Growth analysis of maize field crops under phosphorus deficiency. II. Radiation-use efficiency, biomass accumulation and yield components

Biomass accumulation by crops depends on both light interception by leaves and on the efficiency with which the intercepted light is used to produce d ry matter. Our aim was to identify which of these processes were affected f or maize (Zea mays L., cv Volga) field crops grown under phosphorus (P) def iciency. In the preceding paper (Plenet et al., 2000), it was shown that P deficiency severely reduced leaf growth. In this paper, the effect of P def iciency on the radiation-use efficiency (RUE) was investigated. The experim ental work was carried out in 1995, 1996 and 1997 on a long-term P fertilis ation trial located on a sandy soil in the south-west of France. Three P fe rtilisation regimes have been applied since 1972: no- P (P0 treatment) and different rates of P fertiliser (P1.5: 1.5 times the grain P export and P3: 3 times the grain P export). These fertilisation regimes have led to contr asted levels of soil P supply. Only slight differences were observed betwee n the P1.5 and P3 treatment for above-ground biomass accumulation and grain yield. Conversely the grain yield was significantly reduced in P0 (-11%). Above-ground biomass production was severely reduced, with the maximum diff erence between treatment (-60% in P0) occurring between 400 and 600 degrees C days after sowing. The lower biomass production in P0 was accounted for b y the reduced amount of photosynthetically active radiation (PAR) absorbed by the canopy, which was itself the consequence of the reduced leaf area in dex (see Plenet et al., 2000). The calculated RUE were found to depend on t he plant stage, especially during the pre-flowering period, and on the aver age air temperature. No effect of P deficiency was observed on the calculat ed RUE, even during the period when above-ground biomass accumulation was t he most severely reduced. These results obtained in field crop conditions s trengthen the idea that P deficiency affects plant growth, especially leaf growth, earlier and to a greater extent than photosynthesis per unit leaf a rea.