How to manage aerobic rice?
Aerobic rice is basically managed like a wheat or a maize crop. The usual establishment method is dry direct seeding. Before sowing, the land should be dry prepared by ploughing and harrowing to obtain a smooth seed bed. Seeds should be dry seeded at 1-2 cm depth in heavy (clayey) soils and 2-3 cm depth in light-textured (loamy) soils. Optimum seeding rates still need to be established but are probably in the 70-90 kg ha-1 range. In experiments so far, row spacings between 25 and 35 cm gave similar yields. The sowing of the seeds can be done manually (eg dibbling the seeds in slits opened by a stick or a tooth harrow) or using direct seeding machinery. An alternative establishment method is transplanting, where seedlings are transplanted into wet soil that is kept around saturation for a few days to ease transplanting shock. Subsequently the fields dry out to field capacity and beyond. This method of crop establishment can only be done in clay soils with good water-holding capacity.
An aerobic rice crop attaining 4-6 t ha-1 yields obtains many of its required nutrients from the soil. But this “indigenous supply” of nutrients is typically not sufficient to meet all the nutrient needs, and fertilizers will need to be applied. Site-specific knowledge about the indigenous nutrients supply is the starting point for formulating fertilizer recommendations. The site-specific nutrient management (SSNM) approach (www.irri.org/irric/ssnm) can be used to determine the need for supplemental nutrients in the form of fertilizers and the optimal management of fertilizers. A useful tool to assist in the application of nitrogen (N) fertilizer is the Leaf Color Chart (LCC; part of the SSNM approach). In the absence of trained extension personnel in SSNM and LCC, an amount of 70-90 kg N ha-1 could be a useful starting point (to be subsequently optimized). Instead of basal application of the first N split, the first application can best be applied 10-12 days after emergence to minimize N losses by leaching (the emerging seedling can’t take up N so fast, so it will easily leach out). Moreover, basal application of N also promotes early weed growth. Second and third split applications of N may be given around active tillering and panicle initiation, respectively. Dry, aerobic, soil can reduce the indigenous supply of phosphorus (P), hence the application of fertilizer P can be more critical for aerobic rice than for conventional flooded lowland rice. On acid soils, aerobic rice will likely be less prone to zinc deficiency than flooded lowland rice; but on high pH soils with calcium carbonate, the reverse may be true.
If the crop is grown in a dry season, a light irrigation application (say 30 mm) should be given after sowing to promote emergence. Subsequent irrigation applications depend on the rainfall pattern, the depth of groundwater, and on the availability and/or cost of irrigation water. Irrigation can be applied by any means as used for upland crops: flash flood, furrow, or sprinkler.
Rice that is not permanently flooded tends to have more weed growth and a broader weed spectrum than rice that is permanently flooded. To control weeds, the use of pre- or post-emergence herbicides is recommended when the weed pressure is high, plus additional manual or mechanical (inter-row cultivation) weeding in the early phases of crop growth.