EFFECT OF THE STABILIZED NITROGEN FERTILIZER ENTEC 26 ON THE YIELD OF ASPARAGUS (ASPARAGUS OFFICINALIS L.)

The cultivation of white asparagus is mostly carried out on sandy soils, where especially the nitrogen (N) supply during plant development might create problems. Because of the high leaching risk growers tend to apply N at excessive rates, which causes an environmental problem. The presence of asparagus ferns in the field lasts only about three months. A nutrient deficiency in this period primarily leads in the following years to the production of thin spears with a diameter of < 10 mm which are hardly marketable. Therefore a field trial with four replications, transplanted in 2000, investigated how the application of the stabilized N-fertilizer ENTEC 26 affects asparagus yield when compared to ammonium sulfate nitrate (ASN). In ENTEC 26, the transformation of ammonium to nitrate is retarded by the inhibitor dimethyl pyrazol phosphate (DMPP), as the nitrification by Nitrosomas bacteria is deactivated. Monthly soil analyses during the assimilation phase of the asparagus showed clear differences in the supply of soluble nitrogen, as well as in plant growth. The number of shoots was counted each autumn. In the plots fertilized with ENTEC 26, both the total number of shoots and the number of spears with a diameter > 10 mm at the soil surface were increased. In 2001 no significant yield differences were found, with a positive trend for ENTEC 26 in the following years. In comparison to ASS the application of ENTEC 26 lead to significant yield increases in 2004.