2.3. Rice production systems
A calendar of the three main production systems and the average monthly rainfall are presented in Table 1. Table 2 lists relative importance, farm size and grain yield for the three production systems. The growing period of rice is from sowing between late September and early December up to harvesting in March–April. The three main production systems differ as follows with respect to intensity and timing of soil tillage and water use:
(a)
Semi-direct: soil preparation is done in September or October (45–60 days before sowing) when the soil is not inundated. This early soil preparation with a disc plough and disc harrow permits the incorporation of the rice straw and the germination of weeds. A herbicide is used to kill these weeds, and rice is sown without seedbed preparation to prevent regrowth of weeds. Fields are inundated after emergence of the rice seedlings, as in the case of the conventional system.
(b)
Conventional: just before sowing, the fields are prepared when the soil is not yet inundated. Deep tillage is employed using a disc plough followed by superficial operations with a disc harrow with the aim to level the soil and prepare a seedbed with a fine tilth. Sowing (drilling) is done with a conventional sowing machine. Water is let onto the field after the rice seedlings have reached a height of approximately 10 cm.
(c)
Pre-germinated: the fields are inundated (early August) before tillage operations start. Tillage is done in September and October. Usually, the same disc implements are used as in the conventional system, often complemented with a pass of a special leveller to smoothen and level the wet surface layer. Seeds are pre-germinated by soaking until the coleoptile is 2–3 mm long. The seed is broadcast in the shallow (5–10 cm) water layer, either by hand or sowing machine, depending on the size of the farm. The water layer allows a more precise levelling of the field and controls weeds.