Nitrogen losses by ammonia volatilization in ryegrass pasture under different urea application rates
Keywords:
forage, Lolium multiflorum, soil fertilityAbstract
Urea is widely used as a nitrogen source in pastures; however, its surface application can lead to considerable nitrogen losses through ammonia volatilization. In this context, the present study aimed to quantify nitrogen losses via volatilization following the application of different nitrogen rates during the tillering stage of ryegrass. The experiment was conducted on a Humic Cambisol at the Epagri Experimental Station in Lages, SC, during the winter of 2023. A randomized block design was adopted, with four replicates and three treatments: no nitrogen application (SN), application of 200 kg ha⁻¹ of N (N200), and application of 50 kg ha⁻¹ of N (N50), both during the tillering stage. Pasture management was carried out under an intermittent stocking system, with grazing starting at 20 cm and ending at 12 cm in height. Ammonia volatilization was monitored for 15 days after each urea application using semi-open collectors and colorimetric analysis. The results indicated that the N200 and N50 treatments showed similar NH₃-N losses, both higher than the treatment without fertilization. However, losses did not exceed 1% of the total nitrogen applied, demonstrating the efficiency of the adopted management strategy. This efficiency was likely favored by climatic conditions during the period, such as soil moisture and mild temperatures, which contributed to reduced volatilization.
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