基于DSSAT模型的吉林省黑土作物-土壤氮循环和土壤有机碳平衡

应用DSSAT模型中的CERES-Maize作物模型和Century土壤模型,分析了作物管理参数、施肥量、土壤初始氮含量和作物桔杆还田对吉林省黑土地区玉米生长、氮循环以及有机碳氮生态平衡的影响.结果表明:在玉米目标产量为12000～15000kg.hm-2条件下,最佳施氮肥量为200～240kgN.hm-2.在该氮肥用量下,玉米地上氮吸收量为250～290kgN.hm-2,其中,120～140kgN.hm-2来自土壤,130～150kgN.hm-2来自肥料;提高氮肥用量(250～420kgN.hm-2)将导致土壤残留氮明显增加(63～183kgN.hm-2);延迟追肥时间同样导致土壤残留氮增加;当玉米秸杆还田量超过6000kg.hm-2时,模拟的土壤活性有机碳、氮可以维持当年的供需平衡.建议在吉林省中部地区黑土玉米带,化肥施氮量控制在200～240kgN.hm-2,适时追肥,秸杆还田量在6000kg.hm-2以上,以确保高产和维持土壤养分生态平衡.     

Trade-offs between the short- and long-term effects of residue quality on soil C and N dynamics

The decline of soil organic matter (SOM) and its associated fertility is one of the most important constraints to enhanced crop productivity in sub-Saharan Africa. Integrated soil fertility management recognizes the potential benefits of the combined use of organic residue and mineral fertilizer inputs for improved crop yield and SOM build up. However, these benefits may be controlled by residue quality. We examined the short- to long-term C and N dynamics following application of different quality residues with and without N fertilizer in a series of experiments comprising different timescales of measurement in a Kenyan Humic Nitisol. The combined results of these studies indicate that residue quality and fertilizer additions alter short-term C and N mineralization. Combining low quality residue and fertilizer inputs immobilized a greater amount of fertilizer-N than high quality residue. Under field conditions, this reduction in available N induced by the combination of low quality residue and fertilizer reduced environmental N losses and created a positive interactive effect on crop N uptake. While input management manipulated short-term nutrient dynamics, it did not influence long-term SOM stabilization. The input of residue, regardless of quality, contributed to long-term soil fertility improvement. In conclusion, organic residue quality can be manipulated to optimize short-term nutrient dynamics while still conferring the same benefits to long-term SOM contents.     

Crop rotation and residue management effects on carbon sequestration,nitrogen cycling and productivity of irrigated rice systems

The effects of soil aeration, N fertilizer, and crop residue management on crop performance, soil N supply, organic carbon (C) and nitrogen (N) content were evaluated in two annual double-crop systems for a 2-year period (1994–1995). In the maize-rice (M-R) rotation, maize (Zea mays, L.) was grown in aerated soil in the dry season (DS) followed by rice (Oriza sativa, L.) grown in flooded soil in the wet season (WS). In the continuous rice system (R-R), rice was grown in flooded soil in both the DS and WS. Subplot treatments within cropping-system main plots were N fertilizer rates, including a control without applied N. In the second year, sub-subplot treatments with early or late crop residue incorporation were initiated after the 1995 DS maize or rice crop. Soil N supply and plant N uptake of 1995 WS rice were sensitive to the timing of residue incorporation. Early residue corporation improved the congruence between soil N supply and crop demand although the size of this effect was influenced by the amount and quality of incorporated residue. Grain yields were 13-20% greater with early compared to late residue incorporation in R-R treatments without applied N or with moderate rates of applied N. Although substitution of maize for rice in the DS greatly reduced the amount of time soils remained submerged, the direct effects of crop rotation on plant growth and N uptake in the WS rice crops were small. However, replacement of DS rice by maize caused a reduction in soil C and N sequestration due to a 33–41% increase in the estimated amount of mineralized C and less N input from biological N fixation during the DS maize crop. As a result, there was 11–12% more C sequestration and 5–12% more N accumulation in soils continuously cropped with rice than in the M-R rotation with the greater amounts sequestered in N-fertilized treatments. These results document the capacity of continuous, irrigated rice systems to sequester C and N during relatively short time periods. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rethinking sources of nitrogen to cereal crops

