Studies on competitive ability of rice and barnyardgrass III. Comparative growth between rice and barnyardgrass

Abstract

Barnyardgrass [Echinochoa crus-galli (L.) Beauv.] is a common and troublesome weed species found in paddy field and damaging to rice yield in Taiwan (Yang, 1995b). However, there is no information available on growth behavior of barnyardgrass grown together with rice under the current cropping system in Taiwan. Field experiments were therefore carried out at the experimental farm of Taiwan Agricultural Research Institute, Taichung Hsien, to study growth patterns of these two species and the variations in competition. Results showed that plant height of rice (Oryza sativa L. cv. Tainung No.67) and barnyardgrass increased rapidly after transplanting in both pure and competed populations and generally barnyardgrass grew faster and taller than rice in either crop. When grown with barnyardgrass, tiller and leaf numbers of rice were lower than the pure stands in both cropping seasons, and vice versa. Barnyardgrass was superior to rice in tillering capacity but fell down dramatically than rice in competition with the opponent. Leaf number and leaf area had the similar phenomenon, but rice produced greater leaf area than barnyardgrass in both crops. Rice and barnyardgrass exhibited marked differences in aboveground plant biomass accumulation. Biomass accumulation of rice was higher than of barnyardgrass, and both were reduced m competition of alien species. By growth analyses, it was shown that ratios of culm (CWR)， leaf (LWR) and panicle (PWR) weights were not altered by the competition in both plants. More biomass was found allocated to culm than to leaves. LWR was in a debasing trend after transplanting. CWR of rice reached the maximum at 60 (2nd crop, 1994) and 75 days (1st crop, 1995) after transplanting and then declined rapidly, whereas bamyardgrass maintained its CWR throughout the growth. Therefore, PWR increased linearly in rice and curvilinearly in barnyardgrass. As the results indicated, the two species exhibited differences in growth and competitiveness. Rice had higher leaf area Per Plant than barnyardgrass that offers an advantage competing for light but barnyanigrass is superior in plant elongation and early maturity to rice that help its Population in competitiveness in the field. 稗草[Echinochoa crus-galli (L.) Beauv.]乃水田常見之雜草，與水稻同步競爭環境自然資源，嚴重干擾水稻的生長及產量表現(Yang，1995b)。有關水稻與稗草在本省兩 期作生產系統下之生長行為及兢爭狀態時之差異•目前尚無文獻资訊可供參考•因此本研究特於臺灣省農業試驗所農場（臺中縣霧峰鄉）進行田間試驗，探討、比較此兩植物之生長差異性及競爭反應。參試水稻臺農67號(Oryza sativa L. cv. Tainung No. 67)栽植密度222,000株/公頃（行株距0.30公尺x 0.15公尺，小區面積2公尺x 7公尺），稗草對照組栽植密度一如水稻者，處理區則以稗草栽植於水稻行間，密度為15株/平方公尺。根據試驗结果，無論係對照或處理區，水稻與裨草在移植至本田後株高迅即增加，而稗草植株在一、二期作均較水稻高且伸長快。在混合族群競爭狀態下，此兩種植物在兩期作的分蘗數及葉片數皆減少。稗草的葉片數與分蘗能力雖然大於水稻，但是在競爭狀況下，其降低幅度高於水稻。兩者之葉面積在到達最高值後便下降，惟兩期作水稻單株葉面積均較稗草多。水稻與稗草地上部生質量的累積曲線呈現明朋差距，水稻之累積量大於稗草，惟兩者皆因競爭而降低。經由生長分析發現，稈重比(CWR)、葉重比(LWR)及穗重比(PWR)都不因競爭關係造成顯著差異，而生質量分佈於稈部多於葉部。兩植物之葉重比自移植後即呈下降趨勢，水稻之稈重比在到達高峰後（二期作約需60天，一期作約需75天）迅速減少，稗草之稈重比則持續維持。水稻之穗重比自抽穗後即呈線性增加，稗草抽穗早於水稻，穗重比以曲線趨勢和緩增加。試驗顯示，水稻與稗草具有不同的生長表現及競爭能力，水稻單株葉面積高於稗草，在光照競爭上較具優勢，有利於生質量的生成與蓄積；稗草植株伸長快而早熟，能在水田迅速建立族群，提升其競爭力。