Field Drying of Rough Rice: Effect on Grain Yield, Milling Quality, and Energy Saved

Harvesting tough rice (Oryza saliva L.) at a low moisture content is one method of reducing energy needs for drying. The objectives of energy-related research were to: 1) determine the economic feasibility of harvesting rice at a low moisture content; 2) identify the harvest moisture level at which head rice yield drops sharply; 3) identify rice cultivars adaptable for field drying; and 4) estimate energy savings to be gained by harvesting at particular moisture levels. Rough rice initially at 25% moisture content was harvested at 11 intervals during a time span of 30 to 36 days to determine the amount of drying in the field and the effect of field drying on grain yield, milling yield, germination, and test weight. Ten tests were run during four harvest seasons. Long-grain cultivars, ‘Labelle’ and ‘Lebonnet’, and medium-grain cultivars, ‘Brazos’ and ‘Nato’, were included in the tests. During each of the tests, rice moisture content dropped steadily during dry weather, but rain and dew caused unpredictable amounts of rewetting. Rice eventually dried to near 16% moisture content in all 10 tests and to 14% moisture content or lower in five of the tests. Grain yields were not greatly affected by delayed harvesting, but tended to decrease before the tests were concluded. The percentage of total milled rice (whole and broken kernels combined) increased with delays in harvest date, but the percentage of head rice (whole kernels of milled rice) reached a maximum at an intermediate harvest date, then declined rapidly with delays in harvesting. Both Brazos and Lebonnet cultivars required harvesting at a higher moisture content than did Labelle and Nato cultivars to maintain a high percentage of head rice. Neither germination nor test weight was adversely affected by delays in harvest dates. Energy for drying may be reduced about 50% by harvesting rice at 16% rather than at 22% moisture content.