Coupling of reduced inorganic fertilizer with plant-based organic fertilizer as a promising fertilizer management strategy for colored rice in tropical regions

Colored rice is a type of high-quality,high-added-value rice that has attracted increasing attention in recent years.The use of large amounts of inorganic nitrogen fertilizer in rice fields results in low fertilizer use efficiency and high environmental pollution.Organic fertilizer is a promising way to improve soil quality and sustain high yields.However,most studies focus on the effect of animal-based organic fertilizers.The effects of different ratios of plantbased organic fertilizer and inorganic fertilizer on the grain yield and quality of colored rice have rarely been reported.Therefore,a two-year field experiment was conducted in 2020 and 2021 to study the effects of replacing inorganic N fertilizers with plant-based organic fertilizers on the yield,nitrogen use efficiency(NUE),and anthocyanin content of two colored rice varieties in a tropical region in China.The experimental treatments included no nitrogen fertilization(T1),100% inorganic nitrogen fertilizer(T2),30%inorganic nitrogen fertilizer substitution with plant-based organic fertilizer(T3),60%inorganic nitrogen fertilizer substitution with plant-based organic fertilizer(T4),and 100% plantbased organic fertilizer(T5).The total nitrogen provided to all the treatments except T1 was the same at 120 kg ha-1.Our results showed that the T3 treatment enhanced the grain yield and anthocyanin content of colored rice by increasing nitrogen use efficiency compared with T2.On average,grain yields were increased by 9 and 8%,while the anthocyanin content increased by 16 and 10% in the two colored rice varieties under T3 across the two years,respectively,as compared with T2.Further study of the residual effect of partial substitution of inorganic fertilizers showed that the substitution of inorganic fertilizer with plant-based organic fertilizer improved the soil physiochemical properties,and thus increased the rice grain yield,in the subsequent seasons.The highest grain yield of the subsequent rice crop was observed under the T5 treatment.Our results suggested that the application of plantbased organic fertilizers can sustain the production of colored rice with high anthocyanin content in tropical regions,which is beneficial in reconciling the relationship between rice production and environmental protection.

Mitigation of N_(2)O emissions in water-saving paddy fields:Evaluating organic fertilizer substitution and microbial mechanisms

Water-saving irrigation strategies can successfully alleviate methane emissions from rice fields,but significantly stimulate nitrous oxide(N_(2)O)emissions because of variations in soil oxygen level and redox potential.However,the relationship linking soil N_(2)O emissions to nitrogen functional genes during various fertilization treatments in water-saving paddy fields has rarely been investigated.Furthermore,the mitigation potential of organic fertilizer substitution on N_(2)O emissions and the microbial mechanism in rice fields must be further elucidated.Our study examined how soil N_(2)O emissions were affected by related functional microorganisms(ammonia-oxidizing archaea(AOA),ammonia-oxidizing bacteria(AOB),nirS,nirK and nosZ)to various fertilization treatments in a rice field in southeast China over two years.In this study,three fertilization regimes were applied to rice cultivation:a no nitrogen(N)(Control),an inorganic N(Ni),and an inorganic N with partial N substitution with organic manure(N_(i)+N_(o)).Over two rice-growing seasons,cumulative N_(2)O emissions averaged 0.47,4.62 and 4.08 kg ha^(−1)for the Control,Ni and N_(i)+N_(o)treatments,respectively.In comparison to the Ni treatment,the N_(i)+N_(o)fertilization regime considerably reduced soil N_(2)O emissions by 11.6%while maintaining rice yield,with a lower N_(2)O emission factor(EF)from fertilizer N of 0.95%.Nitrogen fertilization considerably raised the AOB,nirS,nirK and nosZ gene abundances,in comparison to the Control treatment.Moreover,the substitution of organic manure for inorganic N fertilizer significantly decreased AOB and nirS gene abundances and increased nosZ gene abundance.The AOB responded to N fertilization more sensitively than the AOA.Total N_(2)O emissions significantly correlated positively with AOB and nirS gene abundances while having a negative correlation with nosZ gene abundance and the nosZ/nirS ratio across N-fertilized plots.In summary,we conclude that organic manure substitution for inorganic N fertilizer decreased soil N_(2)O emissions primarily by changing the soil NO_(3)^(−)-N,pH and DOC levels,thus inhibiting the activities of ammonia oxidation in nitrification and nitrite reduction in denitrification,and strengthening N_(2)O reduction in denitrification from water-saving rice paddies.

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.

