摘要:

The development of European agriculture has always depended heavily on nitrogen supply. Until the middle of the 20th century nitrogen was probably the most important single factor. The paper deals with the introduction of clover in Europe, particularly in Denmark, where clover became a major crop between the 1740s and the beginning of the 19th century. The reasons for and the consequences of the disappearence of clover after 1945 are discussed. The author believes that, industrial agriculture being unsustainable, the 21st century will bring back a more sustainable clover-based agriculture.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754689

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Nitrogen management in organic agriculture is discussed focussing on strategies maximizing nitrogen input (source: N2-fixation) and minimizing nitrate losseson-site(field losses) andoff-site(losses from manure heaps).

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754690

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Nitrate contamination of ground and surface waters by leaching has increased over the past four decades. The productive capacity of intensive farming has become a problem and the environmental and social consequences are unacceptable. ‘Alternative’ approaches to food production are increasingly important. Organic farming systems represent the most well defined alternative with inherent characteristics which can limit the potential disruption which is the inevitable consequence of ‘conventional’ farming.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754691

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

For three ecological mixed arable-dairy farms on sandy soils in the Netherlands the nutrient balances for N, P and K have been assessed on the basis of inputs and outputs of products, manure, fodder and straw. For nitrogen the assessment of N-fixation and NH4volatilization from deep litter stables offer new problems because of the special farming methods in ecological agriculture. The nitrogen surpluses for the organic farms are 83 kg N per ha against 444 kg N per ha for conventional extensive dairy farms on sandy soils. The average nitrogen efficiency for the three organic farms is 31%, conventionally this was 12% in 1986. The leaching of N has been estimated on the basis of soil moisture analysis for most fields of the separate farms. The average N loss by leaching was 20 kg N*ha−1*yr−1. The average nitrogen content of shallow ground water was 11 mg NT*1−1, which will be lower in deeper layers as a result of denitrification. The results of the research over three consecutive years showed possibilities for improvement in farm management that will be necessary to meet recommendations for improvement of groundwater quality in the future.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754692

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Studies were made of plant nutrients, especially the flow, supply and losses of nitrogen in different agricultural and community systems in Sweden at the farm, regional and national levels. Nitrogen losses from the agricultural systems exceeded 100 kg/ha/year in southern Swedish regions. Losses exceeded 200 kg/ha/year in association with animal husbandry. Nitrogen can be conserved by maximizing the recycling of crop nitrogen within the agroecosystem and between the agricultural and the community systems. This requires that the level of animal production on a given farm must be adjusted on the basis of the farm's crop—and feed-production capacities which in turn are determined partly by the climatic and soil conditions. Such an adjustment on mixed farm, regional and national levels, would contribute to minimize nitrogen and other plant nutrient losses to the environment. This would also decrease the costs to the environment associated with artificial fertilizers.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754693

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In the DOC trial the influence of the three farming systems bio-dynamic (D), bio-organic (O) and conventional (C) with various fertilizer levels on crop yield and quality and on soil processes has been studied. The experiment has been carried out since 1978 on a loamy loess soil at Therwil near Basel over two 7-year crop rotation periods.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754694

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A crop rotation representative of a typical Danish dairy farm was established at the Taastrup field station in 1988. Detailed information of the manuring, nitrogen fixation, harvested dry matter and harvested nitrogen was available for the period 1988–1992, indicating that the harvested nitrogen almost exactly countered the input, including the biologically fixed nitrogen. As no measurements of N-losses were available a deterministic model (DAISY) was applied in order to obtain an estimate. Dry matter harvest (R = 0.9) and N harvest (R = 0.93) were simulated adequately, and only in the case of spring barley the model slightly overpredicted in a consistent manner, indicating that the use of N as delimiter of crop production in this ecological crop rotation was realistic. Considerable leaching losses of N (as high as 100–180 kg ha−1yr−1) were predicted in connection with the application of 50 tonnes of solid manure to bare soil in winter time preceeding the sowing of fodderbeet. Thus the model interpretation of the available data indicated that the apparent balance between harvested nitrogen and input nitrogen was non- sustainable and achieved by a depletion of soil organic nitrogen in the order of 40 kg N ha−1yr1. Strategies for achieving sustainability are discussed in the light of the model results.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754695

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Nitrogen supply of crops on organic farming systems mainly depends on mineralization of soil organic matter nitrogen. Mineralization was studied by taking soil samples from 30 plots in the crop rotation of two organic farms at intervals of 7 to 14 days during the growing season. On fallow plots net-mineralization alternated with net-immobilization three times from April to November. These soil inherent dynamics were modified by cultivation and the growing cycles of the different crops. Several cases could be observed which led to high accumulations of leacheable nitrate in soils: 1. fallow during growing season, 2. fallow during autumn and winter, 3. manuring in autumn, 4. leaching of chopped green manure by rain, 5. low nitrogen uptake of crops because of diseases, 6. transfer of mineralizable nitrogen from spring to autumn. The concept of the soil merely as a storage place for plant nutrients was one of the main factors for mistakes in nitrogen management. Understanding the interactions of plant residues, soil microbial biomass, net- mineralization intensity and the phases of N-uptake of different crops can lead to a practice of organic agriculture with good yield levels and low losses of nitrate-nitrogen to groundwater.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754696

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A cropping system project aimed at developing cropping systems which minimise nutrient leaching and maximise food quality and economy, was started at Apelsvoll Research Station in 1990. The experiment involves cash crop and forage crop systems with conventional and ecological farming. The systems are different with regard to crop rotation, nitrogen fertilization, soil tillage and plant protection. They are going to be improved by step-by-step changes. In the first experimental period, 1990/93, more than 80% of the nitrogen runoff was lost as nitrate in the drainage water. Averaged over all years and cropping systems the nitrate losses were 21.2 kg/ha. The nitrate runoff in the conventional cash crop system was more than twice as high as in the ecological cash crop system. For the forage crop systems the nitrate loss in the ecological system was reduced by 36% as compared to the conventional system. There was high variation in nitrate losses between the years. The most important factors influencing the nitrogen runoff in the different cropping systems seem to be crop rotation, soil tillage, time of manure application and amount of fertilizer.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754697

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

70 fields on a total of 17 farms in South East Norway, which were either ecological or in the process of converting to ecological farming, have been followed for a period of 2–3 years by sampling for soil mineral N content and crop N content. The nitrogen leaching potential was estimated from soil nitrate nitrogen content during late October, and was lowest on fields with plant growth in late autumn. On average leaching potential was lowest in leys (6 kg NO3ha−1). Undersown grain (13 kg NO3ha−1) and green fodder (14 kg NO3ha−1) had a low leaching potential. Turnips/vegetables (17 kg NO3ha−1), grain without undersown ley (30 kg NO3ha−1) and potatoes (33 kg N03ha−1) had a higher leaching potential. Fallow led to a much higher leaching potential (100 kg NO3ha−1). Autumn ploughing generally led to a higher nitrogen leaching potential than unploughed soils. A large proportion of legumes in a ley and in green fodder did not correlate with a higher leaching potential. Only in exceptional cases were large nitrogen losses found during the winter, even where the leaching potential was large. This was primarily due to the winter climate during the years of the study.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754698

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor