An assessment of granular urea/ammonium sulphate and urea/potassium nitrate fertilizers on nitrogen recovery by ryegrass
Fertilizer Research 18(1): 19-29
The comparative effects of ammonium sulphate (AS), potassium nitrate (KNO3), urea (U) or combined 1:1 (w/w) U/KNO3, U/AS granular products were investigated on dry matter (DM) yield and 15N utilisation by perennial ryegrass grown under controlled environmental conditions. The DM yield and apparent N recovery with the single N sources was in the order KNO3 > AS > U. The 15N budget in shoots, roots and soil indicated that only 55% of the urea N was recovered at the end of the experiment compared with 87% and 86% for AS and KNO3 respectively. The DM yield and apparent N recovery from the combined U/AS source was significantly higher than would be expected (P < 0.01) based on the proportions of each N source in the mixture. Differentially labelling the U and AS with 15N indicated that AS enhanced the shoot % utilisation of urea by 38% (P < 0.001) whereas urea reduced the shoot % utilisation of AS by 14% (P < 0.01). These results indicate that an interaction occurred between U and AS when combined in a 1:1 (w/w) ratio in the same pellet.