Combined application of organic fertilizer and chemical fertilizer alleviates the kernel position effect in summer maize by promoting post-silking nitrogen uptake and dry matter accumulation

Adjusting agronomic measures to alleviate the kernel position effect in maize is important for ensuring high yields.In order to clarify whether the combined application of organic fertilizer and chemical fertilizer(CAOFCF)can alleviate the kernel position effect of summer maize,field experiments were conducted during the 2019 and 2020 growing seasons,and five treatments were assessed:CF,100%chemical fertilizer;OFCF1,15%organic fertilizer+85%chemical fertilizer;OFCF2,30%organic fertilizer+70%chemical fertilizer;OFCF3,45%organic fertilizer+55%chemical fertilizer;and OFCF4,60%organic fertilizer+40%chemical fertilizer.Compared with the CF treatment,the OFCF1 and OFCF2 treatments significantly alleviated the kernel position effect by increasing the weight ratio of inferior kernels to superior kernels and reducing the weight gap between the superior and inferior kernels.These effects were largely due to the improved filling and starch accumulation of inferior kernels.However,there were no obvious differences in the kernel position effect among plants treated with CF,OFCF3,or OFCF4 in most cases.Leaf area indexes,post-silking photosynthetic rates,and net assimilation rates were higher in plants treated with OFCF1 or OFCF2 than in those treated with CF,reflecting an enhanced photosynthetic capacity and improved postsilking dry matter accumulation(DMA)in the plants treated with OFCF1 or OFCF2.Compared with the CF treatment,the OFCF1 and OFCF2 treatments increased post-silking N uptake by 66.3 and 75.5%,respectively,which was the major factor driving post-silking photosynthetic capacity and DMA.Moreover,the increases in root DMA and zeatin riboside content observed following the OFCF1 and OFCF2 treatments resulted in reduced root senescence,which is associated with an increased post-silking N uptake.Analyses showed that post-silking N uptake,DMA,and grain yield in summer maize were negatively correlated with the kernel position effect.In conclusion,the combined application of 15-30%organic fertilizer and 70-85%chemical fertilizer alleviated the kernel position effect in summer maize by improving post-silking N uptake and DMA.These results provide new insights into how CAOFCF can be used to improve maize productivity.

Effects of Fertilization Patterns on Chemical Forms of Nitrogen in Dark Brown Soil and Its Distribution in Different Aggregates

[Objective] This study was conducted to investigate the effects of tradition-al fertilization and formula fertilization by soil testing on the chemical forms of nitro-gen in dark brown soil and its distribution in different aggregates. [Method] A physi-co-chemistry method was adopted in a comparative study on the chemical forms of nitrogen and their distribution in different-sized aggregates of dark brown soil under traditional fertilization and formula fertilization by soil testing respectively. [Result] Compared with traditional fertilization in spring and autumn, the formula fertilization by soil testing averagely decreased, the total nitrogen in soil by 23.2% in spring and by 20% in autumn in the soil layer of 0-20 cm, by 48.8% in the layer of 20-40 cm. Ammonium nitrogen was so sensitive to the methods of fertilization that the content of ammonium nitrogen was reduced much more under formula fertitization by soil testing in autumn than under traditional fertilization. Nitrogen in soil under traditional fertilization pattern was mainly distributed in the aggregates of 0-0.25 and 0.5-1 mm, while in formula fertilization by soil testing it was mainly distributed in the aggregates of 0.25-0.5 and 0-0.25 mm. [Conclusion] The study proved that for-mula fertilization by soil testing helped to reduce the risk of nitrogen pol ution and had huge effects on the chemical forms and distribution of nitrogen in different ag-gregates in dark brown soil.

Effect of chemical and organic fertilization on soil carbon and nitrogen accumulation in a newly cultivated farmland

Increased food demand from the rapidly growing human population has caused intensive land transition from desert to farmland in arid regions of northwest China. In this developing ecosystem, the optimized fertilization strategies are becoming an urgent need for sustainable crop productivity, efficient resources use, together with the delivery of ecosystems services including soil carbon（C） and nitrogen（N） accumulation. Through a 7-year field experiment with 9 fertilization treatments in a newly cultivated farmland, we tested whether different fertilizations had significant influences on soil C and N accumulation in this developing ecosystem, and also investigated possible mechanisms for this influence. The results showed that applying organic manure in cultivated farmland significantly increased the soil C and N accumulation rates; this influence was greater when it was combined with chemical fertilizer, accumulating 2.01 t C and 0.11 t N ha^（–1） yr^（–1） in the most successful fertilization treatment. These high rates of C and N accumulation were found associated with increased input of C and N, although the relationship between the N accumulation rate and N input was not significant. The improved soil physical properties was observed under only organic manure and integrated fertilization treatments, and the significant relationship between soil C or N and soil physical properties were also found in this study. The results suggest that in newly cultivated farmland, long term organic manure and integrated fertilization can yield significant benefits for soil C and N accumulation, and deliver additional influence on physical properties.

