Investigation of Water Use via a Modified Lysimetric Approach and Changes in Soil Physical Properties in Puddled and Nonpuddled Rice Fields

A two-year experiment was conducted to investigate the amount and route of water use and soil physical properties in puddled transplanted and nonpuddled aerobic direct seeded rice fields. The results revealed that the total amount of water used for transplanted rice was significantly greater than that used for direct-seeded rice, at 98 and 59 cm, respectively, which included transpiration, evaporation, and drainage, with values of 61, 20, and 16.5 cm for transplanted rice and 26, 20, and 13.5 cm for direct-seeded rice. The soil drainage rate was 1.5 to 2.5 mm/day in the puddled field. The effective precipitation was linearly related, with a coefficient of 0.63 from total rainfall, which was higher than the relationship suggested by the FAO and may be due to a greater distribution of rain at a time when there was less crop cover. The obtained single crop coefficient, Kc, was 1.2, 1.75, and 1.05 for the initial, middle, and late growth stages, respectively, for transplanted rice, which were higher values than those recommended by the FAO. The values for direct seeded rice were 0.95, 1.4, and 1 and were close to the FAO values. Despite the 20% decrease in yield in direct seeded cultivation, there was a 23% increase in applied water efficiency. The coefficient of linear extensibility for nonpuddled fields showed a decreasing trend from 0.027 to 0.016 after two years, indicating an improvement in soil physical conditions. The mean weight diameter of soil aggregate showed an increasing trend from 0.63 to 0.76 mm, indicating the beneficial effects of reducing soil disturbance activity in improving soil physical conditions.