Functional equilibrium of the rice root system
1994
Samson, M.I. | Redulla, C.A. | Descalsota, J.P. | Cassman, K.G. (International Rice Research Inst., Los Banos, Laguna (Philippines). Agronomy, Plant Physiology and Agroecology Div.)
The effect of nutrient supply on root length and distribution of rice was examined in field studies at PhilRice (Nueva Ecija) and IRRI (Laguna) [Philippines]. Roots from 0-5, 5-10, 10-20, and 20-30 cm, and aboveground biomass were sampled at flowering in two cultivars (IR72 and IR29723-143-3-2-1) with and without NPK inputs (t/-NPK) in 1991 WS [wet season] and 1992 DS [dry season]. In the 1993 DS, a pot experiment was conducted in the IRRI phytotron under controlled day/night temperature (28.5/21.5 deg C). Treatments and measurements were the same as in the field experiments. Grain yield was 2.7 t/ha in - NPK and 4.5 t/ha in + NPK in the WS, and 3.4 and 7.8 t/ha in the DS, respectively. At flowering, shoot weight in + NPK treatments was 70 percent (WS) and 190 percent (DS) greater than in - NPK. By contrast, root length increased by only 15 percent (WS) and 24 percent (DS) in + NPK. In the pot experiment, shoot dry matter increased by 180 percent and root mass by 33 percent with + NPK, while total root length was equivalent for + and - NPK. Stability of root relative to shoot growth resulted in a decrease in the root/shoot dry matter ratio from 17 percent in -NPK to 8 percent in +NPK. Tiller number per pot increased from 16 in -NPK to 43 in +NPK, but root length per tiller decreased from 48 m in -NPK to 14 m in +NPK. These results indicate a dynamic functional equilibrium in root-shoot partitioning of rice in response to the external nutrient supply such that when nutrients are deficient, rice allocates relatively more dry matter to root development than when nutrient supply is abundant
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