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.

Carbon Sequestration in Soil Humic Substances Under Long-Term Fertilization in a Wheat-Maize System from North China

The changes in humic substances （HS） is fundamental in detecting soil carbon sequestration mechanisms in natural and cultivated environments. Based on a long-term trial, the amounts of water dissolved substances （WSS）, humic acid （HA）, fulvic acid （FA） and humin （HU） were determined to explore the impact of long-term fertilization on HS. Increases in the amounts of WSS, HA, FA and HU were significant different among the treatments with manure. A significant correlation was found between the increased soil organic carbon （SOC） and HS （R^2=0.98, P〈0.01）. The change in the E4/E6 ratio was significantly correlated with the increased SOC （R2=0.88, P〈0.01）, HA （R^2=0.91, P〈0.01）, FA （R^2=0.91, P〈0.01） and HU （R^2=0.88, P〈0.01）. The cluster was mainly divided into two parts as manure fertilization and inorganic fertilization, based on the increases in HA, FA and HU. These results suggest that long term fertilization with manure favours carbon sequestration in HS and is mainly stabilized as HU, while the HA becomes more aliphatic. We conclude that increases in SOC can be linked to changes in the molecular characteristics of HS fractions under long term fertilization.

Impact of Long-Term Fertilization on Cropland Soil Fauna Community at Loess Soil, Shannxi, China

The relationship between long-term fertilization and cropland network for soil fertility and fertilizers in Loess soil of Shannxi soil fauna was studied at the station＇s experiment research Provincefrom Jul. 2001 to Oct. 2002. Six types of long-term fertilizer were carried out for this study including non-fertilizer （CK）, abandonment （ABAND）, nitrogenous and phosphors and potassium fertilizers combined （NPK）, straw and NPK （SNPK）, organic material and NPK （MNPK） and 1.5 times MNPK （1.5MNPK）. 72 soil samples were collected and 5 495 species of cropland soil fauna obtained by handsorting and Cobb methods at 4 times, belonging to 6 Phyla, 11 Classes, 22 Orders, 2 Superfamilies, 61 Families and 35 Genera. The result showed that different fertilizer had significantly impacted on the cropland soil fauna （F = 2.24, P〈0.007）. The number of the cropland soil fauna was related to the soil physicochemical properties caused by long-term fertilization. The result by principal component analysis, focusing on the number of 15 key soil fauna species group＇s diversity, evenness of community and the total soil fauna individuals indicated that the effects of SNPK, NPK, MNPK and 1.5MNPK were significantly different from that of the cropland soil fauna, in which, SNPK and NPK had the positive effect on cropland soil fauna, and MNPK and 1.5 MNPK had the negative affect, others could not be explained. By principal component I, the synthetic effect of different fertilization on the total soil fauna individuals and the group was most significant, and the effect was little on evenness and diversity. By value of eigenvectors, the maximum one was 9.6248, and the minimum one was - 1.0904, that means the 6 types of fertilization did not affect evenly the cropland soil fauna.

Basic Soil Productivity of Spring Maize in Black Soil Under Long-Term Fertilization Based on DSSAT Model