Understanding how to manage N inputs to identify the practices that maximize N recovery has been an organizing principle of agronomic research. Because growth in N fertilizer inputs is expected to continue in an ongoing effort to boost crop production over coming decades, understanding how to efficiently manage recovery of fertilizer N will be important going forward. Yet synthesis of published data that has traced the fate of ¹⁵N‐labeled fertilizer shows that less than half of the N taken up by crops is derived from current‐year N fertilizer. The source of the majority of N in crops is something other than current‐year fertilizer and the sources are not really known. This is true for maize (only 41% of N in crops was from current‐year N fertilizer), rice (32%), and small grains (37%). Recovery of organic fertilizer N (manure, green manure, compost, etc.) in crops is low (27%), though N recovery in subsequent years (10%) was greater than that for mineral fertilizers. Thus, while research on efficiency of N fertilizer use through improved rate, type, location, and timing is important, this research fails to directly address management of the majority of the N supplied to crops. It seems likely that the majority of non‐fertilizer N found in crops comes from turnover of soil and crop residue N. We encourage the research community to revisit the mental model that fertilizer is a replacement for N supply from turnover of soil organic N (SON) and consider a model in which N fertilizer augments ongoing SON turnover and makes an important longer term contribution to SON maintenance and turnover. Research focused on the efficient recovery of N current‐year fertilizer inputs neglects this potential role for building soil N and managing soil N turnover, which seems likely to be the most important source of crop N.     

Mycorrhizal mediation of plant N acquisition and residue decomposition: Impact of mineral N inputs

Mycorrhizas are ubiquitous plant–fungus mutualists in terrestrial ecosystems and play important roles in plant resource capture and nutrient cycling. Sporadic evidence suggests that anthropogenic nitrogen (N) input may impact the development and the functioning of arbuscular mycorrhizal (AM) fungi, potentially altering host plant growth and soil carbon (C) dynamics. In this study, we examined how mineral N inputs affected mycorrhizal mediation of plant N acquisition and residue decomposition in a microcosm system. Each microcosm unit was separated into HOST and TEST compartments by a replaceable mesh screen that either prevented or allowed AM fungal hyphae but not plant roots to grow into the TEST compartments. Wild oat (Avena fatua L.) was planted in the HOST compartments that had been inoculated with either a single species of AM fungus, Glomus etunicatum, or a mixture of AM fungi including G. etunicatum. Mycorrhizal contributions to plant N acquisition and residue decomposition were directly assessed by introducing a mineral ¹⁵N tracer and ¹³C‐rich residues of a C₄ plant to the TEST compartments. Results from ¹⁵N tracer measurements showed that AM fungal hyphae directly transported N from the TEST soil to the host plant. Compared with the control with no penetration of AM fungal hyphae, AM hyphal penetration led to a 125% increase in biomass ¹⁵N of host plants and a 20% reduction in extractable inorganic N in the TEST soil. Mineral N inputs to the HOST compartments (equivalent to 5.0 g N m^?2 yr^?1) increased oat biomass and total root length colonized by mycorrhizal fungi by 189% and 285%, respectively, as compared with the no‐N control. Mineral N inputs to the HOST plants also reduced extractable inorganic N and particulate residue C proportion by 58% and 12%, respectively, in the corresponding TEST soils as compared to the no‐N control, by stimulating AM fungal growth and activities. The species mixture of mycorrhizal fungi was more effective in facilitating N transport and residue decomposition than the single AM species. These findings indicate that low‐level mineral N inputs may significantly enhance nutrient cycling and plant resource capture in terrestrial ecosystems via stimulation of root growth, mycorrhizal functioning, and residue decomposition. The long‐term effects of these observed alterations on soil C dynamics remain to be investigated.     

