Effect of N and P on the root system architecture in upland rice

In upland rice, water uptake capacity by dense roots from the deep soil layer is a critical factor to enhance growth. Therefore, it is important to identify the optimum cultural conditions for forming deep root systems. In rice root system, nodal roots are formed in each internode and their elongation determine the rooting zone. Root density at a certain depth is controlld by the density of lateral root branching. In this study, the effect of P and N on root architecture was analyzed in terms of nodal root growth and lateral root branching with emphasis on the internode-root connection. Improved upland indica variety, UPLRi-5, and traditional upland japonica variety Moroberekan were grown in root boxes for 70 days under different P and N levels in acidic Ultisol from Siniloan, Laguna [Philippines]. The soil volumetric water content was kept at 50 percent. Moroberekan had more nodal roots per tiller than UPLRi-5. The number of nodal roots in each internode in the main tiller was also higher in Moroberekan than in UPLRi-5. More nodal roots were associated with larger tiller size in Moroberekan. P increased root and shoot dry weights. Nitrogen increased root and shoot dry weights when P was applied. Phosphorus raised to total number of nodal roots, which could be attributed to the greater tiller number and number of nodal roots in each tiller, especially the main tiller. Phosphorus also increased the number of long nodal roots (40 cm) because of the greater number of long nodal roots in the main tiller and first order tillers. The increase in long nodal roots caused by P in the main tiller mainly occurred in early internodes. Lateral root length per unit length of nodal root was also enhanced by P. The greater number of long nodal roots due to N was primarily attributed to the increase in first order tillers. Nitrogen also enhanced the elongation of nodal roots in most internodes in the main tiller in UPLRi-5. Results indicated that P increases root length density in deep layers mainly by enhancing the growth of long nodal roots in early internodes in the main tiller with greater branching of lateral roots. Nitrogen affects root architecture through enhanced tillering