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Crop Species Diversity Affects Productivity and Weed Suppression in Perennial Polycultures under Two Management Strategies

^a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
^b Dep. of Statistics, Iowa State Univ., Ames, IA 50011
^c Dep. of Ecology, Evolution, and Organismal Biology, Iowa State Univ., Ames, IA 50011
^d Dep. of Crop and Soil Sciences, Center for Applied Genetic Technologies, Univ. of Georgia, Athens, GA 30602. This journal paper of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA, Project No. 6631, was supported by the Hatch Act and State of Iowa funds

View larger version (14K): [in this window] [in a new window]   Figure 1. Mean biomass of seeded species, cultivated species biomass (seeded species plus cultivated weeds), and total biomass (cultivated species plus wild weeds) by seeded species richness and log-linear regression lines as a function of seeded species richness in two Iowa locations under two harvest managements averaged over 2 yr: (A) Boone–one harvest; (B) Boone–three harvests; (C) Ames–one harvest; and (D) Ames–three harvests. All linear regressions are significant at P < 0.0001.

View larger version (14K): [in this window] [in a new window]   Figure 2. Biomass of seeded species means by entries and log-linear trends for plots including the driver species (closed symbols) and not including the driver species (open symbols) as a function of seeded species richness in each environment: (A) Boone–one harvest; (B) Boone–three harvests; (C) Ames–one harvest; and (D) Ames–three harvests. P values for the contrasts of the log-linear trends on the means are shown. Equations for regressions with slopes different from zero (P < 0.10) are shown.

View larger version (15K): [in this window] [in a new window]   Figure 3. Total weed biomass means by entries and exponential trends for plots including the most weed suppressive species (closed symbols) and excluding such species (open symbols) as a function of seeded species richness in two Iowa locations under two harvest managements averaged over 2 yr: (A) Boone–one harvest; (B) Boone–three harvests; (C) Ames–one harvest; and (D) Ames–three harvests. P values for the linear contrasts on log-transformed weed biomass are shown. Equations for significant regressions (P < 0.05) are shown. The two slopes in each graph for environments B, C, and D, are not different at P = 0.05.