RESIDUAL EFFECT AND LEACHING OF N AND K IN CROPPING SYSTEMS WITH LEGUME AND NON-LEGUME CATCH CROPS ON A COARSE SAND

Kurzfassung

The objective of this investigation was to explore the possibility to use clover catch crops instead of ryegrass in organic crop production on coarse sand. Two field experiments were performed, which included different animal manure regimes and different soil K- and N-levels. The residual effect of the clover catch crop on the yields of a succeeding spring barley test crop was significantly higher than for the ryegrass. When animal manure (70 kg total-N ha-1) was added to the succeeding spring barley in the ryegrass system the difference between the clover and ryegrass catch crops disappeared. Thus clover appeared to have the potential for substituting animal manure. Leaching of nitrate-N and K were estimated by means of porous ceramic suction cups installed at 0.8 m depth. The annual N leaching from a spring barley reference treatment without catch crops were approximately 100 kg ha-1. Clover and ryegrass catch crops reduced the losses significantly by 40 to about 80% depending on the year, and there were no significant differences between the two catch crop types. However, there was a tendency to higher N-leaching losses after clover. Both the clover and ryegrass catch crops reduced the annual flow-weighted nitrate concentrations from 13-16 mg L-1 to 5-8 mg L-1, which is below the WHO maximum for drinking water. The catch crops did not affect the K leaching significantly, because a relatively larger amount of K than N was leached during the winter period, where the activity of the catch crops is low. The clover catch crops seemed to be suitable in low-N cropping systems on coarse sand with respect to both production and environment. However, the clover catch crop should not be established continously in the same field.