Wheat-maize Rotation System Research Articles

A multi-criteria evolutionary-based algorithm as a regional scale decision support system to optimize nitrogen consumption rate; A case study in North China plain

Nitrogen mismanagement is a serious concern worldwide since farmers usually overuse chemical fertilizers to increase yield, and consequently their income. The oversupply of chemical fertilizers, particularly nitrogen-based fertilizers, has brought about serious environmental problems, among others, deterioration of water quality, global warming impacts, soil acidification, and water eutrophication. In the present study, a decision support system coupled with an evolutionary algorithm was developed to optimize nitrogen consumption rate in a Wheat-Maize rotation system in the North China Plain. The developed model integrated eight indicators, i.e., yield, nitrogen uptake by grain and whole plant, economic, enviro-economic, nitrogen use efficiency, nitrogen balance, and single score (i.e., an aggregated and normalized environmental indicator), to propose the optimal consumption rates. The indicators, used in this model, were measured and/or calculated from a three-year field experiment conducted in six different monitoring sites in four Provinces. Such approach helped introduce the spatially explicit optimal nitrogen application rates for different regions. Having integrated enviro-economic indices, the decision support system returned regional optimum consumption rates which would maximize profit and minimize environmental pollution. Moreover, the decision support system was also supplemented with two sensitivity analysis models, from one hand, to investigate the consequences of changes in decision criteria, and from the other hand, return a range of optimal consumption rate for each specific region. The results achieved showed that the proposed approach succeeded in finding the best nitrogen practices for each specific region and also returning a safe range for nitrogen application in order to guarantee a high-profit and an environmental friendly agricultural production.

Metagenome analysis reveals potential microbial functions in topsoil of wheat–maize rotation system with five-year application of fertilizers

Fertilization mode affects soil quality and ecological health. The effects of four fertilization regimens on lignocellulose content, readily degradable carbohydrate decomposition, and potential microbial functions in the topsoil of a wheat–maize rotation system between 2012 and 2017 were investigated. The fertilization regimens of control (control NFNB), high chemical fertilizer (HCF), high biochar plus low chemical fertilizer (HBLCF), and biochar-based fertilizer (BBF) were compared on soil fundamental properties, microbial structure, and potential function in soil carbohydrate degradation based on metagenome analysis. The diversity of carbohydrate-active enzyme genes in the topsoil microbial consortia in the four trials was primarily distributed within the ten ecologically most dominant phyla. Application of BBF was associated with the lowest decline in total nitrogen and P2O5 (2012-2017: 6.5% and 28.1%, respectively) and the most effective carbohydrate decomposition (2015-2017: 67.0% for cellulose and 59.9% for readily degradable carbohydrate). Carbohydrate transport and metabolism accounted for 6.0% of reads assigned functional classification under the BBF regimen. These findings reveal the ecologically functional diversity of topsoil microorganisms and suggest BBF application as a promising strategy for sustainable agriculture and beneficial to soil health. Keywords: biochar-based fertilizer, carbohydrate decomposition, genetic function, microbial community, topsoil DOI: 10.25165/j.ijabe.20191206.4849 Citation: Shen Y J, Zhao L X, Meng H B, Cheng H S, Ding J T, Wang J R, et al. Metagenome analysis reveals potential microbial functions in topsoil of wheat–maize rotation system with five-year application of fertilizers. Int J Agric & Biol Eng, 2019; 12(6): 177–184.

Effects of three types of soil amendments on yield and soil nitrogen balance of maize-wheat rotation system in the Hetao Irrigation Area, China

Excessive fertilization combined with unreasonable irrigation in farmland of the Hetao Irrigation Area (HIR), China, has resulted in a large amount of nitrogen (N) losses and agricultural non-point source pollution. Application of soil amendments has become one of the important strategies for reducing N losses of farmland. However, there is still no systematic study on the effects of various soil amendments on N losses in the HIR. In this study, three types of soil amendments (biochar, bentonite and polyacrylamide) were applied in a maize-wheat rotation system in the HIR during 2015–2017. Yields of maize and wheat, soil NH3 volatilization, N2O emission and NO3- leaching were determined and soil N balance was estimated. The results showed that applications of biochar, bentonite and polyacrylamide significantly increased yields of maize by 9.2%, 14.3% and 13.3%, respectively, and wheat by 9.2%, 16.6% and 12.3%, respectively, compared with the control (fertilization alone). Applications of biochar, bentonite and polyacrylamide significantly reduced soil N leaching by 23.1%, 35.5% and 27.1%, soil NH3-N volatilization by 34.8%, 52.7% and 37.8%, and soil N surplus by 23.9%, 37.4% and 30.6%, respectively. Applications of bentonite and polyacrylamide significantly reduced N2O-N emissions from soil by 37.3% and 35.8%, respectively, compared with the control. Compared with application of biochar, applications of bentonite and polyacrylamide increased yields of maize and wheat by 5.1% and 3.5%, respectively. Our results suggest that soil amendments (bentonite and polyacrylamide) can play important roles in reducing N losses and increasing yield for the maize-wheat rotation system in the HIR, China.

