Influence of Fine Particle Suspension of Urea and Urease Inhibitor on Nitrogen and Water Use Efficiency in Grassland using Nuclear Techniques

摘要

Controlled environment experiments were conducted to assess the effects of urea applied as fine particle suspension (FPA) together with urease inhibitor, (N-(n-butyl) thiophosphoric triamide (nBTPT), trade-name Agrotai~R to ryegrass swards on nitrogenuse efficiency (NUE) and water use efficiency (WUE). Perennial ryegrass was sown 7-10 seeds per plastic pot. After eight weeks of sowing, the ryegrass sward pots (36 pots) were transferred to a growth cabinet which was maintained at 20°C, 70% relativehumidity (RH), 700 mmolrrrV photosynthetic available radiation (PAR) during the 16-h light period, and 15°C, 70% RH during the 8-h dark period. After two weeks in the growth cabinet, ryegrass from each pot was trimmed to 6 cm height to achieve uniformity followed by applying six treatments that include: (1) control (no N), (2) control + leaf spray irrigation (equivalent of 10 mm of rain to wash applied urea) after d-1, (3) urea applied as fine particle suspension (FPA) on d 0, (4) urea applied on d 0 +leaf irrigation one d after of urea application, (5) Agrotain treated urea in FPA form, and (6) Agrotain treated urea + leaf irrigation after d-1. Each treatment had three replicates. To determine herbage 15N uptake, chosen swards of ryegrass were treated with 15N labelled urea (10% atom excess) with or without Agrotain at a rate equivalent to 25 kg-Nha"1. Twenty-eight d after initial treatment application, ryegrass plants were harvested, separated into new (newly grown) and old (tissue grown after uniformity cut before application of treatments) plant tissue, weighed and analysed for 15N content. For intrinsic water use efficiency (WUEj) measurements, 18 additional pots of ryegrass receiving the above six treatments were chosen. Pre- and post-treatment measurements of leaf-level gas exchange and on-line photosynthetic carbon and oxygen isotope discrimination were carried out to calculate WUEi. Urea applied with Agrotain in FPA form significantly increased herbage dry matter yield and WUEi compared to urea alone. The herbage 15N data showed that Agrotain improved NUE. Ryegrass receiving the urea+Agrotain+irrigation treatment took up 49% of N from applied urea, compared to 38% by the urea+irrigation treatment. Irrigating the leaves one d after applying urea + Agrotain further increased ryegrass growth and also resulted in the highest WUEi compared to no leaf irrigation.