Winter Wheat-summer Maize Cropping System Research Articles

Determination of threshold crop water stress index for sub-surface drip irrigated maize-wheat cropping sequence in semi-arid region of Punjab

A thorough understanding of how crops respond to water stress is essential for effective irrigation management under changing climate conditions and declining water resources. Amongst the various methods of irrigation, crop water stress index (CWSI)-based irrigation is popular due to its non-invasive techniques that require less data and can precisely indicate the severity of crop water deficiency. The present study focuses on establishing the upper- and lower-baselines of canopy-air temperature difference (Tc-Ta) for the estimation of the CWSI and to determine the CWSI threshold for maize and wheat crops. The upper- and lower-baseline of (Tc-Ta) was established using the relationship between (Tc-Ta) and vapor pressure deficit (VPD) for different irrigation treatments such as 60 %ETc, 70 %ETc, 80 %ETc, 90 %ETc, and 100 %ETc with irrigation interval of 1-day, 2-days, and 3-days. The study showed that the baselines varied with the growth stages of the crop and with irrigation treatments and reached the maximum in Anthesis and Silking growth stage for wheat and maize, respectively. The threshold of CWSI was estimated by developing a relationship between the normalized values of grain yield (GY) and irrigation water productivity (WPI). For the Rabi wheat, a quadratic correlation was identified between CWSI and WPI (r2 = 0.89), and GY (r2 = 0.93). Similarly, for Kharif maize, a quadratic relationship was noted between CWSI and both WPI (r2 = 0.75) and GY (r2 = 0.85). From the study, it was found that the CWSI thresholds of Rabi wheat and Kharif maize are 0.29 and 0.31, respectively. Based on the study, it can be concluded that by utilizing the thresholds for a winter wheat-summer maize cropping system, high GY and WPI can be achieved.

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

Winter wheat–summer maize cropping system in the North China Plain often experiences drought-induced 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.

Manure replacing synthetic fertilizer improves crop yield sustainability and reduces carbon footprint under winter wheat–summer maize cropping system

Manure replacing synthetic fertilizer is a viable practice to ensure crop yield and increase soil organic carbon (SOC), but its impact on greenhouse gas (GHG) emissions is inconsistent, thus remains its effect on CF unclear. In this study, a 7-year field experiment was conducted to assess the impact of replacing synthetic fertilizer with manure on crop productivity, SOC sequestration, GHG emissions and crop CF under winter wheat–summer maize cropping system. Five treatments were involved: synthetic nitrogen, phosphorus, and potassium fertilizer (NPK) and 25%, 50%, 75%, and 100% of manure replacing synthetic N (25%M, 50%M, 75%M, and 100%M). Compared with NPK treatment, 25%M and 50%M treatments maintained annual yield (winter wheat plus summer maize) and sustainable yield index (SYI), but 75%M and 100%M treatments significantly decreased annual yield, and 100%M treatment also significantly reduced annual SYI. The SOC content exhibited a significant increasing trend over years in all treatments. After 7 years, SOC storage in manure treatments increased by 3.06–11.82 Mg ha−1 relative to NPK treatment. Manure treatments reduced annual GHG emissions by 14%–60% over NPK treatment. The CF of the cropping system ranged from 0.16 to 0.39 kg CO2 eq kg−1 of grain without considering SOC sequestration, in which the CF of manure treatments lowered by 18%–58% relative to NPK treatment. When SOC sequestration was involved in, the CF varied from −0.39 to 0.37 kg CO2 eq kg−1 of grain, manure treatments significantly reduced the CF by 22%–208% over NPK treatment. It was concluded that replacing 50% of synthetic fertilizer with manure was a sound option for achieving high crop yield and SYI but low CF under the tested cropping system.