No-tillage did not increase organic carbon storage but stimulated N2O emissions in an intensively cultivated sandy loam soil: A negative climate effect

Although numerous studies have been conducted on the effects of no-tillage on carbon (C) sequestration in agricultural systems, there is still no consensus on the balance between the potential of C sequestration and nitrous oxide (N2O) or nitric oxide (NO) emissions. A no-tillage field experiment in the North China Plain was established in 2006 and the influence of no-tillage on N2O and NO emissions was monitored under an annual wheat-maize cropping system. The study included four treatments: no-tillage (NT) and conventional tillage (CT) soils amended with N fertilizer at a rate of 225 kg N ha–1 for wheat and 195 kg N ha–1 for maize (NTN and CTN) and without N fertilizer (NT0 and CT0). Three years of no-tillage significantly (p < 0.05) increased soil organic C (SOC) content by 12.2% in the 0–5 cm soil layer, possibly due to the surface aggregation of organic C derived from crop roots and exudates, but did not alter SOC pool in the 0–30 cm profile. Annual N2O emissions in the NT0 and CT0 treatments were 0.53 and 0.57 kg N2O-N ha–1, respectively, and were significantly (p < 0.05) increased to 0.96 kg N2O-N ha–1 in CTN and to 1.23 kg N2O-N ha–1 in NTN. Remarkable differences in N2O emissions between CTN and NTN were observed during the maize growing season. In contrast, NO emissions were not affected by the tillage regimes regardless of N fertilization. The mean ratios of NO/N2O fluxes in N-unfertilized plots were 0.26–0.29 and 1.79–2.11 for the maize and wheat season, respectively, indicating that both NO and N2O were primarily derived from denitrification during the maize growing season and from nitrification under wheat cultivation. Under N-fertilized plots, the ratios increased to 1.44–2.02 and 5.00–6.03 for the maize and wheat season, respectively, with significantly (p < 0.05) lower values in NTN plots than in CTN plots. The N2O emission factors for N applied in the wheat-maize rotation system were 0.16% and 0.09% for NTN and CTN, respectively, which was far lower than the IPCC Tier 1 default value (1.0%), primarily due to the absence of irrigation after fertilization in maize season and low temperature in wheat season. The results suggest that the 3-year no-tillage regime with residue removal did not substantially increase C storage in the 0–30 cm profile, but stimulated N2O emissions primarily by increasing denitrification.

Changes in soil physical and chemical characteristics in intensively cultivated greenhouse vegetable fields in North China

The total area of greenhouse crop production is increasing in China. However, this adversely influences soil physical and chemical properties due to special environmental conditions and agricultural management in greenhouse production. In this study, we evaluated soil properties of greenhouse vegetable systems with different planting years, a long-term greenhouse strawberry system, and an open-field wheat-maize rotation system in a typical agricultural production area of North China. The annual fertilizer application rates of nitrogen (N), phosphorus (P), and potassium (K) in the greenhouse vegetable system were 842.15, 809.14, and 931.55 kg ha−1, respectively, which were 3 times more than those in the wheat-maize rotation system and led to great changes of soil properties. Bulk density and soil pH gradually declined with increased cultivation time from new to 15 years in the greenhouse vegetable system. Bulk density declined from 1.58 g/cm3 in the new greenhouse fields to 1.25 g/cm3 in the 15-year greenhouse fields, and pH decreased from 5.72 to 4.55 with a rate of 0.08 unit per year. The contents of soil organic carbon (SOC), soil soluble salts, total NPK, and available NPK rose steadily until the 10th or 11th year, then decreased. By comparison with another two cropping systems, the greenhouse vegetable fields showed the lowest bulk density and pH, but the highest contents of SOC, soil soluble salts, total NPK, and available NPK due to heavy fertilizer inputs. The contents of soil N, P, and K in greenhouse vegetable fields were imbalanced, as indicated by C:N (11.58), C:P (16.06), and N:P (1.71) molar ratios in soils, which were significantly lower than the level in China and the rest of the world. In addition, the C:P and N:P ratios of greenhouse vegetable fields were also lower than those of wheat-maize rotation fields and greenhouse strawberry fields. Regression analysis indicated that the contents of SOC and soluble salts were positively correlated with pH, while available N and P contents showed negative linear relationships. These results demonstrate dramatic adverse changes of soil properties in intensive greenhouse vegetable fields in China. Our results also emphasize the need to regulate appropriate fertilizer application for intensive greenhouse vegetable management.

