평균온도를 이용한 전북지역 단수수의 출수기 추정 및 파종시기별 수량 변화

Estimation of Heading Date using Mean Temperature and the Effect of Sowing Date on the Yield of Sweet Sorghum in Jellabuk Province

Abstract

단수수(Sorghum bicolor L. Moench)는 전통적인 식량작물보다 높은 환경적응성과 다양한 용도로 유용한 작물로 평가받아 왔지만, 국내에서는 관련 연구 및 정보의 부족으로 재배가 확대되지 못하고 있다. 본 연구는 단수수 '초롱'의 전라북도 6개 지역(전주, 부안, 정읍, 임실, 남원, 장수)의 최근 30년(1989-2018년)간 기상자료에 근거한 출수기를 추정하고, 파종시기(4월 10일, 4월 25일, 5월 10일, 5월 25일, 6월 10일, 6월 25일)에 따른 생육 및 품질요인 등을 비교하고자 수행하였다. 파종부터 출수까지의 소요일수는 파종시기가 빠를수록 107, 96, 83, 70, 59, 64, 65일로 길어지는 경향을 보였으며, 평균출수소요일수는 77.7일이었다. 유효적산온도는 평균 $1,120.3^{\circ}C$이었다. 지역별 연평균온도는 전주, 정읍, 부안, 남원, 임실, 장수 순으로 높았으며, 평균온도는 지역별 출수소요일수와도 비슷한 경향이었다. 특히 유효적산온도로 산출한 최근 30년 동안 6개 지역의 출수소요일수는 모든 파종처리구에서 점차 감소하는 경향이었다. 또한 6개 지역에서 출수소요일수는 평균온도(파종~출수까지)와 부의 상관관계가 있는 것으로 나타났고, 2017, 2018년 평균온도를 이용하여 산출한 출수소요일수의 예측값은 관측값($R^2=0.9987**$)을 89%로 확률로 설명되었다. 수확기, 4월과 7월 파종은 각각 생경수량과 가용성 고형물 함량이 높았으나, 최종적인 당수량은 5월 10, 25일 파종이 각각 3.4, $3.1Mg{\cdot}ha^{-1}$로 가장 높았다. 4, 7월에 파종한 경우 각각 품질과 수량이 낮고 서리피해의 위험성이 있으므로 5월 파종하는 것이 효과적일 것으로 판단된다. 최종적인 파종시기의 결정은 적정 수확기, 작부체계, 수확대상(착즙액 또는 이삭), 재배지대, 미기상 등을 고려해야 할 것이다.

Sweet sorghum (Sorghum bicolor L. Moench), compared to traditional crops, has been evaluated as a useful crop with high adaptability to the environment and various uses, but cultivation has not expanded owing to a lack of related research and information in Korea. This study was conducted to estimate heading date in 'Chorong' sweet sorghum based on climate data of the last 30 years (1989 - 2018) from six regions (Jeonju, Buan, Jeongup, Imsil, Namwon, and Jangsu) in Jellabuk Province. In addition, we compared the growth and quality factors by sowing date (April 10, April 25, May 10, May 25, June 10, June 25, and July 10) in 2018. Days from sowing to heading (DSH) increased to 107, 96, 83, 70, 59, 64, and 65 days in order of the sowing dates, respectively, and the average was 77.7 days. The effective accumulated temperature for heading date was $1,120.3^{\circ}C$. The mean annual temperature was the highest in Jeonju, followed in descending order by Jeongup, Buan, Namwon, Imsil, and Jangsu. The DSH based on effective accumulated temperature gradually decreased in all sowing date treatments in the six regions during the last 30 years. DSH of the six regions showed a negative relationship with mean temperature (sowing date to heading date) and predicted DSH ($R^2=0.9987**$) calculated by mean temperature was explained with a probability of 89% of observed DSH in 2017 and 2018. At harvest, fresh stem weight and soluble solids content were higher in the April and July sowings, but sugar content was higher in the May 10 ($3.4Mg{\cdot}ha^{-1}$) and May 25 ($3.1Mg{\cdot}ha^{-1}$) sowings. Overall, the April and July sowings were of low quality and yield, and there is a risk of frost damage; thus, we found May sowings to be the most effective. Additionally, sowing dates must be considered in terms of proper harvest stage, harvesting target (juice or grain), cultivation altitude, and microclimate.

Fig. 1. Changes in stem length (A), diameter (B), and number of additional tillers (C) at the different sowing dates of sweet sorghum ‘Chorong’ in 2018. Vertical bars represent standard error of the means (n = 15).

Fig. 2. Cardinal temperature (A) and precipitation (B) from sowing to heading date of the experimental area in 2018. Annual mean temperature (C) daily temperature range (D), and mean (E) and minimum temperature (F) in one quarter (May to July) of the six regions (Jeonju, Buan, Imsil, Jeongup, Namwon, and Jangsu) in Jellabuk-do measured automatic weather system in the last 30 years (1989 - 2018). The legends for C - F are the same.

Fig. 4. Quadric regression results between mean temperature (sowing date to heading date) and days from sowing to heading (DSH) based on effective accumulated temperature (1,120.3℃) of sweet sorghum ‘Chorong’ of the six regions in Jellabuk-do in the last 30 years (1989 - 2018).

Fig. 5. Linear regression results between predicted and observed days from sowing to heading (DSH) of sweet sorghum ‘Chorong’ in 2017 and 2018.

Fig. 3. Changes in heading dates with different sowing dates based on effective accumulated temperature (1,120.3℃) of sweet sorghum ‘Chorong’ of the six regions in Jellabuk-do in the last 30 years (1989 - 2018). Y axis: days from sowing to heading. The graphs represent April 10 (A), April 25 (B), May 10 (C), May 25 (D), June 10 (E), June 25 (F), and July 10 (G) sowings.

Table 1. Changes in growing and developmental stage at the different sowing dates of sweet sorghum ‘Chorong’ in 2018.

Table 2. Changes in mean and range values of days from sowing to heading for the different sowing dates based on effective accumulated temperature (1,120.3℃) of sweet sorghum ‘Chorong’ of the six regions in Jellabuk-do in the last 30 years (1989 - 2018).

Table 3. Comparison of soluble solids content (SSC), fresh stem yield (FSY), dry stem yield (DSY), juice yield (JY), sugar yield (SY), sucrose content (SC), juice purity (JP), and ear weight (EW) by the different sowing dates in sweet sorghum ‘Chorong’ at harvest (50 days after heading date).