Comparative Analysis of Organic and Compound Fertilizers on the Yield and Metabolites of Platostoma palustre

To explore the effect of fertilizers on the yield and quality of Platostoma palustre,in this study,P.palustre was utilized as the research material,and field experiments were conducted with different application rates of compound fertilizer and organic fertilizer and non-targeted metabolomics analysis was further employed to compare and analyze the differences in the metabolic components between the compound fertilizer and organic fertilizer treatments.The results of field experiments demonstrated that both compound and organic fertilizers could promote the fresh weight,shade dry weight,and dry weight of P.palustre,with 450 kg hm−2 compound fertilizer and 4500 kg hm−2 organic fertilizer presenting the optimum effects.Non-targeted metabolomics revealed that 1096 metabolites were identified in 450 kg hm−2 compound fertilizer and 4500 kg hm−2 organic fertilizer,and 885 metabolites were annotated in the Human Metabolome Database(HMDB).There were 318 differential metabolites(DMs)found between the two treatments,and 263 metabolites were annotated in HMDB.The abundance of 2 phenolic compounds and 12 organic oxygen compounds in the treatment of 4500 kg hm−2 organic fertilizer was significantly higher than that of the 450 kg hm−2 compound fertilizer,while the abundance of 21 organic oxygen compounds,14 flavonoids,3 phenolic compounds,and 5 cinnamic acids and their derivatives was significantly up-regulated in 450 kg hm−2 compound fertilizer treatment.In addition,5 metabolic pathways were significantly enriched,and the flavone and flavonol biosynthesis was the most significantly differential metabolic pathway.These results suggested that the application of both compound fertilizers and organic fertilizers can increase the yield of P.palustre,but their effects on metabolites were different.This study has considerable implications for the planting and cultivation of P.palustre,furnishing a scientific foundation for an efficient and rational application of fertilizer.

Application of organic fertilizer for improving soybean production under acidic stress

The presence of acidic soil in rural areas poses difficulties for agricultural production.One factor regulating soil pH is the overuse of inorganic fertilizer.The increased use of fertilizers in soybean production not only raises sustainability concerns but also contributes to soil acidity.Therefore,the use of organic fertilizer could offer a solution for addressing both issues related to soil acidity and sustainability.The purpose of this study was to investigate the manipulation of soil pH using organic fertilizer for soybean production under acidic stress.The planting medium,consisting of a mixture of topsoil,rice husk charcoal,and organic fertilizer(in a ratio of 2:1:1),was supplemented with 0.5 g of NPK fertilizer as a basal treatment in each planting medium.To regulate the soil acidity to pH 4,we added FeSO_(4) and allowed the mixture to incubate for 30 days.The results demonstrate that the application of three types of organic fertilizers chicken manure(P1),oil palm empty bunch fertilizer(P2),and vermicompost(P3)positively impacts the growth of three soybean varieties.The findings indicate that the application of P2 organic fertilizer can increase vegetative growth almost 50%in soybeans on acidic soil,including plant height,leaf count,and root length.Meanwhile,applying P3 organic fertilizer can boost reproductive growth responses in soybeans on acidic soil,such as pod number(from around 0-4 unit to 42-51 unit),grain number(from around 0-5 unit to 88-90 unit),and grain weight(from around 0-0.37 g to 12-25 g).Organic fertilizer has the potential to regulate soil pH,promoting higher yields of soybeans under acidic stress.

Improvement of Wolfberry(Lycium barbarum L.)Fruit Yield and Quality and Enhancement of Soil Fertility by Nitrogen Reduction Combined with Organic Fertilizers

Excessive amounts of nitrogen(N)fertilizers are applied during wolfberry production,resulting in some soil problems as well as potential environmental risks in the Qinghai-Tibet Plateau.In this study,organic fertilizers were used to replace part of the N fertilizer in wolfberry fields with different fertility levels.N fertilizer rates had 0,50,100,150,200,and 250 g N/plant.Organic fertilizer rates had 0,2,4,6,8,and 10 kg organic fertilizer/plant.The experimental treatments included 6 combinations of N0M10,N50M8,N100M6,N150M4,N200M2,and control was N250M0.The results showed that in the high-fertility soils,combinations of N150M4,N100M6 and N50M8 treatments were increased in yields,fruit shape index,flavonoid content,total phenol content,mineral nutrient content,and antioxidant activity of wolfberry fruits.Also they were improved in soil fertility and decreased in residual nitrate through the soil depth of 0-300 cm.In the soil with less fertility,fruit yield,amino acid contents,flavonoids,total phenols,mineral nutrients and antioxidant activity of fruits were increased by the N200M2,N150M4 and N100M6 treatments and soil fertility was improved as well.Also more residual nitrate was found in the depth of 0-100 cm of soil with both chemical and organic fertilizer compared with the control.Therefore,in the Qinghai-Tibet Plateau,combining decreased N fertilizer with organic fertilizer rather than chemical fertilizer alone could help farmers achieve satisfactory yields and quality of wolfberry fruits and reduce the risk of nitrate leaching.In conclusion,50-150 g/plant of N fertilizer combined with 4-8 kg/plant of organic fertilizer in high-fertility gardens and 100-200 g/plant of N fertilizer combined with 2-6 kg/plant of organic fertilizer in low-fertility gardens are recommended for wolfberry cultivation.