A long‐term nitrogen fertilizer gradient has little effect on soil organic matter in a high‐intensity maize production system

Global maize production alters an enormous soil organic C (SOC) stock, ultimately affecting greenhouse gas concentrations and the capacity of agroecosystems to buffer climate variability. Inorganic N fertilizer is perhaps the most important factor affecting SOC within maize‐based systems due to its effects on crop residue production and SOC mineralization. Using a continuous maize cropping system with a 13 year N fertilizer gradient (0–269 kg N ha^?1 yr^?1) that created a large range in crop residue inputs (3.60–9.94 Mg dry matter ha^?1 yr^?1), we provide the first agronomic assessment of long‐term N fertilizer effects on SOC with direct reference to N rates that are empirically determined to be insufficient, optimum, and excessive. Across the N fertilizer gradient, SOC in physico‐chemically protected pools was not affected by N fertilizer rate or residue inputs. However, unprotected particulate organic matter (POM) fractions increased with residue inputs. Although N fertilizer was negatively linearly correlated with POM C/N ratios, the slope of this relationship decreased from the least decomposed POM pools (coarse POM) to the most decomposed POM pools (fine intra‐aggregate POM). Moreover, C/N ratios of protected pools did not vary across N rates, suggesting little effect of N fertilizer on soil organic matter (SOM) after decomposition of POM. Comparing a N rate within 4% of agronomic optimum (208 kg N ha^?1 yr^?1) and an excessive N rate (269 kg N ha^?1 yr^?1), there were no differences between SOC amount, SOM C/N ratios, or microbial biomass and composition. These data suggest that excessive N fertilizer had little effect on SOM and they complement agronomic assessments of environmental N losses, that demonstrate N₂O and NO₃ emissions exponentially increase when agronomic optimum N is surpassed.     

Contribution of above‐ and belowground bioenergy crop residues to soil carbon

GHG mitigation by bioenergy crops depends on crop type, management practices, and the input of residue carbon (C) to the soil. Perennial grasses may increase soil C compared to annual crops because of more extensive root systems, but it is less clear how much soil C is derived from above‐ vs. belowground inputs. The objective of this study was to synthesize the existing knowledge regarding soil C inputs from above‐ and belowground crop residues in regions cultivated with sugarcane, corn, and miscanthus, and to predict the impact of residue removal and tillage on soil C stocks. The literature review showed that aboveground inputs to soil C (to 1‐m depth) ranged from 70% to 81% for sugarcane and corn vs. 40% for miscanthus. Modeled aboveground C inputs (to 30 cm depth) ranged from 54% to 82% for sugarcane, but were 67% for miscanthus. Because 50% of observed miscanthus belowground biomass is below 30 cm depth, it may be necessary to increase the depth of modeled soil C dynamics to reconcile modeled belowground C inputs with measured. Modeled removal of aboveground corn residue (25–100%) resulted in C stock reduction in areas of corn–corn–soybean rotation under conventional tillage, while no‐till management lessoned this impact. In sugarcane, soil C stocks were reduced when total aboveground residue was removed at one site, while partial removal of sugarcane residue did not reduce soil C stocks in either area. This study suggests that aboveground crop residues were the main C‐residue source to the soil in the current bioethanol sector (corn and sugarcane) and the indiscriminate removal of crop residues to produce cellulosic biofuels can reduce soil C stocks and reduce the environmental benefits of bioenergy. Moreover, a switch to feedstocks such as miscanthus with more allocation to belowground C could increase soil C stocks at a much faster rate.     

模拟降雨对黄土高原典型草原土壤化学计量及微生物多样性的影响

以宁夏固原云雾山自然保护区封育19年天然草地为研究对象,利用遮雨棚和滴灌技术对研究区的降水量进行人为调控,系统分析了草原土壤生态化学计量及其微生物多样性在50%、100%和150%不同降雨处理下的响应。结果表明:经过一年的水分控制处理(1)不同降雨梯度对土壤有机碳(SOC)、全氮(TN)、全磷(TP)、碳氮比(C/N)、碳磷比(C/P)、氮磷比(N/P)无显著性影响,但100%降水处理下SOC、TN、TP、N/P均高于50%和150%降水处理。(2)在3种不同降水梯度处理下,各处理不同土层深度SOC、TN、TP、C/N、C/P、N/P有显著性差异(P0.05),且随土层深度加深,土壤化学计量及其比值逐渐降低。(3)降雨对土壤微生物多样性影响不大,但増雨和减雨均能增加真菌多样性,引起细菌菌群结构发生相应的变化,且真菌优势种相对丰度随降雨增加呈下降趋势。(4)土壤SOC、TP、C/N与微生物多样性无显著相关,C/P、N/P与细菌多样性呈显著负相关关系(P0.05),与真菌多样性呈极显著正相关关系(P0.01)。短期(一年)降雨变化对土壤养分及微生物多样性影响较弱,但微生物多样性与土壤养分二者之间关系密切,研究结果为探讨长期降雨处理对草地生态系统影响提供参考。     