Evaluating the adoption of irrigation technology in a well-irrigated winter wheat－summer maize cropping system

Determining suitable irrigation technology is of paramount for promoting water-saving agriculture, particularly for winter wheat-summer maize rotation system in well-irrigated regions. To optimize and assess the efficacy of various irrigation technologies (specifically, semi-fixed sprinkler irrigation, walking sprinkler, semi-automatic buried telescopic sprinkler irrigation, thin-soft spray tape irrigation, drip irrigation, self-driven winch sprinkler and manually moving spray gun irrigation, marked as A, B, C, D, E, F and G) applied in south central North China Plain, we first conducted an economic analysis for the winter wheat-summer maize rotation. Subsequently, employing a comprehensive set of 20 indicators spanning economic, societal, technological, ecological, and resource aspects, we employed a TOPSIS model with integrative weighting approach using “AHP + Entropy”. We also employed principal component analysis and the Sankey diagram method to explore characteristics of different irrigation techniques and indexes. Irrigation mode E, conserving energy by 63.19% compared to mode B and offering labor savings five times greater than the mode D. The highest economic benefit for the rotation system was observed with the mode C, resulting in a 25.26% increase compared to the mode G. The top three irrigation modes based on scores were D, G, and E, with scores of 0.532, 0.490, and 0.474, respectively. The Sankey diagram revealed distinct preferences among different agricultural entities for specific irrigation modes. For specific stakeholders, we recommend irrigation modes D, G, F, and B for small farmers, large and specialized family businesses, family farms, and farmer cooperatives, respectively. In conclusion, our findings provide valuable scientific support and recommendations for the practical application of irrigation technology in agricultural production.

Mixed application of controlled-release urea and normal urea can improve crop productivity and reduce the carbon footprint under straw return in winter wheat-summer maize cropping system

An important goal of sustainable agriculture is reducing the environmental risk while also ensuring food security. The mixed application of controlled-release urea and normal urea (CRUNU) is a potential nitrogen (N) management strategy for achieving this goal. However, few studies have focused on whether optimizing the N application rate of CRUNU can balance crop yield and greenhouse gas emissions, especially when straw is returned. Thus, we conducted a five-year field experiment in a winter wheat–summer maize planting system in Northwest China to determine the effects of different N fertilizer types (NU: normal urea; CRUNU) and N application levels (low N, 135 kg ha–1; medium N, 180 kg ha–1; high N, 225 kg ha–1) with straw return on the crop yield and stability, N fertilizer partial factor productivity (NFPF), and soil organic carbon (SOC). Life cycle assessment was also conducted to quantify the GHG emissions from farmland and carbon footprint (CF). Compared with NU, CRUNU improved the winter wheat and summer maize grain yield, biomass, and NFPF at all three N application levels. The crop grain yields increased significantly as the N application level increased under NU, but the crop grain yields did not differ significantly between the medium and high N application levels under CRUNU (P > 0.05). The SOC contents increased as the duration of straw return increased. Compared with NU, CRUNU significantly increased the SOC content, and correlation analysis showed that this increase was related to the increased amount of returned straw. Compared with NU, CRUNU increased the GHG emissions in the production process but reduced the GHG emissions in the application process, as well as increasing soil CO2 fixation to ultimately reduce the total GHG emissions. CRUNU increased the crop grain yield while also reducing the total GHG emissions, and thus the CF decreased significantly by 14.53–23.03% compared with NU, especially at the medium N application level. Therefore, this comprehensive analysis of the crop productivity and GHG emissions indicates that CRUNU combined with an appropriate N application level can be used as a nitrogen fertilizer management strategy for sustainable winter wheat–summer maize cropping in Northwest China.

Externalities of Pesticides and Their Internalization in the Wheat–Maize Cropping System—A Case Study in China’s Northern Plains

When the production or use of a product imposes a cost or benefit on a third party, this is referred to as an externality. Externalities of pesticides are associated with social and environmental costs. However, there is still a lack of a systematic method for evaluating and internalizing the externalities of pesticides. This study utilizes the pesticide’s environmental impact quotient and environmental accounting methods to assess the external costs associated with pesticide usage in the winter-wheat–summer-maize cropping system in China’s northern plains, with a specific focus on the pesticide use in Botou City during the year 2020 as a case study. Additionally, we introduce the concept of the net external value of pesticides and propose a methodology for its internalization, aiming to quantify the external costs induced by pesticide usage and explore the possibility of integrating them into market transactions. The results showed that the total external costs of pesticide use are 423.9 USD ha−1, with a positive external value of 171.9 USD ha−1 and a net external value of −252.0 USD ha−1. The negative external costs associated with pesticide use outweigh the positive external values. External costs varied significantly according to environmental receptors, after retaining two significant figures: applicators accounted for 45% of the total external costs, followed by pickers (32%), consumers (11%), groundwater (4.5%), fish (3.9%), beneficial insects (1.7%), birds (1.3%), and bees (1.1%). The external costs of maize cultivation were 33% higher than those of wheat cultivation. The application of herbicides resulted in the highest external costs compared with fungicides and insecticides. Based on the internalization of the results, imposing an ecological tax on pesticide users is recommended, with rates of 3.29% for wheat and 6.76% for maize. This research contributes to sustainable agricultural development by providing valuable insights for farmers in selecting environmentally friendly pesticides and informing the implementation of ecological taxes on pesticide usage.

