N-balances in an Organic, Stockless Crop Rotation S13
Schmidt, H.1 ; Fragstein, P. von1 ; Kölsch, E.1 & Vogtmann, H.2
1) University of Kassel, Department of Ecological Agriculture, D-37213 Witzenhausen;
2) Hessian Government Office for Regional Development and Agriculture.
|Since 1992 a stockless crop rotation is running
as a field experiment at the Research Farm of the University of Kassel. The basis of the
N-nutrition is an annual green fallow of clover-grass. The following main crops are
potatoes, winter wheat and spring barley. Catch crops are grown after tillage of the green
fallow in August and after wheat. All crops are grown each year. Beside the unamended
control three treatments with a low level of N-fertilization are included: biological
waste compost, sugar beet vinasse and a combination of both. All fertilizers are only
applied to the cereals. Crop residues are not removed. Results of the first four years are
The estimated amounts of N-input by fixation of clover ranged from nearly 300 kg/ha in 1992 to only 13 kg/ha in 1994. The differences were mainly caused by high clover losses over winter in some years. The potato yield in 1993 was 340 dt/ha (35-65 mm tubers) after a well developed clover-grass as precrop. The following wheat reached a grain yield of 42 dt/ha. The spring barley in 1995 produced only 20 dt/ha.
The combination of plant N-uptake and nitrate dynamics in soil shows that the N-nutrition of the potatoes was high and of the winter wheat sufficient. One reason for the low yield of barley seems to be a low N-mineralisation rate.
The estimated nitrate leaching below 90 cm reached a maximum of 40 kg N/ha under wheat after potatoes. In each other leaching period of the crop rotation lower values up to 15 kg N/ha were estimated.
The N-input of a well developed green fallow meets the calculated requirements of this crop rotation. The additional fertilization caused a higher N-uptake and higher yields of the cereals in most cases.