Dramatic loss of inorganic carbon by nitrogen‐induced soil acidification in Chinese croplands

Intensive crop production systems worldwide, particularly in China, rely heavily on nitrogen (N) fertilization, but left more than 50% of fertilizer N in the environment. Nitrogen (over) fertilization and atmospheric N deposition induce soil acidification, which is neutralized by soil inorganic carbon (SIC; carbonates), and carbon dioxide (CO₂) is released to the atmosphere. For the first time, the loss of SIC stocks in response to N‐induced soil acidification was estimated for Chinese croplands from 1980 to 2020 and forecasts were made up to 2100. The SIC stocks in croplands in 1980 were 2.16 Pg C (16.3 Mg C/ha) in the upper 40 cm, 7% (0.15 Pg C; 1.1 Mg C/ha) of which were lost from 1980 to 2020. During these 40 years, 7 million ha of cropland has become carbonate free. Another 37% of the SIC stocks may be lost up to 2100 in China, leaving 30 million ha of cropland (37.8%) without carbonates if N fertilization follows the business‐as‐usual (BAU) scenario. Compared to the BAU scenario, the reduction in N input by 15%–30% after 2020 (scenarios S1 and S2) will decrease carbonate dissolution by 18%–41%. If N input remains constant as noted in 2020 (S3) or decreases by 1% annually (S4), a reduction of up to 52%–67% in carbonate dissolution is expected compared to the BAU scenario. The presence of CaCO₃ in the soil is important for various processes including acidity buffering, aggregate formation and stabilization, organic matter stabilization, microbial and enzyme activities, nutrient cycling and availability, and water permeability and plant productivity. Therefore, optimizing N fertilization and improving N‐use efficiency are important for decreasing SIC losses from acidification. N application should be strictly calculated based on crop demand, and any overfertilization should be avoided to prevent environmental problems and soil fertility decline associated with CaCO₃ losses.     

Microbial mechanisms of carbon priming effects revealed during the interaction of crop residue and nutrient inputs in contrasting soils

Agronomic practices such as crop residue return and additional nutrient supply are recommended to increase soil organic carbon (SOC) in arable farmlands. However, changes in the priming effect (PE) on native SOC mineralization in response to integrated inputs of residue and nutrients are not fully known. This knowledge gap along with a lack of understanding of microbial mechanisms hinders the ability to constrain models and to reduce the uncertainty to predict carbon (C) sequestration potential. Using a ¹³C‐labeled wheat residue, this 126‐day incubation study examined the dominant microbial mechanisms that underpin the PE response to inputs of wheat residue and nutrients (nitrogen, phosphorus and sulfur) in two contrasting soils. The residue input caused positive PE through “co‐metabolism,” supported by increased microbial biomass, C and nitrogen (N) extracellular enzyme activities (EEAs), and gene abundance of certain microbial taxa (Eubacteria, β‐Proteobacteria, Acidobacteria, and Fungi). The residue input could have induced nutrient limitation, causing an increase in the PE via “microbial nutrient mining” of native soil organic matter, as suggested by the low C‐to‐nutrient stoichiometry of EEAs. At the high residue, exogenous nutrient supply (cf. no‐nutrient) initially decreased positive PE by alleviating nutrient mining, which was supported by the low gene abundance of Eubacteria and Fungi. However, after an initial decrease in PE at the high residue with nutrients, the PE increased to the same magnitude as without nutrients over time. This suggests the dominance of “microbial stoichiometry decomposition,” supported by higher microbial biomass and EEAs, while Eubacteria and Fungi increased over time, at the high residue with nutrients cf. no‐nutrient in both soils. Our study provides novel evidence that different microbial mechanisms operate simultaneously depending on organic C and nutrient availability in a residue‐amended soil. Our results have consequences for SOC modeling and integrated nutrient management employed to increase SOC in arable farmlands.     

