Lysimeter Investigations on the Effect of Winter Catch Crops and Weeded Fallow on the N-Dynamics in a Sandy Treposol Soil of Northeast Germany

Abstract

Lysimeter experiments (soil: sandy treposol, from the region “Havelländisches Luch”, Brandenburg, Germany) with application of ¹⁵N labelled fertilizer (80 kg N per ha as ¹⁵NH₄ ¹⁵NO₃, 10 at.-%¹⁵N exc.; for simulating mineralization in the early autumn period) were carried out to determine to what extent the amount of mineral- N was temporary conserved by winter catch crops, taken up subsequently in the vegetation periods by following crops, taken by subsequently in the vegetation periods by following crops, or percolated in the leaching water, respectively. The results were as follows:

1) Until winter or spring respectively, the catch crop uptake rates of applied mineral-N were 32% for phacelia (Phacelia tanacetifolia BENTH.), 25% for winter rape (Brassica napus L. cv. ‘AKELA’), and 16% for white mustard (Sinapis alba L.).

2) In the year after, following maize incorporated from 2.1 to 4.5% of the fertilizerborne N. The following plant community of fallow took up from 0.2 to 0.5% N originating from the fertilizer-N.

3) In comparison with the catch crops, N-leaching losses under fallow conditions were highest and equivalent to 17% of the applied fertilizer-N amount. In contrast to 3% of white mustard, phacelia and winter rape reduced N-leaching losses to 0.2 and 0.3% of the applied fertilizer-N amount.

4) In spring of the first year after the beginning of investigations, N-leaching losses were highest under fallow conditions and white mustard cultivation. Thus, the amounts of nitrate losses would exceed the EU limit for drinking water.

5) Three years after the investigations had been started, 10% (white mustard) and 20% (fallow) of the applied fertilizer-N was still found in th lysimeter soil.