Effects of Applying Organic Fertilizer on Rice Lodging Resistance and Yield

[Objective]The aim was to provide a scientific basis for the reasonable application of organic fertilizer to improve lodging resistance and yield of rice.[Method]The application of four different kinds of organic fertilizer was applied to study their effects on rice lodging resistance and yield of late rice Yuzhengxiang that with high quality.[Result] The effect of applying organic fertilizer for improving rice lodging resistance capability was:biogas residues> chicken manure > rapeseed cake> tobac...

Investigation on the Accumulation of Heavy Metals from Organic Fertilizer in Soil and Plant

ObjectiveThis study aimed to investigate the accumulation of heavy metals from organic fertilizer in soil and plant. MethodThree plots were chosen in Shanghai suburb to measure the heavy metal accumulation by monitoring their concentrations in soil and plant after organic fertilizer was applied. We also analyzed the correlations of the heavy metals in soil and plants. Single-factor pollution index and Nemerow’s synthetical pollution index were adopted to evaluate the heavy metal contamination in soils. Moreover, how many years before the heavy metal accumulation will exceed the environmental capability if 45 t/hm 2 organic fertilizer is applied every year was also estimated in the present study. ResultThe rules of heavy metals’ accumulation in soil changed with the various soil characters and pH. The average concentrations of Pb, Cd and As in the tested plants exceeded the limits. The average concentration of Cu in the tested soil shared positive correlation with that in the tested plants. The average concentration of Pb in the tested soil was negatively correlated with that in the tested plant while the other heavy metals didn’t show the rule like that. Organic fertilizer application caused no obvious pollution to the soils. Cu would exceed the standard environmental capacity within 15 years if 45 t/hm 2 organic fertilizer is applied every year, while for Hg, it will be 2 000 years. ConclusionWhen the excessive organic fertilizer is put into the land, the heavy metals from organic fertilizer would accumulate in soil and plant. With continued excessive fertilization, the heavy metals especially Cu would exceed the stan- dard environmental capacity. More attention should be paid to the inputting amount of the organic fertilizer.

Effects of Biological Organic Fertilizer on Flue-cured Tobacco Chemical Composition

Through field experiment,special biological fertilizer and cake fertilizer were applied collectively to tobacco,and chemical compositions of Wanxi flue-cured tobacco leaves were researched.The results showed that the increase of biological organic fertilizer would significantly improve soil nutrient supplying capacity.Compared with conventional fertilization,the contents of reducing sugar,total sugar and starch in different parts of tobaccos which were applied with biological organic fertilizer were closer to standards of excellent tobacco.In the treatment,the ratio of reducing sugar and nicotine in tobacco was more suitable in middle and lower parts of the plant and the contents of total N,nicotine and chlorine in tobacco were lowered,improving tobacco quality.

Farmers' Willingness on Organic Fertilizer Application Based on Logit Model and Influencing Factors——A case of Shandong Province

[Objective] The matter of chemical fertilizer being overused but organic fertilizer being deficiently used causes environment pollution and soil fertility degradation and holds back agricultural sustainable development in China at present.[Method] A survey of 200 farmers selected from Shandong province was conducted in 2008 to identify the factors influencing farmers willingness to use organic fertilizer.[Result] Logit model results showed that the proportion of non-farm income in total income,awareness of...

Effects of Several Organic Fertilizers on Organic Peach

The research explored the effects of compound management model on soil fertility and peach tree production, involving free-range chicken and returning chicken manure to fields. The results showed that the effects of chicken manure on soil fertility were poorer compared with organic fertilizers, but the former would bet-ter promote peach tree growth and improve yields. On the other hand, the peach fruits applied with chicken manures were smal in size and poor in commercial val-ue. What’s worse, disease rate reached 31.2% and the fruits could not be stored for a long term. Therefore, the compound management model combining agriculture and animal husbandry should intensify epidemic prevention to take place of organic fertilizers.