Temporal changes in soil C‐N‐P stoichiometry over the past 60 years across subtropical China

Controlled experiments have shown that global changes decouple the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P), resulting in shifting stoichiometry that lies at the core of ecosystem functioning. However, the response of soil stoichiometry to global changes in natural ecosystems with different soil depths, vegetation types, and climate gradients remains poorly understood. Based on 2,736 observations along soil profiles of 0–150 cm depth from 1955 to 2016, we evaluated the temporal changes in soil C‐N‐P stoichiometry across subtropical China, where soils are P‐impoverished, with diverse vegetation, soil, and parent material types and a wide range of climate gradients. We found a significant overall increase in soil total C concentration and a decrease in soil total P concentration, resulting in increasing soil C:P and N:P ratios during the past 60 years across all soil depths. Although average soil N concentration did not change, soil C:N increased in topsoil while decreasing in deeper soil. The temporal trends in soil C‐N‐P stoichiometry differed among vegetation, soil, parent material types, and spatial climate variations, with significantly increased C:P and N:P ratios for evergreen broadleaf forest and highly weathered Ultisols, and more pronounced temporal changes in soil C:N, N:P, and C:P ratios at low elevations. Our sensitivity analysis suggests that the temporal changes in soil stoichiometry resulted from elevated N deposition, rising atmospheric CO₂ concentration and regional warming. Our findings revealed that the responses of soil C‐N‐P and stoichiometry to long‐term global changes have occurred across the whole soil depth in subtropical China and the magnitudes of the changes in soil stoichiometry are dependent on vegetation types, soil types, and spatial climate variations.     

Nutrient constraints to tropical agroecosystem productivity in long‐term degrading soils

Soil degradation is one of the most serious threats to sustainable crop production in many tropical agroecosystems where extensification rather than intensification of agriculture has occurred. In the highlands of western Kenya, we investigated soil nitrogen (N) and phosphorus (P) constraints to maize productivity across a cultivation chronosequence in which land‐use history ranged from recent conversion from primary forest to 100 years in continuous cropping. Nutrient treatments included a range of N and P fertilizer rates applied separately and in combination. Maize productivity without fertilizer was used as a proxy measure for indigenous soil fertility (ISF). Soil pools of mineral nitrogen, strongly bound P and plant‐available P decreased by 82%, 31% and 36%, and P adsorption capacity increased by 51% after 100 years of continuous cultivation. For the long rainy season (LR), grain yield without fertilizer declined rapidly as cultivation age increased from 0 to 25 years and then gradually declined to a yield of 1.6 Mg ha^?1, which was maintained as time under cultivation increased from 60 to 100 years. LR grain yield in the old conversions was only 24% of the average young conversion grain yield (6.4 Mg ha^?1). Application of either N or P alone significantly increased grain yield in both the LR and short rainy (SR) seasons, but only application of 120 kg N ha^?1 on the old conversion increased yield by >1 Mg ha^?1. In both SR and LR, there was a greater average yield increment response to N and P when applied together (ranging from 1 to 3.8 Mg ha^?1 for the LR), with the greatest responses on the old conversions. The benefit–cost ratio (BCR) for applying 120 kg N ha^?1 alone was <1 except on the old conversions, while BCRs were>1 for applying 25 kg P ha^?1 alone at all levels of conversion for both seasons. Application of both N (120 kg N ha^?1) and P (25 kg P ha^?1) on the old conversions resulted in the greatest BCRs. This study clearly indicates that maize productivity responses to N and P fertilizer are significantly affected by the age of cultivation and its influence on ISF, but that loss of productivity can be restored rapidly when these limiting nutrients are applied. Management strategies should consider ISF and economic factors to determine optimal N and P input requirements for achieving and sustaining profitable crop production on degraded soils.     

Management-induced changes in soil organic carbon and related crop yield dynamics in China's cropland

Enhancing soil organic carbon (SOC) sequestration and food supply are vital for human survival when facing climate change. Site-specific best management practices (BMPs) are being promoted for adoption globally as solutions. However, how SOC and crop yield are related to each other in responding to BMPs remains unknown. Here, path analysis based on meta-analysis and machine learning was conducted to identify the effects and potential mechanisms of how the relationship between SOC and crop yield responds to site-specific BMPs in China. The results showed that BMPs could significantly enhance SOC and maintain or increase crop yield. The maximum benefits in SOC (30.6%) and crop yield (79.8%) occurred in mineral fertilizer combined with organic inputs (MOF). Specifically, the optimal SOC and crop yield would be achieved when the areas were arid, soil pH was ≥7.3, initial SOC content was ≤10 g kg⁻¹, duration was >10 years, and the nitrogen (N) input level was 100–200 kg ha⁻¹. Further analysis revealed that the original SOC level and crop yield change showed an inverted V-shaped structure. The association between the changes in SOC and crop yield might be linked to the positive role of the nutrient-mediated effect. The results generally suggested that improving the SOC can strongly support better crop performance. Limitations in increasing crop yield still exist due to low original SOC level, and in regions where the excessive N inputs, inappropriate tillage or organic input is inadequate and could be diminished by optimizing BMPs in harmony with site-specific conditions.     

