Field Drying of Rough Rice: Effect on Grain Yield, Milling Quality, and Energy Saved¹

Abstract

Harvesting rough 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.

Harvest Location and Moisture Content Effects on Rice Kernel-to-Kernel Breaking Force Distributions

“…The formation of fissures due to rapid moisture adsorption by low MC kernels is the primary reason for reductions in HRY often observed at low HMCs. Research has demonstrated this fissuring phenomenon (Kunze and Prasad, 1978) and that HRY reduction can occur due to various means of moisture adsorption (Calderwood et al, 1980;Siebenmorgen and Jindal, 1986;Jindal and Siebenmorgen, 1994). Exposure duration, initial MC, and air relative humidity (RH) were significant factors influencing HRY reductions caused by moisture adsorption (Banaszek and Siebenmorgen, 1990).…”

Effects of introduction of combine harvester and flatbed dryer on milling quality of three glutinous rice varieties in Lao PDR

“…Combine harvester not only harvests crops but also thresh, and rough rice can be dried in the sun on a concrete floor. Grain may crack during the process as dried grain adsorbs water, with subsequent breakage during threshing and milling (Calderwood, Bollich, & Scott, 1980;Jindal & Siebenmorgen, 1994). However, HRY of sun-dried rough rice may increase greatly if grain is stirred frequently and kept under shade during the time of intensive solar radiation (Meas, Cleland, Bronlund, Mawson, & Hardacre, 2013;Meas et al, 2011).…”

Effects of Nitrogen Rate and Harvest Moisture Content on Physicochemical Properties and Milling Yields of Rice

“…Harvesting prematurely at elevated harvest moisture contents (HMCs) can lead to increased immature kernels (Kocher et al 1990), which can break during milling. Delaying harvest, with consequently decreasing HMC, has also been shown to reduce HRY (Kester et al 1963;Calderwood et al 1980;Geng et al 1984;Dilday 1989). However, such harvest delays are prevalent, most often a result of logistical issues or of extended in-field drying to reduce postharvest drying costs.…”