中文摘要：

【目的】千金子是直播稻田的恶性杂草,严重危害水稻生长发育,降低水稻产量。研究直播稻田千金子对水稻生长的影响及其经济阈值,为制定稻田千金子的防治指标和措施提供科学依据。【方法】在大田条件下,采用添加系列试验法研究不同密度千金子（0、1、3、6、9、12、15、18和21株/m2）对直播中稻和双季早、晚稻生长和产量的影响,采用模型拟合法研究不同密度千金子与水稻产量构成因子及其损失率间的函数关系,依据经济危害允许水平（EIL）公式推导不同类型稻田千金子的防治经济阈值。【结果】直播水稻在千金子的竞争干扰下,植株的株高、分蘖数、有效穗数、每穗实粒数、千粒重及产量均随千金子密度的增加而逐渐降低。与无千金子对照比较,在千金子密度为21株/m2时,早稻、中稻和晚稻株高分别下降11.73%、4.80%和7.82%,分蘖力分别下降22.08%、29.67%和19.22%,有效穗数分别下降12.00%、25.57%和21.43%,每穗实粒数分别下降13.28%、15.07%和14.82%,千粒重分别下降12.11%、11.99%和7.03%,从而导致产量分别降低39.22%、44.36%和37.80%。采用二次曲线函数y=ax2＋bx＋c可较好地拟合千金子密度与早稻（y=-0.0037x2-0.1389x＋57.2631,P〈0.001）、中稻（y=-0.0007x2-0.0816x＋77.0617,P〈0.001）和晚稻（y=-0.0006x2-0.2032x＋78.0150,P〈0.001）株高的关系,与早稻（y=0.0229x2-3.5944x＋331.5809,P〈0.001）、中稻（y=-0.0529x2-5.3734x＋464.9348,P〈0.001）和晚稻（y=0.0302x2-3.7612x＋399.7899,P〈0.001）分蘖力的关系,以及与早稻（y=-0.0259x2-1.3288x＋282.2607,P〈0.001）、中稻（y=0.0208x2-4.9362x＋366.0443,P〈0.001）和晚稻（y=0.0412x2-3.6170x＋326.3593,P〈0.001）有效穗数的关系;而采用对数函数y=alnx＋b可较好地拟合千金子密度与早稻（y=-2.8309lnx＋87.8309,P〈0.001）每穗实粒数的关系,二次曲线函y=ax2＋bx＋c可较好地拟合中稻（y=0.0434x2-1.6046x＋94.99

英文摘要：

【Objective】 Red sprangletop（Leptochloa chinensis（L.） Nees.） is a troublesome weed seriously damaging rice growth and reducing rice yield in direct-seeding rice fields. The objective of this study is to investigate the effects of L. chinensis on rice growth in direct-seeding rice fields and its economic threshold, and provide a scientific basis for the formulation of control parameters on L. chinensis in direct-seeding rice fields and its control measures. 【Method】 A field experiment was carried out to study the effects of L. chinensis of different densities（0, 1, 3, 6, 9, 12, 15, 18 and 21 plant/m2） on the growth of middle, early and late rice of double seasons and their yields by the method of additive series experiment. The function relation between L. chinensis of different densities and forming factors of rice yields and their yield loss were investigated by the method of curve fits. Control economic thresholds on L. chinensis in different types of paddy fields were derived on the basis of the economic infestation level（EIL） formula. 【Result】 The plant height, tillers, effective spikes, filled grains per panicle, 1000-grain weight and grain yield of direct-seeding rice decreased gradually with the interference of L. chinensis as the weed density increased. Compared with the control, plant height of early, middle and late rice dropped by 11.73%, 4.80% and 7.82% at L. chinensis density of 21 plant/m2, respectively, tillers dropped by 22.08%, 29.67% and 19.22%, respectively, effective spikes dropped by 12.00%, 25.57% and 21.43%, respectively, filled grains per panicle dropped by 13.28%, 15.07% and 14.82%, respectively, and 1000-grain weight dropped by 12.11%, 11.99% and 7.03%, respectively, which resulted in rice yield dropped by 39.22%, 44.36% and 37.80%, respectively. The quadratic regression model y=ax2＋bx＋c was relatively better for describing the relationship between L. chinensis density and plant height of early rice（y=-0.0037x2-0.1389x＋57.2631, P〈0.001）, middle rice