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.

Nitrate leaching of winter wheat grown in lysimeters as affected by fertilizers and irrigation on the North China Plain

Proper application of nitrogen（N） fertilizers and irrigation management are important production practices that can reduce nitrate leaching into groundwater and improve the N use efficiency（NUE）. A lysimeter/rain shelter facility was used to study effects of the rate of N fertilization, type of N fertilizer, and irrigation level on key aspects of winter wheat production over three growing seasons（response variables were nitrate transport, N leaching, and NUE）. Results indicated that nitrate concentration in the soil profile and N leaching increased with the rate of N fertilization. At the end of the third season, nitrate concentration in the top 0–75 cm layer of soil was higher with manure treatment while urea treatments resulted in higher concentrations in the 100–200 cm layer. With normal irrigation, 3.4 to 15.3% of N from applied fertilizer was leached from the soil, yet no leaching occurred under a stress irrigation treatment. The manure treatment experienced less N leaching than the urea treatment in all cases except for the 180 kg N ha^-1 rate in 2011–2012（season 3）. In terms of grain yield（GY）, dry matter（DM） or NUE parameters, values for the manure treatment were lower than for the urea treatment in 2009–2010（season 1）, yet were otherwise higher for urea treatment in season 3. GY and crop nitrogen uptake（NU） were elevated when the rate of N fertilizer increased, while the NUE decreased; GY, DM, and NU increased with the amount of irrigation. Data indicated that reduced rates of N fertilization combined with increased manure application and proper irrigation management can lower nitrate levels in the subsoil and reduce potential N leaching into groundwater.

Effect of Indigenous Nitrogen Supply of Soil on the Grain Yield and Fertilizer-N Use Efficiency in Rice

The effects of application of N fertilizer on wheat on the grain yield and N use efficiency （FNUE） of rice in the wheat-rice rotation system, as well as on the soil fertility were studies. N-fertilizer application on wheat significantly increased total N, arnrnoniurn-N and nitrate-N contents in paddy field, resulting in high indigenous N supply of soil （INS）. Compared with low INS, the effect of N rate on the grain yield of rice was reduced significantly, and FNUE was decreased under high INS. These results indicated that high INS was one of the main reasons for the low FNUE in rice.

Effect of Reducing Application of Chemical Fertilizers and Chemical Pesticides on Physiological Traits,Yield and Quality of Radish

This paper studied the effect of reducing application of chemical fertilizer,increasing application of functional organic fertilizer and trace elements and fully using biological pesticides on physiological traits,yield and quality of radish. The results showed that applying functional organic fertilizer and trace elements and fully using biological pesticides could help to significantly improve the radish fleshy root yield,increase soluble sugar and vitamin C content,reduce crude fiber and nitrate content,but had no significant influence on radish moisture content,glucosinolates and chlorpyrifos content in organophosphorus pesticides.

Study on the Influence of Sowing Rate,Water and Fertilizer Coupling on Water Use Efficiency of Fodder Millet

To study the influence of sowing rate,water and fertilizer( N,P and K) coupling on water use efficiency of fodder millet grown in autumn fallow field,taking " Jigu 18" as the tested material,a orthogonal rotation combination with five factors was designed in pot experiment. Results showed that both water and phosphate fertilizer had important impacts on water use efficiency,in which water had the maximum impact,followed by phosphate fertilizer,and nitrogen fertilizer,potassium fertilizer and sowing rate all had no obvious impact. Significant item of sowing rate,water and fertilizer coupling had the below sequence: potassium fertilizer + sowing rate > nitrogen fertilizer + phosphate fertilizer > water + phosphate fertilizer > water + sowing rate > water + potassium fertilizer,and other items had no obvious impact. Mathematical model was established: y = 44. 26- 1. 311x1- 2. 298x2- 3. 682x3- 6. 401x4- 34. 540x5+ 0. 273x1x3+ 0. 118x1x4+ 0. 843x1x5- 1. 948x2x3+ 6. 631x4x5. The optimal scheme taking economic benefit as the examining index was cleared,that is,soil water content maintained 10%,and sowing rate of fodder millet was 15 kg / hm2. By the scheme,water use efficiency was 26. 24 g / kg,and hay yield was13980. 90 kg / hm2,with economic benefit of 13830. 90 yuan/hm2,which was 3063. 73 yuan/hm2 more than the optimized combination with the highest hay yield,with increase magnitude of 22. 15%,and was 6215. 15 yuan / hm2 more than the optimized combination with the highest water use efficiency,with increase magnitude of 44. 94%. The research could provide theoretic basis and technical support for production practice of fodder millet grown in autumn fallow field.

