effects of different drain depths on nutrient leaching of lowland soils in north-east germany

摘要

In the North-East German lowland, fens and further hydromorphic soils are widely spread. They are prone to intensive transformation processes due to their high organic matter and potential leaching losses of solutes by drainage, soil tillage and fertilization. During the last 30 years extensive experiments in 103 groundwater lysimeters have been carried out to analyse the relationship between nutrient leaching and depth of draining. The drain depths varied between 5 and 150 cm below the surface. Datashowed increased nitrogen leaching with deeper drainage due to higher mineralization. Nitrogen balances of several years showed intensive outputs by harvested plants. Though fen soils were well fertilized (150 - 200 kg N /ha) about the twice the fertilization rate was found in the plant biomass. A yearly balance deficit of about 200 kg N /ha indicated a great amount of was mineralised from the peat became available for plants. At shallow water tables and anaerobic submerged conditions considerable losses of ammonium were measured. Soils are prone to high potassium losses by vegetation and by leaching. With deeper drainage higher losses were measured. Fertilization of potassium should be done during the vegetation period only and not in periods of drainage. Leaching of phosphorus was quite low in calcium and iron enriched fen soils (< 3 kg P/ha), because phosphorus is mainly fixed at calcium- or iron compounds in a slight basic environment. Deep drainage leads to high Ca-leaching losses (> 500 kg Ca /ha in fen soils). The reason for that is mainly the high Ca-release within the process of peat mineralization and a relatively low demand of plants. We concluded that relatively high water tables and discharge control are proper measures of efficient andsustainable soil use and to minimize Ieachate losses from lowland soils.