Carbon sequestration rate,nitrogen use efficiency and rice yield responses to long-term substitution of chemical fertilizer by organic manure in a rice–rice cropping system

Combined application of chemical fertilizers with organic amendments was recommended as a strategy for improving yield,soil carbon storage,and nutrient use efficiency.However,how the long-term substitution of chemical fertilizer with organic manure affects rice yield,carbon sequestration rate(CSR),and nitrogen use efficiency(NUE)while ensuring environmental safety remains unclear.This study assessed the long-term effect of substituting chemical fertilizer with organic manure on rice yield,CSR,and NUE.It also determined the optimum substitution ratio in the acidic soil of southern China.The treatments were:(i)NPK0,unfertilized control;(ii)NPK1,100%chemical nitrogen,phosphorus,and potassium fertilizer;(iii)NPKM1,70%chemical NPK fertilizer and 30%organic manure;(iv)NPKM2,50%chemical NPK fertilizer and 50%organic manure;and(v)NPKM3,30%chemical NPK fertilizer and 70%organic manure.Milk vetch and pig manure were sources of manure for early and late rice seasons,respectively.The result showed that SOC content was higher in NPKM1,NPKM2,and NPKM3 treatments than in NPK0 and NPK1 treatments.The carbon sequestration rate increased by 140,160,and 280%under NPKM1,NPKM2,and NPKM3 treatments,respectively,compared to NPK1 treatment.Grain yield was 86.1,93.1,93.6,and 96.5%higher under NPK1,NPKM1,NPKM2,and NPKM3 treatments,respectively,compared to NPK0 treatment.The NUE in NPKM1,NPKM2,and NPKM3 treatments was higher as compared to NPK1 treatment for both rice seasons.Redundancy analysis revealed close positive relationships of CSR with C input,total N,soil C:N ratio,catalase,and humic acids,whereas NUE was closely related to grain yield,grain N content,and phenol oxidase.Furthermore,CSR and NUE negatively correlated with humin acid and soil C:P and N:P ratios.The technique for order of preference by similarity to ideal solution(TOPSIS)showed that NPKM3 treatment was the optimum strategy for improving CSR and NUE.Therefore,substituting 70%of chemical fertilizer with organic manure could be the best management option for increasing CSR and NUE in the paddy fields of southern China.

Evaluating the Effects of Sustainable Chemical and Organic Fertilizers with Water Saving Practice on Corn Production and Soil Characteristics

The rapidly growing world population,water shortage,and food security are promising problems for sustainable agriculture.Farmers adopt higher irrigation and fertilizer applications to increase crop production resulting in environmental pollution.This study aimed to identify the long-term effects of intelligent water and fertilizers used in corn yield and soil nutrient status.A series of field experiments were conducted for six years with treatments as:farmer accustomed to fertilization used as control(CON),fertilizer decrement(KF),fertilizer decrement+watersaving irrigation(BMP1);combined application of organic and inorganic fertilizer+water-saving irrigation(BMP2),and combined application of controlled-release fertilizer(BMP3).A significant improvement was observed in soil organic matter(14.9%),nitrate nitrogen(106.7%),total phosphorus(23.9%),available phosphorus(26.2%),straw yield(44.8%),and grain yield(54.7%)with BMP2 treatment as compared to CON.The study concludes that integrating chemical and organic fertilizers with water-saving irrigation(BMP2)is a good approach to increasing corn productivity,ensuring water safety and improving soil health.The limitations of the current study include the identification of fertilizer type and its optimum dose,irrigation water type,and geographical position.