Increasing basic farmland soil productivity has significance in reducing fertilizer application and maintaining high yield of crops. In this study, we defined that the basic soil productivity （BSP） is the production capacity of a farmland soil with its own physical and chemical properties for a specific crop season under local environment and field management. Based on 22-yr （1990-2011） long-term experimental data on black soil （Typic hapludoll） in Gongzhuling, Jilin Province, Northeast China, the decision support system for an agro-technology transfer （DSSAT）-CERES-Maize model was applied to simulate the yield by BSP of spring maize （Zea mays L.） to examine the effects of long-term fertilization on changes of BSP and explore the mechanisms of BSP increasing. Five treatments were examined： （1） no-fertilization control （control）; （2） chemical nitrogen, phosphorus, and potassium （NPK）; （3） NPK plus farmyard manure （NPKM）; （4） 1.5 time of NPKM （1.5NPKM） and （5） NPK plus straw （NPKS）. Results showed that after 22-yr fertilization, the yield by BSP of spring maize significantly increased 78.0, 101.2, and 69.4% under the NPKM, 1.5NPKM and NPKS, respectively, compared to the initial value （in 1992）, but not significant under NPK （26.9% increase） and the control （8.9% decrease）. The contribution percentage of BSP showed a significant rising trend （P〈0.05） under 1.5NPKM. The average contribution percentage of BSP among fertilizations ranged from 74.4 to 84.7%, and ranked as 1.5NPKM〉NPKM〉NPK〉NPKS, indicating that organic manure combined with chemical fertilizers （I.5NPKM and NPKM） could more effectively increase BSP compared with the inorganic fertilizer application alone （NPK） in the black soil. This study showed that soil organic matter （SOM） was the key factor among various fertility factors that could affect BSP in the black soil, and total N, total P and/or available P also played important role in BSP increasing. Compared with the chemical fertilization, a balanced chemical plus manure or straw fertilization （NPKM or NPKS） not only increased the concentrations of soil nutrient, but also improved the soil physical properties, and structure and diversity of soil microbial population, resulting in an iincrease of BSP. We recommend that a balanced chemical plus manure or straw fertilization （NPKM or NPKS） should be the fertilization practices to enhance spring maize yield and improve BSP in the black soil of Northeast China.

Effect of Long-Term Fertilization on Soil Enzyme Activities Under Different Hydrothermal Conditions in Northeast China

Human activities have altered weather patterns by causing an increase in greenhouse gas. The effects of climate change have been studied, including effects on some ecosystems throughout the world. There are many studies on changes in the soil due to climate change, but much of them did not extend their research to soil enzyme that integrates information on soil microbial status and soil physical-chemical conditions. Meanwhile, there are lots of experimental fields established to study effects of long-term fertilization on soil enzyme activities, but many did not compare the difference of soil enzyme activities and did not analyze the effect of climatic factors on soil enzyme activities with long-term fertilization under different hydrothermal conditions. In this study, we compared soil enzyme activities of three long-fertilization stations which had different hydrothermal conditions in Northeast China, and analyzed the relationship of hydrothermal condition, soil chemical properties with soil enzyme activities. Hydrothermal conditions （annual temperature and total rainfall） decreased in order of Gongzhuling （Jilin Province, China ） Harbin （Heilongjiang Province, China） Heihe （Heilongjiang Province, China） over the course of the long-term fertilization experiment. Sunshine hours showed the longest in Gongzhuling, the second in Heihe, and the last in Harbin. However, the order of soil enzymes was not in agreement with hydrothermal conditions. Overall, the order of soil enzymes for the same treatment among three stations was consistent in 2008 with in 2009. Correlation analysis demonstrated that different soil enzymes achieved the different affected levels by climatic factors under different fertilization treatments. Urease activity showed a significant relationship with sunshine hours in no fertilizer （CK） treatment （R=-0.91, P0.01） and relative humidity in mineral fertilizers plus manure （MNPK） treatment （R=0.82, P0.05）. Phosphatase activity exhibited a negative correlation with annual mean temperature, annual mean maximum temperature and annual mean minimum temperature, and their correlation coefficients were separately -0.83, -0.79, and -0.83 at P0.05 in CK treatment. Invertase activity was highly and positively correlated with sunshine hours in CK treatment （R=0.94, P0.01）. Catalase activity showed significant negative correlations with minimum relative humidity in CK treatment （R=-0.81, P0.05）, and positive correlations with sunshine hours in M treatment （R=0.83, P0.05）. There were no climatic factors which strongly affected on dehydrogenase in all treatments. Soil enzyme activities were closely related to the soil chemical properties. Soil urease activity was positively correlated with available P （P0.05）. With exception of correlation between invertase and total P at P0.05, phosphase, invertase, catalase, and dehydrogenase showed significant positive correlations with soil chemical properties （P0.01）. It was a comprehensive process that biologic and abiotic factors were effect on soil enzyme activities under different fertilization treatments. To sum up, the variation of hydrothermal conditions in different climate zones and soil chemical properties affect integrally metabolic activity and metabolic finger print of microbial communities in black soil.