Nitrogen and harvest effects on soil properties under rainfed switchgrass and no‐till corn over 9 years: implications for soil quality

Nitrogen fertilizer and harvest management will alter soils under bioenergy crop production and the long‐term effects of harvest timing and residue removal remain relatively unknown. Compared to no‐tilled corn (NT‐C, Zea mays L.), switchgrass (Panicum virgatum L.) is predicted to improve soil properties [i.e. soil organic C (SOC), soil microbial biomass (SMB‐C), and soil aggregation] due to its perennial nature and deep‐rooted growth form, but few explicit field comparisons exist. We assessed soil properties over 9 years for a rainfed study of N fertilizer rate (0, 60, 120, and 180 kg N ha^?1) and harvest management on switchgrass (harvested in August and postfrost) and NT‐C (with and without 50% stover removal) in eastern NE. We measured SOC, aggregate stability, SMB‐C, bulk density (BD), pH, P and K in the top 0–30 cm. Both NT‐C and switchgrass increased SMB‐C, SOC content, and aggregate stability over the 9 years, reflecting improvement from previous conventional management. However, the soils under switchgrass had double the percent aggregate stability, 1.3 times more microbial biomass, and a 5–8% decrease in bulk density in the 0–5 and 5–10 cm depths compared to NT‐C. After 9 years, cumulative decrease in available P was significantly greater beneath NT‐C (?24.0 kg P ha^?1) compared to switchgrass (?5.4 kg P ha^?1). When all measured soil parameters were included in the Soil Management Assessment Framework (SMAF), switchgrass improved soil quality index over time (ΔSQI) in all depths. NT‐C without residue removal did not affect ΔSQI, but 50% residue removal decreased ΔSQI (0–30 cm) due to reduced aggregate stability and SMB‐C. Even with best‐management practices such as NT, corn stover removal will have to be carefully managed to prevent soil degradation. Long‐term N and harvest management studies that include biological, chemical, and physical soil measurements are necessary to accurately assess bioenergy impacts on soils.     

Responses of soil pH to no-till and the factors affecting it: A global meta-analysis

No-till (NT) is a sustainable option because of its benefits in controlling erosion, saving labor, and mitigating climate change. However, a comprehensive assessment of soil pH response to NT is still lacking. Thus, a global meta-analysis was conducted to determine the effects of NT on soil pH and to identify the influential factors and possible consequences based on the analysis of 114 publications. When comparing tillage practices, the results indicated an overall significant decrease by 1.33 ± 0.28% in soil pH under NT than that under conventional tillage (p < .05). Soil texture, NT duration, mean annual temperature (MAT), and initial soil pH are the critical factors affecting soil pH under NT. Specifically, with significant variations among subgroups, when compared to conventional tillage, the soil under NT had lower relative changes in soil pH observed on clay loam soil (?2.44%), long-term implementation (?2.11% for more than 15 years), medium MAT (?1.87% in the range of 8–16℃), neutral soil pH (?2.28% for 6.5 < initial soil pH < 7.5), mean annual precipitation (?1.95% in the range of 600–1200 mm), in topsoil layers (?2.03% for 0–20 cm), with crop rotation (?1.98%), N fertilizer input (the same for NT and conventional tillage) of 100–200 kg N ha^?1 (?1.83%), or crop residue retention (?1.52%). Changes in organic matter decomposition under undisturbed soil and with crop residue retention might lead to a higher concentration of H⁺ and lower of basic cations (i.e., calcium, magnesium, and potassium), which decrease the soil pH, and consequently, impact nutrient dynamics (i.e., soil phosphorus) in the surface layer under NT. Furthermore, soil acidification may be aggravated by NT within site-specific conditions and improper fertilizer and crop residue management and consequently leading to adverse effects on soil nutrient availability. Thus, there is a need to identify strategies to ameliorate soil acidification under NT to minimize the adverse consequences.     