Yields and Nitrogen Use Efficiencies of Rice (Oryza sativa) at Different Sites Using Different Nitrogen Fertilizer Application Rates and Controlled-release Urea to Conventional Urea Ratios

Rice yields and nitrogen use efficiencies were studied at five sites in southwest China using two nitrogen fertilization rates and five controlled-release urea（ CRU） to ordinary urea（ U） ratios. The fertilizer treatments significantly increased rice yields compared with the control（ no nitrogen added） yields to different degrees at different sites. Applying CRU and U increased the rice yield more than adding the same amount of nitrogen as U only. Higher increasing production rate were found using a nitrogen application rate of 105 kg/hm2 than 150 kg/hm2. A 70∶ 30 CRU∶ U ratio increased the yield more than other four ratios. Nitrogen use efficiency was 21. 9% higher using a nitrogen application rate of 105 kg/hm^2 than 150 kg/hm^2,and 46. 6%,38. 1%,34. 7%,and 22. 2% higher than when only U was applied when CRU∶ U ratios of 70 ∶ 30,50 ∶ 50,100 ∶ 0,and 30 ∶ 70,respectively,were used. A 70 ∶ 30 CRU ∶ U ratio gave the highest economic output（ yuan/hm^2）. Applying both CRU and U gave an output 3 078. 87 yuan/hm^2 higher at a nitrogen application rate of 150 kg/hm^2 than at a nitrogen application rate of 105 kg/hm^2. Economic output was always higher using both CRU and U than using U only. The highest economic output was given using a 70∶ 30 CRU∶ U ratio.Increasing the amount of nitrogen added decreased the output efficiency（ per hm2） because CRU is expensive. Significant relationships were found between the yield increase rate and the proportion of CRU added（ regression equation y = 7. 429 x-185. 7,R^2= 0. 663） and between the total rainfall over the whole growth period and the proportion of CRU added（ y =-0. 087 1 x ＋ 112. 29,R^2= 0. 687 9）. These regression equations can be used to determine the appropriate proportion of CRU that should be added at a site,depending on the rainfall and target rice yield.

Effect of Fertilization on the Dynamics and Activity of Iron-Reducing Bacterial Populations in a West African Rice Paddy Soil Planted with Two Rice Varieties: Case Study of Kou Valley in Burkina Faso

