BALANCE SHEETS FOR WATER, POTASSIUM, AND NITROGEN FOR TOMATOES CROWN IN 2 CLOSED CIRCULATED HYDROPONIC SYSTEMS

Tomato (Lycopersicon lycopersicum cv. Suso) was grown in the greenhous e from April to October 1993 in two closed recirculated hydroponic sys tems, Nutrient Film Technique (NFT) and Plant Plane Hydroponics (PPH) to investigate inputs and losses of water, potassium, and nitrogen. An average of 33 m(3) water per hectare and day were applied in the two hydroponic systems. This amount includes 26% of the water that drained and was recycled. The transpiration coefficient was 360 l kg(-1) dry matter. NFT showed a lower water use efficiency than PPH. Potassium an d nitrogen balance sheets were similar between the growing systems. Po tassium and nitrogen uptake of the tomato were 459 kg ha(-1) and 303 k g ha(-1), respectively. Input of nutrients almost balanced output, i.e . nutrient losses were negligible.