深松和秸秆还田对旋耕农田土壤有机碳活性组分的影响

土壤有机碳(soil organic carbon,SOC)及其活性组分能够敏感响应耕作方式变化及有机物输入。为对比长期旋耕农田进行深松后土壤有机碳各活性组分及比例变化,该研究基于连续7a的旋耕转变为深松和秸秆管理长期定位试验,对比了旋耕无秸秆还田处理(rotary tillage with straw removal,RT)、旋耕秸秆还田处理(rotary tillage with straw return,RTS)、旋耕转变为深松无秸秆还田处理(rotary tillage conversion to subsoiling with straw removal,RT-DT)、旋耕转变为深松秸秆还田处理(rotary tillage conversion to subsoiling with straw return,RTS-DTS)下土壤有机碳(soil organic carbon,SOC)、颗粒有机碳(particulate organic carbon,POC)、易氧化有机碳(readily oxidizable organic carbon,ROC)、微生物生物量碳(microbial biomass carbon,MBC)、溶解性有机碳(dissolved organic carbon,DOC)、活性有机碳(labile organic carbon,LOC)在土壤有机碳中比例的变化及各组分间的相互关系。研究结果表明,耕作方式从旋耕转变为深松和秸秆还田对SOC及其各活性组分均产生显著影响,耕作方式转变、秸秆还田及两者的交互效应是影响SOC及其活性组分的主要因素。秸秆还田显著提高了RTS处理和RTS-DTS处理的SOC含量,分别比RT和RT-DT处理高6.1%~15.6%和19.1%~32.3%。并且转变耕作方式后RTS-DTS处理比于RTS处理SOC含量提高16.9%~20.0%。同时,RTS-DTS处理的POC含量比RTS处理高13.6%~53.8%;但RT-DT和RTS-DTS处理的土壤ROC含量较RT和RTS处理都呈下降趋势,RTS-DTS处理的ROC含量比RTS处理下降4.6%~10%;MBC含量降低23.8%~30.6%。虽然秸秆还田显著提高了各处理的DOC含量,但RTS转变为RTS-DTS处理后,其3个土层的DOC含量下降了8%~41%。相比于RT和RTS处理,RT-DT和RTS-DTS处理0~30 cm各土层中LOC在SOC中的比例显著下降。相关性分析结果表明,除POC与ROC之间无显著性相关关系外,SOC及各组分间均呈显著(P<0.05)或极显著(P<0.01)的相关关系。耕作方式转变为深松和秸秆还田提高了SOC含量的同时,显著降低了SOC中的活性有机碳组分,这更有利于SOC的有效积累,促进土壤碳库的稳定固存。

Effects of Long-term Located Fertilization on Evolution of Available Phosphorus and Phosphorus Pool in Shandong Fluvo-aquic Soil

This study was conducted to investigate the effects of long-term located fertilization on soil phosphorus,the changes of soil available phosphorus（ OlsenP）,the evolution of soil total phosphorus（ TP） and the ratio change of Olsen-P to TP（ PAC） by 33-year fertilization experiments in winter wheat-summer maize rotation system in Shandong fluvo-aquic soil. Eight treatments were designed as no fertilization（ CK）,nitrogen fertilizer（ N）,nitrogen and phosphate fertilizer（ NP）,nitrogen and potassium fertilizer（ NK）,phosphate and potassium fertilizer（ PK）,nitrogen-phosphate-potassium fertilizer（ NPK）,reduced NPK fertilizer（ N（15） PK）,and increased NPK fertilizer（ N（25） PK）. Meanwhile,eight organic fertilizer-added treatments were designed based on the application of inorganic fertilizer the same as the above ones. The results showed that TP,Olsen-P and PAC of treatments added with organic fertilizer were higher than those without organic fertilizer,and those of the treatments applied with phosphate fertilizer were higher than those of no phosphate fertilizer. With the increase of years,soil P pool decreased due to crop absorption,nutrient loss and morphological transformation and other causes under the treatments of without and only phosphate fertilizer,while remained stable under the treatments added with organic fertilizer. The PAC values were generally lower in fluvo-aquic soil,and it could be improved by the application of organic fertilizer. On the whole,the application of chemical phosphate fertilizer combined with organic fertilizer could improve the phosphorus content in soil and ensure the supply of phosphorus nutrition. This study would provide scientific basis for fertilization management and soil fertility in fluvo-aquic soil.