Iron toxicity is a major stress to rice caused by a high concentration of reduced iron, in the soil in many lowlands worldwide. To reduce iron toxicity in the West African lowlands, an investigation was performed at the site of the University of Ouagadougou, in pots containing an iron toxic soil from the Kou Valley (West of Burkina Faso). The experiment objective was to study the effect of mineral fertilizer on Iron Reducing Bacteria (IRB) dynamics and activity during rice cultivation, iron accumulation in rice plant and rice biomass yield under iron toxicity conditions. BOUAKE-189 and ROK-5 rice varieties, sensitive and tolerant to iron toxicity, respectively, were used for the experiment. The pots were amended with chemical fertilizers (NPK + Urea and NPK + Urea + Ca + Mg + Zn complex). Control pots without fertilization were prepared similarly. The kinetics of IRB and ferrous iron content in soil near rice roots were monitored throughout the cultural cycle using MPN and colorimetric methods, respectively. The total iron content was evaluated in rice plant using spectrometric method. Data obtained were analyzed in relation to fertilization mode, rice growth stage and rice yield using the student’s t-test and XLSTAT 2014 statistical software. The experiment revealed that NPK + Urea and NPK + Urea + Ca + Mg + Zn fertilization, decreased significantly (p < 0.0001) the number of IRB in the soil for BOUAKE-189 rice varieties. In most pots, highest IRB densities and ferrous iron content in soil were recorded from rice tillering and flowering to maturity stages, indicating that rice plants promoted microbial processes and iron reduction in soil. From the study, the NPK + Urea amendment decreased significantly ferrous iron content (p < 0.0001) in soil near BOUAKE-189 and ROK-5 rice varieties roots relatively to control pots. However, NPK + Urea + Ca + Zn + Mg amendment increased significantly ferrous iron content (p < 0.0001) in the soil near roots, Fe accumulation in plant biomass and rice yield for the two rice varieties.

Effects of single basal application of coated compound fertilizer on yield and nitrogen use efficiency in double-cropped rice

Fertilizer plays an important role in increasing rice yield. More than half of all fertilizer applied to the field is not taken up, resulting in environmental damage and substantial economic losses. To address these concerns, a low-cost, coated compound fertilizer named "Xiang Nong Da"(XND), requiring only a single basal application, was studied. A two-year field experiment was conducted to test the effects of XND application on rice yield and nitrogen fertilizer use efficiency. An ordinary uncoated compound fertilizer(UNCF), with 20% more nutrients and split application was selected as the control. The yield of XND-treated rice was only 3.1% lower than that of the control, an insignificant difference. There were no significant differences between N use efficiency indices of the two fertilizer treatments except for N partial factor productivity(PFP_N). PFP_Nof XND treatment was 19.7%–23.2% higher than the control, a significant difference. This result indicates that a 20% decrease in N application rate is possible with XND without yield reduction and with savings in both labor and time.

Effect of Nitrogen Fertilizer on Herbivores and Its Stimulation to Major Insect Pests in Rice

Nitrogen is one of the most important factors in development of herbivore populations. The application of nitrogen fertilizer in plants can normally increase herbivore feeding preference, food consumption, survival, growth, reproduction, and population density, except few examples that nitrogen fertilizer reduces the herbivore performances. In most of the rice growing areas in Asia, the great increases in populations of major insect pests of rice, including planthoppers （Nilaparvata lugens and Sogatella furcifera）, leaffolder （ Cnaphalocrocis rnedinalis）, and stem borers （Scirpophaga incertulas, Chilo suppressalis, S. innotata, C. polychrysus and Sesarnia inferens） were closely related to the long-term excessive application of nitrogen fertilizers. The optimal regime of nitrogen fertilizer in irrigated paddy fields is proposed to improve the fertilizer-nitrogen use efficiency and reduce the environmental pollution.

Recent Advances on the Technologies to Increase Fertilizer Use Efficiency

To increase fertilizer use efficiency （FUE） and to minimize its negative impact on environment have been the focal points in the world for a long time. It is very important to increase FUE in China for its relatively low FUE and serious losses of nutrients. Recent advances of the technologies to increase FUE are reviewed in this article. These include site-specific and real-time nitrogen management, non-destructive quick test of the nitrogen status of plants, new types of slow release and controlled release fertilizers, site-specific nutrient management, and use of urease inhibitor and nitrification inhibitor to decrease nitrogen losses. Future outlook in technologies related to FUE improvement is also discussed.

