Effects of forms and rates of organic and inorganic nitrogen fertilisers on the yield and some quality indices of tomatoes ( Lycopersicon esculentum Miller)

The effects of two organic (blood and bone, compost) and two inorganic (potassium nitrate, KNO 3 ; ammonium sulphate, (NH 4 ) 2 SO 4 ) forms of nitrogen (N) fertilisers on the yield and some quality indices of tomatoes were studied in a pot experiment using Waimairi peaty loam soil obtained from an area currently used for vegetable production. Four rates (0,150, 300, 600 kg N/ha, based on soil bulk density) of each fertiliser form were used. Fruit yield was significantly correlated with foliage N concentration, but not with fruit N concentration. Increasing rates of all N fertilisers, except compost, produced significant increases in fruit yield. Compared with the control, at 600 kg N/ha applied, compost increased fruit yield by 40% only whereas the other N fertilisers studied increased fruit yield by 120%. Fruit quality indices measured showed variable response to treatments. Fruit colour increased significantly on application of blood and bone, (NH 4 ) 2 SO 4 , and KNO 3 , whereas compost showed no effect. Fruit vitamin C concentrations decreased when all N fertilisers were applied. Increasing N rate produced significant negative linear trends with vitamin C concentration decreasing by 18–28% depending on the form applied. Fruit size was unaffected by treatments but visual quality of fruit decreased when N in any form was applied.