Fertilizers are heavily applied in orchards of the hilly and mountainous topography of South China and may increase nutrient loadings to receiving waters.A simple runoff collecting system was used to measure the effec...Fertilizers are heavily applied in orchards of the hilly and mountainous topography of South China and may increase nutrient loadings to receiving waters.A simple runoff collecting system was used to measure the effects of different fertilization treatments on total N and P concentrations of surface runoff in a Chinese chestnut (Castanea mollissima Blume) orchard in Dongyuan County,Guangdong Province,China.In such orchards,fertilizer was typically applied in two short furrows or pits on either side of each tree.Treatments included three application depths (surface,10cm and 20 cm),and three application rates (low,median and high).Results showed that 90.5% of the runoff water samples had a total N concentration higher than 0.35 mgL^(-1) and 54.2% had a total P concentration higher than 0.1 mgL^(-1).Fertilizer application at all depths and at all but the lowest rate significantly increased total N and P concentrations in runoff water.Fertilization with chemical compound fertilizer at a soil depth of 20cm produced significantly lower (P<0.05) total N concentration in runoff than both surface and 10-cm depth fertilization,and significantly lower (P<0.05) total P concentration in runoff than surface fertilization.Total N and P concentrations in runoff significantly increased with the application rate of organic fertilizers.With the exception of total P concentrations,which were not significantly different between the control and fertilization at a rate of 119 kg P ha-1 in organic form,all the other fertilization treatments produced significantly higher total N and total P concentrations in runoff than the control.A fertilization depth≥20cm and an application rate≤72 kg N ha^(-1) or 119 kg P ha^(-1) for compound organic fertilizer was suggested to substantially reduce N and P runoff losses from hillslope orchards and to protect receiving waters in South China.展开更多
A child is born to a father and a mother.This fact,however,is yet to be recognized by demography,in which fertility refers to women’s natural ability to give birth.The main reason for the absence of men is that data ...A child is born to a father and a mother.This fact,however,is yet to be recognized by demography,in which fertility refers to women’s natural ability to give birth.The main reason for the absence of men is that data on births are more often available for women than for men.But in the last few decades,data availability has greatly improved.Recent studies show that total fertility rates(TFRs)of men can be calculated for most countries in the world and that the difference between the TFRs of men and women can be quite large.For low-fertility countries,nonetheless,these studies show little difference between the TFRs of men and women,giving rise to the question:Is men’s fertility worth further investigation?To avoid ambiguity in describing a particular difference as small or big,this paper provides a formula for probabilistic TFRs.Using hypothesis test on probabilistic TFRs,we can say that the difference between the TFRs of men and women is statistically significant for all the G7 countries,except for France.To explain the differences between the TFRs of men and women,this study uses models of stable populations and concludes that the one-sex stable population models cannot explain the results whereas a two-sex joint stable population model can do so.By using the two-sex population model,we can explain why the TFR of men in France is almost the same as that of women,and why it is lower than that of women in the other six G7 countries.More specifically,by using the model,we can help explain 76%of the variance in the difference between the TFRs of men and women.Future studies may be able to show that men’s TFR is significantly lower than women’s in other countries too and explain why it is so.The above findings,however,require closer attention and further investigation,because low fertility could lead to socioeconomic problems.Beyond TFRs,extending fertility studies from women to men as well,that is,conducting fertility studies on both women and men,will fundamentally improve our knowledge about fertility age patterns,trends,determinants,policies and other related issues.展开更多