Responses of Phosphorus Use Efficiency, Grain Yield, and Quality to Phosphorus Application Amount of Weak-Gluten Wheat

Phosphorus （P） is one of the most widely occurring nutrients for development and growth of wheat. In this study, the effects of P application amount on grain yield, protein content, and phosphorus use efficiency （PUE） were studied by agronomic management of P fertilizer on spring weak-gluten wheat （Triticum aestivum L.） grown under field conditions for 2 yr. The experiments were performed at five levels of P205 application amount, including 0, 72, 108, 144, and 180 kg ha-1. As a result, with increase in P fertilizer, grain yield, and P agricultural efficiency （AEp） increased in a quadratic equitation, but partial factor productivity of P （PFPp） decreased in a logarithmic eq. When 108 kg ha-1 P2Os was applied, the grain yield reached the highest level, but the protein content in gain was lower than 11.5%, a threshold for the protein content to evaluate weak-gluten wheat suitable for production of cake and biscuit. Yangmai 13 and Ningmai 9 could tolerate to higher P level of soils than Yangmai 9 that had more loss in grain yield when P fertilizer was over-applied. AEp had a concomitant relationship with grain yield and was a better descriptor for P use efficiency in the wheat. A high P use efficiency resulted in leaf area index （LAI）, increased chlorophyll content and photosynthetic rate, and stable acid phophatase （APase） activity to accumulate more dry matter after anthesis, which explained that the optimum P fertilizer increased grain yield and improved grain quality of weak-gluten wheat.

Differences of yield and nitrogen use efficiency under different applications of slow release fertilizer in spring maize

Excessive or insufficient application of fertilizer has raised broader concerns regarding soil and environmental degradation.One-time application of slow release fertilizer (SF) has been widely used to reduce yield gap with potential maize yield and improve nitrogen use efficiency (NUE).A 2-year field experiment (2018–2019) was conducted to evaluate the effects of SF rates from 0 to 405 kg N ha^(–1) (named F0,SF225,SF270,SF315,SF360,and SF405) and 405 kg N ha^(–1) of common fertilizer(CF405) on the grain yield,biomass and N accumulation,enzymatic activities related with carbon–nitrogen metabolism,NUE and economic analysis.Results indicated that the highest grain yields,NUEs and economic returns were achieved at SF360in both varieties.The enzymatic activities related with carbon–nitrogen metabolism,pre-and post-silking accumulation of biomass and N increased with increasing SF rate,and they were the highest at SF360 and SF405.The grain yield at SF360had no significant difference with that at SF405.However,the N partial factor productivity,N agronomic efficiency and N recovery efficiency at SF360 were 9.8,6.6 and 8.9% higher than that at SF405.The results also indicated that the average grain yields,NUE and economic benefit at SF405 were 5.2,12.3 and 18.1% higher than that at CF405.In conclusion,decreasing N rate from 405 kg ha^(–1)(CF) to 360 kg ha^(–1)(SF) could effectively reduce the yield gap between realized and potential maize yields.The N decreased by 11.1%,but the yield,NUE and economic benefit increased by 3.2,22.2 and 17.5%,which created a simple,efficient and business-friendly system for spring maize production in Jiangsu Province,China.

Modified fertilization management of summer maize(Zea mays L.) in northern China improves grain yield and efficiency of nitrogen use

Improving the yield of maize grain per unit area is needed to meet the growing demand for it in China, where the availability of fertile land is very limited.Modified fertilization management and planting density are efficient methods for increasing crop yield.Field experiments were designed to investigate the influence of modified fertilization management and planting density on grain yield and nitrogen use efficiency of the popular maize variety Zhengdan 958, in four treatments including local farmer＇s practice（FP）, high-yielding and high efficiency cultivation（HH）, super high-yielding cultivation（SH）, and the control（CK）.Trials were conducted in three locations of the Huang-Huai-Hai Plain in northern China.Compared with FP, SH was clearly able to promote N absorption and dry matter accumulation in post-anthesis, and achieve high yield and N use efficiency by increasing planting density and postponing the supplementary application of fertilizers.However, with an increase in planting density, the demand of N increased along with grain yield.Due to the input of too much N fertilizer, the efficiency of N use in SH was low.Applying less total N, ameliorating cultivation and cropping management practices should be considered as priority strategies to augment production potential and finally achieve synchronization between high yield and high N efficiency in fertile soils.However, in situations where soil fertility is low, achieving high yield and high N use efficiency in maize will likely depend on increased planting density and appropriate application of supplementary fertilizers postpone to the grain-filling stage.