Effect of Different Fertilization Practices on Soil Microbial Community in a Wheat–Maize Rotation System

Little information is known about the effects of different fertilization practices on soil microbiome in intensively managed crop rotations. The objective of this research was to investigate the response of microbial community composition (phospholipid fatty acid, PLFA) and extracellular enzyme activity to fertilization treatments through a three-year experiment. Treatments were: Control (without fertilizer, CK), chemical fertilizer (NPK), NPK + pig manure (NPKM), NPK + straw (NPKS), and NPK + both manure and straw (NPKMS). We found that fertilization had no effect on the microbial abundance except arbuscular mycorrhizal fungi (AMF) PLFA. Soil microbial community composition was significantly affected by crop species and to a lesser extent by fertilization, with a greater influence on the wheat harvest. In addition, soil enzyme activities were enhanced by fertilization, especially in wheat season. Over three years, compared with NPK treatment, addition of organic manure or straw (NPKS and NPKMS) significantly increased the activities of the enzymes except invertase and urease, and the effect was greater at wheat harvest than the maize harvest. Our results indicate that the response of soil microbial community structure and enzyme activities to fertilization takes precedence than microbial biomass in the short term. The temporal variation in soil microbial community structure and enzyme activities in the crop rotation indicate that crop species may be carefully considered for sustainable agricultural intensification management.

Modeling soil water balance and irrigation strategies in a flood-irrigated wheat-maize rotation system. A case in dry climate, China

Demand for irrigation water has been steadily increasing in arid regions where intensification of crop production is supported by flood-irrigation. An assessment of irrigation performance, water productivity, and irrigation schedules is critical to water conservation in dry climates. In this study, we conducted a field experiment to compare soil water balance in a flood-irrigated wheat-maize rotation system during the growing season of 2015–2016. We then modeled the soil water balance and improved irrigation strategies by coupling Hydrus-1D with the CROPWAT model, and using evapotranspiration calculated from climatic data. The calibrated Hydrus-1D model was used to simulate the temporal and spatial variation of evapotranspiration and deep percolation based on measured soil water distribution of soil profiles in the unsaturated zone. Results showed that using soil hydraulic parameters from inversion modeling can simulate soil water flow in multi-layer soil during a crop growing season. Simulation results indicated that about 36.6 and 40.6% (478.6 and 680.1 mm) of total water input in 2015 and 2016, respectively, was consumed by evapotranspiration. Furthermore, simulated deep percolation amounted for approximately 32.3 and 42.9% (403.9 and 696.6 mm) of the total amount of irrigation water in 2015 and 2016, respectively. These results indicated that only a small proportion of irrigation water was used by crops for transpiration. In addition, irrigation performance indicators such as relative water supply, relative irrigation supply, depleted fraction, and overall consumed ratio values indicated poor performance of irrigation practices in the study area. Particularly, crop yields did not increase with increases in irrigation water in flood-irrigated fields during the last ten years. Results of the CROPWAT model indicated that combinations of a fixed irrigation depth and timing, of 40 mm every 10 days, and 50 mm every 10 days were reasonable for wheat and maize, respectively, given the sandy soil in the study area. The improved irrigation strategies will limit water irrigation loss to 20% without significant effects on crop yields. This study provides an alternative approach for estimating deep percolation and crop water requirements supporting management efforts in water conservation in dry climates.

