Simulating nitrate retention in soils and the effect of catch crops use and rooting pattern under the climatic conditions of Northern Europe

Summary

A model analysis of catch crop effects on nitrate leaching was carried out covering three soil types and three precipitation regimes in temperate climate. Catch crops with varying root properties (barssica and rye grass) were used to analyse the effect on nitrate retention in different soil layers. Climate data was taken from 3 different precipitation regimes over 43 years with an average annual amount of rainfall of 709, 796 and 1026 mm. The three soil types were typical Danish sandy soil, a loamy sand soil and a sandy loam. These soil types cover 65 % of the Danish arable area. Simulations covered a winter season from harvest to 1 May the following year. To illustrate the effect of rooting depth of the succeeding crop soil mineral N content is calculated to three soil depths 0-0.25 m for shallow rooted crops, 0-0.75 m for medium rooted crops and 0-2.0 m for deep rooted crops. The sandy soil only had limited ability to retain nitrate in upper soil layers regardless of the precipitation regime. The low precipitation regime average nitrate retention fraction was from 0.4 to 0.8 in soil depth 0-2.0 m depending on soil type. Loamy sand soil and sandy soil showed low retention in upper soil layers (0-0.25 m and 0-75 m) for all precipitation regimes but in deeper soil layers (0-2.0 m) the soils retained an average of 0.31 to 0.83 of the nitrate. With the use of catch crops such as ryegrass and brassica showed that the soil mineral N will accumulate in the top soil in plant litter. In autumn brassica emptied the soil layer 0- 0.75 m better than ryegrass and became of the deep root development also a part of the nitrate accessible below 0.75 m.