Effects of Soil Improver on Wheat in Saline-Alkali Lands in the Yellow River Delta

Field experiment carried out to test the effects of soil improver on wheat yield and soil physical-chemical properties. The results indicated that soil improver could optimize soil aggregates structure, decrease soil bulk density, soil pH and soil salt content, increase soil organic matter and 1 000-grain weight, thereby enhancing wheat yield. With the increase of soil improver application amount, soil physical-chemical properties became better and wheat yield increased. However, there was no significant difference in the treatments with the application amounts of 3%, 4% and 5%. In addition, the treatment of reducing nitrogen showed no superiority in soil physical-chemical properties and wheat yield, indicating that sufficient nitrogen was essential for the growth of wheat.

Toward to agricultural green development by multi-objective zoning and nitrogen nutrient management:a case study in the Baiyangdian Basin,China

Although China has achieved great advancements toward national food security,the country is still confronted with a range of challenges,including natural resource stress,imbalanced diets and environmental pollution.Optimized management of crop–livestock systems is the key measure to realize agricultural green transformation.However,optimized management of crop–livestock systems that use multi-objective zoning is lacking.This study employed a multi-objective zoning management approach to comprehensively analyze four indicators:ammonia volatilization,nitrogen surplus,soil carrying capacity and ecological red line area.With its significant ecological integrity and a strong emphasis on sustainability,the Baiyangdian Basin serves as a unique and suitable test case for conducting analyses on multi-objective nutrient optimization management,with the aim to facilitate the agricultural green transformation.This study finds that less than 8%of the area in the Baiyangdian Basin meet the acceptable environmental indicator standard,whereas around 50%of the area that had both nitrogen surplus and ammonia volatilization exceeded the threshold.Implementation of unified management,that is,the same management technique across the study areas,could result in an increase of areas meeting environmental indicator thresholds to 21.1%.This project developed a novel multi-indicator partition optimization method,in which distinct measures are tailored for different areas to satisfy multiple environmental indicators.Implementation of this method,could potentially bring more than 50%area below the threshold,and areas with ammonia emissions and nitrogen surplus could be reduced to 15.8%.The multi-indicators partition optimization method represents a more advanced and efficiency-oriented management approach when compared to unified management.This approach could be regarded as the best available option to help China achieve agricultural transformation to improve efficient production and reduce environmental pollution.It is recommended that current policies aimed at nutrient management toward sustainable agricultural development should shift toward the application of multi-indicators partition optimization.

Responses of soil microbial communities and functions associated with organic carbon mineralization to nitrogen addition in a Tibetan grassland

Alpine grasslands with a high soil organic carbon(SOC)storage on the Tibetan Plateau are experiencing rapid climate warming and anthropogenic nitrogen(N)deposition;this is expected to substantially increase the soil N availability,which may impact carbon(C)cycling.However,little is known regarding how N enrichment influences soil microbial communities and functions relative to C cycling in this region.We conducted a 4-year field experiment on an alpine grassland to evaluate the effects of four different rates of N addition(0,25,50,and 100 kg N ha^-1 year^-1)on the abundance and community structure(phospholipid fatty acids,PLFAs)of microbes,enzyme activities,and community level physiological profiles(CLPP)in soil.We found that N addition increased the microbial biomass C(MBC)and N(MBN),along with an increased abundance of bacterial PLFAs,especially Gram-negative bacterial PLFAs,with a decreasing ratio of Gram-positive to Gram-negative bacteria.The N addition also stimulated the growth of fungi,especially arbuscular mycorrhizal fungi,reducing the ratio of fungi to bacteria.Microbial functional diversity and activity of enzymes involved in C cycling(β-1,4-glucosidase and phenol oxidase)and N cycling(β-1,4-N-acetyl-glucosaminidase and leucine aminopeptidase)increased after N addition,resulting in a loss of SOC.A meta-analysis showed that the soil C/N ratio was a key factor in the response of oxidase activity to N amendment,suggesting that the responses of soil microbial functions,which are linked to C turnover relative to N input,primarily depended upon the soil C/N ratio.Overall,our findings highlight that N addition has a positive influence on microbial communities and their associated functions,which may reduce soil C storage in alpine grasslands under global change scenarios.