Effect of reducing N and regulated fertilization on N loss from wheat-maize rotation system of farmland in Chao soil region of North China Plain

The application of large amounts of nitrogen (N) fertilizer can result in soil N accumulation and consequently N loss. To address these problems in a wheat-maize rotation area of the North China Plain, a two-year field experiment (2016-2017) was conducted to examine the effects of three different N fertilizer strategies on crop yield, N uptake, N loss and soil inorganic N content. The treatments were: controlled-release fertilizer, microbial fertilizer, nitrification inhibitor and farmer's practice (control). The results showed that the wheat yield from the microbial fertilizer treatment in 2016 was significantly lower than that from the controlled-release fertilizer treatment and the nitrification inhibitor treatment, but was not significantly different from conventional farmer fertilization. The N uptake of wheat and annual crops in the microbial fertilizer treatment was significantly reduced. There was no significant difference in crop yield and N uptake among the treatments in 2017. Soil fertility of the tillage layer was maintained or improved in all three treatments compared with the control, and the contents of alkali-hydrolyzed nitrogen, available potassium and organic matter increased with the increase of plant growth period in the microbial fertilizer treatment. Microbial fertilizer and nitrification inhibitor reduced the inorganic N content in the 40-100 cm soil profile, while controlled-release fertilizer increased the inorganic N content in the 0-40 cm soil layer. N loss through ammonia volatilization was higher than that through leaching, which was greater than the loss through N2O emission. Runoff loss was negligible. Among the treatments, N loss in farmer's practice treatment was the highest. Microbial fertilizer significantly reduced N loss through ammonia volatilization, but the loss through leaching was larger. In conclusion, with reduced N application compared with the farmer's practice, controlled release fertilizer and nitrification inhibitor could maintain crop yield and N uptake, and microbial fertilizer could ensure crop yield and N uptake for a longer plant growth period. The results suggested that inorganic N content in the 40-100 cm soil layer could be reduced in the soil by adding microbial fertilizer and nitrification inhibitors, and the amount of inorganic N was not reduced significantly by application of controlled release fertilizer. Several N reduction measures could reduce N loss. The microbial fertilizer treatment needed to be modified to reduce N leaching.

Crop Productivity and Nitrogen Balance as Influenced by Nitrogen Deposition and Fertilizer Application in North China

In spite of the importance of N management in agricultural production, closing the full nitrogen balance remains a challenge, mainly due to the uncertainties in both fluxes of nitrogen input and output. We analyzed N deposition and its influence on crop productivity and field nitrogen balance based on data from three of 15 years (1990–2005) of experiments in North China. The results showed that the average annual nitrogen deposition was 76, 80, and 94 kg N/ha at Changping, Zhengzhou, and Yangling in a wheat-maize rotation system, respectively. The deposited N could support a corresponding total biomass production (wheat plus maize) of 9.6, 10.6, and 8.8 Mg/ha with a total grain yield of 3.8, 4.8, and 3.7 Mg/ha, however, that did not cause a further decline in soil organic matter. N fertilizer application could increase total biomass (grain) by 244% (259%) and 74% (119%) for wheat and maize, respectively. Under optimal N management, N deposition accounted for 17–21% of the total N inputs, which affected significantly the recovery efficiency of applied N. N deposition showed a significant spatial variation in terms of the fraction of dry and wet depositions. On an annual average, N deposition roughly balanced out N losses due to NH3 volatilization and N2O loss from nitrification and denitrification. NH3 volatilization and NO3−-N leaching each accounted for 16–20% of the total N outputs. A system modeling approach is recommended to investigate the spatial variation of N leaching as affected by climatic conditions, and to fully account for the nitrogen fluxes. The N deposition derived from this study can be used as the background N input into the wheat-maize double cropping system for N balance.

Effects of afforestation on soil nitrous oxide emissions in a subtropical montane agricultural landscape: A 3-year field experiment

Afforestation, through the conversion of upland cropland to forest, is of great significance to land use change in montane (hilly) agricultural landscapes worldwide. Such afforestation is implemented to improve soil and water conservation and facilitate terrestrial carbon sequestration. However, particularly for subtropical and tropical regions, the effects of afforestation on soil N2O emissions have not been well investigated. Therefore, a three-year field experiment was conducted to simultaneously monitor N2O emissions from three paired sites of afforestation with cypress (Cypressus funebris) and adjacent cropland under a wheat-maize rotation system. The experiment was carried out in a subtropical montane agricultural landscape in southwest China. In both forest and cropland ecosystems, the N2O emissions exhibited a pronounced spatial and temporal variability. These variations in N2O emissions can be well explained by the spatiotemporal dynamics of environmental variables, such as soil temperature, WFPS, soil NH4+ or NO3− availability, because these environmental variables correlated significantly with the N2O emissions across different experimental sites and years. The average annual N2O fluxes were 2.69 kg N ha-1 for cropland and 0.13 kg N ha-1 for afforestation. It is noteworthy that the annual N2O fluxes for afforestation found in the present study constitute one of the lowest recorded N2O fluxes for unfertilized forest ecosystems globally. Overall, across all experimental sites and years, afforestation with cypress (Cypressus funebris) stands significantly decreased N2O fluxes by over twenty times relative to the adjacent cropland. This outcome suggests that afforestation could be an effective mitigation strategy for soil N2O emissions in a subtropical montane agricultural landscape.

