Field Crops Research 120 (2011) 311–319 Contents lists available at ScienceDirect Field Crops Research journal homepage: www.elsevier.com/locate/fcr Ecophysiological determinants of biomass and grain yield of wheat under P deficiency Patricio Sanda ˜ na a,b,∗ , Dante Pinochet b a Graduate School, Faculty of Agricultural Sciences, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile b Institute of Agricultural Engineering and Soil Science, Faculty of Agricultural Sciences, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile article info Article history: Received 16 August 2010 Received in revised form 7 November 2010 Accepted 11 November 2010 Keywords: Wheat P deficiency Spike biomass Grain number Radiation interception Radiation use efficiency Photothermal quotient abstract Grain yield of crops can be expressed as a function of the intercepted radiation, the radiation use effi- ciency and the partitioning of above-ground biomass to grain yield (harvest index). When a wheat crop is grown under P deficiency the grain yield is reduced but it is not clear how these three components are affected. Our aim was (i) to identify which of these components were affected in spring bread wheat under P deficiency at field conditions and (ii) to relate the grain yield responses to processes of grain yield formation during the spike growth period. Three field experiments were conducted in the poten- tially high wheat yielding environment of southern Chile. All experiments had two levels of P availability: with (155 kg P ha -1 ) or without P fertilization (average soil P-Olsen concentration of 10 ppm, a medium level of P availability). High wheat grain yields were obtained varying between 815 and 1222 g m -2 with P applications. Experiments showed a grain yield reduction caused by P deficiencies of 35, 16 and 18% in experiments 1, 2 and 3, respectively. This was related (R 2 = 0.99, P < 0.01) to a reduction in the total above- ground biomass at harvest and not to the harvest index. Reductions in above-ground biomass were due to a reduction in radiation intercepted under P deficiency without effecting radiation use efficiency. Grain number per square meter was the main yield component (R 2 = 0.99, P < 0.01) that explained the grain yield reduction caused by the P deficiency which was due to low spike biomass at anthesis (R 2 = 0.96, P < 0.05). The reduction in spike biomass at anthesis was related (R 2 = 0.86, P < 0.01) to reductions in crop growth rate during the spike growth period as a consequence of a lower radiation intercepted during this period. This study showed that under high wheat yield conditions the main effect of a P deficiency on grain yield reduction was a negative impact on the total above-ground biomass due to the negative impact on intercepted radiation, particularly during the spike growth period, affecting negatively spike biomass at anthesis and consequently grain number and yield. © 2010 Elsevier B.V. All rights reserved. 1. Introduction According to Monteith (1977) crop biomass accumulation is related to the amount of photosynthetically active radiation inter- cepted by the crop. Several studies have shown the strong linear relationship between biomass accumulation and the cumulative solar radiation intercepted by different crops. The slope of this rela- tionship represents the radiation use efficiency, defined as crop biomass produced per unit of total solar radiation or photosynthet- ically active radiation (PAR) intercepted by the canopy (Sinclair and Muchow, 1999). In this context, grain yield (g m -2 ) of crops (Eq (1)), can be expressed in its simplest form as a product of the cumulative ∗ Corresponding author at: Graduate School, Faculty of Agricultural Sciences, Uni- versidad Austral de Chile, Campus Isla Teja, Valdivia, Chile. Tel.: +56 63 221430. E-mail addresses: patricio.sandana@postgrado.uach.cl, patriciosandana@hotmail.com (P. Sanda ˜ na). solar radiation intercepted (RI, MJ m -2 ) during the crop cycle, radi- ation use efficiency (RUE, g MJ -1 ), and the partitioning of biomass to yield, or harvest index (HI, g g -1 ): Grain yield = RI × RUE × HI (1) The RI depends on the fraction of radiation intercepted by the canopy (FRI) each day during the crop cycle and the total incident solar radiation. The FRI depends on the leaf area index (LAI) and the light extinction coefficient (k)(Massignam et al., 2009). Several studies have shown that RI is negatively affected by N deficiency (Hall et al., 1995; Salvagiotti and Miralles, 2008; Massignam et al., 2009), sulfur deficiency (Salvagiotti and Miralles, 2008) and alu- minum toxicity (Sierra et al., 2003; Valle et al., 2009a) during crop cycle due to reductions in LAI associated with those restrictions. Today there is much less information, particularly in wheat, about the effects of P deficiency on RI and its impact on above-ground biomass and grain yield. In the same way that was described for other nutrients, P deficiency in maize and sunflower decreased 0378-4290/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2010.11.005