Yield, nitrate accumulation, cation-anion balance and oxalate production of spinach and beetroot as affected by rates and forms of applied nitrogen fertilizers

Abstract

Both pot and field experiments were conducted to study the effects of nitrogen (N) fertilizers on the yield and quality of spinach and beetroot – particularly with respect to the accumulation of nitrate and oxalate in these vegetables in view of their potential hazard to the health of consumers. Nitrogen fertilizers used included those containing ammonium (NH₄⁺), and chloride (Cl), and also in the presence of nitrification inhibitor (N-serve). Nitrate contents in plants are affected by both rates and forms of N fertilizers. The plants were found to accumulate NO₃⁻ to a potentially health hazardous level, only at the highest rate (600 kg N/ha) of KNO₃, (NH₄)₂SO₄ and urea applied. These were most probably brought about by large amounts of NO₃⁻ being supplied directly to the plants by KNO₃ treatment and indirectly through nitrification of NH₄⁺ in (NH₄)₂SO₄ and urea treatments.