植冠微氣象在高溫及不同栽培密度下對水稻產量及品質之影響

Abstract

臺灣為亞熱帶之海島國家，自1970年以降，臺灣地區的夜溫上升、日夜溫差下降及平均日照時數縮短，如果未來全球暖化的趨勢持續，臺灣水稻之栽培環境將會面臨高溫、高濕以及低光照等環境壓力之挑戰。本研究藉由調整栽培密度以及植冠內微氣象之收集分析，期望瞭解田間微氣象與水稻產量品質間的相關性，並針對未來的高溫環境提出適合的栽培密度。本研究設計在田間之延後插秧期作中，以行株距分別為30 x 15 cm、30 x 20 cm及30 x 30 cm進行水稻栽培，並以MINCER (Micrometeorological Instrument for Near Canopy Environment of Rice)裝置紀錄水稻生育期間植冠內外之溫、濕度資料，評估高溫下不同栽培密度水稻生長相關指標及植冠結構發展對田間微氣象之可能影響，最後探討溫、濕環境與穀粒產量品質之相關性。 密度試驗結果指出，在相同日期基準下，低栽培密度夜晚之植冠內溫、濕度都較其他密度高。在高溫期作，低栽培密度的葉綠素計值較高且營養生長期延長，造成抽穗日期延後，導致其在抽穗後0-15天遭遇高溫的風險相對增加；此外，在9點至12點的開花過程中，低栽培密度遭遇之溫度環境可高出其他密度1-2 ℃，不僅降低小花稔實率也造成穀粒品質之下降。而高栽培密度在全生育期皆具有較高之截光率，且在穀粒充實階段具有較高的葉面積指數和較高的穀粒充實率，且單位面積之穗數也較多，故產量表現佳。外觀品質方面，高栽培密度的完整米率高、未熟米率低，穀粒外觀品質較佳。此外，高栽培密度亦有較佳之黏度品質。而在食味品質上，一期作之食味品質明顯高於二期作，然而在密度處理間則無顯著差異。綜合以上之結果，建議農民在未來高溫環境下，可採高密度 (30 x 15 cm)進行水稻栽培，避免因延後抽穗而遭遇高溫，以維持一定的產量與品質。 本研究顯示，水稻開花過程中植冠內之溫度與稔實率呈顯著負相關，該期間最高溫提高1 ℃，稔實率可能下降15 %。濕度為影響田間熱量平衡另一重要因子，由於水稻植冠內外濕度梯度驅動之蒸發散冷卻作用，水稻植冠內溫度明顯低於大氣溫度，且植冠溫度更能直接反映水稻遭受之溫度逆境。台灣的大氣濕度偏高，造成水田植冠內散熱不佳，進而加劇高溫逆境對水稻生產的衝擊。故田間微氣象在評估高溫對水稻生育衝擊上有其重要性，栽培密度試驗需探討田間之熱量平衡，進而釐清微氣象因子與水稻生育及品質形成之關係，以規劃更精準之栽培策略。

Taiwan is an island located in subtropical zone. Since 1970, the rice cultivation environment of Taiwan has been confronted with the threat of environmental pressures, such as high temperature (HT), high humidity and low solar radiation. These trends make the rice production in Taiwan even harder. The objective of this study was to understand the interactions among field microclimate, rice yield and quality; besides, a suitable planting density was also proposed for the future HT environment. Field trial of adjusting planting density and collection of microclimate data inside rice canopy were conducted in this study. In late transplanting, we cultivated rice with 11.1, 16.6 and 22.2 hills / m2 and recorded the temperature and humidity data around rice panicle position with MINCER (Micrometeorological Instrument for Near Canopy Environment of Rice) to evaluate the possible influences on rice growth physiological indices and canopy development, and further to discuss the correlations among microclimate environment, rice yield and quality. The results of density trial indicated that the temperature and humidity inside canopy of low density were higher than those of other treatments in the same spatiotemporal environment, especially at night. In late transplanting trail, the low density plots performed higher SPAD value and prolonged the vegetative growth so that it had a higher risk of encountering HT during DAF (Days after flowering) 0-15 owing to the delay of heading date; in addition, the temperature environment during flowering in low density plots was 1-2 ℃ higher than those of other treatments, and the higher temperature not only reduced the spikelet fertility but it also decreased the grain quality. The high density plots showed better yield performance because of high light interception, leaf area index, grain filling ratio, and more panicle number per area. In terms of grain appearance quality, high density performed well with higher perfect grain ratio and it had better viscosity quality as well. The taste quality in the first crop was better than that in the second crop, but there were no significant differences between density treatments. The results suggested that farmers may cultivate their rice with a high planting density (22.2 hills / m2) in future HT environment to maintain the rice yield and quality. With the aspect of microclimate, the present results showed that the temperature environment inside the rice canopy was negatively correlated with fertility during flowering. With 1 ℃ increase of the maximum temperature during spikelet flowering, the fertility would decline about 15 %. Humidity is also a critical factor to affect the field thermal balance. Because of the evapotranspiration cooling effect triggered by humidity gradient, the temperature inside canopy was lower than air temperature recorded from nearby weather station; furthermore, the canopy temperature might more directly reflect the heat stress on the rice. The present results suggested that the high humidity environment in Taiwan may result in a poor cooling effect inside canopy and exacerbate the HT impacts on rice production. Since the microclimate plays an important role in evaluating HT impacts on rice growth and development, it is essential to conduct further studies on the complicated field thermal balance to clarify the interaction between microclimate factors and rice growth,