Flore-Anne C. Relente and Luz G. Asio1*
Nitrogen is one of the most critical nutrients affecting sweetpotato yield. This study was conducted to 1) evaluate the growth and yield response of sweetpotato NSIC SP 33 to different levels of N; and 2) determine the relationship between N level and root yield. A screenhouse experiment laid out in Completely Randomized Design (CRD) was carried out using five (5) N levels: 0, 40, 80, 120 and 160kg ha-1, each replicated thrice. Thetotal amount of N (as urea) was applied twice, one-half at planting and the other half at six weeks after planting (6 WAP) along with a blanket application of solophos and muriate of potash at 40 and 60kg ha-1 P2O5and K2O. An alluvial Umingan sandy loam soil (lnceptisol) was used as medium.
Levels of N significantly increased the leaf area, fresh herbage, total root yield, biomass, dry matter yield, shoot-root ratio, weight and number of marketable roots. Harvest index (HI) of plants applied with 40 and 80kg N ha-1 were comparable to those applied with 0 N. Increasing levels of N from 0 to 1 60kg ha-1 resulted in higher total crude protein (CP) and total N in the leaves. N uptake was higher in N-applied plants. Application of 40 and 80kg ha-1 N produced the highest root yield, above which root yield declined. Relationship between N level and root yield developed through regression analysis showed a quadratic function of Y=111.1794+1.2098x-0.00897×2 and R-square of 0.9904 which suggest that inherent soil N affected root development.
Keywords: regression analysis, quadratic function, storage roots, N fertilization, sweetpotato