Drivers of the Chemical Quality of Market Gardening Soils in the Urban and Peri-Urban Environment of Bobo-Dioulasso (Burkina Faso): Impact of Fertilizers Sources and Sites Location

Urban and peri-urban agriculture plays a key role by providing many goods and services. In particular, it provides diversified food and employment for vulnerable groups (youth and women). However, it often involves negative externalities due to non-conventional soils fertility management practices. This study aimed to investigate the chemical quality of soils over six (06) sites of the market gardening area of Bobo-Dioulasso (Burkina Faso) as affected by fertilizers uses and sites location. Thirty (30) representative market gardening farms, located in urban, semi-urban and rural areas, were randomly selected from a baseline survey database. Within each farm, composite soil samples made up of 3 individual cores were taken over the 0 - 15 cm soil depth for determining soils carbon, total nitrogen, available phosphorus contents and pH-water. These data were normalized and summarized to compute a synthetic Soil Fertility Index (SFI). The data processing was focused on a Principal Component Analysis and an Ascendant Hierarchical Classification in order to make a typology of the vegetable farms. Fertilizers management effects on soils quality were compared through Variance Analysis (ANOVA) following a GLM procedure in Rstudio software. As main results, soils chemical parameters, except for available K, were affected by the location of the sites. Soils in urban farms are less acidic (on average pH = 6.9), while semi-urban and rural sites (Samadeni, Nakaguana) have more acidic soils. However, the latter site had the highest values of C and N. Moreover, the long-term application of organic matter sources results in improving of the chemical quality of the market garden soil. The SFI is positively correlated with the rate of applied organic fertilizers, and the cultivation duration. On the other hand, soil quality tends to decrease with the expansion of the area, due to a dilution effect of the organic fertilizer doses. All these results suggest that there is a real scope to reinforce the position of the market garden as an opportunity for recycling organic wastes and sequestration of carbon by promoting relevant fertilization packages that strongly rely on organic matters sources (Compost, Biochar, etc.).

Effect of Reducing Chemical Fertilizer on Rice Yield,Output Value,Content of Soil Carbon and Nitrogen after Utilizing the Milk Vetch

A located field experiment was carried out to study the effects of different amount of chemical fertilizer usage on rice yield,economic benefits of rice,soil carbon（C） and total nitrogen（TN） under ploughing back of Chinese milk vetch for 5consecutive years.Six treatments were included in the experiment,they are CK（unfertilized）,CF（100% chemical fertilizer with the amount of N,P2O5,K2 O being150,75,120 kg/hm^2respectively）,A1（22 500 kg/hm^2 Chinese milk vetch and 100%chemical fertilizer）,A2（Chinese milk vetch and 80% nitrogen and potassium fertilizer and 100% phosphate fertilizer）,A3（Chinese milk vetch and 60% nitrogen and potassium fertilizer and 100% phosphate fertilizer）,A4（Chinese milk vetch and 40% nitrogen and potassium fertilizer and 100% phosphate fertilizer）.The results were as follows：application of fertilizer could increase the yield of rice,while Chinese milk vetch combined with fertilizer application had a much more increase effect in rice yield.Under the condition of milk vetch application with 22 500 kg/hm^2,the early rice yield of the treatment A1 was significantly increased by 7.7% compared with that of CF.And the yield of treatment A3 was basically identical to or slight increase in comparison with that of CF.Decreasing amount of fertilizers cloud improve output value of rice in the case of the utilization of Chinese milk vetch.The treatment A1 increased output value of rice by 5.92% in comparison of CF,and treatment A2 was by 4.08% in the next.Treatment A4 showed much better effect in increasing soil organic carbon and total nitrogen in the paddy soil than those of treatments applying mineral fertilizer only.There was a significant reduction on soil organic carbon and TN in treatment A2 in comparison with that of CF.In general,amount of application of milk vetch with 22 500 kg/hm^2 could replace chemical fertilizer partially,it also could improve rice yield,decrease the production cost,and raise the utilization efficiency of nutrients.

Paddy Soil Stability and Mechanical Properties as Affected by Long-Term Application of Chemical Fertilizer and Animal Manure in Subtropical China

