Study on water-saving irrigation of cabbage(Brassica oleracea L. var. capitata)

• Main Authors: Hsin-Kai Huang, 黃新凱
• Other Authors: Hsiao-Feng Lo
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/3r6nfk

碩士 === 國立臺灣大學 === 園藝暨景觀學系 === 106 === Abstract Cabbage (Brassica oleracea L. var. capitata) is one of the important essential vegetable crops in Taiwan. Growth season in production area of lowland cabbage is relatively low in precipitation. Climate change causes precipitation reduction year by year and the agricultural irrigation water is limited. It is expected to lower the application of irrigation amount with good product quality and raise the crop water use efficiency (WUE). In this thesis, cabbage ‘KY cross’ was used as experimental material. The physiology of spread leaves and the yield and quality of leafy head under irrigation based on the range of medium volumetric water content (VWC) and crop water requirement (CWR) were investigated to select useful index for water saving irrigation. From initial head formation to harvest, VWC will drop to below 30% after only 4 days of water dis-supply. But after re-supply water for 24 days, fresh weight of leafy head would be insignificantly different with the control. On the 12th day of water dis-supply, VWC dropped to below 15% and SPAD value significantly raised up. SPAD value could reflect plant status under serious water deficit stress. From head formation to harvest, VWC dropped to below 30% after any 4 days of water dis-supply. After re-water, fresh weight of leafy head was not significantly different with the control. Four days of water dis-supply showed no effect on leafy head fresh weight. Nitrate and ascorbic acid contents in leafy head of control are significantly lower than any 4-days water dis-supply treatments from head formation to harvest. From head filling to harvest, irrigation were based on CWR 100%~50% per 2 days. In all treatments, VWC would maintain at higher than 50% and leafy head showed no significant difference with the control. Dry matter in CWR 50% treatment was the highest, while nitrate and ascorbic acid contents in CWR 100% the lowest. From head formation to harvest, irrigation was further based on CWR 100%, 60%, 50%, 40%, 30% and 20% per 2 days. In CWR 30% treatment, VWC dropped to below 50% after 12th day and fresh weight and equatorial diameter of leafy head were significantly lower. In organoleptic evaluation, crispy, firmness, sweetness, spice, bitterness and odd flavor showed no difference among all treatments. Hence, CWR 40% was suggested as the lowest irrigation rate. From initial head formation to harvest, with maintaining VWC in specific ranges of >60%, 60%~50%, 50%~40%, 40%~30%, re-water to field capacity after 4 days of 40%~30%, and re-water to field capacity after 4 days of 50%~40%. SPAD value, Fv/Fm and NDVI began to show significant difference among all treatments after 20th, 6th, 10th days, respectively. Leafy head fresh weight, polar diameter, equatorial diameter and core length were the lowest in VWC 30%~40% treatment. When water was re-supplied to the field capacity after 4 days of both VWC value 50%~40% and VWC 40%~30%, the head side firmness was the lowest. Hence, VWC 50%~40% was suggested as the lowest irrigation rate. The best treatments in previous trials, irrigation rates of CWR 45% and VWC 50%~40%, along with CWR 60%, CWR 35%, VWC 60%~50%, VWC 40%~30%, were applied to confirm the effect and efficiency. Medium VWC variation and leafy head shape index of VWC 50%~40% treatment had similar trends with those of CWR 60% and CWR 45%. VWC 40%~30% had the lowest VWC, fresh weight and shape index of leafy head among all treatments. In conclusion, cabbage cultivated with peat medium in the green house should irrigate based on CWR 50%~40% and avoid peat VWC below 40% continuously longer than 4 days. Although the water use efficiency of this practice did not increase, it could save about 30% irrigation water with maintaining fresh weight and quality of leafy head.