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Effects of Nitrogen and Sulfur Fertilization on Commercial-Scale Wheat Quality and Mixing Requirements

¹New Zealand Institute for Crop & Food Research Ltd, Private Bag 4704, Christchurch, New Zealand. ²Present address: 2 Turi Ave, Whenuapai, Auckland, New Zealand. ³Corresponding author. E-mail: wilsona@crop.cri.nz Phone: +64 3 3256 400. Fax: +64 3 3252 074. ⁴Plant Breeding Institute, Woolley Bldg., University of Sydney, NSW 2006, Australia.

The effect on physical dough properties of nitrogen and sulfur fertilizer applied during cultivation was observed in two trials using the bread wheat (Triticum aestivum) cultivar Otane. Wheat flours from both trials were evaluated for physical dough properties under laboratory conditions and also under industrial conditions in the second trial. The laboratory and industrial optimum mechanical dough development (MDD) work input (WI) significantly increased when nitrogen (N) fertilizer was applied without sulfur fertilizer (S) during crop cultivation. With combined N and S fertilization, laboratory and industrial WI remained close to levels for grain grown without fertilizer. Reductions in extensigraph resistance to extension (Rmax) and increases in extensigraph extensibility (Ext) due to S fertilization also were observed. None of the observed changes in WI, Rmax, or Ext due to S fertilization significantly affected end-product quality as measured by loaf volume, crumb grain, and bake score. The nexus between WI and Rmax was weakened by combined N and S fertilization in the first trial, but remained strong in the second trial. Both WI and Rmax increased as N fertilizer and flour nitrogen increased, but at different rates. This observation indicated that by applying N fertilizer to improve dough strength, a disproportionate and disadvantageous increase in WI also resulted, which could be tempered by S fertilization. In this regard, an optimum N:S fertilizer ratio of 3:1 was indicated, although this ratio would be dependent on the balance of available N and S in the soil. Flour N:S ratios <12.5 kept WI to levels desirable in an industrial MDD bakery. Correlations between laboratory WI, mixograph development time (except in the SN1 trial), and farinograph development time were significant. The 125-g MDD mixers appeared to be more responsive when measuring mixing requirements than the mixograph and farinograph to variations in quality due to environmental and agronomic influences and correlated better with industrial performance.