Mitigating greenhouse gas emissions by replacing inorganic fertilizer with organic fertilizer in wheat–maize rotation systems in China

Combining organic and inorganic fertilizer applications can help reduce inorganic fertilizer use and increase soil fertility. However, the most suitable proportion of organic fertilizer is unknown, and the effect of combining organic and inorganic fertilizers on greenhouse gas (GHG) emissions is inconclusive. This study aimed to identify the optimum ratio of inorganic fertilizer to organic fertilizer in a winter wheat–summer maize cropping system in northern China to achieve high grain yields and low GHG intensities. The study compared six fertilizer treatments: no fertilization (CK), conventional inorganic fertilization (NP), and constant total nitrogen input with 25% (25%OF), 50% (50%OF), 75% (75%OF), or 100% (100%OF) organic fertilizer. The results showed that the 75%OF treatment increased the winter wheat and summer maize yields the most, by 7.2–25.1% and 15.3–16.7%, respectively, compared to NP. The 75%OF and 100%OF treatments had the lowest nitrous oxide (N2O) emissions, 187.3% and 200.2% lower than the NP treatment, while all fertilizer treatments decreased methane (CH4) absorption (by 33.1–82.0%) compared to CK. Carbon dioxide flux increased in the summer maize growing season (by 7.7–30.5%) compared to CK but did not significantly differ between fertilizer treatments. The average global warming potential (GWP) rankings across two wheat–maize rotations were NP > 50%OF > 25%OF > 100%OF > 75%OF > CK, and greenhouse gas intensity (GHGI) rankings were NP > 25%OF > 50%OF > 100%OF > 75%OF > CK. We recommend using 75% organic fertilizer/25% inorganic fertilizer to reduce GHG emissions and ensure high crop yields in wheat–maize rotation systems in northern China.

Improving Soil Fertility and Wheat Yield by Tillage and Nitrogen Management in Winter Wheat–Summer Maize Cropping System

Soil degradation and high environmental costs impede agricultural production in North China. A 6-year field experiment was conducted to determine the effects of tillage practice and nitrogen application rate on changes in soil fertility and wheat yield. Four tillage systems (rotary tillage without maize straw return through 6 years, RT; rotary tillage with maize straw return through 6 years, RS; deep tillage with maize straw return through 6 years, DS; and rotary tillage through 2 years followed by deep tillage next year with maize straw applied for two cycles, RS/DS) and three N levels (HN, 300 kg N ha−1, refers to traditional farming practice; MN, 0.75 × HN, 225 kg N ha−1, to recommended N rate; and LN, 0.5 × HN, 150 kg N ha−1, to reduced N rate) were tested. The soil organic carbon, labile organic carbon, inorganic N, available phosphorus, and available potassium under straw return treatments were significantly higher than RT in the 0–30 cm soil layer (p < 0.05). The microbial diversity, invertase, urease, and alkaline phosphatase activities also increased when maize straw was returned. Tillage practices could distribute maize straw in different depths of the soil and then affect soil nutrients, enzyme activity, and microbial diversity. The RS treatment presented the greatest effects in the 0–10 cm layer, while more significant impacts were observed in DS and RS/DS treatments at the 10–30 cm depths. The levels of soil nutrients and enzyme activity increased with an increased N rate. Compared to that under LN, wheat yields increased under HN and MN treatments, whereas there were no significant differences between HN and MN (p > 0.05). An increasing tendency of grain yield was observed in DS and RS/DS, while conversely so in RS. RS/DS had lower farm costs than DS during the study duration. Thus, RS/DS at 225 kg N ha−1 is the best method for improving soil fertility and wheat yield.

