Back Does your maize need more nitrogen?

Date: 13 November 2015

Maize crops produce high yields and consequently, have a high requirement for nitrogen (N). While applying too much N is expensive and can contribute to environmental pollution, applying too little can cost you yield, so how do you know if your crop needs more N, and when and how should you apply it?

Soil test to determine N requirements

If you are growing a crop in a long-term pasture paddock there is a reasonable chance you will not need to apply N whereas crops planted in lower fertility paddocks (including repeat cropping ground) usually need a sidedress application. The best way to determine whether your crop needs more N is to conduct a deep N soil test prior to sidedressing.

Your fertiliser representative can arrange collection of a 60 cm soil sample, testing and interpretation. Deep N results can be run through AmaizeN, a fertiliser forecasting tool developed for maize, to determine how much additional N is required.

Time of application

Maize needs little nitrogen from emergence through to about the fifth leaf development stage. The largest portion of total nitrogen uptake occurs during the eighth leaf to tasselling development stages. Ideally N should be applied around the sixth leaf stage (about gumboot height) which is prior to row cover and when standard sidedressing equipment can still easily pass over the crop.

Application methods

Using sidedress equipment which knives the N fertiliser between the rows is the best way to sidedress because this application can reduce volatilisation of urea and protect the crop from foliar damage.

If sidedressing equipment is not available broadcast applications of nitrogen are the next alternative. Urea granules will have the least impact on leaf burn compared to dry products such as ammonium nitrate or sulphate of ammonia. To minimise adhesion of dry products to the leaves, it is best to apply when the foliage is dry. Urea is subject to volatilisation if rain does not fall within three to four days after application. As much as 30% of broadcast urea can volatilise if there is no rainfall within approximately 10 days after the application.

Late season N deficiency

Yellowing of leaf blades from tip to base in a “V” shape starting from the bottom of the plant and progressing upwards is a sign of N deficiency in maize. Note that under dry growing conditions crops with adequate N can also show nitrogen deficiency symptoms simply because there is not enough moisture to allow N uptake.

If your crop shows signs of N deficiency and it is too late to sidedress the only alternative is aerial application of nitrogen. While the per hectare cost is high, it can still be economically viable under some circumstances. For crop specific advice, talk to your local merchant, contractor or Pioneer representative.