The effects of crop husbandry and nitrogen fertilizer on nitrate leaching from a shallow limestone soil growing a five course combinable crop rotation

Abstract. Nitrogen (N) leaching losses from a shallow limestone soil growing a five course combinable croprotation (oilseed rape, wheat, peas, wheat, barley) were measured from 1990 until 1995 using porous ceramic cups, at 60 cm depth, and drainage estimates. The crops were grown with three husbandry systems and two levels of N fertilizer. The husbandry systems were designed to reflect local practice (Standard), the best possible techniques to reduce N loss (Protective) and an Intermediate system which was a compromise between the two. Nitrogen was applied at full and half recommended rates. Drainage started during September in four years and November in one year, with above average drainage in three years. Losses of N were largest after peas (58 kg/ha) and oilseed rape (42 kg/ha), and least (17 kg/ha) before peas sown in spring after a cover crop. Over five years, the Protective management system, which used early sowing and shallow cultivation wherever possible, lost least N (31 kg/ha/y) and the Standard system, with conventional drilling dates and ploughing as the primary cultivation, lost most (49 kg/ha/y). Halving the N fertilizer decreased N loss by 11 kg/ha/y, averaged over the rotation. None of the treatments gave mean drainage water nitrate concentrations of less than 50 mg/l, averaged over the five years. Changes to arable cropping alone will not eliminate the need for other measures to control nitrate concen-trations in public drinking water supplies.     

Competition for electron donors among nitrate reducers,ferric iron reducers,sulfate reducers,and methanogens in anoxic paddy soil

Slurries of anoxic paddy soil were either freshly prepared or were partially depleted in endogenous electron donors by prolonged incubation under anaerobic conditions. Endogenous NO ₃ ^– was reduced within 4 h, followed by reduction of Fe³⁺ and SO ₄ ^2– , and later by production of CH₄. Addition of NO ₃ ^– slightly inhibited the production of Fe²⁺ in the depleted but not in the fresh paddy soil. Inhibition was overcome by the addition of H₂, acetate, or a mixture of fatty acids (and other compounds), indicating that these compounds served as electron donors for the bacteria reducing NO ₃ ^– and/or ferric iron. Addition on NO ₃ ^– also inhibited the reduction of SO ₄ ^2– in the depleted paddy soil. This inhibition was only overcome by H₂, but not by acetate or a mixture of compounds, indicating that H₂ was the predominant electron donor for the bacteria involved in NO ₃ ^– and/or SO ₄ ^2– reduction. SO ₄ ^2– reduction was also inhibited by exogenous Fe³⁺, but only in the depleted paddy soil. This inhibition was overcome by either H₂, acetate, or a mixture of compounds, suggesting that they served as electron donors for reduction of Fe³⁺ and/or SO ₄ ²⁺ . CH₄ production was inhibited by NO ₃ ^– both in depleted and in fresh paddy soil. Fe³⁺ and SO ₄ ^2– also inhibited methanogenesis, but the inhibition was stronger in the depleted than in the fresh paddy soil. Inhibition of CH₄ production was paralleled by a decrease in the steady state concentration of H₂ to a level which provided a free enthalpy of less than G=–17 kJ mol^-1 CH₄ compared to more than G=–32 kJ mol^-1 CH₄ in the control. The results indicate that in the presence of exogenous fe³⁺ or SO ₄ ²⁺ , methanogenic bacteria were outcompeted for H₂ by bacteria reducing Fe³⁺ or SO ₄ ²⁺ .Deceased on 27 December 1992     

Denitrification and fermentation in plant-residue-amended soil

Summary Nitrous oxide production (denitrification) during anaerobic incubation of ground-alfalfa-, red-clover-, wheat-straw-, and cornstover-amended soil was positively related to the initial water-soluble C content of the residue- amended soil. The water-soluble C concentration decreased in all treatments during the first 2 days, then increased in the alfalfa-, red-clover-, and wheat-straw-amended soil until the end of the experiment at 15 days. An accumulation of acetate, propionate, and butyrate was partly responsible for the increased water-soluble C concentration. Denitrification rates were much higher in the alfalfa-and red-clover-amended soil, but NO ₃ ^– was not fully recovered as N₂O in these treatments. Supported by earlier experiments in our laboratory, we conclude that some of the NO ₃ ^– was reduced to NH ₄ ⁺ through fermentative NO ₃ ^– reduction, otherwise known as dissimilatory NO ₃ ^– reduction to NH ₄ ⁺ . Acetate, the primary product of anaerobic fermentation, accumulated in the alfalfa- and red-clover-amended soil in the presence of NO ₃ ^– , supporting previous observations that the processes of denitrification and fermentation occur simultaneously in C-amended soil. The partitioning of NO ₃ ^– between denitrification and fermentative NO ₃ ^– reduction to NH ₄ ⁺ depends on the activity of the denitrifying and fermentative bacterial populations. NO₂ concentration may be a key in the partitioning of NO ₃ ^– between these two processes.     