Metagenome analysis reveals potential microbial functions in topsoil of wheat–maize rotation system with five-year application of fertilizers

Fertilization mode affects soil quality and ecological health. The effects of four fertilization regimens on lignocellulose content, readily degradable carbohydrate decomposition, and potential microbial functions in the topsoil of a wheat–maize rotation system between 2012 and 2017 were investigated. The fertilization regimens of control (control NFNB), high chemical fertilizer (HCF), high biochar plus low chemical fertilizer (HBLCF), and biochar-based fertilizer (BBF) were compared on soil fundamental properties, microbial structure, and potential function in soil carbohydrate degradation based on metagenome analysis. The diversity of carbohydrate-active enzyme genes in the topsoil microbial consortia in the four trials was primarily distributed within the ten ecologically most dominant phyla. Application of BBF was associated with the lowest decline in total nitrogen and P2O5 (2012-2017: 6.5% and 28.1%, respectively) and the most effective carbohydrate decomposition (2015-2017: 67.0% for cellulose and 59.9% for readily degradable carbohydrate). Carbohydrate transport and metabolism accounted for 6.0% of reads assigned functional classification under the BBF regimen. These findings reveal the ecologically functional diversity of topsoil microorganisms and suggest BBF application as a promising strategy for sustainable agriculture and beneficial to soil health. Keywords: biochar-based fertilizer, carbohydrate decomposition, genetic function, microbial community, topsoil DOI: 10.25165/j.ijabe.20191206.4849 Citation: Shen Y J, Zhao L X, Meng H B, Cheng H S, Ding J T, Wang J R, et al. Metagenome analysis reveals potential microbial functions in topsoil of wheat–maize rotation system with five-year application of fertilizers. Int J Agric & Biol Eng, 2019; 12(6): 177–184.

Metagenome analysis reveals potential microbial functions in topsoil of wheat–maize rotation system with five-year application of fertilizers

Fertilization mode affects soil quality and ecological health. The effects of four fertilization regimens on lignocellulose content, readily degradable carbohydrate decomposition, and potential microbial functions in the topsoil of a wheat–maize rotation system between 2012 and 2017 were investigated. The fertilization regimens of control (control NFNB), high chemical fertilizer (HCF), high biochar plus low chemical fertilizer (HBLCF), and biochar-based fertilizer (BBF) were compared on soil fundamental properties, microbial structure, and potential function in soil carbohydrate degradation based on metagenome analysis. The diversity of carbohydrate-active enzyme genes in the topsoil microbial consortia in the four trials was primarily distributed within the ten ecologically most dominant phyla. Application of BBF was associated with the lowest decline in total nitrogen and P2O5 (2012-2017: 6.5% and 28.1%, respectively) and the most effective carbohydrate decomposition (2015-2017: 67.0% for cellulose and 59.9% for readily degradable carbohydrate). Carbohydrate transport and metabolism accounted for 6.0% of reads assigned functional classification under the BBF regimen. These findings reveal the ecologically functional diversity of topsoil microorganisms and suggest BBF application as a promising strategy for sustainable agriculture and beneficial to soil health. Keywords: biochar-based fertilizer, carbohydrate decomposition, genetic function, microbial community, topsoil DOI: 10.25165/j.ijabe.20191206.4849 Citation: Shen Y J, Zhao L X, Meng H B, Cheng H S, Ding J T, Wang J R, et al. Metagenome analysis reveals potential microbial functions in topsoil of wheat–maize rotation system with five-year application of fertilizers. Int J Agric & Biol Eng, 2019; 12(6): 177–184.