Effects of long-term organic fertilization on soil microbiologic characteristics,yield and sustainable production of winter wheat

We investigated the soil microbiologic characteristics, and the yield and sustainable production of winter wheat, by conducting a long-term fertilization experiment. A single application of N, P and K （NPK） fertilizer was taken as the control （CK） and three organic fertilization treatments were used： NPK fertilizer＋pig manure （T1）, NPK fertilizer＋straw return （T2）, NPK fertilizer＋pig manure＋straw return （T3）. The results showed that all three organic fertilization treatments （T1, T2 and T3） significantly increased both soil total N （STN） and soil organic carbon （SOC） from 2008 onwards. In 2016, the SOC content and soil C/N ratios for T1, T2 and T3 were significantly higher than those for CK. The three organic fertilization treatments increased soil microbial activity. In 2016, the activity of urease （sucrase） and the soil respiration rate （SRS） for T1, T2 and T3 were significantly higher than those under CK. The organic fertilization treatments also increased the content of soil microbial biomass carbon （SMBC） and microbial biomass nitrogen （SMBN）, the SMBC/SMBN ratio and the microbial quotient （qMB）. The yield for T1, T2 and T3 was significantly higher than that of CK, respectively. Over the nine years of the investigation, the average yield increased by 9.9, 13.2 and 17.4% for T1, T2 and T3, respectively, compared to the initial yield for each treatment, whereas the average yield of CK over the same period was reduced by 6.5%. T1, T2, and T3 lowered the coefficient of variation （CV） of wheat yield and increased the sustainable yield index （SYI）. Wheat grain yield was significantly positively correlated with each of the soil microbial properties （P〈0.01）. These results showed that the long-term application of combined organic and chemical fertilizers can stabilize crop yield and make it more sustainable by improving the properties of the soil.

Soil pH Dynamics and Nitrogen Transformations Under Long-Term Chemical Fertilization in Four Typical Chinese Croplands

Long-term fertilization experiment provides the platform for understanding the proton budgets in nitrogen transformations of agricultural ecosystems. We analyzed the historical （1990-2005） observations on four agricultural long-term experiments in China （Changping, Chongqing, Gongzhuling and Qiyang） under four different fertilizations, i.e., no-fertilizer （control）, sole chemical nitrogen fertilizer （FN）, sole chemical phosphorous and potassium fertilizers （FPK） and chemical nitrogen, phosphorous and potassium fertilizers （FNPK）. The significant decline in topsoil pH was caused not only by chemical N fertilization （0.29 and 0.89？pH at Gongzhuling and Qiyang, respectively） but also by chemical PK fertilization （0.59？pH at Gongzhuling）. The enhancement of available nutrients in the topsoil due to long-term direct nutrients supply with chemical fertilizers was in the descending order of available P （168-599%）〉available K （16-189%）〉available N （9-33%）. The relative rate of soil pH decline was lower under long-term judicious chemical fertilization （-0.036-0.034 ？pH yr-1） than that under long-term sole N or PK fertilization （0.016-0.086 ？pH yr-1）. Long-term judicious chemical fertilization with N, P and K elements decreases the nutritional limitation to normal crop growth, under which more N output was distributed in biomass removal rather than the loss via nitrate leaching. We concluded that the N distribution percentage of nitrate leaching to biomass removal might be a suitable indicator to the sensitivity of agricultural ecosystems to acid inputs.

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.

Impact of Long-Term Fertilization on Community Structure of Ammonia Oxidizing and Denitrifying Bacteria Based on amoA and nirK Genes in a Rice Paddy from Tai Lake Region,China