Wet stability, penetration resistance （PR）, and tensile strength （TS） of paddy soils under a fertilization experiment for 22 years were determined to elucidate the function of soil organic matter in paddy soil stabilization. The treatments included no fertilization （CK）, normal chemical fertilization （NPK）, double the NPK application rates （2NPK）, and NPK mixed with organic manure （NPK＋OM）. Compared with CK, Fertilization increased soil organic carbon （SOC） and soil porosity. The results of soil aggregate fragmentation degree （SAFD） showed that fast wetting by water was the key fragmentation mechanism. Among the treatments, the NPK＋OM treatment had the largest size of water-stable aggregates and greatest normal mean weight diameter （NMWD） （P ≤ 0.05）, but the lowest PR and TS in both cultivated horizon （Ap） and plow pan. The CK and 2NPK treatments were measured with PR 〉 2.0 MPa and friability index 〈 0.20, respectively, in the Ap horizon, suggesting that the soils was mechanically unfavourable to root growth and tillage. In the plow pan, the fertilization treatments had greater TS and PR than in CK. TS and PR of the tested soil aggregates were negatively correlated to SOC content and soil porosity. This study suggested that chemical fertilization could cause deterioration of mechanical properties while application of organic manure could improve soil stability and mechanical properties.

Effect of Biochar on the Chemical Fertility of Vegetable Soil

[Objective] To investigate the effect of biochar on the chemical fertility of vegetable soil. [Method] By pot experiments, the effect of biochar the soil pH and the content of organic matter, available nitrogen, readily available potassium, avail- able phosphorus, water-soluble phosphorus, exchangeable calcium and magnesium were investigated. The experiment contained five treatments, i.e., CK （no biochar）, T1 （0.10% biochar）, T2 （0.25% biochar）, T3 （0.50% biochar） and T4 （1.00% biochar）. [Result] As the application amount of biochar increases in the treatments, the soil pH, the content of organic matter and readily available potassium ascended significantly, with a trend of T4〉T3 〉T2〉TI〉CK; the contents of available phospho- rus and water-soluble phosphorus first show upward trend then downward trend, with T3 being the highest and CK the lowest; the contents of available nitrogen and exchangeable magnesium did not assume obvious change; compared with control, an appropriate amount of char could significantly increase the content of exchangeable calcium. [Conclusion] Biochar can significantly improve the chemical fertility of vegetable soil, and the application amount in T3 （0.50% biochar） brings the best effects.

Effects of Dairy Cattle Manure and Chemical Fertilizers on Fertility of Soils Grown with Cichorium intybus

[Objective] The aim was to explore recycling utilization of manure of dairy cattle through returning of manures into fields. [Method] Effects of dairy cattle ma- nure and chemical fertilizer on fertility of soils grown with Cichorium intybus were in- vestigated through a pot experiment. [Result] After manure of dairy cattle was ap- plied, it can be concluded that organic matter, total N, total P, alkali-hydrolyzable ni- trogen, available P, activities of urease and invertase in soils increased by 0.14-1.28 times, 43.8%-79.7%, 17.4%-30.8%, 147%-188%, 7 times, 17.2%-38.5%, and 1.36%- 3.34%, respectively. Furthermore, organic matter, total N. urease and invertase activi- ties in group of M7F3 increased most; total P and available P achieved the best in group of M3F7. These indicated that the applied manures of dairy cattle would maintain and improve soil fertility, providing better soils for Cichorium intybus. [Conclusion] The research provides reference for recycling of cattle manures and construction of ecological cyclical pattern of ＂grass planting-cattle breeding-methane fermentation-returning of manures into fields＂.

Impacts of chemical fertilizer reduction and organic amendments supplementation on soil nutrient,enzyme activity and heavy metal content

Excessive use of agro-chemicals （such as mineral fertilizers） poses potential risks to soil quality. Application of organic amendments and reduction of inorganic fertilizer are economically feasible and environmentally sound approaches to de- velop sustainable agriculture. This study investigated and evaluated the effects of mineral fertilizer reduction and partial substitution of organic amendment on soil fertility and heavy metal content in a 10-season continually planted vegetable field during 2009-2012. The experiment included four treatments： 100% chemical fertilizer （CF100）, 80% chemical fertilizer （CF80）, 60% chemical fertilizer and 20% organic fertilizer （CF60＋OM20）, and 40% chemical fertilizer and 40% organic fertilizer （CF40＋OM40）. Soil nutrients, enzyme activity and heavy metal content were determined. The results showed that single chemical fertilizer reduction （CF80） had no significant effect on soil organic matter content, soil catalase activity and soil heavy metal content, but slightly reduced soil available N, P, K, and soil urease activity, and significantly reduced soil acid phosphatase activity. Compared with CF100, 40 or 60% reduction of chemical fertilizer supplemented with organic fertilizer （CF60＋OM20, CF40＋OM40） significantly increased soil organic matter, soil catalase activity and urease activity especially in last several seasons, but reduced soil available P, K, and soil acid phosphatase activity. In addition, continu- ous application of organic fertilizer resulted in higher accumulation of Zn, Cd, and Cr in soil in the late stage of experiment, which may induce adverse effects on soil health and food safety.

