Applying urea with urease inhibitor (N-(n-butyl) thiophosphoric triamide) in fine particle application improves nitrogen uptake in ryegrass (Lolium perenne L.)

Abstract

Two glasshouse-based studies investigated the impact of urea with urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT – “Agrotain”) applied in fine particle application (FPA) or in granular forms, on nitrogen (N) uptake in ryegrass (Lolium perenne L.). Ryegrass was grown from seed in topsoil collected from a pasture site near Lincoln, New Zealand. Fertilizer treatments were applied, either in FPA or in granular form, at a rate equivalent to 25 kg N ha−1. Herbage was harvested 42 days after fertilizer application to assess dry matter (DM) production and N uptake. In a separate pot experiment, 15N labelled urea (10 atom %), with or without Agrotain, was applied to ryegrass at 25 kg N ha−1 either to the shoots and leaves only or to the soil surface. After 4 hours, 8 hours, 1, 2, 3, 5, 10 and 21 days, pots were destructively sampled to determine urea hydrolysis, herbage DM and 15N uptake. In both experiments, herbage DM yield and N uptake were significantly higher in the FPA treatments than in those receiving granular application. Urea applied with Agrotain in FPA form increased the N-response efficiency (N-RE) by ∼31% and ∼96%, respectively, compared with FPA urea or granular urea. N-response efficiency following addition of Agrotain-treated urea in FPA form was even higher than that following addition of other forms of ammonium () and nitrate () based fertilizers. Nitrate reductase activity was significantly affected by the added fertilizer treatments and generally decreased with time. Tissue amino acids and and contents were not significantly influenced by any fertilizer treatment. Results from the 15N experiment support the hypothesis that Agrotain treatment improved the N-RE of urea applied in FPA form due to a delayed hydrolysis of urea on the leaves and in the soil, thus providing herbage an opportunity to absorb the added urea directly through leaves, cuticles and roots. We conclude that applying urea with Agrotain by FPA method has the potential to increase N-RE further than either granular urea or FPA urea alone.