Ammonia oxidizing （AOB） and denitrifying bacteria （DNB） play an important role in soil nitrogen transformation in natural and agricultural ecosystems. Effects of long-term fertilization on abundance and community composition of AOB and DNB were studied with targeting ammonia monooxygenase （amoA） and nitrite reductase （nirK） genes using polymerase chain reaction- denaturing gradient gel electrophoresis （PCR-DGGE） and real-time PCR, respectively. A field trial with different fertilization treatments in a rice paddy from Tai Lake region, centre East China was used in this study, including no fertilizer application （NF）, balanced chemical fertilizers （CF）, combined organic/inorganic fertilizer of balanced chemical fertilizers plus pig manure （CFM）, and plus rice straw return （CFS）. The abundances and riehnesses of amoA and nirK were increased in CF, CFM and CFS compared to NF. Principle component analysis of DGGE profiles showed significant difference in nirK and amoA genes composition between organic amended （CFS and CFM） and the non-organic amended （CF and NF） plots. Number of amoA copies was significantly positively correlated with normalized soil nutrient richness （NSNR） of soil organic carbon （SOC） and total nitrogen （T-N）, and that of nirK copies was with NSNR of SOC, T-N plus total phosphorus. Moreover, nitrification potential showed a positive correlation with SOC content, while a significantly lower denitrification potential was found under CFM compared to under CFS. Therefore, SOC accumulation accompanied with soil nutrient richness under long-term balanced and organic/inorganic combined fertilization promoted abundance and diversity of AOB and DNB in the rice paddy.

Long-term inorganic plus organic fertilization increases yield and yield stability of winter wheat

An understanding of wheat yield and yield stability response to fertilization is important for sustainable wheat production. A 36-year long-term fertilization experiment was employed to evaluate the yield and yield stability of winter wheat. Five fertilization regimes were compared,including(1) CK, no fertilizer;(2) NPK, inorganic fertilizer only;(3) O, organic fertilizer only;(4)NPKO, 50% of NPK plus 50% of O, and(5) HNPKO, 80% of NPK plus 80% of O. The greatest yield increase was recorded in HNPKO, followed by NPKO, with O producing the lowest mean yield increase. Over the 36 years, the rate of wheat yield increase in fertilized plots ranged from95.31 kg ha-1 year-1 in the HNPKO to 138.65 kg ha-1 year-1 in the O. Yield stability analysis using the additive main effects and multiplicative interactions(AMMI) method assigned 62.3%, 26.3%,and 11.4% of sums of squares to fertilization effect, environmental effect, and fertilization ×environment interaction effect, respectively. The combination of inorganic and organic fertilization(NPKO and HNPKO) appeared to produce more stable yields than O or NPK, with lower coefficients of variation and AMMI stability value. However, wheat grown with O seemed to be the most susceptible to climate change and the least productive among the fertilized plots.Significant correlations of grain yield with soil properties and with mean air temperature were observed. These findings suggest that inorganic + organic fertilizer can increase wheat yield and its stability by improvement in soil fertility and reduction in variability to climate change.

Effects of long-term fertilization on oxidizable organic carbon fractions on the Loess Plateau,China

The effects of long-term fertilization on pools of soil organic carbon （SOC） have been well studied, but limited information is available on the oxidizable organic carbon （OOC） fractions, especially for the Loess Plateau in China. We evaluated the effects of a 15-year fertilization on the OOC fractions （F1, F2, F3 and F4） in the 0-20 and 20-40 cm soil layers in flat farmland under nine treatments （N （nitrogen, urea）, P （phosphorus, monocalcium phosphate）, M （organic fertilizer, composted sheep manure）, N＋P （NP）, M＋N （MN）, M＋P （MP）, M＋N＋P （MNP）, CK （control, no fertilizer） and bare land （BL, no crops or fertilizer））. SOC content increased more markedly in the treatment containing manure than in those with inorganic fertilizers alone. F1, F2, F4 and F3 accounted for 47%, 27%, 18% and 8% of total organic carbon, respectively. F1 was a more sensitive index than the other C fractions in the sensitivity index （SI） analysis. F1 and F2 were highly correlated with total nitrogen （TN） and available nitrogen （AN）, F3 was negatively correlated with pH and F4 was correlated with TN. A cluster analysis showed that the treatments containing manure formed one group, and the other treatments formed another group, which indicated the different effects of fertilization on soil properties. Long-term fertilization with inorganic fertilizer increased the F4 fraction while manure fertilizer not only increased labile fractions （F1） in a short time, but also increased passive fraction （F4） over a longer term. The mixed fertilizer mainly affected F3 fraction. The study demonstrated that manure fertilizer was recommended to use in the farmland on the Loess Plateau for the long-term sustainability of agriculture.