Improved yield and water storage of the wheat-maize rotation system due to double-blank row mulching during the wheat stage

Mulching techniques have been widely used in dryland regions in northern China. It is necessary to develop water-saving cultivation techniques in irrigation regions in northern China to relieve water scarcity. Planting and mulching on separate rows has been widely used to improve wheat yield and involves a pattern of a double row of planting and a blank row of mulching. However, whether the mulching pattern during the wheat season can be applied to the wheat-maize system to increase the yield of both crops and to reduce the use of irrigation water remains unclear. Three mulching practices (conventional planting (CP), conventional planting with mulching (CPM) and double-blank planting with mulching (DPM)) during the wheat season were conducted to verify the potential roles of DPM in increasing wheat and maize yields, improving soil temperature and enhancing water storage under the DPM practice. The results show that the DPM practice significantly increased the efficiency spike number, aboveground biomass and grain yield (7.8% higher than CP and 11.3% higher than CPM) of wheat. The heat conservation effect of the DPM practice was stronger in the early stage of growth and was more effective in minimizing fluctuations in soil temperature in the wheat season compared with CPM. The development and yield of maize that was sowed in the mulching lines of DPM were less improved, although the amount of aboveground biomass at the maturity stage was higher. Additionally, the soil temperature of the maize season under DPM showed a narrowing trend of changes during the early stage with slight effects in the middle stage and a resumption of heat conservation in the late stage. Compared with CP, both mulching patterns decreased soil evaporation during the two crops’ seasons by an average 5.3% in CPM and 7.8% in DPM, which is particularly evident when the crops’ leaf area index was low. Therefore, the DPM pattern could more effectively optimize soil temperature and water storage. Furthermore, this pattern may have positive effects on the yields of winter wheat and on reducing the soil water requirement of the maize season.

Relationship of crop yield and soil organic carbon and nitrogen under long term fertilization in black loessial soil region on the Loess Plateau in China.

The feedbacks between crop yield and soil organic carbon and total nitrogen contents were examined in a long-term experiment, which was established on black loessial soil on the Loess Pla-teau in China. There were six treatments, including CK (no fertilizer), N (single nitrogen fertilizer), NP (chemical fertilizers NP), SNP (straw and chemical fertilizers NP), M (organic manure) and MNP (organic manure and chemical fertilizers NP). Results showed that balanced application of chemical fertilizers, single application of organic manure, the combined application of chemical fertilizers with organic manure and chemical fertilizers coupled with straw returning to the field all significantly increased crop yield and its stability compared with control (CK). The yields of maize and wheat in NP, SNP, M and MNP treatments increased by 92%, 97%, 93%, 141% and 147%, 164%, 139%, 214%, respectively, compared with the control. The annual mean yields of maize and wheat in NP treatment were equal to or higher than those of the local conventional fertilization practices and quite stable among different years, which indicated that the fertilization rates with N 90 kg·hm-2 and P2O5 75 kg·hm-2 were enough for crop growth in wheat-maize rotation system. Application of chemical fertilizer P every other year combined with straw returning to the field (SNP) had similar crop yield values with NP treatment, with the P application amount could be reduced by 50%. The balanced application of chemical fertilizers, organic manure application, the combined application of chemical fertilizers with organic manure, and chemical fertilizers coupled with straw returning to the field could significantly increase soil organic carbon content, whereas chemical fertilizer application had no significant influence on soil total nitrogen content. Across all treatments, the contents of soil organic carbon and total nitrogen were significantly and positively correlated. Under different fertilization treatments, organic carbon sequestration rate was between 15% and 41%. In SNP treatment, the soil organic carbon content enhanced 0.06 g·kg-1 when the amount of organic carbon input every increased 1 t·hm-2, while in CK, N, NP, M and MNP treatments, the increments was between 0.12 and 0.15 g·kg-1. The yields of both maize and wheat were positively correlated with soil total nitrogen content. Maize yield constantly increased with the increases of soil organic carbon content, but wheat yield increased at first and then kept stable with the increases of soil organic carbon content, with a threshold of 6.8 g·kg-1. In conclusion, long-term balanced application of chemical fertilizers, organic manure application, chemical fertilizers combined with manure and chemical fertilizers coupled with straw returning to the field could significantly increase soil organic carbon and total nitrogen contents, consequently resulted in higher crop yield and stubble amount returned to soil, the increase of stubble returned to soil further led to the increase of soil organic carbon and total nitrogen contents, which formed the mutual promotion feedback relationship each other in the black loessial soil region of Loess Plateau in China.

