Stewart Duncan1, Scott Staggenborg2, William Schapaugh2, Larry Maddux2, Barney Gordon2, and Kraig L. Roozeboom3. (1) Kansas State Univ., Throckmorton Hall, Manhattan, KS 66506, (2) KSU, Throckmorton Hall, Manhattan, KS 66506, (3) Kansas State University, 2014 Throckmorton Hall, Manhattan, KS 66506
Summer crop stand evaluation tools for making replant or crop destruction decisions are limited and most often based on uniform, within-row plant spacing. Cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.] studies were established in 2005, and corn (Zea mays L.) was added in 2006, to compare crop responses to desired vs. reduced plant populations with uniform vs. variable within-row spacing across Kansas. All crops were planted in irrigated and rain fed environments. Plots with uniform and variable within-row plant spacing were established by hand thinning and with herbicides. Final stands of cotton (58%) and soybean (80%) were lower than anticipated, but desired differences between populations were achieved. Cotton lint yields were reduced 45% and 13% when final stands were ¼ and ½, respectively, of recommended populations, but no lint yield reductions were measured at ¾ stands. Soybean yields were reduced 18% at ¼ stands, 5% at ½ stands and 2 % at ¾ stands. Soybean at ¼ desired populations with variable within-row spacing experienced 26% yield losses vs. the same population with uniform within-row plant spacing. No soybean yield differences were noted between any other treatments when similar populations of uniform vs. variable within-row spacing were compared. Stand losses in the field may be more likely to be variable than uniform within the row. Initial results of cotton lint yields from fields with stand reductions of 50% or less indicate that replanting would not be necessary. Preliminary yield results suggest that replanting soybean stands with 50% reductions in healthy plant populations is not necessary, and that a uniform stand with only 25% of the targeted population should not be destroyed.