Fractal Characteristics of Soil under Different Land-Use Patterns in the Arid and Semi-Arid Region of the Western Tibet Plateau, China

The fractal geometry to the study of soil structure, its dynamics, andphysical processes appears to be a useful tool in reaching a better understanding of systemperformance. This research was designed to apply fractal models for mass into computingD_p and D_avalues. As a result, the relationships among land use methods, fractal dimension and soil fertilityhave been discussed. The study conclusions include that (i) fractal dimension indicates not onlycharacteristics of soil texture but also effects of natural environment changes and human activitieson soil properties, (ii) soil fertility is best when D_p< 2.65 and D_a < 2.44, (iii) maximal valuesof D_p under all land use patterns are equal and appear in the range the depth of 15-20 cm inthestudy area, but maximal values of D_a are different and distribute in various profile depth.These results can provide an important support to understand soil properties in plateau soil-formingenvironment, and be helpful to conduct scientific soil tillage and management.

Release Characteristics of Different N Forms in an Uncoated Slow/Controlled Release Compound Fertilizer

This study examined the release characteristics of different N forms in an uncoated slow/controlled-release compound fertilizer （UCRF） and the N uptake and N-use efficiency by rice plants. Water dissolution, soil leaching, and pot experiments were employed. The dynamics of N release from the UCRF could be quantitatively described by three equations： the first-order kinetics equation [N1=N0 （1-e^-kt）], Elovich equation （N1=a ＋ blnt）, and parabola equation （N1=a ＋ bt^0.5）, with the best fitting by the first-order kinetics equation for different N （r= 0.9569^＊＊-0.9999^＊＊）. The release potentials （No values estimated by the first-order kinetics equation） of different N in the UCRF decreased in the order of total N 〉 DON 〉 urea-N 〉 NH4^＋-N 〉 NO3^-N in water, and total N 〉 NH4^＋-N 〉 DON 〉 urea-N 〉 NO3^--N in soil, respectively, being in accordance with cumulative amounts of N release. The constants of N release rate （k values and b values） for different N forms were in decreasing order of total N 〉 DON 〉 NH4^＋-N 〉 NO3^--N in water, whereas the k values were urea- N 〉DON 〉 NH4^＋-N 〉 total N 〉 NO3^--N, and the b values were total N 〉 NH4^＋-N 〉 DON 〉 NO3^--N 〉 urea-N in soil. Compared with a common compound fertilizer, the N-use efficiency, N-agronomy efficiency, and N-physiological efficiency of the UCRF were increased by 11.4%, 8.32 kg kg^-1, and 5.17 kg kg^-1, respectively. The ratios of different N to total N in the UCRF showed significant correlation with N uptake by rice plants. The findings showed that the first-order kinetics equation [Nt=N0 （l-e^kt）] could be used to describe the release characteristics of different N forms in the fertilizer. The UCRF containing different N forms was more effective in facilitating N uptake by rice compared with the common compound fertilizer containing single urea-N form.

The relationship between farm size and fertilizer use efficiency:Evidence from China

Low fertilizer use efficiency is commonly found in China’s agriculture sector. It is critical to understand the drivers of fertilizer use in order to increase fertilizer use efficiency(FUE). The purpose of this paper is to investigate the relationship between farm size and FUE based on farm-level data in China. The results suggest a positive farm size–FUE relationship. The estimated elasticities of farm size for rice, maize, wheat–maize, and rice–maize are similar, and the average elasticity of farm size is around 0.2. Statistically, a 1% increase in farm size is associated with a 0.2%increase in FUE. The positive effect of farm size on FUE is not due to the increase in yield, but the reduction in fertilizer use while keeping yield largely unchanged. The findings suggest that promoting the expansion of farm size may increase FUE, and thus reduce environmental pollution caused by fertilizer overuse.

