Plot Technique Studies on Sweetpotato Yield Trials

The objective of this research was to determine optimum plot size and number of replications to evaluate yield of sweetpotato (Ipomoea batatas Lam.) clones. The optimum plot size was estimated using the methods of maximum curvature and comparison of variances. The adequate number of replications was determined using the Hatheway method. Using the maximum curvature method, the estimated optimum plot size was 10 basic units (b.u. = six plants or 1.2 m) for La Molina and San Ramon, and 5 b.u. for Tacna, Peru. Using the comparison of variances method, the optimum plot size was 15 b.u. for all locations tested. The adequate number of replications with a plot size of 15 b.u. was four. Sweetpotato has many desirable characteristics such as high yield, wide adaptability, multifunctional usage, and a wide range of nutritional components, yet requires low production inputs. These attributes make sweetpotato an attractive crop for tropical regions. However, field experiments carried out with sweetpotatoes often have large coefficients of variation (cv). This may be due in part to inherent crop variation or to inadequate field plot techniques. Sweetpotato researchers use field trials to determine the potential of cultivars and experimental lines. In a breeding program, this procedure is a routine in which the main objective is to identify promising genotypes to be evaluated in additional trials as clonal accessions. To increase efficiency, optimum plot size and an adequate number of replications must be used. Federer (1967) defined the experimental unit as the total amount of material to which a treatment in a particular replication is applied. The optimum plot size depends on the nature of the experimental material, experiment design, number of entries, number of replications, and available resources. The variability of the experimental material constitutes a main component of the experimental error that must be minimized using adequate experimental techniques. In general, experimental error is reduced by increasing plot size (Immer and Raleigh, 1933; McClelland, 1926; McKenzie et al., 1964). Conversely, others found that the experimental error was reduced significantly when the number of replications rather than plot size was increased (Rampton and Petersen, 1962; Thomas and Abou-El Fittouh, 1968). Li (1971) in Taiwan found that the optimum plot size for the winter sermon sweetpotato crop was 6 to 12 m long and three rows wide (18 to 36 m) in Changlma, and 8 to 12 m long and three rows wide (24 to 36 m) in Hsinchu. In the fall crop, the optimum plot size was 6 to 12 m long and two rows wide (12 to 24 m) in Yunlin, and 6 to 12 m long and two to three rows wide (12 to 36 m) in Tainan. Boudreaux and Jones (1978) used 12% as an arbitrary level of acceptability for the cv, and found that a one-row plot of 15 to 20 hills 30.5 cm apart in length (4.6 to 9 m) and with nine for publication 18 May 1990. Accepted for publication 28 Aug. 1991. efully acknowledge the technical assistance of Jorge A. Espinoza in ng this research. This project was entirely supported by the International enter. The cost of publishing this paper was defrayed in part by the of page charges. Under postal regulations, this paper therefore must y marked advertisement solely to indicate this fact.