Crop Yield and Nutrient Efficiency under Organic Manure Substitution Fertilizer in a Double Cropping System: A 6-Year Field Experiment on an Anthrosol

The combination of organic manure and inorganic fertilizer plays a role in increasing crop yield and nutrient efficiency, but such effectiveness varies with crop, soil, management, and climate. Here, a 6-year field experiment was conducted to evaluate the effects of substituting organic manure with inorganic fertilizer on crop yield, grain protein content, and nitrogen and phosphorus efficiency under a winter wheat-summer maize cropping system on Anthrosol. Five treatments were included: recommended nitrogen (N), phosphorus (P) and potassium (K) fertilizers (NPK), 75% NPK + 25% organic manure (M), 50% NPK + 50% M, 25% NPK + 75% M, and 100% M, respectively. Wheat, maize, and annual yield were 1643–8438 kg ha−1, 4847–11,104 kg ha−1, and 10,007–17,496 kg ha−1. Organic manure treatments produced the same crop yield as NPK treatment except for 100% M. Grain protein content of wheat and maize was 7.9–15.1% and 5.6–12.6%. Organic manure treatments yielded significantly lower wheat grain protein content but had no significant effect on maize grain protein content relative to NPK treatment. Nitrogen uptake efficiency and nitrogen use efficiency at the cropping system level were 0.67–1.16 and 35.7–60.5 kg kg−1. Phosphorus uptake efficiency and phosphorus use efficiency were 0.28–0.75 and 167–531 kg kg−1. Compared with NPK treatment, 50% M, 75% M, and 100% M improved nitrogen use efficiency but decreased nitrogen uptake efficiency and phosphorus efficiencies. Annual N and P budgets were −1.3–79.1 kg ha−1 a−1 and 25.6–100.1 kg ha−1a−1, and both increased with the increase in organic manure input. Based on crop yield, grain protein content, nitrogen, and phosphorus efficiency and their budget, substitution of 25% inorganic fertilizer with organic manure is the rational combination under the winter wheat–summer maize system on an Anthrosol.

Tillage strategies optimize SOC distribution to reduce carbon footprint

Tillage methods and nitrogen (N) application are critical for soil organic carbon (SOC) sequestration and crop production. However, both tillage and N are the main contributors to the carbon footprint (CF) in agricultural production. A 6-year-long field experiment was conducted under a winter wheat-summer maize cropping system in Northern China to test how tillage methods (RT, annual rotary tillage; DT, annual deep tillage; and TT, RT applied annually with a DT interval of two years) and N rates (300 kg ha–1, N300; 225 kg ha–1, N225; 165 kg ha–1, N165) affect SOC sequestration, greenhouse gas (GHG) emissions, and annual grain yield. And, the CF was used to evaluate ecological sustainability. RT preferentially sequestrated SOC in the 0–10 cm soil layer. In the 10–30 cm soil layers, 2.87–3.82 and 1.85–2.53 Mg ha–1 greater SOC were respectively observed under DT and TT than RT, which was conducive to maximizing annual grain yield with less N application (N225) relative to traditional farming practice (RT-N300). Both increasing N rate and deep tillage resulted in obvious increases in the total GHG emissions. N fertilizer production and transportation were the greatest contributors, accounting for 40.4–47.0% of the total GHG emissions, followed by direct N2O and CH4 emissions (23.5–30.5%). TT-N225 significantly reduced CF (CF including SOC sequestration was 0.49 Mg CO2 eq ha–1 year–1 lower than DT-N225, and was 1.87 Mg CO2 eq ha–1 year–1 lower than RT-N300) and maintained high crop productivity while creating appropriate soil conditions and thus may be a much cleaner agricultural strategy in Northern China. And, the strategy of reducing N application in agricultural production by improving soil properties of the plow layer in this study can also be referred to in other ecological regions.