Long-term effects of biochar addition and straw return on N2O fluxes and the related functional gene abundances under wheat-maize rotation system in the North China Plain

To evaluate long-term effects of biochar addition and straw return (SR) on N2O fluxes in wheat-maize rotation system, a 2-year field experiment following a 7-year biochar addition and SR was investigated in an intensively managed agricultural soil in the North China Plain (NCP). Four treatments were included: 1) no biochar addition (CK); 2) biochar treatment with 4.5 t ha−1 yr−1 (C1); 3) biochar treatment with 9.0 t ha−1 yr−1 (C2); and 4) all the wheat/maize straw return (SR). The results showed the annual cumulative N2O emissions from C1 treatment were increased by 15.9–16.5%, while C2 treatment suppressed the annual cumulative N2O emissions by 22.8–26.3%. In comparison, straw return suppressed N2O emissions by 13.4–43.6% in the wheat season but increased N2O emissions remarkably by 45.3–53.9% in the maize season. Biochar addition enhanced the copies of AOA, AOB, nirK, nirS, and nosZ genes, while straw return decreased the copies of AOB, nirK, nirS, and nosZ genes at the high N2O emission period in the maize season. The production of N2O in the maize season was mainly driven by the AOB and nosZ genes, and by AOB gene in the wheat season. These results suggest that application of 9.0 t ha−1 yr−1 biochar is a more optimum agricultural strategy for reducing N2O emission in the wheat-maize system.

Soil biochemical parameters in the rhizosphere contribute more to changes in soil respiration and its components than those in the bulk soil under nitrogen application in croplands

Soil respiration (RS), which is the second largest carbon flux between the atmosphere and terrestrial ecosystems, has significant impact on atmospheric CO2 concentration and climatic dynamics. Nitrogen (N) fertilizer has been heavily applied in agroecosystems at the global scale for high crop yields, and plays a major role in regulating RS. Although the respective response of soil biochemical property and RS to N addition has been widely studied, the contributions of soil biochemical parameters especially in the rhizosphere to changes in RS and its components (soil heterotrophic (RH) and autotrophic (RA) respiration) under N application remain poorly understood. The present study aimed to examine whether the rhizosphere effect alters the relationship between soil biochemical properties and RS under N addition in croplands. We conducted N application experiment in a wheat-maize rotation system in the North China Plain. N fertilizer was applied at four different levels during both wheat and maize growing seasons: 0, 120, 180 and 240 kg N ha−1. Soil biochemical parameters (e.g. soil enzyme activities, available N, and glomalin contents), RS and its components were measured under all N treatments. First, N addition only significantly enhanced RA in 2014 (the fifth year of N application) but increased both RA and RH in 2015 (the sixth year of N application) because RH had lower N sensitivity than RA or lower soil moisture in 2014 which weakened the effect of N on RH. Second, soil enzyme activities, glomalin and available N contents in both the rhizosphere and bulk soil were significantly improved by N addition. Third, soil biochemical parameters in the rhizosphere explained the changes in RS and its components than those in the bulk soil. Specifically, soil enzyme activities in the bulk soil were more related to RS and its components than those in the rhizosphere, however, available N and glomalin contents showed contrary results. Our study indicated that the contributions of soil biochemical parameters to RS and its components under nitrogen application vary between the bulk and rhizosphere soil, which should be considered in Earth system models to improve their predictive abilities.

AHC: An integrated numerical model for simulating agroecosystem processes—Model description and application

This article introduces the AHC model as a new tool for modeling and assessing the agroecosystem processes. The AHC, as a one-dimensional numerical physical model, simulates the soil water and salt/nitrogen dynamics, heat transport, and crop growth and yield in various soil-crop environments. The key features of the AHC include that it provides the optional function for simulating the fate of salt or nitrogen; it has an efficient global method for sensitivity analysis and parameter estimation; and it is useful in a wide range of field conditions, especially for those in northern China. A menu-driven program is developed as a user-friendly interface for efficient data manipulation. This paper primarily describes the main structures and algorithms of the AHC and presents its field applicability. Model testing and application was conducted with two cases: (1) a salinity case with maize growing in salt-affected fields under arid and shallow groundwater environments (Hetao, upper Yellow River basin, northwest China); and (2) a nitrogen case with a wheat-maize rotation system in the semihumid monsoon region (Tai’an, North China Plain). Good agreement was obtained between the simulated and observed data, including the soil water contents, salt/nitrogen contents, and crop growth indicators. The soil water and salt/nitrogen dynamics, crop growth processes, and their complex interactive effects were also well interpreted using the AHC. Rational simulation proves the good applicability of the AHC for practical field use.