Bacterial Community Structure and Diversity in a Black Soil as Affected by Long-Term Fertilization

Black soil （Mollisol） is one of the main soil types in northeastern China. Biolog and polymerase chain reactiondenaturing gradient gel electrophoresis （PCR-DGGE） methods were used to examine the influence of various fertilizer combinations on the structure and function of the bacterial community in a black soil collected from Harbin, Heilongjiang Province. Biolog results showed that substrate richness and catabolic diversity of the soil bacterial community were the greatest in the chemical fertilizer and chemical fertilizer＋manure treatments. The metabolic ability of the bacterial community in the manure treatment was similar to the control. DGGE fingerprinting indicated similarity in the distribution of most 16S rDNA bands among all treatments, suggesting that microorganisms with those bands were stable and not influenced by fertilization. However, chemical fertilizer increased the diversity of soil bacterial community. Principal com- ponent analysis of Biolog and DGGE data revealed that the structure and function of the bacterial community were similar in the control and manure treatments, suggesting that the application of manure increased the soil microbial population, but had no effect on the bacterial community structure. Catabolic function was similar in the chemical fertilizer and chemical fertilizer＋manure treatments, but the composition structure of the soil microbes differed between them. The use of chemical fertilizers could result in a decline in the catabolic activity of fast-growing or eutrophic bacteria.

Effect of Long-Term Application of Chemical Fertilizers on Microbial Biomass and Functional Diversity of a Black Soil

An experiment with seven N, P, K-fertilizer treatments, i.e., control (no fertilizer), NP, NK, PK, NPK, NP2K, and NPK2 where P2 and K2 indicate double amounts of P and K fertilizers respectively, was conducted to examine the effect of long-term continuous application of chemical fertilizers on microbial biomass and functional diversity of a black soil (Udoll in the USDA Soil Taxonomy) in Northeast China. The soil microbial biomass C ranged between 94 and 145 mg kg-1, with the NK treatment showing a lower biomass; the functional diversity of soil microbial community ranged from 4.13 to 4.25, with an increasing tendency from control to double-fertilizer treatments, and to triple-fertilizer treatments. The soil microbial biomass, and the microbial functional diversity and evenness did not show any significant differences among the different fertilizer treatments including control, suggesting that the long-term application of chemical fertilization would not result in significant changes in the microbial characteristics of the black soil.

Effects of Organic Manure Application with Chemical Fertilizers on Nutrient Absorption and Yield of Rice in Hunan of Southern China

To evaluate the effect of organic manure application with chemical fertilizers on rice yield and soil fertility under long-term double-rice cropping system, a six year field experiment was conducted continually in the paddy soil derived from Quaternary red clay in Hunan Province of southern China. Four different treatments, i.e., no nitrogen with chemical P and K （PK）, swine manure only （M）, N, P and K chemical fertilizers only （NPK）, and half chemical fertilizers combined with half swine manure （NPKM） with four replications were included. Each N, P and K application rate was the same at all the treatments （except the N application rate at PK） and N application rate was 150 kg N ha^-1. All fertilizers were applied to soil tillage layer with once application as baseal fertilizers. The nutrients uptake rate, grain yield, nitrogen use efficiency, and soil organic matter content at each treatment were investigated. The NPKM treatment achieved the highest mean annual yield of 12.2 t ha^-1 （68% higher than that of PK）. Higher dry matter accumulation and nutrients absorption were observed during the middle-late growth period in the NPKM treatment, with higher panicle number per unit and filled-grain number per panicle. Its average nitrogen use efficiency was 36.3% and soil organic matter increased by 18.5% during the experimental period in the NPKM treatment, which were significantly higher than those in the NPK treatment. Organic manure application with chemical fertilizers increased the yield and nitrogen use efficiency of rice, reduced the risk of environmental pollution and improved soil fertility greatly. It could be a good practical technique that protects the environment and raises the rice yield in this region.