Response of soil Olsen-P to P budget under different long-term fertilization treatments in a fluvo-aquic soil

The concentration of soil Olsen-P is rapidly increasing in many parts of China, where P budget(P input minus P output) is the main factor influencing soil Olsen-P. Understanding the relationship between soil Olsen-P and P budget is useful in estimating soil Olsen-P content and conducting P management strategies. To address this, a long-term experiment(1991–2011) was performed on a fluvo-aquic soil in Beijing, China, where seven fertilization treatments were used to study the response of soil Olsen-P to P budget. The results showed that the relationship between the decrease in soil Olsen-P and P deficit could be simulated by a simple linear model. In treatments without P fertilization(CK, N, and NK), soil Olsen-P decreased by 2.4, 1.9, and 1.4 mg kg^(–1) for every 100 kg ha^(–1) of P deficit, respectively. Under conditions of P addition, the relationship between the increase in soil Olsen-P and P surplus could be divided into two stages. When P surplus was lower than the range of 729–884 kg ha^(–1), soil Olsen-P fluctuated over the course of the experimental period with chemical fertilizers(NP and NPK), and increased by 5.0 and 2.0 mg kg^(–1), respectively, when treated with chemical fertilizers combined with manure(NPKM and 1.5 NPKM) for every 100 kg ha^(–1) of P surplus. When P surplus was higher than the range of 729–884 kg ha^(–1), soil Olsen-P increased by 49.0 and 37.0 mg kg^(–1) in NPKM and 1.5 NPKM treatments, respectively, for every 100 kg ha^(–1) P surplus. The relationship between the increase in soil Olsen-P and P surplus could be simulated by two-segment linear models. The cumulative P budget at the turning point was defined as the "storage threshold" of a fluvo-aquic soil in Beijing, and the storage thresholds under NPKM and 1.5 NPKM were 729 and 884 kg ha^(–1)P for more adsorption sites. According to the critical soil P values(CPVs) and the relationship between soil Olsen-P and P budget, the quantity of P fertilizers for winter wheat could be increased and that of summer maize could be decreased based on the results of treatments in chemical fertilization. Additionally, when chemical fertilizers are combined with manures(NPKM and 1.5 NPKM), it could take approximately 9–11 years for soil Olsen-P to decrease to the critical soil P values of crops grown in the absence of P fertilizer.

Effect of Long-Term Fertilization on Soil Productivity and Nitrate Accumulation in Gansu Oasis

A long-term （1982-2001） field experiment was conducted in a calcareous soil under wheat （Triticum aestivum L.）-wheat （Triticum aestivum L.）-maize （Zea mays L.） rotation system at Zhangye, Gansu Province, China to determine the effects of long-term fertilization on crop yield, nutrients interactions, content and accumulation of nitrate-N in soil profiles. Twenty- four plots in a split-plot factorial with a combination of eight treatments （from nitrogen （N）, phosphorus （P）, potassium （K） and farmyard manure （M） applications） and 3 replications were selected. Main treatments were M and without M, and the sub-treatments were no-fertilizer （CK）, N, NP and NPK. When P and K fertilizers were part of treatments, their ratio to N was 1N：0.22P：0.42K. All M, P and K fertilizers were applied as the basal dressing. The grain yield was harvested each experimental period and straw yield for the period from 1988 to 1997. After crop harvest in 2000, the soil was sampled from the 0-20, 20-60, 60-100, 100-140 and 140-180 cm depths to determine NO3^--N content. Maize yield of CK in 2000 was only 28.2% of that in 1984, and wheat in 2001 was 25.7% of that observed in 1982. Average impact of fertilizers on grain yield decreased in the order of N 〉 M 〉 P 〉 K. Yield response to N and P fertilizers increased with progress of the experiment. The impact of K fertilizer showed no increase in grain yield during the initial 6 years （1982-1987）, moderate increase in the next 5 years （1988-1992）, and considerable increase in the last 9 years （1993-2001）. The straw yield trend was similar to grain yield. Accumulation and distribution of NO3^--N in soil was significantly affected by annual fertilizations. Mineral fertilizers （NP and NPK） led to NO3^- -N accumulation in most subsoil layers, with major impact in the 20-140 cm depth. The combination of mineral fertilizers and farmyard manure （MNP and MNPK） reduced soil NO3^--N accumulation in comparison to mineral fertilizers, It can be argued that long-term fertilization significantly enhanced grain and straw yield in this rotation scheme. The findings of this research suggest that it is important to balance application of mineral fertilizers and farmyard manure in order to protect soil and underground water from potential NO3^--N pollution while sustaining high productivity in the oasis agro-ecosystem.