In this paper we present the accurate estimation of total fertility rates, prove the theorem of upper and lower bounds of double-edged limit and provide the formulas of upper and lower bounds of total fertility rates....In this paper we present the accurate estimation of total fertility rates, prove the theorem of upper and lower bounds of double-edged limit and provide the formulas of upper and lower bounds of total fertility rates. Based on these estimations and statistical data, we calculate the upper and lower bounds of the double-edged limit for 46 countries including China. Furthermore, we describe the positive growth rate, negative growth rate and zero growth rate of population development. These results are of great importance for us to control population not only in theory but also in practice.展开更多
【目的】提高土壤碳固持,特别是增加有机碳累积、减少碳损失,对于提高旱地土壤肥力、缓解大气温室效应具有重要意义。黄土高原旱地土壤有机碳含量低,增施氮肥是这一地区重要的作物增产措施,但氮肥投入对土壤碳的影响如何,一直没有报道...【目的】提高土壤碳固持,特别是增加有机碳累积、减少碳损失,对于提高旱地土壤肥力、缓解大气温室效应具有重要意义。黄土高原旱地土壤有机碳含量低,增施氮肥是这一地区重要的作物增产措施,但氮肥投入对土壤碳的影响如何,一直没有报道。【方法】利用黄土高原旱地持续23年的长期定位试验,在每年施磷39 kg P2O5·hm-2条件下,设置0、45、90、135、180 kg N·hm-2 5个氮水平种植冬小麦,在小麦收获期采集0—40 cm不同土层的土壤样品,研究长期施用不同用量的氮肥对旱地土壤总碳、有机碳、轻质有机碳及无机碳的影响,分析不同氮肥用量引起的土壤有机碳、轻质有机碳及无机碳累积量的变化,定量分析氮肥用量对旱地土壤不同形态碳的影响。【结果】随氮肥用量增加,旱地土壤不同土层总碳无显著变化,但0—30 cm土层有机碳含量却随之增加,与不施氮肥相比,增幅可达7%—28%;0—40 cm土层轻质有机碳含量也增加,增幅达31%—106%,但施氮量过高不利于有机碳累积。对不同形态土壤碳累积量与氮肥用量的回归分析表明,施氮量120 kg N·hm-2时,0—30 cm土层有机碳累积量达最高值36.6 Mg;施氮量161 kg N·hm-2时,0—40 cm土层轻质有机碳累积量达最高值2.69 Mg;每千克肥料氮每年可使土壤有机碳增加1.34 kg·hm-2,轻质有机碳增加0.31 kg·hm-2;0—20 cm表层土壤轻质有机碳占有机碳的百分比也随施氮量增加而升高。相反,5—20 cm土层土壤无机碳含量却随氮肥用量增加而显著降低,施氮量180 kg N·hm-2时,无机碳累积量比不施氮减少2.8 Mg,每千克肥料氮每年可使无机碳减少0.67 kg·hm-2。【结论】在黄土高原旱地长期施用不同用量的氮肥虽不显著影响土壤的总碳数量,却显著地改变了旱地土壤碳的组成,即通过增加土壤的轻质有机碳,增加了土壤的有机碳累积量,同时降低了土壤的无机碳累积。因此,合理调控氮肥用量,不仅是旱地作物增产的关键措施,对增加土壤有机碳固持、培肥土壤也有重要意义。同时,施用氮肥引起的土壤无机碳损失不容忽视,其潜在的农业、生态与环境效应需引起大众关注。展开更多
基金Project supported by the Science and Technology Department of Guangdong Province,China (No.2004B33301007)the Rockefeller Brothers Fund,America.
文摘Fertilizers are heavily applied in orchards of the hilly and mountainous topography of South China and may increase nutrient loadings to receiving waters.A simple runoff collecting system was used to measure the effects of different fertilization treatments on total N and P concentrations of surface runoff in a Chinese chestnut (Castanea mollissima Blume) orchard in Dongyuan County,Guangdong Province,China.In such orchards,fertilizer was typically applied in two short furrows or pits on either side of each tree.Treatments included three application depths (surface,10cm and 20 cm),and three application rates (low,median and high).Results showed that 90.5% of the runoff water samples had a total N concentration higher than 0.35 mgL^(-1) and 54.2% had a total P concentration higher than 0.1 mgL^(-1).Fertilizer application at all depths and at all but the lowest rate significantly increased total N and P concentrations in runoff water.Fertilization with chemical compound fertilizer at a soil depth of 20cm produced significantly lower (P<0.05) total N concentration in runoff than both surface and 10-cm depth fertilization,and significantly lower (P<0.05) total P concentration in runoff than surface fertilization.Total N and P concentrations in runoff significantly increased with the application rate of organic fertilizers.With the exception of total P concentrations,which were not significantly different between the control and fertilization at a rate of 119 kg P ha-1 in organic form,all the other fertilization treatments produced significantly higher total N and total P concentrations in runoff than the control.A fertilization depth≥20cm and an application rate≤72 kg N ha^(-1) or 119 kg P ha^(-1) for compound organic fertilizer was suggested to substantially reduce N and P runoff losses from hillslope orchards and to protect receiving waters in South China.