Straw return strategies to improve soil properties and crop productivity in a winter wheat-summer maize cropping system

Crop straw return is widely implemented in winter wheat and summer maize rotation systems. Nevertheless, research characterizing how different straw return methods affect soil properties and grain yield in this double cropping system has been limited. A fixed-site field trial was carried out from 2017 to 2020 to examine the impacts of four straw return methods on the annual changes of soil properties within the top 0–20 cm of soil and grain yield in a winter wheat-summer maize cropping system in North China. The four treatments were: (1) both wheat and maize straw removal (CK), (2) application of only maize straw (W0M1), (3) application of only wheat straw (W1M0), and (4) both wheat and maize straw application (W1M1). The cumulative carbon inputs under the four straw return methods ranged from 11.87 to 36.51 Mg ha−1, which led to changes in SOC stock of −1.30–2.16 Mg ha−1 from 2017 to 2020. Straw return significantly increased the contents of soil organic carbon, mineral nitrogen and available phosphorus. In addition, the soil urease, alkaline phosphatase activities and microbial diversity under straw returning treatment were significantly higher than those in CK. Significant linear relationships existed between annual carbon inputs and soil nutrient contents. And annual straw return had cumulative effects on changes of soil properties. Straw return significantly increased grain yield in the double-cropping system, and significant correlations were observed between the annual changes of grain yield and soil properties. Overall, the W1M1 treatment was the most effective strategy for improving soil properties and crop yield. Return of maize straw alone also maintained relatively high soil fertility with significantly lower carbon inputs, which allows the unused wheat straw to be used for other purposes and maximize the utilization efficiency of all straw resources.

Determining Threshold Values for a Crop Water Stress Index-Based Center Pivot Irrigation with Optimum Grain Yield

The temperature-based crop water stress index (CWSI) can accurately reflect the extent of crop water deficit. As an ideal carrier of onboard thermometers to monitor canopy temperature (Tc), center pivot irrigation systems (CPIS) have been widely used in precision irrigation. However, the determination of reliable CWSI thresholds for initiating the CPIS is still a challenge for a winter wheat–summer maize cropping system in the North China Plain (NCP). To address this problem, field experiments were carried out to investigate the effects of CWSI thresholds on grain yield (GY) and water use efficiency (WUE) of winter wheat and summer maize in the NCP. The results show that positive linear functions were fitted to the relationships between CWSI and canopy minus air temperature (Tc − Ta) (r2 > 0.695), and between crop evapotranspiration (ETc) and Tc (r2 > 0.548) for both crops. To make analysis comparable, GY and WUE data were normalized to a range of 0.0 to 1.0, corresponding the range of CWSI. With the increase in CWSI, a positive linear relationship was observed for WUE (r2 = 0.873), while a significant inverse relationship was found for the GY (r2 = 0.915) of winter wheat. Quadratic functions were fitted for both the GY (r2 = 0.856) and WUE (r2 = 0.629) of summer maize. By solving the cross values of the two GY and WUE functions for each crop, CWSI thresholds were proposed as being 0.322 for winter wheat, and 0.299 for summer maize, corresponding to a Tc − Ta threshold value of 0.925 and 0.498 °C, respectively. We conclude that farmers can achieve the dual goals of high GY and high WUE using the optimal thresholds proposed for a winter wheat–summer maize cropping system in the NCP.

Optimized fertilizer recommendation method for nitrate residue control in a wheat–maize double cropping system in dryland farming

The recommendations for soil fertilization based on soil testing are time-critical and labor-intensive for farmers in the winter wheat–summer maize double cropping system. Understanding the relationships between the crop yield, nitrogen requirement, and nitrate residue level under the combined N and P fertilizer application is necessary to optimize the fertilizer recommendation method in order to reduce the nitrate residue levels. In 2009, we established a long-term field fertilization experiment with five N application rates and four P application rates in the winter wheat-summer maize double cropping system. The grain yield, N requirement, and soil nitrate residue were determined during 2016–2019 to optimize the N inputs for nitrate residue control. The crop yield was increased by N application and it increased further when combined with P fertilizer. The N requirement of crops increased by N application but decreased when combined with P. The calculated maximum winter wheat yield was 7235 kg ha−1 and the theoretical N requirement for 1000 kg grain formation (NR) was 28.68 kg Mg−1. The maximum summer maize yield was 7866 kg ha−1, and the theoretical NR was determined as 23.43 kg Mg−1. The residual nitrate-N was increased by N application but decreased by combined P fertilizer. The correlation between the nitrate-N content in 0–20 cm top soil (SNC) and nitrate-N residue in 0–100 cm soil (SNR) was linear at the winter wheat harvest but exponential at the summer maize harvest. Thus, the SNR can be predicted by the SNC according to their correlation at the harvest. The predicted SNR at the harvest of the previous crop, the target yield and NR for the subsequent crop obtained from long-term in-situ observations can be used to guide the fertilizer amounts applied to the following crop. Therefore, we developed a convenient method to optimize the fertilizer recommendation method for the winter wheat–summer maize cropping system.