Effect of Long-Term Fertilization on Organic Nitrogen Forms in a Calcareous Alluvial Soil on the North China Plain

In order to illustrate the change of nitrogen （N） supply capacity after long-term application of manure and chemical fertilizer, as well as to properly manage soil fertility through fertilizer application under the soil-climatic conditions of the North China Plain, organic N forms were quantified in the topsoil with different manure and chemical fertilizer treatments in a 15-year fertilizer experiment in a Chinese calcareous alluvial soil. Soil total N （TN） and various organic N forms were significantly influenced by long-term application of chemical fertilizer and manure. TN, total hydrolysable N, acid-lnsoluble N, amino acid N and ammonium N in the soil increased significantly （P 〈 0.05） with increasing manure and fertilizer N rates, but were not influenced by increasing P rates. Also, application of manure or N fertilizer or P fertilizer did not significantly influence either the quantity of amino sugar N or its proportion of TN. Application of manure significantly increased （P 〈 0.05） hydrolysable unknown N, but adding N or P did not. In addition, application of manure or N fertilizer or P fertilizer did not significantly influence the proportions of different soil organic N forms.

Effect of Long-Term Fertilization on Organic Carbon and Nitrogen in a Subtropical Paddy Soil

A long-term experiment beginning in 1981 in Jinxian County of Jiangxi Province, subtropical China, was conducted in a paddy field under a double rice cropping system with four different fertilization regimes, including 1) no fertilizer as control (CK), 2) balanced chemical N, P, and K fertilizers (NPK), 3) organic manure using milk vetch and pig manure in the early and late rice growing season, respectively (OM), and 4) balanced chemical fertilizers combined with organic manure (NPKM). Samples (0-17 cm) of the paddy field soil, which was derived from Quaternary red clay, were collected after the late rice harvest in November 2003 for determination of total organic carbon (TOC) and total nitrogen (TN) and fractions of organic C and N. Results showed that TOC and TN in the NPKM and OM treatments were significantly higher than those in other two treatments (CK and NPK). Application of organic manure with or without chemical fertilizers significantly increased the contents of all fractions of organic C and N, whereas chemical fertilizer application only increased the contents of occluded particulate organic C (oPOC) and amino acid N. In addition, application of organic manure significantly enhanced the proportions of free particulate organic carbon (fPOC) and oPOC in total C, and those of amino sugar N and amino acid N (P < 0.01) in total N. In contrast, chemical fertilizer application only increased the proportions of oPOC and amino acid N (P < 0.05). There were no significant differences in either contents or proportions of soil organic C and organic N fractions between the NPKM and OM treatments. These indicated that organic manure application with or without chemical fertilizers played the most significant role in enhancing soil organic C and N quantity and quality in the paddy field studied.

Environmental Issues Related to Chemical Fertilizer Use in China

The current status of chemical fertilizers production and consumption in China as well as their important roles in Chinese modern agriculture are discussed with special concerns to the environmental issues related to chemical fertilizer use. On the one hand, the total amount of chemical fertilizer produced is insufficient to meet the agricultural needs. On the other hand, the production and consumption of chemical fertilizers in China are obviously not balanced. In some areas over application of nitrogen fertilizers and loss of phosphate fertilizer due to soil erosion have resulted in some undesirable environmental problems such as increase of nitrate in water and eutrophication of water bodies. Maximum scientific uses of organic manures in combination with reasonable use of chemical fertilizers are part of good practices not only in increasing soil productivity and keeping sustainable agriculture development but also in mimimizing their detrimental effects on the environment.

Partial organic substitution weakens the negative effect of chemical fertilizer on soil micro-food webs

Soil biotic communities play vital roles in enhancing soil nutrient cycling and soil fertility.Long-term excessive nitrogen(N)application is disadvantageous to the stability of soil food webs and affects arable soil health and sustainable utilization.Proper organic substitution is essential to improve soil health and alleviate the disadvantages of excessive chemical fertilization.However,the biological effects of various organic amendments on soil micro-food webs are poorly understood.In order to explore the effects of various organic amendments including stover,biochar and manure on soil micro-food webs(microbial and nematode communities),a field plot experiment with maize having five treatments viz.,100%urea(100%N),70%urea(70%N),70%urea plus stover(Stover),70%urea plus cattle manure(Manure)and 70%urea plus biochar(Biochar)was conducted.Manure treatment increased the carbon(C)to N use efficiency of soil microbes,which contributed to the retention of soil C,while Biochar treatment elevated soil organic C(SOC)and soil p H.Additionally,Biochar treatment mitigated the negative effects of soil acidification on the soil micro-food web and reduced the abundance of plant parasites.Overall,the biological effect of organic amendments was distinguished from chemical fertilization(100%N and 70%N)through principal co-ordinates analysis.Negative relationships among soil properties,microbial and nematode biomass in the 100%N treatment were diminished in treatments where chemical fertilizer was reduced.The bottom-up effects on soil food webs were observed in organic substitution treatments.In conclusion,organic amendments improved soil fertility by regulating soil microbial and nematode communities in the cropland ecosystem,alleviated the negative effects of chemical fertilizer on the micro-food webs and controlled the trophic cascades among soil biota.

