EFFECTS OF MISSING AND 2-PLANT HILLS ON CORN GRAIN-YIELD

Missing plants (''skips'') in corn (Zea mays L.) rows cause yield loss by decreasing plant population. The effect on yield of two plants gro wing in the space normally occupied by one (''doubles'') is not known. A 2-yr study at Monmouth and Urbana, IL, measured the effects of skip s and doubles on grain yields of individual corn plants grown at diffe rent target populations. As plant population increased from 18 000 to 30 000 plants/acre, grain yield per plant of two corn hybrids decrease d from 8.40 to 6.32 oz/plant, while yield increased from 169 to 211 bu /acre. The net effect of doubles was an increase in yield at all popul ations. Yield of each plant in a double was 10 to 17% less than that o f plants spaced uniformly, but together the two plants in the double y ielded 81% more than the controls at the lowest population, and 67% mo re at the highest population. Plants next to doubles yielded from 2% l ess than the controls at the lowest population to 12% less at the high est population. The two plants on either side of a skip compensated fo r only 47% and 19% of the yield lost due to the missing plant at the l owest and highest populations, respectively, so skips always decreased yield. Skips and doubles affected grain yields almost entirely throug h their effects on plant population. While both contribute to plant sp acing variability, their effects on yield are in opposite directions. Yield decreases due to skips can be minimized by increasing plant popu lation.