NITROGEN AND POTASSIUM BALANCES IN CHRYSANTHEMUM (DENDRANTHEMA-GRANDIFLORUM) HYBRIDS GROWN IN A PLANT PLANE HYDROPONIC CULTIVATION SYSTEM

Chrysanthemum (Dendranthema Grandiflorum) hybrids were grown in a non-recirculating plant plane hydroponic system with fleece mat (polyester 80 g m(-2)) to investigate possible potassium and nitrogen losses from the system. Cuttings were planted either in January (WI) or July (SO). Nutrient solution was applied in two ways: (a) at increasing (0.6 rising to 1.7 mS cm(-1)) (b) at constant (1.5 mS cm(-1)) electrical conductivity. the nutrient balance sheets showed that there was no detectable loss of potassium under any treatment. There was a large difference in cumulative nitrogen deficit between January (59 +/- 8.5 kg ha(-1) N) plantings, equivalent to 22 and 31% of the input. Mode of nutrient supply (a) or (b) did not affect this cumulative N deficit. Nitrogen loss was proportional to cumulative nitrogen supply with a mean rate of 344 g kg(-1) N. It is assumed that gaseous N losses were caused by nitrification and/or denitrification.