Crop growth rate during the critical period is associated with grain number under sulfur deficiency in barley crops subjected to different levels of nitrogen availability

Context. Sulfur deficiency is a limiting factor of cereal crops, causing significant crop losses associated with a decrease in the number of grains. In barley (Hordeum vulgare L.) crops, grain number (and grain yield) is associated with spike biomass at anthesis, which is related to crop growth rate during the period preceding anthesis (i.e. the 'critical period') when spike growth occurs. These relationships have been established for various cultivars under varying radiation intensity and in different locations, and have been confirmed in crops grown under nitrogen and phosphorus deficiencies. Aims, The objective of this study was to determine, for malting barley, whether the effects of sulfur, nitrogen and their interaction on the number of grains per unit area could be explained by changes in crop growth rate or photothermal quotient (ratio of intercepted photosynthetically active radiation to temperature) during the critical period. Methods. Three field experiments were conducted in the Pampean region of Argentina to evaluate the effects of sulfur fertilisation under three levels of nitrogen availability on the number of grains per unit area. Key results. Changes in grain number were associated with crop growth rate or photothermal quotient during the critical period. This association was maintained when sulfur fertilisation changed grain number. Crop growth rate during the critical period varied mainly as a result of changes in accumulated intercepted radiation. Conclusions. Sulfur fertilisation increases grain number and grain yield by increasing radiation interception during the critical period, probably as a consequence of increased leaf area. Implications. The determination of grain number under sulfur deficiency is similar to that observed under deficiencies of other nutrients.