文摘A child is born to a father and a mother.This fact,however,is yet to be recognized by demography,in which fertility refers to women’s natural ability to give birth.The main reason for the absence of men is that data on births are more often available for women than for men.But in the last few decades,data availability has greatly improved.Recent studies show that total fertility rates(TFRs)of men can be calculated for most countries in the world and that the difference between the TFRs of men and women can be quite large.For low-fertility countries,nonetheless,these studies show little difference between the TFRs of men and women,giving rise to the question:Is men’s fertility worth further investigation?To avoid ambiguity in describing a particular difference as small or big,this paper provides a formula for probabilistic TFRs.Using hypothesis test on probabilistic TFRs,we can say that the difference between the TFRs of men and women is statistically significant for all the G7 countries,except for France.To explain the differences between the TFRs of men and women,this study uses models of stable populations and concludes that the one-sex stable population models cannot explain the results whereas a two-sex joint stable population model can do so.By using the two-sex population model,we can explain why the TFR of men in France is almost the same as that of women,and why it is lower than that of women in the other six G7 countries.More specifically,by using the model,we can help explain 76%of the variance in the difference between the TFRs of men and women.Future studies may be able to show that men’s TFR is significantly lower than women’s in other countries too and explain why it is so.The above findings,however,require closer attention and further investigation,because low fertility could lead to socioeconomic problems.Beyond TFRs,extending fertility studies from women to men as well,that is,conducting fertility studies on both women and men,will fundamentally improve our knowledge about fertility age patterns,trends,determinants,policies and other related issues.
文摘In this paper we present the accurate estimation of total fertility rates, prove the theorem of upper and lower bounds of double-edged limit and provide the formulas of upper and lower bounds of total fertility rates. Based on these estimations and statistical data, we calculate the upper and lower bounds of the double-edged limit for 46 countries including China. Furthermore, we describe the positive growth rate, negative growth rate and zero growth rate of population development. These results are of great importance for us to control population not only in theory but also in practice.
文摘【目的】提高土壤碳固持,特别是增加有机碳累积、减少碳损失,对于提高旱地土壤肥力、缓解大气温室效应具有重要意义。黄土高原旱地土壤有机碳含量低,增施氮肥是这一地区重要的作物增产措施,但氮肥投入对土壤碳的影响如何,一直没有报道。【方法】利用黄土高原旱地持续23年的长期定位试验,在每年施磷39 kg P2O5·hm-2条件下,设置0、45、90、135、180 kg N·hm-2 5个氮水平种植冬小麦,在小麦收获期采集0—40 cm不同土层的土壤样品,研究长期施用不同用量的氮肥对旱地土壤总碳、有机碳、轻质有机碳及无机碳的影响,分析不同氮肥用量引起的土壤有机碳、轻质有机碳及无机碳累积量的变化,定量分析氮肥用量对旱地土壤不同形态碳的影响。【结果】随氮肥用量增加,旱地土壤不同土层总碳无显著变化,但0—30 cm土层有机碳含量却随之增加,与不施氮肥相比,增幅可达7%—28%;0—40 cm土层轻质有机碳含量也增加,增幅达31%—106%,但施氮量过高不利于有机碳累积。对不同形态土壤碳累积量与氮肥用量的回归分析表明,施氮量120 kg N·hm-2时,0—30 cm土层有机碳累积量达最高值36.6 Mg;施氮量161 kg N·hm-2时,0—40 cm土层轻质有机碳累积量达最高值2.69 Mg;每千克肥料氮每年可使土壤有机碳增加1.34 kg·hm-2,轻质有机碳增加0.31 kg·hm-2;0—20 cm表层土壤轻质有机碳占有机碳的百分比也随施氮量增加而升高。相反,5—20 cm土层土壤无机碳含量却随氮肥用量增加而显著降低,施氮量180 kg N·hm-2时,无机碳累积量比不施氮减少2.8 Mg,每千克肥料氮每年可使无机碳减少0.67 kg·hm-2。【结论】在黄土高原旱地长期施用不同用量的氮肥虽不显著影响土壤的总碳数量,却显著地改变了旱地土壤碳的组成,即通过增加土壤的轻质有机碳,增加了土壤的有机碳累积量,同时降低了土壤的无机碳累积。因此,合理调控氮肥用量,不仅是旱地作物增产的关键措施,对增加土壤有机碳固持、培肥土壤也有重要意义。同时,施用氮肥引起的土壤无机碳损失不容忽视,其潜在的农业、生态与环境效应需引起大众关注。