Strategic tillage achieves lower carbon footprints with higher carbon accumulation and grain yield in a wheat-maize cropping system

Continuous single tillage has the potential to increase greenhouse gas (GHG) emissions and decrease the accumulation of soil organic carbon (SOC), thus increasing carbon footprints (CFs). However, in a wheat-maize cropping system, limited information was available about the effects of strategic tillage on CFs. Thus, a four-year field experiment was conducted, including continuous rotary tillage (RT), continuous no-till (NT), RT + subsoiling (RS), and NT + subsoiling (NS), to investigate the effects of NS (strategic tillage) on the unit area and unit yield. The results showed that CO2 emission was the highest contributor to CFs (73.92%) in a winter wheat-summer maize cropping system, following the order of NS < NT < RS < RT. The direct N2O emissions from fertilizers and residues were 4.43–4.51 t CO2-eq ha−1 yr−1 during the wheat and maize seasons, and indirect N2O emissions from irrigation and fertilizer inputs had a proportion of >80% from total agricultural inputs. The differences in SOC storage significantly affected the CFs. Although the NS treatment increased the amount of GHG emissions from the residues returned and consumption of diesel, the enhancement of SOC storage by deeper SOC increased. Thus, lower area-scaled CFs were observed in the NS treatment. Furthermore, a higher grain yield and an annual change of SOC storage compared with other treatments were observed under the NS system, which helped to reduce the CFs. The yield-scaled CFs followed the order of RT > RS > NT > NS when considering the changes in SOC storage. Therefore, the NS treatment resulted in a higher grain yield and SOC sequestration with lower CFs, and thus, it could be recommended as the best tillage method to achieve sustainable production and environmental balance in a wheat-maize cropping system.

Carbon footprint of a winter wheat-summer maize cropping system under straw and plastic film mulching in the Loess Plateau of China

The objective of this study was to calculate the carbon footprint (CF) of straw and plastic film mulching practices in order to identify the optimum field management for low-carbon agriculture. A four-year field experiment was conducted to determine the effects of different mulching measurements on greenhouse gas (GHG) emissions, grain yield, and CF of a winter wheat-summer maize cropping system in the Loess Plateau of China. Mulching treatments were no mulching (NM), straw mulching (SM), half plastic film mulching (HPM); full plastic film mulching (FPM), and ridge-furrow planting with film mulching over ridges (RPM). Plastic film mulching decreased N2O emissions compared with NM. However, SM significantly increased direct N2O emissions by 59.2% and indirect N2O emissions by 16.2%. Average annual total GHG emissions calculated by life cycle assessment were 5199–7631 kg CO2-eq ha−1 yr−1. Nitrogen (N) fertilizer was the largest contributor to total GHG emissions, accounting for >41%. For plastic film mulching treatments, the second greatest contributor was plastic film, accounting for 21.1–35.7% of total GHG emissions. In contrast, the second greatest contributor was direct and indirect N2O and CH4 emissions under NM (17.2%) and SM (21.6%). Emissions from diesel consumption was the third largest component of total GHG emissions. All mulching treatments showed significantly greater annual grain yield than the NM treatment. The CF of summer maize yield was higher than that of winter wheat. SM showed the lowest CF (0.38 kg CO2-eq kg−1), and plastic film mulching increased CFs compared with NM. These results suggest that SM should be the priority mulching practice used to increase yield and to reduce the CF of winter wheat-summer maize production in the Loess Plateau, China. Optimizing N fertilizer application rates should be one of the key production strategies employed to mitigate agricultural GHG emissions.