Characterization of Nitrogen Uptake Pattern in Malaysian Rice MR219 at Different Growth Stages Using ^(15)N Isotope

Nitrogen （N） use efficiency is usually less than 50%, and it remains a major problem in rice cultivation. Controlled release fertilizer （CRF） technology is one of the well-known efforts to overcome this problem. The efficiency of CRF, however, is very much dependent on the timing of nutrient release. This study was conducted to determine the precise time of N uptake by rice as a guideline to develop efficient CRF. Fertilizer N uptake by rice at different growth stages was investigated by using 15N isotopic technique. Rice was planted in pots, with 15N urea as N source at the rate of 120 kg/hm2. Potassium and phosphorus were applied at the same rate of 50 kg/hm2. Standard agronomic practices were employed throughout the growing periods. Rice plants were harvested every two weeks until maturation at the 14th week and analyzed for total N and 15N content. Nitrogen derived from fertilizer was calculated. Total N uptake in plants consistently increased until the 11th week. After that, it started to plateau and finally declined. Moreover, N utilization by rice plants peaked at 50%, which occurred during the 11th week after transplanting. N derived from fertilizer in rice plants were in the range of 18.7% to 40.0% in all plant tissues. The remaining N was derived from soil. Based on this study, N release from CRF should complete by the 11th week after planting to ensure the maximum fertilizer N uptake by rice plants. Efficient CRF should contribute to higher N derived from fertilizer which also resulted in a higher total N uptake by rice plants, increasing the potential of rice to produce higher yield while at the same time of reducina loss.

Effects of mechanized deep placement of nitrogen fertilizer rate and type on rice yield and nitrogen use efficiency in Chuanxi Plain, China

This paper investigates the yield and nitrogen use efficiency (NUE) of machine-transplanted rice cultivated using mechanized deep placement of N fertilizer in the rice–wheat rotation region of Chuanxi Plain,China.It provides theoretical support for N-saving and improves quality and production efficiency of machine-transplanted rice.Using a single-factor complete randomized block design in field experiments in 2018 and 2019,seven N-fertilization treatments were applied,with the fertilizer being surface broadcast and/or mechanically placed beside the seedlings at (5.5±0.5) cm soil depth when transplanting.The treatments were:N0,no N fertilizer;U1,180 kg N ha^(–1) as urea,surface broadcast manually before transplanting;U2,108 kg N ha^(–1) as urea,surface broadcast manually before transplanting,and 72 kg N ha^(–1) as urea surface broadcast manually on the 10th d after transplanting,which is not only the local common fertilization method,but also the reference treatment;UD,180 kg N ha^(–1) as urea,mechanically deep-placed when transplanting;M1,81.6 kg N ha^(–1) as urea and 38.4 kg N ha^(–1) as controlled-release urea (CRU),mechanically deep-placed when transplanting;M2,102 kg N ha^(–1) as urea and48 kg N ha^(–1) as CRU,mechanically deep-placed when transplanting;M3,122.4 kg N ha^(–1) as urea and 57.6 kg N ha^(–1) as CRU,mechanically deep-placed when transplanting.The effects of the N fertilizer treatments on rice yield and NUE were consistent in the 2 yr.With a N application rate of 180 kg ha^(–1),compared with U2,the N recovery efficiency (NRE),N agronomic use efficiency (NAE) and yield under the UD treatment were 20.6,3.5 and 1.1% higher in 2018,and 4.6,1.7 and 1.2% higher in 2019,respectively.Compared with urea alone (U1,U2 or UD),the NRE,NAE and yield achieved by M3 (combined application of urea and controlled-release urea) were higher by 9.2–73.3%,18.6–61.5% and 6.5–16.5%(2018),and 22.2–65.2%,25.6–75.0% and 5.9–13.9%(2019),respectively.Compared with M3,the lower-N treatments M1 and M2 significantly increased NRE by 4.0–7.8% in 2018 and 3.1–4.3% in 2019,respectively.Compared with urea surface application (U1 or U2),the yield under the M2 treatment was higher by 4.3–12.9% in 2018 and 3.6–10.1% in 2019,respectively.Compared with U2,the NRE and NAE under the M2 treatment was higher by 36.9 and 36.3% in 2018,and 33.2 and 37.4% in 2019,mainly because of higher N uptake.There was no significant difference in the concentration of nitrate in the top 0–20 cm soil under U1,U2 and M2 treatments during the full heading and maturity stages.During the full heading stage,U2 produced the highest concentration of nitrite in 0–20 cm and 20–40 cm soil among the N fertilizer treatments.In conclusion,mechanized deep placement of mixed urea and controlled-release urea (M2) at transplanting is a highly-efficient cultivation technology that enables increased yield of machine-transplanted rice and improved NUE,while reducing the amount of N-fertilization applied.