Effects of long-term fertilization on soil gross N transformation rates and their implications

Application of fertilizer has been found to significantly affect soil N cycling. However, a comprehensive understanding of the effects of long-term fertilization on soil gross N transformation rates is still lacking. We compiled data of observations from 10 long-term fertilization experiments and conducted a meta-analysis of the effects of long-term fertilization on soil gross N transformation rates. The results showed that if chemical fertilizers of N, P and K were applied in balance, soil p H decreased very slightly. There was a significantly positive effect of long-term fertilization, either chemical or organic fertilizers or their combinations, on gross N mineralization rate compared to the control treatment（the mean effect size ranged from 1.21 to 1.25 at 95% confidence intervals（CI） with a mean of 1.23）, mainly due to the increasing soil total N content. The long-term application of organic fertilizer alone and combining organic and chemical fertilizer could increase the mineralization-immobilization turnover, thus enhance available N for plant while reduce N losses potential compared to the control treatment. However, long-term chemical fertilizer application did not significantly affect the gross NH4＋ immobilization rate, but accelerated gross nitrification rate（1.19; 95% CI： 1.08 to 1.31）. Thus, long-term chemical fertilizer alone would probably induce higher N losses potential through NO3– leaching and runoff than organic fertilizer application compared to the control treatment. Therefore, in the view of the effects of long-term fertilization on gross N transformation rates, it also supports that organic fertilizer alone or combination of organic and chemical fertilizer could not only improve crop yield, but also increase soil fertility and reduce the N losses potential.

Changes in soil organic carbon pools following long-term fertilization under a rain-fed cropping system in the Loess Plateau,China

Understanding the mechanism of soil organic carbon(SOC)sequestration is of paramount importance in sustaining crop productivity and mitigating climate change.Long-term trials were employed to investigate the responses of total SOC and its pools,i.e.,mineral-associated OC(MOC),particulate OC(POC,containing Light-POC and Heavy-POC),to fertilization regimes at Yangling(25-year),Tianshui(35-year)and Pingliang(37-year)under a rain-fed cropping system in the Loess Plateau.The fertilization regimes in each trial included three treatments,i.e.,control(no nutrient input,CK),chemical fertilizers(CF),and organic manure plus chemical fertilizers(MCF).Relative to the CK,long-term fertilization appreciably increased SOC storage by 134,89 and 129 kg ha^(–1)yr^(–1)under CF,and 418,153 and 384 kg ha^(–1)yr^(–1)under MCF in plough layer soils(0–20 cm),respectively,at the Yangling,Tianshui and Pingliang sites.The MOC pools accounted for 72,67 and 64%of the total SOC at the above three sites with sequestration rates of 76,57 and 83 kg ha^(–1)yr^(–1)under CF and 238,118 and 156 kg ha^(–1)yr^(–1)under MCF,respectively.Moreover,the MOC pool displayed a saturation behavior under MCF conditions.The POC accordingly constituted 27,33 and 36%of SOC,of which Light-POC accounted for 11,17 and 22%and Heavy-POC for 17,16 and 15%of SOC,respectively.The sequestration rates of POC were 58,32 and 46 kg ha^(–1)yr^(–1)under CF,and 181,90 and 228 kg ha^(–1)yr^(–1)under MCF at the three respective sites,in which Light-POC explained 59,81 and 72%of POC under CF,and 60,40 and 69%of POC under MCF,with Heavy-POC accounting for the balance.Compared with CK,the application of CF alone did not affect the proportions of MOC or total POC to SOC,whereas MCF application markedly reduced the proportion of MOC and increased the POC ratio,mainly in the Light-POC pool.The distribution of SOC among different pools was closely related to the distribution and stability of aggregates.The present study confirmed that organic manure amendment not only sequestered more SOC but also significantly altered the composition of SOC,thus improving SOC quality,which is possibly related to the SOC saturation level.