Factors affecting crack formation in rice varieties during wetting and field stresses.

The critical moisture contents for the appearance of cracks in each of 4 rice var. were 14.2% for (i) Halubbulu, 16.4% for (ii) Kaddi Bhatha, 16.9% for (iii) IR 20 and 18.3% for (iv) Madhu. 100% cracked grains were obtained at 9.9% moisture in (i) and at 10.7% in (ii)-(iv). Paddy samples with different moisture levels were soaked for 3 h in water, which showed that cracking depends on the initial moisture content of paddy used for soaking; the lower the moisture content, the greater the cracking. Grains from var. (i) and (ii) were soaked in water at temp. of 5 degree , 30 degree , 45 degree , 55 degree , 70 degree , 78 degree or 85 degree C; increase in the temp. of soak water induced quicker cracking and greater proportion of cracked grains, but at higher temp. gelatinization and healing effect on cracks was noted. Paddy was the most highly susceptible to cracking, followed by brown rice and milled rice. Cracking was more pronounced in yellow grains than in greenish (immature) grains when soaked in water. Exposure of paddy crop to sun and dew during late maturity stages induced cracks in the grain, thereby lowering the milling quality.