Effects of Corn Stalk-composted Organic Fertilizer on Physiochemical Properties of Tobacco-growing Soil

In order to explore the method of returning corn stalk into field, the effects of returning corn stalk direcfly into soil and applying corn stalk-composted orgar^c fertilizer into soil on the physiochemical properties of tobacco-growing soil were studied. The results showed that returning corn stalk into soil could reduce soil bulk density and increase soil porosity, so as to improve the water and fertilizer retention capacity of tobacco-growing soil. At the same time, returning corn stalk into soil could also increase the organic matter, available phosphorus and available potassi- um contents in tobacco-growing soil. In the early field growth stage of tobacco, soil alkali-hydrolyzable nitrogen content decreased slightly; but in the middle and later field growth stage, the alkali-hydrolyzable nitrogen content in tobacco-growing soil increased. The treatment effect of corn stalk＋urea＋fermentation bacteria and corn stalk＋urea＋BM was better than that of the control （returning corn stalk directly into soil）, indicating that the corn stalk-composted organic fertilizer had certain popular- ization value.

Study on Effect of Engran Series of Microbial Organic Fertilizers on Flue-cured Tobacco

[Objective] This study was conducted to provide theoretic support for improving yield and quality of flue-cured tobacco by applying microbial organic fertilizers. [Method] A field plot experiment was conducted to study the effects of the Engran series of microbial organic fertilizers on growth and development, diseases and pests and economic traits of flue-cured tobacco. [Result] The result showed that the treatment of conventional fertilization ＋ Engran microbial agent could promote the growth and dry matter accumulation of flue-cured tobacco during the growth period in the field, enhance the disease resistance of tobacco, and improve yield and output value of flue-cured tobacco and income of tobacco growers. Compared with T1,the proportion of high-grade tobacco, the proportion of mid-high grade tobacco,yield, output value and average price increased by 4.4%, 3.8%, 5.48%, 11.51% and5.73% respectively. [Conclusion] The treatment of conventional fertilization ＋ Engran microbial agent showed outstanding performance, is optimum for field production,and could be applied to Flue-cured tobacco.

Effect of Different Organic Fertilizers on Chinese Chives(Allium tuberosum) Growth and Yield

[Objeclive] This study was conducted to select suitable organic fertilizer for Chinese chives, so as to improve yield and benefit of Chinese chives. [Method] Pot experiments were carried out to investigate effects of 3 organic fertilizers peanut cake fertilizer, chicken manure and mushroom residue on growth and yield of Chi- nese Chives. [Result] The 3 organic fertilizer treatments had better effects on plant height, stem diameter and leaf width than the CK. Treatment 1 showed the best effect on growth and development of Chinese chives, treatment 2 exhibited the sec- ond best effect, and treatment 3 showed the poorest effect. Treatment 1 showed the highest yield and economic benefit, of 65.514 t/hm^2 and 175.556×10^4 Yuardhm2, respectively, treatment 2 showed the second highest effects, and treatment 3 showed the lowest yield and economic benefit. [Conclusion] Selecting peanut cake fertilizer for production of Chinese chives could significantly improve yield and eco- nomic benefit of Chinese chives.

Persistence of fertilization effects on soil organic carbon in degraded alpine wetlands in the Yellow River source region

In the restoration of degraded wetlands,fertilization can improve the vegetation-soil-microorganisms complex,thereby affecting the organic carbon content.However,it is currently unclear whether these effects are sustainable.This study employed Biolog-Eco surveys to investigate the changes in vegetation characteristics,soil physicochemical properties,and soil microbial functional diversity in degraded alpine wetlands of the source region of the Yellow River at 3 and 15 months after the application of nitrogen,phosphorus,and organic mixed fertilizer.The following results were obtained:The addition of nitrogen fertilizer and organic compost significantly affects the soil organic carbon content in degraded wetlands.Three months after fertilization,nitrogen addition increases soil organic carbon in both lightly and severely degraded wetlands,whereas after 15 months,organic compost enhanced the soil organic carbon level in severely degraded wetlands.Structural equation modeling indicates that fertilization decreases the soil pH and directly or indirectly influences the soil organic carbon levels through variations in the soil water content and the aboveground biomass of vegetation.Three months after fertilization,nitrogen fertilizer showed a direct positive effect on soil organic carbon.However,organic mixed fertilizer indirectly reduced soil organic carbon by increasing biomass and decreasing soil moisture.After 15 months,none of the fertilizers significantly affected the soil organic carbon level.In summary,it can be inferred that the addition of nitrogen fertilizer lacks sustainability in positively influencing the organic carbon content.

