영남 평야지에서는 추석전 햅쌀 출하를 목적으로 조기재배나 극조기재배가 증가하고 있는 추세이다. 그러나 극조기 벼 수확 이후에 후작물로 적합한 작목이 없어서 휴경을 하는 농가가 많아 적합한 작부체계 개발을 위한 재배법 개발이 필요한 실정이다. 따라서 본 시험은 극조기 벼 수확 후 이모작 작부체계에 적합한 벼 품종 및 재배시기 설정을 위해 수행하였다. 조생종 14개 품종을 4월 7일, 4월 14일, 4월 21일, 4월 28일에 각각 이앙하였을 때, 극조기 벼 이모작을 위한 기준 출수기인 7월 10일 이전에 출수가능한 품종은 백일미, 주남조생, 중모1032, 진옥이었다. 이 품종들의 적산온도로 추정한 적정 이앙시기는 4월 10일에서 4월 20일 사이로, 이 시기에 이앙할 경우 8월 20일 이내에 수확이 가능하여 8월 하순 후작물과의 작기연결성에 유리한 적합 품종으로 판단된다.

To identify rice (Oryza sativa L.) cultivars suitable for Italian ryegrass (Lolium multiflorum Lam.)–rice double cropping systems, we investigated the yield and grain quality of four different midseason maturing rice cultivars (‘Daebo’, ‘Haepum’, ‘Haiami’, and ‘Samdeog’) and four midseason-to-late maturing rice cultivars (‘Hyunpoom’, ‘Saeilmi’, ‘Saenuri’, and ‘Samkwang’) in single rice cropping and Italian ryegrass–rice double cropping systems in paddy fields of Miryang, South Korea. We found that organic matter and available P2O5 content slightly decreased, whereas Na content increased, in the soil where Italian ryegrass was cultivated during winter compared to that in the soil that remained fallow during winter. The pH, electrical conductivity, organic matter, and contents of K+, Ca2+, Mg2+, and Na+ decreased, whereas the available P2O5 content slightly increased, in the soil where rice was harvested in both single and double cropping systems. However, compared to the optimum soil conditions for rice cultivation, available P2O5 and K+ content were high and Mg2+ content was low in both single and double cropping systems. At the heading stage, the culm length and leaf color slightly increased in most of the rice cultivars, whereas the panicle length and number slightly decreased, in the double cropped system. After harvesting, spikelet number and milled rice yield did not show a significant difference between single and double cropping systems. However, the ripened grain rate and weight per thousand grains increased slightly in the ‘Saeilmi’ and ‘Samkwang’ cultivars but remained either stable or slightly low in other cultivars in the double cropping system. The milled rice yield was high (> 500 kg/10a) in ‘Daebo’ and ‘Haepum’ among midseason maturing rice cultivars, and in ‘Saeilmi’ and ‘Saenuri’ among midseason-to-late maturing rice cultivars, in both single and double cropping systems. The head rice rate was high in midseason maturing rice cultivars in the double cropping systems, reaching > 70% in ‘Haepum’ and ‘Haiami’ cultivars, whereas it decreased in most midseason-to-late maturing rice cultivars (excluding ‘Samkwang’ cultivar), in double cropping systems. Particularly, it exceeded > 70% in the ‘Saenuri’ cultivar in both single and double cropping systems. The protein content in milled rice increased, whereas the amylose content either remained stable or slightly increased, in double cropping systems. The Toyo taste value decreased in all midseason-to-late maturing rice cultivars and slightly increased in the ‘Daebo’ and ‘Haiami’ cultivars among midseason maturing rice cultivars in double cropping systems. However, Toyo taste values in the ‘Haepum’, ‘Haiami’, and ‘Saenuri’ cultivars exceeding > 80% in both single and double cropping systems. Therefore, we recommend ‘Haepum’, ‘Haiami’, and ‘Saenuri’ cultivars as candidates for Italian ryegrass–rice double cropping systems due to high yield, head rice rate, and Toyo taste value.

The physicochemical properties of soil and the yield and quality of rice (Oryza sativa L. cv. Sailmi) were assessed using Italian ryegrass (Lolium multiflorum Lam. cv. Kowinearly)-rice double cropping systems in the paddy fields at Goseong and Miryang in southern Korea. The average temperatures during the ripening period were approximately 1 °C higher than the optimal temperature for rice ripening and the sunshine duration was reduced by frequent rainfall. Consequently, it was slightly below the optimal conditions required for rice ripening. In the soil at Goseong, winter Italian ryegrass cropping increased the pH, electrical conductivity, and the contents of organic matter, total nitrogen (T-N), available P2O5, K, Ca, and Mg than winter fallowing. Particularly, the contents of T-N and available P2O5increased significantly. In the soil at Miryang, Italian ryegrass slightly increased the electrical conductivity and the T-N, Mg, and Na contents. Therefore, winter Italian ryegrass cropping improved the physicochemical properties of paddy soils; however, Italian ryegrass-rice double cropping slightly reduced the culm length at both Goseong and Miryang, without markedly changing the panicle length or number compared to fallow-rice cropping. Furthermore, at Goseong, Italian ryegrass-rice double cropping slightly decreased the spikelet number and milled rice yield, and increased the ripened grain rate; however, at Miryang, contrasting results were observed. In addition, fallow-rice cropping revealed no differences in the head rice or opaque rice rates. The protein content was slightly increased in Italian ryegrass-rice double cropping, without significant changes in the amylose content or Toyo value, compared to that in fallow-rice cropping. The peak and breakdown viscosities were slightly decreased. These results indicate that winter Italian ryegrass cropping might alter rice taste but may not exhibit remarkable negative effects on rice cultivation. Therefore, Italian ryegrass-rice double cropping system is recommended for paddy fields in southern Korea. Nevertheless, to increase the rice yield and quality, fertilization standards for rice cropping that consider the changes in the T-N and organic matter contents in paddy fields caused by winter Italian ryegrass cropping need to be established.