COS 136-5 - CANCELLED - Can the Law of Constant Final Yield be used to delineate plant productivity limited by competition for water?

Abstract: The plant dynamics of biomass production under competing resources are commonly understood through the empirical generalization of Constant Final Yield (CFY). This law has considerable utility for crop management decisions that often center on altering resources and planting density to maximize plant productivity. Most studies on yield-density relationships have focused on well-watered conditions for maize (Zea mays). We investigated the hypothesis that the yield-density relationship in dryland maize will approximate CFY, with the point of plateau determined by water availability. We tested this concept by planting maize at a range of stand densities (20, 30, 40, 50 thousand plants/ha) under four water regimes in a semi-arid region in Colorado, USA. Plant productivity increased under greater water availability, as planting density increased. A quadratic plateau model best fit the yield-density relationship. Treatments with less water availability did not exhibit yield-limiting thresholds at the densities included. Plant functioning in terms of chlorophyll fluorescence, grain N uptake and proportional allocation to grain (i.e. harvest index) remained relatively unaffected by resource availability to the plants. Results of our study indicate dryland maize systems can reach a maximum yield while forgoing decreases in reproductive biomass allocation and physiological costs. In conclusion, the pattern of CFY was approximated, with water availability corresponding to a higher asymptotic point at a greater population density.