密度、施肥对旱地春小麦产量、水分利用效率和籽粒养分含量的补偿效应

为了探明旱作条件下无机营养对作物产量和水分利用效率的补偿效应,我们在宁南黄土高原半干旱地区开展了为期两年的春小麦密度与肥料试验。通过4种播种密度和5种肥力水平的综合研究结果表明,在不同处理的籽粒产量和水分利用效率排序中,播种密度为500粒／m^2时,以施肥量90kg／hm^2N和135kg／hm^2P2O5处理的产量和水分利用效率为最大。与不施肥的对照相比,增施肥料与籽粒产量和水分利用效率的提高成显著的正相关关系,相关系数分别达到0．959和0．894,而播种密度则与产量和水分利用效率的相关性不显著。增施肥料虽然能够提高可育小花数,但随着播种密度的增大,穗粒数和千粒重反而呈下降趋势,表明可育小花数对肥料水平反应敏感,而穗粒数和千粒重主要受播种密度的影响。施肥能够促进春小麦根系的生长发育,特别是促进浅层根量的增加,增强了作物的水分养分吸收。另外,不同种类肥料配施的结果表明,单施P肥或者N、P、K配合施用,可使春小麦产量分别提高44．6％和55．4％。N、P、K配合施肥还能够提高品质,使籽粒中的P、N、K含量分别提高18．5％、18．4％和8．1％。上述研究结果说明,控制播种密度、改善土壤肥力对于促进旱地春小麦高效利用有限水分具有明显的补偿效应。     

农田减氮调控施肥对华北潮土区小麦-玉米轮作体系氮素损失的影响

针对华北平原麦玉轮作区氮肥用量大、氮损失及土壤氮素累积严重的问题,探索不同减氮调控施肥措施对作物产量、氮损失及土壤无机氮累积的影响.通过(2016—2017年)设置两年大田试验,以农民施肥为对照,研究控释肥处理、微生物肥处理及配施硝化抑制剂处理减少氮用量后对小麦、玉米产量和地上部吸氮量、氮损失及土壤无机氮含量的影响.结果表明: 2016年微生物肥处理的小麦产量显著低于控释肥处理和硝化抑制剂处理,与农民施肥处理无显著性差异;且小麦和周年作物地上部吸氮量都显著降低.2017年各处理间作物产量和吸氮量无显著性差异.3种减氮调控施肥处理均能保持和改善耕层土壤肥力;且微生物肥处理随种植时间延长对土壤碱解氮、速效钾和有机质含量均有提升.随种植时间延长无机氮累积严重,微生物肥处理和添加硝化抑制剂处理均可降低40～100 cm土壤剖面的无机氮含量,而控释肥处理可提高0～40 cm土层无机氮含量.氮损失中氨挥发>淋溶量>N₂O排放>径流,径流损失可忽略不计,其中以农民施肥处理氮损失最大,微生物肥处理可显著降低氨挥发损失量,但淋溶量较大.综上所述,减量施氮条件下,控释肥处理和添加硝化抑制剂处理可保证作物产量及地上部吸氮量,微生物肥处理随种植年限的延长可保证作物产量和吸氮量.微生物肥和添加硝化抑制剂处理可降低40～100 cm土层无机氮含量,控释肥处理对削减无机氮量效果不明显;几种减氮调控措施均可降低氮损失,但微生物肥处理需调整措施来降低氮的淋溶量.     

Nitrogen management in `adequate' input maize-based agriculture in the derived savanna benchmark zone of Benin Republic

