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Rice productivity is often limited by soil fertility depletion, water availability and access. Conservation Agriculture (CA) cropping systems have been designed and tested with the main objectives of restoring soil fertility, increasing productivity and profitability. This study assessed changes in soil health under rain-fed lowland rice under (i) conventional tillage (CT), (ii) CA (CA7: 7 years under CA) and (iii) green manure management for one year (CGM1) and for two years CGM2). Biofunctool®, a multi-functional soil assessment approach based on a set of seven soil indicators, was used to evaluate changes in three main soil functions (C transformation, nutrient cycling, and soil structure). In addition, soil chemical analyses were conducted in the 0-5, 5-10, 10-20 and 20-40 cm soil layers to assess changes in nutrient contents. Our results emphasized positive impacts of CA on C transformation, soil structure and nutrient contents. Soil organic carbon and total N were significantly higher (p < 0.05) under CA7 in the 0-5 cm layer with up to +7.5 g C kg-1 and +0.74 g N kg-1 , respectively. Higher values of labile C and soil respiration (p < 0.05) were observed under CA in the 0-5 and 5-10 cm layers. More stable soil aggregates and improved VESS values (p < 0.05) were also observed under CA. CA and CGM had 2 to 3 times more available phosphorus than CT in the 0-5 cm layer, and higher values were observed under CA from a depth of 0-20 cm. Higher Ca, Mg and K contents were recorded under CA and CGM in the 0 to 40-cm soil layer. A SOC stabilization trend was observed in soils under CA (0-5 and 5-10 cm layers) while a SOC mineralization trend was observed under CT and CGM. These results emphasize the positive impacts of CA on maintaining and/or enhancing soil health and in contributing to SOC accumulation. A diachronic analysis is now needed to assess the long-term on-farm impacts of CA on soil health and crop performances. [ABSTRACT FROM AUTHOR]

The effects of genotype and environment on the leaf area index of rice are well documented, but the rules governing leaf area distribution among main stem and tillers are less well understood. This study investigated the ontogenetic patterns of leaf blade area and dimensions on the main stem and tillers of three rice cultivars, IAC47, Javaé (Oryza sativa L.) and CG14 (O. glaberrima Steud.) grown in pots without competition among plants. No differences in phyllochron were observed among culms, but leaves on tillers appeared 0.5 to 0.8 phyllochrons earlier than the genealogically corresponding leaves on the main stem (system of Katayama). Cohorts were thus not fully synchronized. All culms produced their largest leaves soon after panicle initiation (PI), despite differences in tiller age. Leaves that appeared subsequently were smaller owing to reduced length but not width, which remained constant. Three different hypothetical rules governing the behaviour of culms were tested: (1) tillers behave as clones of the main stem; (2) cohorts behave uniformly, and (3) behaviour is determined by leaf position (sum of genealogical leaf and tiller indices). The results were best explained by hypotheses (2) and (3), with leaf blade width and length showing markedly different patterns. Copyright 2001 Annals of Botany Company [ABSTRACT FROM AUTHOR]