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

Abstract

Abstract The effects of two organic (blood and bone, compost) and two inorganic (potassium nitrate, KNO3; ammonium sulphate, (NH4)2 SO4) 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, (NH4)2 SO4, and KNO3, 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.