Wide variation in optimum amount of N for spring barley

Results from trials carried out by Teagasc has shown that there is a wide variation the optimum amount of fertiliser N required for spring barley yield between sites and seasons.

The findings were outlined to attendees at the recent National Tillage Conference by Richie Hackett of Teagasc.

He outlined that the trials were carried out in response to wide fluctuations in grain proteins in malting barley in recent years and feed barley grower concerns that N allowances are not sufficient to optimise yield.

While the trial found that differences in the economic optimum between sites can to some extent be explained by the differences in soil N supply and yield potential of a site, much of the variation is difficult to explain.

He said: “This suggests that predicting the optimum N to apply to spring barley at the normal N application timing is difficult as it would be difficult to predict yield potential with accuracy and methods used abroad to predict soil N supply at early stages of crop growth are currently unproven in Irish conditions.”

Hackett outlined that results indicate that in relation to the effect of fertiliser N on protein content, total amount applied rather than when it is applied, is the most important factor. However he noted that there is considerable variation between sites and seasons in protein content achieved at a given fertilizer N rate.

He cited that this makes the determination of the N requirement to achieve the protein content necessary for malting for every site every year very difficult. The results of the trial indicate the fertiliser N rates of 150-160kgN/ha gives the highest probability of meeting the specifications for malting barley in sites were N supply is modest.

Results also showed there appears to be little consistent effect of applying the first nitrogen in the seedbed compared to applying it at emergence of the crop on either yield or protein.

Hackett also stated results from the trial suggested there was little effect on yield of splitting the main split of nitrogen (i.e. keeping back some of the main split to apply as a third split). However he did say there was a small effect on protein; delaying a portion of the main split tended to lead to increased protein contents.

Concluding he said examining the reasons for variation in protein content over the past three seasons would indicate that the low protein levels experienced in 2011 were due to reduced soil N supply combined with relatively low fertiliser N recovery.

He added in 2012 the higher proteins were due to higher soil N supply compared to 2011. In 2013 soil N supply was similar to 2012 but fertiliser N recovery was higher and in some areas yields appeared to have been limited by drought which further increased proteins.

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