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111.
112.
T. P. Burt 《CATENA》2001,42(2-4)
Until recently, ‘land use’ was regarded as a single function: in rural areas of the UK this simply meant ‘farming’ or, in the uplands, ‘forestry’. However, there is now growing recognition of the multiple use of land, and farming or forestry must compete with other functions, in particular water supply. Links between hydrological pathways and stream water quality are described as a context for understanding the transport of pollutants to the river system. The concept of landscape sensitivity is then described and applied to the topics of soil erosion and nitrate leaching. Based on these analyses, guidelines for integrated management of sensitive catchment systems are proposed. 相似文献
113.
Summary The nitrogen metabolism of wheat plants inoculated with various Azospirillum brasilense strains and nitrate reductase negative (NR–) mutants was studied in two monoxenic test tube experiments. The spontaneous mutants selected with chlorate under anaerobic conditions with nitrite as terminal electron acceptor fixed N2 in the presence of 10 mM NO3
– and were stable after the plant passage. One strain (Sp 245) isolated from surface-sterilized wheat roots produced significant increases in plant weight at both NO3 levels (1 and 10 mM) which were not observed with the NR– mutants or with the two other strains. Similar effects were observed in a pot experiment with soil on dry weight and total N incorporation but only at the higher N fertilizer level. In the monoxenic test tube experiments plants inoculated with the mutants showed lower nitrogenase activities than NR+ strains at the low NO3
– level (1 = mM) but maintained the same level of activity with 10 mM NO3
– where the activity of all NR+ strains was completely repressed. The nitrate reductase activity of roots increased with the inoculation of the homologous strains and with the mutants at both NO3
– levels. At the low NO3
– level this also resulted in increased activity in the shoots, but at the high NO3
– level the two homologous strains produced significantly lower nitrate reductase activity in shoots while the mutants more than doubled it. The possible role of the bacterial nitrate reductase in NO3
– assimilation by the wheat plant is discussed. 相似文献
114.
施肥对蔬菜硝酸盐累积的影响研究 总被引:38,自引:1,他引:38
试验研究施肥对福州市多种蔬菜硝酸盐含量影响结果表明 ,农户传统施肥方式蔬菜硝酸盐含量为 5 9.5~374 3.1mg/kg,平均硝酸盐含量为绿叶菜类 >白菜类 >葱蒜类 >根茎类 >瓜类 >豆类 >茄果类 ,且同类不同品种蔬菜硝酸盐含量也存在差异。以WHO/FAO规定的允许值为标准评价绿叶菜类超标最重 ,其次为白菜类和葱蒜类 ,其他 4类未超标。化肥纯N施用量为 4 5 0kg/hm2 时 ,化学N肥对蔬菜硝酸盐累积的贡献率 >85 % ,其中不同品种N肥贡献率依次为NH4NO3 >NH4HCO3 >CO(NH2 ) 2 >(NH4) 2 SO4>NH4Cl。N肥施用量与蔬菜硝酸盐累积量呈正相关 ,双氰胺施用量与蔬菜硝酸盐累积量呈负相关。等N量下蔬菜硝酸盐累积量随基肥所占比例减少、追肥所占比例增大而增大 ,且随追肥后时间推移呈直线下降。配施有机氮可降低蔬菜硝酸盐含量 ,降幅施厩肥 >土杂肥。调整与优化蔬菜品种及施肥结构 ,采用“重头、稳中、控尾”施N方式 ,根据蔬菜食用卫生要求选择N肥用量及其使用安全期与双氰胺用量 ,可降低蔬菜硝酸盐含量。 相似文献
115.
Nitrate leaching losses and their control in a mixed farm system in the Cotswold Hills, England 总被引:3,自引:0,他引:3
K.D. Allingham R. Cartwright D. Donaghy J.S. Conway K.W.T. Goulding S.C. Jarvis 《Soil Use and Management》2002,18(4):421-427
Abstract. Nitrate leaching was measured for four years at the Royal Agricultural College 's Coates Farm in the Cotswolds, England. Coates is a typical Cotswold mixed farm with thin, well-drained calcareous soils especially prone to leaching. Over the duration of this study there were dairy, sheep and arable enterprises on the farm. A 'Farm Gate' nitrogen (N) budget was constructed. Small 120 m × 20 m 'farmlets' were sited in ten fields across the farm, covering all parts of the rotation, as the sites for detailed measurements. Each farmlet received the same management as the rest of the field in which they were situated. Using ceramic probes inserted to 60 cm, soil water was sampled every two weeks throughout the winter drainage season. The annual drainage varied from 135 mm under grassland in 1996/7 to 600 mm under cereals in 1998/9. Average N losses by leaching were determined mostly by rainfall and were 65 kg N ha–1 yr–1 , accounting for 25% of the N inputs. Especially leaky parts of the rotation were the ploughing out of a lucerne ley and the grazing of stubble turnips with sheep, both typical Cotswold farm practices. The research highlights some of the difficulties in developing practicable, profitable management practices to decrease nitrate losses. 相似文献
116.
Summary Studies of the effects of different forms of N on urease production in soils amended with organic C showed that although microbial activity, as measured by CO2 production, was stimulated by the addition of NH4
+ or NO3
- to C-amended soils (200 mol glucose-C g–1 soil), urease production was repressed by these forms of N. The addition of L-methionine sulfoximine, an inhibitor of inorganic N assimilation by microorganisms, relieved the NH4
+ and NO3
- repression of urease production in C-amended soil. The addition of sodium chlorate, an inhibitor of NO3
- reduction to NH4
+ by microorganisms, relieved the NO3
- repression of urease production, but did not eliminate the repression associated with NH4
+. These observations indicate that microbial production of urease in C-amended soils is not directly repressed by NH4
+ or NO3
-, but by products formed by microbial assimilation of these forms of N. This conclusion is supported by our finding that the biologically active L-isomers of alanine, arginine, asparagine, aspartate, and glutamine, repressed urease production in C-amended soil, whereas the D-isomers of these amino acids had little or no influence on urease production. This work suggests that urease synthesis by soil microorganisms is controlled by the global N regulon. 相似文献
117.
118.
为摸清烤烟在保山地区气候条件下的碳氮代谢规律,探索丙二醛含量与碳氮代谢关键酶间的相互关系,以品种k326为试验材料进行相关研究。试验结果表明,在移栽后0~50 d内,烟叶中硝酸还原酶、蔗糖转换酶活性均呈上升趋势,均在旺长期间表现为最为活跃,之后均呈现出下降趋势;在整个大田生长过程中,烟叶中丙二醛含量一直呈上升趋势,在0~65 d内变换幅度较小,但在65~80 d内含量急剧上升。相关性分析结果表明,烟叶中丙二醛含量与硝酸还原酶、蔗糖转换酶活性呈负相关关系,与硝酸还原酶活性/蔗糖转换酶活性的比值呈正相关关系,但均未达到显著水平。 相似文献
119.
[目的]研究不同强度火烧迹地中土壤硝态氮的动态变化,为将来计划烧除提供科学依据。[方法]通过野外采样和室内分析,研究大兴安岭地区不同强度火烧迹地中土壤硝态氮动态变化及差异。[结果]对照样地和轻、中和重度火烧样地中土壤硝态氮含量分别为1.53~8.90、1.83~9.01、1.99~10.79、2.22~9.99 mg/kg。土壤硝态氮在不同强度火烧迹地和对照样地上均具有明显的季节动态变化,季节变化显著(P0.05)。[结论]不同强度火烧样地和对照样地中硝态氮含量在不同月份有不同的变化和差异。 相似文献
120.