Rice root growth and nutrient uptake as influenced by organic manure in continuously and alternately flooded paddy soils

Rice (Oryza sativa L.) root systems play an important role in uptake of water and nutrients from soil. A 4-year field experiment was conducted to determine the effects of different nutrient and water regimes on root growth by measuring the root diameter, root density, and root activity. Three nutrient regimes were used: (i) combined application of chemical fertilizers with farmyard manure (CM), (ii) integrated use of chemical fertilizers and wheat straw (CS), (iii) chemical fertilizers only (CK). Two soil moisture regimes included continuous waterlogging (CWL) and alternate wetting and drying (AWD). Incorporation of organic sources into paddy soil markedly improved root morphological characteristics of rice plant. In the alternate wetting and drying (AWD), root length density (RLD), and root weight density (RWD) for organic fertilization treatments (CS and CM) increased by 30 and 40%, respectively, as compared with the sole chemical fertilization (CF). Relative to root activity, CWL had adverse effects on root active absorption area (AAA), root oxidation ability of alpha-naphthylamine (alpha-NA) (ROA), and root surface phosphatase (RSP) of rice plants treated by integrated application of organic and inorganic fertilizers. In particular for the CM treatment, the AAA, ROA, and RSP of rice plants by the continuous flooding decreased by 22, 28, and 35%, respectively, compared to the alternately flooded regime. In the water regime of AWD, incorporation of organic manure significantly increased N, P, and K uptake by rice plants and facilitated the allocation and transfer of nutrient elements, especially P to rice ears and grains. This resulted in significant increases in the filled grains panicle(-1), 1000-grain weight and grain yield. The beneficial effects of integrated use of organic and mineral fertilizers on grain yield were significantly (P < 0.05) decreased by the water regime of CWL. (C) 2004 Elsevier B.V. All rights reserved.