BYG, barnyard grass; RCC, relative crowding coefficient; RY, relative yield, RYT, relative yield total.
Relative yield (RY) and relative yield totals (RYT) for leaf area, aboveground dry weights and root dry weights were calculated according to the following equations .
Relative yield totals equal to 1 indicate that species A and B are making demands on the same limiting resources.
jik] = productivity or nitrogen yield of functional group i in mixture with functional group j in block k (k = 1-6), and the same for functional group j in mixture with i; [Y.sub.ik], [Y.sub.jk] = productivity or nitrogen yield of functional groups i and j in single functional group plots in block k; dividing by n accounts for differences in planting density; where n = number of functional groups in mixture; RY[T.sub.ijk] = Relative Yield Total of mixture with functional groups i and j in block k; RY[T.sub.ij] = average Relative Yield Total (across blocks) of mixture with groups i and j.
As with total biomass Relative Yield Total, this lack of difference appears to result from the shift to lower root:shoot ratio in the mixed plot than expected based on the component groups planted alone.
I planted each group alone as well as in more diverse combinations, which allowed evaluation of complementarity in two different ways: first, by testing for an absolute increase in productivity with increasing diversity, and second, by measuring Relative Yield Totals (Trenbath 1974, Harper 1977, Vandermeer 1990, Swift and Anderson 1993).
I used Relative Yield Totals (RYT) to assess the degree of complementary resource use of the functional groups grown in mixture treatments (de Wit and van den Bergh 1965, Harper 1977).
For Relative Yield Totals, I used a one-way ANOVA (treatment is PLOT = EL, EP, LP, ELP, or ELPN, plus a block variable) for testing for significance of D and RYT.
Relative Yield Totals (RYT) offer an alternative to assessing the degree to which species are complementary in their resource use (Trenbath 1974, Harper 1977), i.e., to what extent interspecific competition is less than intraspecific competition (Naeem et al.
For these spring cereal mixtures, the relative yield totals of nine mixtures were not significantly different than 1.0, indicating that yields were as expected based on the yields of the monocrops, while three mixtures had relative yield totals significantly higher than expected (Table 5).
Of the nine location-years where relative yield totals could be calculated for these winter mixtures, none were significantly different than one (Table 7).
Generally, the mixtures were as productive as the monocrops with relative yield totals not significantly different than unity.