Tracking the spatio-temporal change of planting area of winter wheat-summer maize cropping system in the North China Plain during 2001–2018

Discriminating winter wheat-summer maize distribution is fundamental for agricultural water resources management in the North China Plain (NCP) which confronts severe conflicts between food production and agricultural water scarcity. However, how the planting area changed since 2000 is still unclear. Therefore, the winter wheat-summer maize from 2001 to 2018 was identified by using the maximum likelihood algorithm of supervised classification based on the Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) product. Three schemes with different temporal resolutions of MODIS data and sample categories were compared to obtain the most reasonable identification results. The results reveal that using 16-day 0.0025° MODIS NDVI data and six sample categories including winter wheat-summer maize, winter wheat-rice, spring maize, cotton, other one cropping systems and other double cropping systems is an effective way for tracking the variation of winter wheat-summer maize distribution. The winter wheat-summer maize planting area showed an insignificant increasing trend at a rate of 34.2 km2/year (p = 0.955, CV = 7.49%) during 2001–2018, while it decreased at the rate of −5065.2 km2/year (p = 0.074) after 2012. Spatially, the planting area shrunk in northern NCP, the piedmont plain of the Taihang Mountains, the west of dry sub-humid zone and the southwest part of the NCP, accounting for 58.6% of the counties during 2001–2018; while 17.3% of the counties significantly expanded winter wheat-summer maize in the irrigation district along the Yellow River in Shandong province, the southeast of Hebei Plain and the central humid zone. Our results provide fundamental information for quantifying the change of crop water consumption and optimizing crop water resource allocation.

Does actual cropland water consumption change with evaporation potential in the Lower Yellow River?

The North China Plain (NCP) is one of the most important regions for food production in China; however, the typical winter wheat–summer maize cropping system has created a continuous decline in groundwater levels, triggering serious ecological problems. Additionally, changes in the evaporation potential in the NCP have altered from decreasing to sharply increasing. Therefore, it is critical to understand the actual cropland water consumption (i.e., the actual evapotranspiration, AET) and crop water use efficiency (WUE) under this new trend. This understanding is significant for agricultural water management in the NCP. This study investigated the historical AET and WUE trends for the winter wheat–summer maize cropping system during 1992–2014. This investigation was based on a long-term AET dataset obtained using a large lysimeter from 1992 to 2014 at the Yucheng Comprehensive Experiment Station of the Chinese Academy of Sciences near the Lower Yellow River. The results showed that annual AET decreased pre-2008 and rebounded post-2008. The rebound rate of annual AET from 2008 to 2014 was more than three times the annual decrease rate of AET from 1992 to 2008. The significant increase in summer maize AET mainly contributed to the rebound of the annual AET after 2008. Following the changes in AET and crop yield, the annual WUE had evidently increased for 1992–2008 and sharply decreased from 2008 to 2014. The significant decrease in winter wheat WUE mainly contributed to the annual decrease in WUE post-2008. Climate change, agricultural management, and crop yields were observed to regulate the changes in AET and WUE. In the context of accelerating climate change and the increased frequency of extreme climatic events, strategies to improve WUE by the Lower Yellow River have been proposed, which may also be helpful in the NCP and similar regions worldwide.

Effects of long-term nitrogen fertilization on N2O, N2 and their yield-scaled emissions in a temperate semi-arid agro-ecosystem

Nitrous oxide (N2O) measured simultaneously with di-nitrogen (N2) emissions from soils are greatly uncertain due to large temporal and spatial variations. This study aims to report N2O, N2, N2/N2O, 15N-N2O, wheat-maize annual grain yields, and yield-scaled N2O and N2O plus N2 emissions on the responses to different nitrogen (N) fertilizer rates in a winter wheat-summer maize cropping system. Furthermore, this study also seeks to determine controlling factors for N2O, N2, and N2/N2O emissions and significantly investigate the relationship between the soil-climate measured factors and 15N-N2O. Three N inputs and control treatments, 0, CK; 200, LN; 400, MN; and 600, HN kg N ha−1 year−1 were set since 1998. Direct measurement method has been used to quantify N2O and N2 emissions. Our results indicated that the effects of long-term N fertilization significantly increased N2O and N2 and also reduced N2/N2O emission ratios as described by exponential functions. Using structural equation modeling (SEM), NH4+, WFPS, NO3-, and DOC were revealed to be main controlling factors for N2O, while N2 by DOC, NO3-, WFPS, and temperature finally N2/N2O was positively related to temperature. Furthermore, the 15N-N2O was positively related to N2/N2O ratios, indicating that denitrification is the dominant process at the study site. The yield-scaled N2O emissions followed the order HM>MN>LN>CK, and they were 1.56, 1.47, and 1.07 times greater than CK, respectively. Total yield-scaled N2O plus N2 were in the order of CK>HN>MN>LN. N fertilization has shown strong impact not only on N2O, N2, and N2/N2O emissions but also on yield-scaled N2O and N2O plus N2 emissions. High agronomic nitrogen use efficiency (NUE), low yield-scaled N2O emissions, and low cumulative N2O plus N2 emissions were observed at 200-LN treatment, suggesting this rate to be an optimum and sustainable agricultural management practice with no significant crop yield reduction as compared to the current farmers’ practice of 400 kg N ha−1 year−1.