Changes in Organic Carbon Index of Grey Desert Soil in Northwest China After Long-Term Fertilization

Soil organic carbon （SOC）, soil microbial biomass carbon （SMBC） and SMBC quotient （SMBC/SOC, qSMBC） are key indexes of soil biological fertility because of the relationship to soil nutrition supply capacity. Yet it remains unknown how these three indexes change, which limits our understanding about how soil respond to different fertilization practices. Based on a 22-yr （1990-2011） long-term fertilization experiment in northwest China, we investigated the dynamics of SMBC and qSMBC during the growing period of winter wheat, the relationships between the SMBC, qSMBC, soil organic carbon （SOC） concentrations, the carbon input and grain yield of wheat as well. Fertilization treatments were 1） nonfertilization （control）; 2） chemical nitrogen plus phosphate plus potassium （NPK）; 3） NPK plus animal manure （NPKM）; 4） double NPKM （hNPKM） and 5） NPK plus straw （NPKS）. Results showed that the SMBC and qSMBC were significantly different among returning, jointing, flowering and harvest stages of wheat under long-term fertilization. And the largest values were observed in the flowering stage. Values for SMBC and qSMBC ranged from 37.5 to 106.0 mg kg1 and 0.41 to 0.61%, respectively. The mean value rank of SMBC during the whole growing period of wheat was hNPKM〉NPK_M〉NPKS〉CK〉NPK. But there were no statistically significant differences between hNPKM and NPKM, or between CK and NPK. The order for qSMBC was NPKS〉NPKM〉CK〉hNPKM〉NPK. These results indicated that NPKS significantly increased the ratio of SMBC to SOC, i.e., qSMBC, compared with NPK fertilizer or other two NPKM fertilizations. Significant linear relationships were observed between the annual carbon input and SOC （P〈0.01） or SMBC （P〈0.05）, and between the relative grain yield of wheat and the SOC content as well （P〈0.05）. But the qSMBC was not correlated with the annual carbon input. It is thus obvious that the combination of manure, straw with mineral fertilizer may be benefit to increase SOC and improve soil quality than using only mineral fertilizer.

Effects of Long-term Fertilization on Soil M icrobial Com m unity Structure,Labile Organic Carbon and Nitrogen and Enzym e Activity in Paddy Field and Upland

To investigate the effects of long-term fertilization systems on soil microbial community structure,labile organic carbon and nitrogen and enzyme activity in yellow sand paddy field and upland,a field experiment was conducted at the experimental station of Dongyang Institute of Maize Research in Zhejiang Province,China in 2009.The experiment consisted of six treatments with three replicates,and they were arranged in a completely randomized design,including no fertilization in paddy field (PCK),conventional fertilization in paddy field (PCF),formulated fertilization by soil testing in paddy field (PSTF),formulated fertilization by soil testing with organic manure in paddy field (PSTF+OF),conventional fertilization on upland (DCF),and formulated fertilization by soil testing with organic manure on upland (DSTF+OF).Soil nutrients,enzyme activity,microbial biomass and community structure were determined in 2015.The results showed that compared with no fertilization in paddy field (PCK),fertilization increased soil phosphorus and potassium content,and decreased pH value.No fertilization in paddy field (PCK) had no significant effect on soil culturable microorganisms in paddy field and upland,but formulated fertilization by soil testing with organic manure on upland (DSTF+OF) significantly increased the number of fungi.Formula fertilization by soil testing with organic manure (PSTF+OF) also significantly increased soil microbial biomass carbon and nitrogen in paddy field and upland.Moreover,fertilization had no significant effect on soil cellulase activity,but formula fertilization by soil testing with organic manure (PSTF+OF) significantly increased soil dehydrogenase and catalase activity.Therefore,long-term application of chemical fertilizer with organic fertilizer can effectively improve soil fertility.

