ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1993.tb00934.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.A quantitative knowledge of nitrogen cycle processes is required to design strategies for decreasing leakage of N from agriculture to the wider environment. However, it is remarkably difficult to make reliable measurements of many of the key processes under realistic field conditions. In impermeable soils hydrologically separated plots provide an invaluable method of measuring leaching and runoff. Estimates of nitrate leaching using porous ceramic cups agree well with lysimeter measurements on sandy soil but are suspect on more structured soils. Estimates of N2O flux from soil are subject to great spatial heterogeneity; developing long path‐length measuring techniques may overcome this problem.15N labelling is valuable for assessing fertilizer N loss, forms of N left in soil and the fate of N from crop residues. The combination of experimental and modelling approaches can provide insights that are otherwise unattainable, including a basis for more precise advice on N fertilization.Mineralization of soil organic matter and crop or animal residues provides much of the nitrate leached during winter under the climatic conditions of north‐west Europe, because mineralization is poorly synchronized with crop N uptake. Maintenance of crop cover during winter can greatly decrease leaching but the long‐term effects on the N cycle of winter cover crops or incorporating cereal straw are not yet

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1993.tb00935.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Recent experiments on soils overlying sand, chalk and limestone aquifers have shown that nitrate leaching losses can be decreased by modifying crop husbandry. Green cover during winter, if established early enough, can reduce nitrate loss. Cultivations can be timed to minimize leaching, and the advantages of irrigation (increased nitrogen offtake and smaller post‐harvest soil mineral nitrogen residues) outweigh the potential disadvantage of increased leaching risk during the growing season. It is important not to over‐fertilize crops. Using these techniques within farm rotations has decreased nitrate losses in small plot experiments. The next step is to measure the effects on commercial farms where the scale of operation might preclude the high level of husbandry that is required for successful nitrogen managem

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1993.tb00936.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.The concern over leakage of nitrate into waters and loss of other forms of N to the environment demands an appraisal of N flows within complete systems. The grassland N cycle is complex, with interactive controls over fluxes and transformations, and has the potential for considerable losses. Although there are data from experimental systems, a total comprehension of flows is not yet possible.Intensive dairy farming has a number of opportunities for leaks. A ‘model’ system in SW England has an annual input of 25.6 tonnes of N: of this only 20% is transferred into protein or milk, a further 46% is lost to the wider environment, 34% is as yet unaccounted for and much is recycled. Recent research has provided new techniques to decrease losses. To meet the joint requirements of production and environmental concerns we need to consider N flows and supplies on an integrated, whole farm basis, and to take better account of mineral N in the soil profile in relation to current crop demand, local climate and past sward managem

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1993.tb00937.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.Organic manures contain valuable quantities of nitrogen, phosphate and potash, but many farmers regard them as ‘waste materials’ rather than as sources of plant nutrients. Utilization of the plant‐available nitrogen content is poor at present because of manure management practices which lead to leaching and atmospheric losses. Experiments studying the effect of timing suggest that, in order to decrease nitrate leaching, applications of manures which contain much available nitrogen should not be made during the period September to December on freely draining grassland and arable soils. Spring top dressings of dilute pig or cattle slurries and poultry manures to growing cereal crops are generally more efficient than autumn applications, particularly on freely draining soils. Legislation requiring manures to be applied in an environmentally acceptable manner and the economic need for farmers to realize the nutrient value of organic manures are likely to change the farming industry's perception of manures as ‘waste mat

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1993.tb00938.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract.About 1.6 million tonnes of fertilizer N are applied to UK crops each year. In net terms, 10–60% of this is not taken up by the crop to which it was applied. Fertilizer N commonly doubles crop yield, but in the short term at least more than 90% of current production would be possible with only half normal use of N. However, costs of crop production other than fertilizer N are a large proportion of gross returns, so profits are sensitive to adjustments in N use and controls on N use could affect land values. Survey data show that compliance with current recommendations is good; recent improvements have come through restricting the use of N applications in autumn. Further improvements are possible by adjusting N use more fully for the extent to which past N applications have exceeded crop removal, and by better targeting the N used to improve protein concentrations of wheat grain. Research now in progress may provide insights into minimizing the crop N necessary for yield formation and the crop N left in the field at harvest, specifying the growing conditions which result in efficient N uptake from soi

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1993.tb00939.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1993.tb00940.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Book Reviewed in this article:Lysimeter Studies of the Fate of Pesticides in the Soil Edited by F. Führ and R. J. Hance

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1993.tb00941.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY