In-row plant spacing and row configuration effects on 'Beauregard' (Ipomoea batatas (L.) Lam.) sweetpotato yield grades

As acreage of sweetpotatoes continues to rise, land suitable land for production is becoming a rarity in the traditional sweetpotato growing region of Mississippi. As production moves to less desirable soils, production and quality diminishes. A two-year study was designed to evaluate increasing plant populations/ha-1 as a means of reducing land requirements for current production levels. Populations were increased using narrow-row beds and multiple-drill wide beds. The experimental design used was a 3 x 4 factorial arrangement of treatments in a randomized complete block design containing four replications. Main treatments were: row spacing (RS)---76, 102, 152 and 203-cm; plant spacing (PS)---23, 30 and 38-cm. Soil type was a Faulkner silt loam (Fine-silty, siliceous, thermic Aquic Paleudalfs). Year*RS and Year*PS interactions were found. These were probably due to below-average rainfall events in 2000 limiting root enlargement. In 2000, the industry standard RS of 102-cm produced more yield than all other treatments in U.S. No. 1, canner, and total marketable root grades. There was a trend for the highest plant density treatment, 152-cm RS, to return the lowest yield in each grade with the exception of jumbo roots. In 2001, the 102-cm RS produced the greatest yield of U.S. No. 1, canner, and total marketable roots. The narrow-row, 76-cm bed produced greater (P ≤ 0.05) yields than did multiple-drill beds in U.S. No. 1, canner and total marketable roots. No significant differences among treatments were seen with the cull grade. Plant spacing (PS) did not cause significant effects for any grade in 2000. U.S. No. 1, total marketable and cull grades were non-significant in 2001. There was a trend for U.S. No. 1 yield to increase as PS increased. The 23-cm PS provided the greatest yield of canner roots while the 30 and 38-cm treatments were not separated. Simple regression analysis revealed weak negative correlations between population and U.S. No. 1 yield (R2 = 0.62) and total marketable root yield (R2 = 0.61). A cost analysis was constructed to determine economical returns. 1/t appears input costs for plants and labor render higher population treatments unprofitable. Thus, the standard combination of 102-cm RS along with a 30 to 38-cm PS is recommended.