IMPACT of Nitrogen RATES and SOURCES On POTATO PRODUCTION.

Potato crops require high applications of fertilizer nitrogen (N) to achieve optimal yields and quality. The recovery of that N, however, may average less than 50% in eastern Canada. Furthermore, effective management of N fertilizer is important from both economic and environmental standpoints. The efficiency of synthetic N fertilization can be improved by selecting the fertilizer type and the application rate that best matches the soil N supply and crop demand. An experiment conducted for two years (2008 and 2009) on sandy soils evaluated the effects of mineral N fertilizer types and application rates on tuber yields and the specific gravity of potato (cv. Russet Burbank). Treatments consisted of four N rates (60, 120, 200, and 280 kg N ha^-1) for each of three sources of N [ammonium nitrate (AN), ammonium sulphate (AS) and a controlled-release N (CRN)] plus an unfertilized control. Statistical analysis indicated no significant interaction between N rates and N sources. Nitrogen fertilizer rates had a significant effect on both total and marketable yields. After two years of experimentation, total and marketable tuber yields increased with increasing N rate until a maximum and then decreased with additional N. The highest total yield was reached with the N rate of 200 kg N ha^-1 but the average yield difference of 3.3 t ha^-1 between the N rate of 120 kg N ha^-1 and 200 kg N ha^-1 was not statistically significant. For the marketable yield, the highest yield was reached with the N rate of 200 kg N ha^-1. Tuber specific gravity was only affected by the year. The study will be conducted for the next three growing seasons to determine the effectiveness of the type of used mineral N fertilizer specifically the controlled-release N.