Abstract
Nitrogen losses from irrigated wheat (cv. Matong) grown on a heavy clay in the Goulburn-Murray Irrigation Region following foliar applications of urea at heading were investigated. Ammonia (NH3) volatilization was determined by a micrometeorological method and total nitrogen (N) loss was determined by a15N balance technique. The effects of the foliar application on grain N concentration and grain yield were determined also.
Little nitrogen was lost by NH3 volatilization following the foliar application. The rate of NH3 loss increased briefly from <11 g N ha−1 hr−1 to >19 g N ha−1 hr−1 following rainfalls of 3 and 2 mm which washed 34% of the applied N from the plant onto the soil and increased the pH of the surface soil. The pH effect was short lived and total NH3 loss amounted to only 2.13 kg N ha−1 or 4.3% of the applied N.
The15N balance study also showed that little N was lost from the plant-soil system until rain had washed the fertilizer from the plant onto the soil. In the period 152 to 206 DAS, the soil component of the applied N decreased from 34% to 9%. This fraction then increased slightly to 12% of the applied N at harvest. At that time, 69% of the applied N was recovered in the plants indicating that 19% of the applied N had been lost from the plant-soil system. As there was no evidence for leaching of N, the difference between total N loss as measured by15N balance (19%) and NH3 loss (4%) is considered to be loss by denitrification (15%).
The fertilizer N assimilated by the plant was efficiently remobilised from the leaves and stems to the head; 78% of the fertilizer N assimilated by the plant tops had been translocated to the head by the time of harvest. Grain N concentration responded to the foliar N application. The fitted response function had significant linear (P = 0.004) and quadratic (P = 0.10) trends to N rate, whereas there was no significant effect on grain yield.
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Smith, C.J., Freney, J.R., Sherlock, R.R. et al. The fate of urea nitrogen applied in a foliar spray to wheat at heading. Fertilizer Research 28, 129–138 (1991). https://doi.org/10.1007/BF01049743
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DOI: https://doi.org/10.1007/BF01049743