Effect of Nitrogen Source and Inhibitors on Spring Barley Grain Yield.

The dominant nitrogen (N) fertilizer used in Ireland is calcium ammonium nitrate (CAN). This contributes to nitrous oxide losses which represents an economic loss to the farmer. An alternative N fertilizer source is urea, which is cheaper per unit N, but contributes to ammonia losses which also represents an economic loss.  The use of inhibitor technologies with urea can reduce these N losses and maintain the N in the soil. This has potential cost saving benefits for the farmer.

The objectives of this study were to assess the effect of nitrogen source (CAN vs. urea) on spring barley grain yield and quality and also to assess the efficiency of the urease inhibitor n-BTPT and/or the nitrification inhibitor dicyandiamide (DCD) when added to urea fertilizer on spring barley production systems. This study was conducted at two contrasting sites (a long-term arable free-draining loam site and a short-term arable moderately draining sandy loam site) both located in the south east of Ireland over three growing seasons. Fertilizer N was applied at a rate of 150 kg N ha^-1, 30 kg N ha^-1 was applied at sowing and 120 kg N ha^-1 was applied during mid-tillering.

Results show that the short-term arable site produced a higher yield than the long-term arable site. CAN and urea with/without inhibitors produced comparable grain yield. There is potential for urea to be used in Ireland as it is cheaper per unit of N than CAN but is known to contribute to ammonia losses. The use of the urease inhibitor n-BTPT can protect against this loss and give farmers assurance of maintaining yields.