Improving nitrogen and water use efficiency in a wheat-maize rotation system in the North China Plain using optimized farming practices

Excessive nitrogen (N) application and shortage of water are the major obstacles to sustainable agricultural development in the high-yielding regions of the North China Plain. New cropping systems need to be created that use integrated management practices to improve the utilization of nitrogen and water and to reduce the emissions of greenhouse gases. We conducted a 4-year (2011–2015) field experiment in Huantai county using three cropping treatments: local farmers’ conventional practices (FP), recommended farming management (REC), and no N fertilization (CK). The study revealed that, the mean annual grain yield of FP and REC was both 16.5 Mg ha−1 which was higher than CK (7.9 Mg ha−1). In comparison with FP, the REC treatment showed N fertilizer and groundwater input reduced by 43% and 28% with increasing of 79.3% and 61.7% of N use efficiency (NUE) and irrigation water use efficiency (IWUE), respectively. The REC treatment demonstrated consistently lower N2O emissions (36% on average) compared with the FP treatment. The annual net global warming potentials of the REC and CK treatments were 37% and 73% lower, respectively, than that of the FP treatment. The water footprint of the REC treatment was 30% (the Water Footprint Assessment method) to 37% (the Life Cycle Assessment method) less than that of the FP treatment. These results indicate that REC is a promising and feasible treatment for ensuring environmentally friendly, and energy-efficient sustainable agriculture in the high-yielding regions of the North China Plain.

Water pollution risk from nitrate migration in the soil profile as affected by fertilization in a wheat-maize rotation system

Reducing nitrogen (N) fertilizer input into the soil is needed by a crop production and environmental pollution control. A field experiment using a wheat-maize rotation system was conducted in North China Plain (NPL) to evaluate agronomic performance and the reduction of nitrate accumulation. The trial consisted of three replicates of five treatments: no nitrogen (CK), recommended N rate (REC) (180 and 210 kg ha−1 N fertilizer as urea for wheat and maize, respectively), same amount N in the form of controlled release fertilizer (CRF), with addition of duck manure to achieve the same total N rate as REC (80% REC + DM) and conventional fertilization (CF) (315 and 270 kg ha−1 N fertilizer as urea for wheat and maize, respectively). During the continued fertilization of the rotation system, the CRF application had an equal yield, N use efficiency (48%) and residual N (175 kg ha−1) but decreased the estimated N loss (18 kg ha-1) when compared to REC (72 kg ha-1). N accumulated below the root zone in the 40–60 cm soil layer was at a high risk of migrating deeper in the soil profile. Application of CRF could effectively reduce the nitrate N accumulating in the soil, slowing down the rate of nitrate migration to the deep soil.

Accumulation and bioavailability of heavy metals in a soil-wheat/maize system with long-term sewage sludge amendments

A long-term field experiment was carried out with a wheat-maize rotation system to investigate the accumulation and bioavailability of heavy metals in a calcareous soil at different rates of sewage sludge amendment. There are significant linear correlations between the contents of Hg, Zn, Cu, Pb, and Cd in soil and sewage sludge amendment rates. By increasing 1 ton of applied sludge per hectare per year in soil, the contents of Hg, Zn, Cu, Pb, and Cd in soil increased by 6.20, 619, 92.9, 49.2, and 0.500 µg kg–1, respectively. For Hg, sewage sludge could be safely applied to the soil for 18 years at an application rate of 7.5 t ha–1 before content exceeded the soil environmental quality standards in China (1 mg kg–1). The safe application period for Zn is 51 years and is even longer for other heavy metals (112 years for Cu, 224 years for Cd, and 902 years for Pb) at an application rate of 7.5 t ha–1 sewage sludge. The contents of Zn and Ni in wheat grains and Zn, Cu, and Cr in maize grains increased linearly with increasing sewage sludge amendment rates. The contents of Zn, Cr, and Ni in wheat straws and Zn, Cu, and As in maize straws were positively correlated with sewage sludge amendment rates, while the content of Cu in wheat straws and Cr in maize straws showed the opposite trend. The bioconcentration factors of the heavy metals in wheat and maize grains were found to be in the order of Zn>Cu>Cd>Hg>Cr=Ni>Pb>As. Furthermore, the bioconcentration factors of heavy metals in wheat were greater than those in maize, indicating that wheat is more sensitive than maize as an indicator plant. These results will be helpful in developing the critical loads for sewage sludge amendment in calcareous soils.