Effects of Bacterial-Feeding Nematodes and Glucose on Phenanthrene Removal by Pseudomonas putida

Bacterial-feeding nematodes can promote the bacterial activity through feeding.Bacterial abundance and their activity affect the degradation of polycyclic aromatic hydrocarbons(PAH) such as phenanthrene.The effects of bacterial-feeding nematodes,bacteria,and their interactions on the degradation of phenanthrene with or without glucose were studied through a microcosm experiment.The results showed that up to 57.0%of phenanthrene in mineral medium contaminated with phenanthrene was degraded in the control with bacteria alone and bacteria with the presence of nematodes and/or glucose increased the degradation of phenanthrene by 25.6%to 36.6%.Although both nematode and bacteria abundance decreased gradually,catechol 2,3-dioxygenase(C230) activity increased during the incubation period.Compared with bacteria alone,the presence of nematodes significantly increased C230 activity as well as the abundance of bacteria;this effect was more pronounced when glucose was present.The results imply that nematodes might promote the removal of phenanthrene from medium by stimulating bacteria and C230 activities.

Yield-scaled nitrous oxide emissions from nitrogen-fertilized croplands in China: A meta-analysis of contrasting mitigation scenarios

Nitrogen(N) losses in cropland resulting from the application of synthetic fertilizers decrease crop productivity and exacerbate environmental pollution.Mitigation measures, such as reduction in N fertilizer application rates, can have unintentional adverse effects on crop yield. We conducted a meta-analysis of soil N_(2)O emissions from agricultural fields across China under contrasting mitigation scenarios as a novel approach to identify the most effective strategy for the mitigation of emissions of N_(2)O derived from N fertilizer use in China. Current standard agricultural practice was used as a baseline scenario(BS), and 12 potential mitigation scenarios(S1–S12) were derived from the available literature and comprised single and combinations of management scenarios that accounted for crop yield. Mitigation scenarios S6(nitrification inhibitor 3,4-dimethylpyrazole phosphate) and S11(20% reduction in N application rate plus nitrification inhibitor dicyandiamide) in maize, rice, and wheat crops led to an average 56.0% reduction in N_(2)O emissions at the national level, whereas scenario S4(nitrification inhibitor dicyandiamide) led to yield optimization, with a 14.0% increase for maize and 8.0% increase for rice as compared to the BS. Implementation of these most effective mitigation scenarios(S4, S6, and S11) might help China, as a signatory to the 2015 United Nations Framework Convention on Climate Change(Paris Agreement), to achieve a 30% reduction in N_(2)O emissions by 2030.

NEW ZEALAND DAIRY FARM SYSTEMS AND KEY ENVIRONMENTAL EFFECTS

This paper provides an overview of the range of dairy pasture grazing systems used in New Zealand(NZ),the changes with increased inputs over time and associated key environmental effects including nitrogen(N)leaching and greenhouse gas(GHG)emissions.NZ dairy farming systems are based on year-round grazing and seasonal milk production on perennial ryegrass/clover pasture where cows are rotationally grazed in paddocks.There was an increase in stocking rate on NZ dairy farms from 2.62 cows ha−1 in 2000/2001 to 2.84 cows ha−1 in 2015/2016.During the same period annual milk solids production increased from 315 to 378 kg·yr−1 per cow.This performance has coincided with an increase in N fertilizer use(by~30%)and a twofold increase in externally-sourced feeds.Externally-sourced feeds with a low protein concentration(e.g.,maize silage)can increase the efficiency of N utilization and potentially reduce N losses per unit of production.Off-paddock facilities(such as standoff or feed pads)are often used to restrict grazing during very wet winter conditions.A systems analysis of contrasting dairy farms in Waikato(largest NZ dairying region)indicates that the increased input would result in an increase in per-cow milk production but little change in efficiency of milk production from a total land use perspective.This analysis also shows that the increased inputs caused an 11%decrease in N footprint(i.e.,N emissions per unit of milk production)and a 2%increase in C footprint(i.e.,greenhouse gas(GHG)emissions per unit of milk production).