甜菜叶片中硝酸还原酶活力的研究

通过对甜菜叶片中硝酸还原酶活力的研究，结果表明：（１）酶活力动态变化规律为块根及糖分增长期以前，酶活力逐渐增加，到糖分积累期活力下降；（２）块根分化形成期，不同类型品种之间的酶活力有差异，即高糖型品种酶活力高于丰产型品种，且酶活性与收获时块根含糖率呈显著正相关；（３）糖分积累期，硝酸还原酶活力与块根产量呈显著负相关。上述特点，可为甜菜育种及合理施用氮肥，从而提高甜菜生产水平提供科学依据。     

影响烤烟叶片硝酸盐积累的因素分析

烟草叶片中的硝酸盐和亚硝酸盐是强致癌物质烟草特有亚硝胺(TSNA)的前体物,凡影响前体物质含量的因素都会影响烟草TSNA的形成和积累。因此,调控TSNA前体物质的积累,进而降低烟草TSNA的含量,对生产优质低害的烟叶原料具有重要的意义。笔者分析了影响烤烟叶片中硝酸盐积累的重要因素,概述了烤烟基因型、烟叶组织部位、环境条件、肥料种类和调制加工过程等众多因素对硝酸盐积累影响的研究进展。     

不同施氮量下氮肥在土壤中的空间分布与作物吸收后残留规律

研究了田间原位条件下,棉田滴灌不同施氮量下氮肥在土壤中的空间分布与作物吸收后残留规律。结果表明硝酸盐在水平方向和垂直方向具有明显的空间变异。同一氮肥用量下,以滴头为中心,硝酸盐在水平方向分布顺序为0 cm<10 cm<20 cm<40 cm<30 cm,在水平方向上硝酸盐随水移动且可以扩散到离湿润锋后部,垂直方向硝酸盐变化顺序为0-20 cm>20-40 cm>40-60 cm,为浅层累积型。无论水平方向还是垂直方向,氮肥用量对硝酸盐分布均有显著性影响。收获后,残留硝酸盐分布在点源水平距离5-40 cm,垂直距离0-60 cm土体内,残留硝酸盐累积量随氮肥用量的增加而增加。这些结果说明土壤硝酸盐存在明显空间变异,施肥显著增加了其浓度和残留量,同时可能会淋洗出根层,造成养分利用率下降和环境污染。因此,适宜的氮肥用量是控制硝酸盐向深层移动和累积的主要措施。     

影响蔬菜硝酸盐含量累积因素的探讨

研究结果表明，不同蔬菜，同一蔬菜不同品种，同一植株不同部位，以及不同栽培环境，ＮＯ３－含量均有较大差异，菠菜不同遗传型可达１０倍以上。叶用芥菜、苋菜品种间含量差异较小。菠菜ＮＯ３－含量，以叶肉部分最低，根部次之，叶柄部分最高，叶用芥菜因类型不同而有变化。不同地区土壤和管理水平对菠菜ＮＯ３－含量可相差４倍左右，秋栽菠菜比冬栽的ＮＯ３－含量明显下降，而喷施微量元素对菠菜ＮＯ３－含量无显著差异。     

两种食用菌硝态氮含量变化研究

采用重氮偶合比色法研究了平菇、木耳硝酸盐、亚硝酸盐含量和不同加工、贮存条件下的含量变化，目的在于提高人们对食用菌硝酸盐、亚硝酸盐毒性的认识。结果表明：鲜平菇、木耳硝酸盐含量分别为86．57mg／kg、118．54mg／kg，比一级标准分别低345mg／kg、226mg／kg；亚硝酸含量分别为3．01mg／kg、2．54mg／kg，都比限量低37mg／kg。从硝酸盐、亚硝酸盐含量角度看，平菇、木耳的安全系数很高，可以放心食用。水煮后硝酸盐含量升高，但仍在安全值内；亚硝酸盐含量降低，降低幅度盐水较小。贮存期间硝酸盐、亚硝酸盐含量均降低。     

紫色土壤氮素不同流失形式的比较研究

土壤氮素流失形式及其量化研究是农业小流域氮素管理及流失过程模拟的核心内容之一,以紫色土区3个具有不同地形和土地利用方式的典型农业小流域为研究对象,比较研究了区域土壤氮素在降雨侵蚀过程中流失的主要形式。结果表明,紫色土区土壤氮素以硝态氮为主要流失形式,其流失浓度一般占硝态氮和铵态氮总浓度的80%以上,农田利用为主流域的则高达90%以上。氮素流失的平均浓度因流域土地利用类型的差异而显著不同,农田的一般为(5.36±2.13)mg/L,而非农田利用的变化在1.70~3.15mg/L之间。农田硝态氮的精确管理应作为减控流域土壤氮素非点源流失的关键措施。     

接种固氮菌对甘蔗组培苗氮营养生理特性的影响

[目的]研究接种固氮菌对甘蔗组培苗氮营养生理特性的影响。[方法]将2种内生固氮菌B16L与B8R接种到甘蔗栽培品种G16、R16与R22的组培苗中,研究这些组培苗的氮营养生理特性的变化。[结果]于分蘖期和拔节期的测定结果表明,R16与R22+1叶的叶绿素含量、Ca2+-ATP酶活性处理均大于对照,G16+1叶的Ca2+-ATP酶活性处理低于对照。相对于分蘖期,拔节期不同品种的处理与对照的+1叶的叶绿素含量、Ca2+-ATP酶活性都有所升高。不同品种的处理与对照+1叶的硝态氮含量没有规律变化。[结论]接种内生固氮菌改善了R16与R22健康组培苗的一些氮营养生理特性,但对G16的影响不大。