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Measurement of full N cycle: arable soils - NT1907

It has been reported that the arable system is the simplest within agriculture since inputs and exports to fields are relatively well defined and distribution of N inputs is more spatially uniform than on grazed grassland. This study will aim to measure and model N losses via leaching, denitrification, ammonia volatilisation and crop offtake, together with wet deposition of N, in arable fields on a range of soil types and crop rotations. The project will be composed of 7 objectives which are outlined as follows, together with ways in which they might be achieved: 1. Measurement of total organic N in the soil. After harvest, 200 representative soil samples will be taken to the depth of cultivation from each field in the study and will be analysed for levels of organic C and N. Soil samples for total soil N will be taken in autumn 1997 at Rosemaund; 2. Measurement of soil mineral N (SMN) at the beginning and end of the field capacity periods and at harvest. Soil samples will be taken to 90 cm, in 30 cm increments, for SMN analysis and will be submitted to laboratory examination for nitrate-N and ammonium-N analysis. Concentrations will be converted to kg/ha N by using a site-specific bulk density based on previous measurements. Field capacity period will be identified using the output for each field from the ADAS Irriguide computer program; 3. Measurement of nitrate leaching over winter using porous ceramic cups. Water will be sampled for nitrate-N during the field capacity period from 20 porous pots installed to a depth of 90 cm in each field. Total quantity of nitrate leached below 90 cm will be calculated from the obtained nitrate concentration and drainage volumes identified by Irriguide; 4. Evaluation of nitrous oxide and dinitrogen evolution following fertilizer application and during the period of greatest expected emission in autumn. Nitrous oxide emissions will be monitored using small chambers located on metal rings embedded in the soil and will be measured weekly between 1st October and 30th November for each cropping year. Weekly measurements will also be made between 1st February and 30th April for each cropping year, while daily measurements will be made following fertilizer application for 5 days. Emissions of dinitrogen will be estimated using a modified version of the acetylene inhibition technique. Calcium carbide will be introduced to the soil in situ immediately beneath 12 randomly selected nitrous oxide monitoring chambers, after which nitrous oxide emissions will be measured 2 hours after calcium carbide introduction; 5. Assessment of ammonia volatilisation from soil/crop system after fertilizer application and during crop senescence. Ammonia fluxes will be determined using passive samplers, with measurements being taken following fertilizer application and during crop senescence; 6. Measurement of wet deposition of N from the atmosphere over a whole season. Rainfall will be collected in 3 litre polythene bottles via a filtered funnel fixed above the bottle. The collecting bottle is held inside a double-skinned metal cylinder designed to insulate the bottle and minimise evaporation. Wet deposition will be measured at one field per site; and 7. Measurement of N offtake by the crop at harvest. Crops will be harvested in 3 replicates and samples will be assessed for dry matter and N concentrations. Calculation of total crop N offtake will be derived from the dry matter harvest index, as estimated by means of replicated grab samples of approximately 100 plants. Data will also be collated on all managed N inputs to the crop, as well as its removal in harvestable fractions.
Time-Scale and Cost
From: 1995

To: 1998

Cost: £151,511
Contractor / Funded Organisations
Fields of Study
Fertilisers and Nitrate Pollution