Plant Density and Equidistant Spacing Effects on Tuber Yield and Size in Red Norland Potatoes.

Standard potato planting practices has traditionally been 91 cm row spacing and 20 cm in-row spacing. This traditional plant spacing practice can be improved by using an equidistant planting which will provide better utilization of soil and sunlight resulting in higher yields, more tubers, and smaller tuber size (more desirable for red potatoes). The equidistant planting pattern could reduce the amount of needed weed control because of earlier canopy closure. This experiment was conducted to determine how plant spacing and planting pattern influences the yield, amount, and size of tubers produced. Experimental design was a randomized complete block design with three replications, and each plot was 3.5 x 3.5 m. The equidistant treatment plant spacings were 18 x 23 cm, 25 x 30.5 cm, 33 x 38 cm, and 38 x 45 cm. The control treatment was the traditional 91 cm row spacing and 20 cm in-row spacing. The potatoes were hand planted and the plots were sprayed with pre-emergent herbicides. Yield was higher  with closer plant spacing , and data collected in 2008 and 2009 showed that yields for the control treatment were 26 and 65 Mg ha^-1, respectively, and 51 and 75 Mg ha^-1 for the 18 x 23 cm equidistant spacing. The number of tubers was also higher at the closer plant spacing with 4 x 10⁵ tubers in 2008 and 2009 for the control and 8.8 x 10⁵ in 2008 and 12 x 10⁵ in 2009 for the 18 x 23 cm equidistant spacing. A comparison of tuber size among the different equidistant spacings and control showed only the 18 x 23 cm spacing had a different mean tuber size that was small. In previous years, weeds occurred less in plots with closer spacing (this was not observed in 2011, because of excellent chemical control of weeds). As for the experiment conducted in 2010, the weather was cooler than normal however the results were similar to trends found in 2008 and 2009. Based on our results, higher yields, tuber count and smaller tuber sizes are expected as plant spacing decreases.