Effects of fertilisers on vegetable production 1. Yield of spinach and beetroot as affected by rates and forms of nitrogenous fertilisers

Pot and field experiments were conducted to evaluate the effects of nitrogenous (N) fertilisers on the yield of spinach and beetroot. The pot trials involved 2 soils (Wakanui silt loam and Kaiapoi sandy loam), 2 varieties of spinach ( Spinacea oleracea L.) 1 variety of beetroot ( Beta vulgaris L.), and 5 application rates (0, 150, 300, 450, and 600 kg N/ha) of 6 different nitrogenous fertilisers (potassium nitrate, ammonium sulphate, ammonium sulphate + N‐serve, poultry manure, urea, and ammonium sulphate + N‐serve + potassium nitrate). The nitrification inhibitor, N‐serve, was used to retard the microbial conversion of ammonium fertilisers to the nitrate form. In the field experiment, 1 soil (Wakanui silt loam), 1 spinach variety, and 5 application rates each of potassium nitrate and ammonium sulphate + N‐serve were used. Most fertilisers gave maximum yields in pot trials when applied at 300‐450 kg N/ha. The highest maximum yields were obtained with potassium nitrate fertiliser and the lowest with poultry manure. Field results showed that significantly higher spinach yields were obtained with the ammonium form of fertiliser compared with the nitrate form, with the maximum yield occurring after application of 300 kg N/ha.