Although the West-African moist savanna zone has a high potential for crop production, yields on farmers' fields are, on average, far below this potential, mainly due to the low use of external sources of nutrients. Since the mid-1990s, it has become clear that in order to upgrade crop production to levels needed to sustain the growing population without further degrading the soil resource base, inorganic fertilizers are required. Due to the physico-chemical nature of these soils and the relatively high cost of inorganic fertilizers, a general consensus exists in the research and development community that these inorganic inputs need to be complemented with organic matter. Here, we explore options to produce organic matter in-situ and evaluate the impact of combining inorganic and organic sources of N on maize yields, focusing on the densely populated derived savanna (DS) benchmark of Benin Republic. Although most of the farmers (93%) in this benchmark use inorganic fertilizer, applications rates are low (on average, 27 kg N ha^–1). A significant response to N was observed for 96% of the studied farmers' fields.Grain and herbaceous legumes were observed to produce between 383 and 8700 kg dry matter ha^–1 in the benchmark area. Inoculation with Rhizobia and inorganic P additions were shown to significantly improve biomass production on sites with low contents of Rhizobia and P. Although maize grain yield was observed to increase significantly following a legume compared with following a maize crop or natural fallow, these increases were insufficient in the case of a cowpea crop or were obtained at the cost of leaving the field `idle' for a whole year in the case of a herbaceous Mucuna fallow. Topping up a cowpea haulms equivalent of 45 kg N ha^–1 with 45 kg urea–N ha^–1 was shown to give maize yields similar to the yields obtained after applying 90 kg urea–N ha^–1 on the poorest fields. Moreover, on these fields, a positive interaction between cowpea–N and urea–N sources of 200 kg grain ha^–1 was observed. On the richest fields, the effects of applied organic matter and fertilizer were additive.Agroforestry systems are alternative cropping systems that produce organic matter in-situ. As tree roots go down below the rooting depth of food crops, sub-soil fertility was observed to influence tree biomass production. Yield increases in tree-crop intercrop systems – such as alley cropping – in the absence of inorganic inputs are often reduced by the occurrence of tree-crop competition. In cut-and-carry systems, where tree prunings are harvested from a field adjacent to the crop land, increases in maize grain yield caused by addition of those prunings were observed to be on the low side. Mixing these residues with urea, however, was shown to lead to added benefits of about 500 kg grains ha^–1, relative to the treatments with sole inputs of organic matter or urea. Although residue quality was shown to affect maize N uptake in a pot trial, its impact under field conditions was minimal for the range of considered residue qualities. In an alley cropping trial, maize yield was shown to be sustained on a non-degraded site and enhanced on a degraded site, when a minimal amount of mineral fertilizer was added with the prunings, whereas fertilizer application alone failed to do so in both cases.     

不同施肥管理措施对农田土壤中植物和微生物残留组分的影响

在农田生态系统中,施肥是维持和提高土壤有机碳(SOC)水平的重要管理措施。微生物代谢和植物组分存留共同控制着有机碳的截获过程。本研究利用肥料与肥力长期(30年)定位试验,以氨基糖和木质素分别作为微生物和植物残留组分标识物,探讨长期不同施肥处理对黑土农田中微生物和植物残体组分积累及有机碳库的影响。结果表明: 与未施肥处理相比,施用无机肥(单施氮肥或有机无机肥配施)可增加作物生物量和土壤氨基糖的积累,但对木质素和SOC含量无显著影响,说明无机肥施入刺激了微生物底物同化,加速了有机碳和木质素在耕层的周转。与无机肥相比,长期施用有机肥促进了SOC的累积(增幅38.3%),但是氨基糖在土壤有机碳中所占的比例并未发生显著变化,说明微生物残留物对SOC积累的贡献具有饱和性;而有机肥施入增加了木质素在SOC中的比例,即增加了植物残体对SOC长期积累的贡献。与单施有机肥相比,有机无机肥配施增加了微生物残留物对SOC的积累。因此,长期施肥可以调节微生物残留物和植物残留组分的不同积累过程,从而影响SOC的积累和稳定机制。     

黑土长期施肥及养分循环再利用的作物产量及土壤肥力质量变化Ⅰ.作物产量

在一丰P黑土(Olsen P25.8mg·kg^-1)上进行13年中长期田间试验的结果表明,氮肥平均增产率为275%,年增产粮食(大豆、玉米、小麦混合)724kg·hm^-2,1kgN增产粮食9.4kg;磷肥前期增产不明显,13年平均增产率为7%,年增产粮食241kg·hm^-2,1kgP增产粮食12.7kg.每年施用循环回田猪圈肥(以处理区收获产品的80%喂猪、垫圈经堆制而成),粮食平均年增产量在不施化肥、施N、施NP基础上,分别为268、258、255kg·hm^-2,相应的增产率为9.8%、7.6%和7.0%.试验期间循环回田猪圈肥的增产效果有逐渐增长趋势,表明存在着猪圈肥残效的叠加效应.