Effect of localized fertilizer application on deep root development during early growth in upland rice under upland condition

Abstract

ABSTRACT The effects of localized fertilizer (LF) application on changes in root system architecture (RSA) of upland rice seedlings under upland condition were evaluated, and root traits important for deep root development were identified using three root box experiments (Exps). Fertilizer was homogeneously mixed and broadcasted on the soil surface in two control treatments, while in three LF treatments, it was point-placed at 2.5, 7.5 and 12.5 cm below the soil surface. Nitrogen (N) fertilizer in Exp. 1, phosphorus (P) fertilizer in Exp. 2 and compound fertilizer with nitrogen, phosphorus and potassium (NPK) in Exp. 3 were used to compare the effects of LF. Localized N and NPK application altered the RSA through root proliferation and increasing root length percentage around the fertilizer-applied area, whereas localized P application had no effect on both root and shoot development. Deep root and shoot development were decreased with localized NPK application compared to homogeneously mixed control treatment but were maintained with localized N application, when applied at deeper soil depths. Furthermore, the increase in deep root length (DRL) was closely related to the increase in both total root length (TRL) and deep root length ratio (DRR). DRR increased with TRL in Exps. 2 and 3, while it was independent from TRL in Exp. 1, suggesting that DRL can be promoted by increasing DRR regardless of TRL. These results showed that localized N application at deeper soil depths could modify RSA of upland rice seedlings grown under upland condition without affecting shoot growth.