Effects of Long-term Fertilization on Phosphorus Accumulation and Migration in Purple Soil

Based on a long-term location test lasting for 20 years, the accumulation and migration of phosphorus in purple soil was studied. The results showed that P2Os input in paddy-upland rotation was 120.0 kg/（ hm2 · a） （a conventional level of phosphorus application）, and P had a surplus of 53.9 kg/（hm2 · a）. Phosphorus accumulating in soil increased available phosphorus （Olsen-P） content, and the positive correlation between P changing balance and Olsen-P change in wheat-rice rotation was extremely significant. The mixed application of organic fertilizer and chemical P fertilizer can speed up accumulation of available phosphorus in soil. Olsen-P content in all treatments with P fertilizer was higher in 0 -60 cm soil than that of treatments without P fertilizer, and Phosphorus applied in surface soil moved to soil at a depth of 60 cm, increasing risk of P leakage and loss. The migration of phosphorus in soil is affected by P input, type of organic fertilizer and planting method. The quantities of phosphorus moving down increased with the increase of P input, and the application of pig manure can lead to migration of phosphorus in soil more easily compared with straw. The migration of phosphorus from soil to water mainly occurred in the first ten days after rice was transplanted, and paddy field drainage should not be conducted in the first 30 days after rice was transplanted.

The Changes in Guilin Paddy Soil Organic Matter and Rice Yield under Long-Term Fertilization

Rational fertilization is an important measure to increase crop yield and soil fertility. Through analysis,this paper aims to master the change characteristics of soil organic matter and rice yield under different fertilizer treatments,in order to provide an important reference for the sustainable use of soil and effective fertilization. Long-term( 19 years) rice crop rotation experiments in waterloggogenic paddy soil were conducted to investigate the change trend of crop grain yield and soil organic matter with time,reveal the dynamic characteristics and relationship between main fertility factors and crop yields using comparative analysis at three sites with conventional fertilization and non-fertilization in Guilin. The results showed that compared with previous years,the rice yield increased by 53% under the fertilization treatment and degreased by 66% under the control. Over the years,the average soil organic matter( SOM) content under fertilization treatment was 23% higher than under CK treatment. This indicates that chemical fertilizer and organic manure application can increase the rice yield and soil organic matter,and high rice yield can be attributed to the SOM increase.

Effects of Long-Term Fertilization on Distribution of Organic Matters and Nitrogen in Cinnamon Soil Macro-Aggregates

Soil samples collected from a 25-year long-term fertilizer experiment carried out on the Earth-cumulic-Orthic Anthrosols in semi-humid farmland ecological system, were used to study the distribution of soil organic matters, total nitrogen, nitrate nitrogen, and ammoniate nitrogen in different grades of soil macro-aggregates in order to study the effects of long-term application of organic manures in combination with chemical fertilizers. It is showed that the percentage of mass of the soil macro-aggregates with long-term application of fertilizers with sizes of 5-2 mm is increased compared with that of the samples with no fertilizer. It is easier to form lager size soil macro-aggregates by the long-term application of organic manures in combination with chemical fertilizers. The contents of organic matters, total nitrogen and nitrate nitrogen are all higher after treatments with different combinations of fertilizers, while there is a little effect on the contents of ammoniate nitrogen. The contents of organic matters, total nitrogen in the grades of soil macro-aggregates from the plough layers of the treated farmland exhibited significant difference. Moreover, the contents of organic matters and total nitrogen in the soil macro-aggregates with the size of 1-0.25 mm is the highest in all treated soil samples. The contents of nitrate nitrogen in soil macro-aggregates increased with the increasing of soil macro-aggregate size except those applied with chemical fertilizer and lower amount of corn stover. The results of correlation analysis revealed that there exists a significantly positive correlation between the percentage of mass of soil macro-aggregates with the size of 5-2 mm and the contents of organic matters, total nitrogen and nitrate nitrogen in the soil samples. However, the correlation between the percentage of mass of soil macro-aggregates with the size of 1-0.25 rnm and the contents of total nitrogen and nitrate nitrogen is significantly negative.The study showed that the highest contributing rates of macro-aggregates fractions to soil fertility is from the soil macro-aggregates fraction with the size of 1-0.25 mm in most of the cases.

