Correlation analysis of the SPAD readings and yield of sweet potato (Ipomoea batatas L.) under different agrotechnical conditions

We studied the effect of planting method (flat and ridge planting) and row spacing (0.75-1.0 m) on the yield and SPAD readings of sweet potato (Ásotthalmi 12 variety) in a small-plot field experiment in 2017 and 2018. The experiment was set up in lattice design with 4 replications. The SPAD readings of sweet potato were measured four (2017) and three (2018) times during vegetation period (by Konica Minolta 502). A high yield level was reached both in 2017 (23.23-50.69 t ha-1 marketable yield) and 2018 (33.26-47.34 t ha-1) due to the effects of the favourable soil (chernozem), the near-optimal agrotechnical background, irrigation and the warmer-than-average vegetation period. In both years, higher yields were obtained with flat planting and 0.75 m row spacing. The proportion of non-marketable tubers was between 9.97-15.57% in 2017 and 8.65-11.01% in 2018. The SPADmax values were measured in July (39.61-50.31 in 2017) and in August (49.90-55.33 in 2018). Strong correlation observed among SPAD readings, the whole yield and the marketable yield in both years (r = 0.632*, r = -0.664* and r = 0.709**, respectively). Also, a strong correlation was observed between the planting method and the obtained SPAD readings (r = -0.847**, -0.682* in 2017 and r = -0.634*, -0.488 in 2018, respectively), while there was no correlation between row spacing and SPAD readings (r = -0.006NS-0.190NS). Crop year had a strong effect on SPAD readings (r = 0.639**-0.871**).