only required an adjustment of N application rate with no other labor costs, which will undoubtedly be more popular.

5. Conclusions

In wheat–maize cropping system in the NCP, of four ratios of allocation of 360 kg N ha-1 between the wheat and maize seasons, a 240:120 allocation under limited irrigation increased wheat yield without affecting maize yield. Under full irrigation, splitting N application equally between the two crops controlled nitrate leaching, resulting in the highest yield and N- and water-use efficiency. Optimal N fertilizer allocation between consecutive cropping seasons depends on the irrigation regime adopted for each.

CRediT authorship contribution statement

Xiaonan Zhou: Investigation, Data curation, Formal analysis. Chenghang Du: Formal analysis, Investigation. Haoran Li: Investigation. Zhencai Sun: Formal analysis. Yifei Chen: Conceptualization, Methodology. Zhiqiang Gao: Investigation, Methodology. Zhigan Zhao: Writing – review & editing. Yinghua Zhang: Funding acquisition, Writing – review & editing. Zhimin Wang: Conceptualization, Writing – review & editing, Funding acquisition, Supervision. Ying Liu: Conceptualization, Funding acquisition, Formal analysis, Writing – original draft.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The study was supported by Hebei Province Key Research Project (21327003D-1), Beijing Science and Technology Planning Project (Z221100006422005), China Postdoctoral Science Foundation (2023M743815), and China Agriculture Research System (CARS301).

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ARTICLE INFO

Article history:

Received 8 January 2024

Revised 17 March 2024

Accepted 6 April 2024

Available online 26 April 2024

Footnote

* Corresponding authors.

E-mail addresses: [email protected] (Z. Wang), [email protected] (Y. Liu).

References

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Appendix A. Supplementary data

Supplementary data for this article can be found online at https://doi.org/10.1016/j.cj.2024.03.010.