Crop yields and soil organic carbon dynamics in a long-term fertilization experiment in an extremely arid region of northern Xinjiang, China

A long-term fertilization experiment was set up in northern Xinjiang, China to evaluate the dynamics of crop production and soil organic carbon （SOC） from 1990 to 2012 with seven fertilization treatments. The seven treatments included an unfertilized control （CK） and six different combinations of phosphorus （P）, potassium （K）, nitrogen （N）, straw （S） and animal manure （M）. The balanced fertilization treatments had significantly （P〈0.05） higher average yields than the unbalanced ones. The treatment with 2/3 N from potassium sulfate （NPK） and 1/3 N from farmyard manure （NPKM） had a higher average yield than the other treatments. The average yields （over the 23 years） in the treatments of NPK, and urea, calcium superphosphate （NP） did not differ significantly （P〉0.05） but were higher than that in the treatment with urea and potassium sulfate （NK; P〈0.05）. The results also show that the highest increases in SOC （P〈0.05） occurred in NPKM with a potential increase of 1.2 t C/（hm2.a）. The increase in SOC was only 0.31, 0.30 and 0.12 t C/（hm2.a） for NPKS （9/10 N from NPK and 1/10 N from straw）, NPK and NP, respectively; and the SOC in the NP, NK and CK treatments were approaching equilibrium and so did not rise or fall significantly over the 23-year experiment. A complete NPK plus manure fertilization program is recommended for this extremely arid region to maximize both yields and carbon sequestration.

Long-term organic and inorganic fertilizations enhanced basic soil productivity in a fluvo-aquic soil

The improvement of soil productivity depends on a rational input of water and nutrients, optimal field management, and the increase of basic soil productivity（BSP）. In this study, BSP is defined as the productive capacity of a farmland soil with its own physical and chemical properties for a specific crop season under local field management. Based on 19-yr data of the long-term agronomic experiments（1989–2008） on a fluvo-aquic soil in Zhengzhou, Henan Province, China, the decision support system for agrotechnology transfer（DSSAT ver. 4.0） crop growth model was used to simulate yields by BSP of winter wheat（Triticum aestivium L.） and summer maize（Zea mays L.） to examine the relationship between BSP and soil organic carbon（SOC） under long-term fertilization. Five treatments were included：（1） no fertilization（control）,（2） nitrogen, phosphorus and potassium fertilizers（NPK）,（3） NPK plus manure（NPKM）,（4） 1.5 times of NPKM（1.5NPKM）, and（5） NPK plus straw（NPKS）. After 19 yr of treatments, the SOC stock increased 16.7, 44.2, 69.9, and 25.2% under the NPK, NPKM, 1.5NPKM, and NPKS, respectively, compared to the initial value. Among various nutrient factors affecting contribution percentage of BSP to winter wheat and summer maize, SOC was a major affecting factor for BSP in the fluvo-aquic soil. There were significant positive correlations between SOC stock and yields by BSP of winter wheat and summer maize（P〈0.01）, and yields by BSP of winter wheat and summer maize increased 154 and 132 kg ha^（–1） when SOC stock increased 1 t C ha^（–1）. Thus, increased SOC accumulation is a crucial way for increasing BSP in fluvo-aquic soil. The manure or straw combined application with chemical fertilizers significantly enhanced BSP compared to the application of chemical fertilizers alone.