Growth analysis of biomass production in sole-crop and double-crop corn systems
Increased biomass productivity could be achieved through double-cropping if extended growth duration could be realized with minimal reductions in growth efficiency relative to sole-cropping. To test this hypothesis, functional growth analysis was used to assess the relative importance of photosynthetic duration and efficiency in determining biomass production by sole-crop corn (Zea mays L.; SC) and double-crop triticale (xTriticosecale Wittmack)–double-crop corn (DT–DC). Aboveground dry matter and leaf area were measured weekly, and net dry matter production was assessed for each crop at harvest. Over 2 yr, average harvested dry matter was 25% greater for DT–DC (22.7 Mg ha–1) than for SC (18.2 Mg ha–1), despite greater maximum leaf area index and greater maximum crop growth rate for SC relative to DT–DC. Leaf area duration was increased by 23% for DT–DC compared with SC, while maximum net assimilation rate and seasonal net assimilation rate did not differ between cropping systems. Across systems, variation in yield was positively related to maximum crop growth rate, maximum leaf area index, and leaf area duration but was not associated with maximum or seasonal net-assimilation rate. Therefore, leaf duration was more important than leaf efficiency in determining productivity in both cropping systems, and greater biomass yield for DT–DC was the outcome of photosynthesis occurring over an extended duration. These results suggest that potential exists to increase biomass productivity by expanding the seasonal interval of photosynthesis, and that in the case of double-cropping, expansion of leaf duration is not necessarily associated with reductions in leaf efficiency.