Changes in soil organic carbon and nitrogen after 26 years of farmland management on the Loess Plateau of China

Soil carbon（C） and nitrogen（N） play a crucial role in determining the soil and environmental quality. In this study, we investigated the effects of 26 years（from 1984 to 2010） of farmland management on soil organic carbon（SOC） and soil N in abandoned, wheat（Triticum aestivum L.） non-fertilized, wheat fertilized（mineral fertilizer and organic manure） and alfalfa（Medicago Sativa L.） non-fertilized treatments in a semi-arid region of the Loess Plateau, China. Our results showed that SOC and soil total N contents in the 0–20 cm soil layer increased by 4.29（24.4%） and 1.39 Mg/hm2（100%）, respectively, after the conversion of farmland to alfalfa land. Compared to the wheat non-fertilized treatment, SOC and soil total N contents in the 0–20 cm soil layer increased by 4.64（26.4%） and 1.18 Mg/hm2（85.5%）, respectively, in the wheat fertilized treatment. In addition, we found that the extents of changes in SOC, soil total N and mineral N depended on soil depth were greater in the upper soil layer（0–30 cm） than in the deeper soil layer（30–100 cm） in the alfalfa land or fertilizer-applied wheat land. Fertilizer applied to winter wheat could increase the accumulation rates of SOC and soil total N. SOC concentration had a significant positive correlation with soil total N concentration. Therefore, this study suggested that farmland management, e.g. the conversion of farmland to alfalfa forage land and fertilizer application, could promote the sequestrations of C and N in soils in semi-arid regions.

Regional Evaluation of Winter Rapeseed Response to K Fertilization, K Use Efficiency, and Critical Level of Soil K in the Yangtze River Valley

The investigation was carried out to study the response of winter rapeseed to potassium （K） feritlization and the critical soil available K level for current winter rapeseed production in the Yangtze River Valley （YRV） of China. A total of 132 field experiments were conducted in fields of farmers in the major winter rapeseed growing areas in YRV in 2000/2001 and 2004/2005 to 2006/2007 during growing season. Results of these field experiments showed that the average rapeseed yield increment resulting from 100 kg K ha-1 application was 358 kg ha-1, an increase over the control CK （no K） of 18.0% in 2005/2006 and 2006/2007. The average internal use efficiency （IE） of K was higher in the CK treatment （21.9 kg grain, kg-1 K uptake） than in the ＋K （100 kg K ha-1） treatment （17.7 kg grain, kg-1 K uptake）. Winter rapeseed required 68.1 kg of K to produce 1 000 kg seed. The recovery efficiency of K fertilizer in rapeseed production averaged 39.3%. The K balance was negative, with an average net removal of 117.6 kg K ha-1 in the CK treatment annually, and 56.8 kg K ha-1 in the ＋K treatment. The results indicated that there was a significant negative relationship between yield increments by K application and soil available K content. Based on the relative yield of CK/＋K at 90% level, the critical level of soil available K （NH4OAc-extractable K） was 135 mg kg-1.