Preliminary Study on the Application of Jiayuan Organic Fertilizer on Tea Plant

A trial was conducted by using Jiayuan organic fertilizer in Chibi to investigate its effect on tea plant and ascertain the possibility of high quality and high yield.The results indicated that such organic fertilizer could achieve the effects of promoting the growth of tea plant,increasing the weight of the plucked flesh leaves,improving tea yield,increasing the contents of main functional substances such as tea polyphenols and amino acids and improving tea quality.It also showed excellent effect in maintaining or improving soil environmental sanitation indicators and contained no plant growth hormones.

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.

Long-Term Application of Organic Manure and Mineral Fertilizer on N_2O and CO_2 Emissions in a Red Soil from Cultivated Maize-Wheat Rotation in China

A long-term field experiment was established to determine the influence of mineral fertilizer and organic manure on soil fertility. A tract of red soil （Ferralic Cambisol） in Qiyang Red Soil Experimental Station （Qiyang County, Hunan Province, China） was fertilized beginning in 1990 and N20 and CO2 were examined during the maize and wheat growth season of 2007-2008. The study involved five treatments： organic manure （NPKM）, fertilizer NPK （NPK）, fertilizer NP （NP）, fertilizer NK （NK）, and control （CK）. Manured soils had higher crop biomass, organic C, and pH than soils receiving the various mineralized fertilizers indicating that long-term application of manures could efficiently prevent red soil acidification and increase crop productivity. The application of manures and fertilizers at a rate of 300 kg N ha-1 yr-1 obviously increased NzO and CO2 emissions from 0.58 kg N20-N ha-~ yr-~ and 10565 kg C ha-~ yr-~ in the CK treatment soil to 3.0l kg N20-N ha-~ yr-~ and 28 663 kg C ha-~ yr-I in the NPKM treatment. There were also obvious different effects on N20 and CO2 emissions between applying fertilizer and manure. More N20 and CO2 released during the 184-d maize growing season than the 125- d wheat growth season in the manure fertilized soils but not in mineral fertilizer treatments. N20 emission was significantly affected by soil moisture only during the wheat growing season, and CO2 emission was affected by soil temperature only in CK and NP treatment during the wheat and maize growing season. In sum, this study indicates the application of organic manure may be a preferred strategy for maintaining red emissions than treatments only with mineral fertilizer. soil productivity, but may result in greater N20 and CO2

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.

Substitution of chemical fertilizer by Chinese milk vetch improves the sustainability of yield and accumulation of soil organic carbon in a double-rice cropping system

The double-rice cropping system is a very important intensive cropping system for food security in China. There have been few studies of the sustainability of yield and accumulation of soil organic carbon (SOC) in the double-rice cropping system following a partial substitution of chemical fertilizer by Chinese milk vetch (Mv). We conducted a 10-year (2008–2017) field experiment in Nan County, South-Central China, to examine the double-rice productivity and SOC accumulation in a paddy soil in response to different fertilization levels and Mv application (22.5 Mg ha^–1). Fertilizer and Mv were applied both individually and in combination (sole chemical fertilizers, Mv plus 100, 80, 60, 40, and 0% of the recommended dose of chemical fertilizers, labeled as F100, MF100, MF80, MF60, MF40, and MF0, respectively). It was found that the grain yields of double-rice crop in treatments receiving Mv were reduced when the dose of chemical fertilizer was reduced, while the change in SOC stock displayed a double peak curve. The MF100 produced the highest double-rice yield and SOC stock, with the value higher by 13.5 and 26.8% than that in the F100. However, the grain yields increased in the MF80 (by 8.4% compared to the F100), while the SOC stock only increased by 8.4%. Analogous to the change of grain yield, the sustainable yield index (SYI) of double rice were improved significantly in the MF100 and MF80 compared to the F100, while there was a slight increase in the MF60 and MF40. After a certain amount of Mv input (22.5 Mg ha^–1), the carbon sequestration rate was affected by the nutrient input due to the stimulation of microbial biomass. Compared with the MF0, the MF100 and MF40 resulted in a dramatically higher carbon sequestration rate (with the value higher by 71.6 and 70.1%), whereas the MF80 induced a lower carbon sequestration rate with the value lower by 70.1% compared to the MF0. Based on the above results we suggested that Mv could partially replace chemical fertilizers (e.g., 40–60%) to improve or maintain the productivity and sustainability of the double-rice cropping system in South-Central China.