Crop yield and N2O emission affected by long-term organic manure substitution fertilizer under winter wheat-summer maize cropping system

Application of organic manure combined with synthetic fertilizer can maintain crop yield and improve soil fertility, but the long-term effects of substituting different proportions of synthetic fertilizers with organic manure on N2O emission remain unclear. In this study, field experiments and DNDC model simulations were used to study the long-term effects of substituting synthetic fertilizers with organic manure on crop yield and N2O emission. The field experiment was conducted at Guanzhong Plain, northern China, under a wheat-maize cropping system. Six treatments were included: no fertilization (CK); synthetic nitrogen (N), phosphorus (P) and potassium (K) fertilizers (NPK); and 25%, 50%, 75% and 100% of the synthetic N substituted by dairy manure (25%M, 50%M, 75%M, and 100%M), respectively. The DNDC model was calibrated using the field data from the NPK treatment from 2014 to 2017 and was validated for the other treatments. The results showed that the DNDC model can successfully simulate the crop yield (e.g. nRMSE < 5%) and annual N2O emission (nRMSE < 20%). In addition, a 30-year simulation found that organic manure substitution treatments could maintain wheat yield well, and the yield variation between different years was small. However, relative to the NPK treatment, the maize yields for the first 6 and 7 years were lower under 50%M and 75%M, and under 100%M maize yields were reduced for the first 15 years. The long-term simulation showed that N2O emission of fertilized treatment had an increasing trend over time, especially the 75%M treatment where the N2O emission was higher than that of NPK treatment after 25 years of fertilization. The annual mean N2O emission under different treatments was, in decreasing order, NPK > 25%M > 50%M > 75%M > 100%M > CK. The yield-scale N2O emission and emission factor were highest for the NPK treatment. Considering crop yield, yield stability and N2O emission, substitution of 25% synthetic fertilizer by organic manure can simultaneously ensure crop productivity and environmental protection under the tested environment.

Spatiotemporal variations in soil CO2 fluxes under a winter wheat-summer maize cropping system in the North China Plain

Most studies on soil CO2 fluxes focus on the upper soil layers (i.e., 0–200 mm); however, there is a lack of investigation into soil layers below 200 mm, even though about half of soil organic carbon (SOC) is stored at these depths. In order to investigate the responses of CO2 fluxes in subsurface soils to crop residue incorporation in the topsoil, a field experiment comprising two treatments (i.e., conventional tillage with and without crop residue incorporation) was carried out under a winter wheat-summer maize cropping system from 2014 to 2016 in the Yucheng Agricultural Station, Shandong Province, China. The results showed that soil CO2 fluxes had large spatiotemporal variabilities and were significantly affected by crop residue applications (P < 0.05). Soil CO2 fluxes increased with soil depth. The CO2 fluxes from 100 to 400 mm soil depths were 1.1–5.1 times higher than those from 0 to 100 mm soil depths. Incorporation of crop residues into the soil significantly increased soil CO2 fluxes in all sampled layers (P < 0.05), and the magnitude increased with increasing soil depth. Soil moisture and the ratio of soil dissolved organic carbon to nitrogen (DOC/DON) were the dominant factors regulating soil CO2 fluxes in the wheat growing season, whereas soil DON concentrations dominated in the maize growing season. Our study indicated that deep soil C was more vulnerable to the incorporation of crop residues than the C present in surface soil. Incorporation of crop residues into surface soil might not increase SOC sequestration in the subsurface soil.