反枝苋对棉花的密度竞争作用

【目的】反枝苋是世界性恶性杂草之一,为安徽省沿江棉区主要杂草,而棉花对杂草竞争十分敏感。论文旨在明确反枝苋对棉花的密度竞争影响,为棉田杂草反枝苋的综合防治提供理论依据。【方法】2013—2015年在安徽省安庆市试验地,采用添加系列试验方法,棉花密度保持不变,设置8个反枝苋密度(0、0.125、0.25、0.5、1、2、4、8株/m)与棉花全生育期竞争,研究不同反枝苋密度竞争对棉花生长、子棉产量及其构成因素、纤维品质的影响。【结果】随着反枝苋密度增加,反枝苋株高、茎直径逐渐减小;相对于0.125株/m的反枝苋,反枝苋茎直径分别于1株/m(2013年和2014年)、0.5株/m(2015年)显著降低12.0%—18.6%;反枝苋株高则在2015年于0.5株/m显著减少24.2%。3年数据平均,单位面积反枝苋生物量由1 156.9 kg·hm-2(0.125株/m)逐渐增加到7 524.0 kg·hm-2(8株/m),较高密度反枝苋种内竞争明显。随着反枝苋与棉花竞争时间的延长,反枝苋株高于52—83 DAE(出苗后天数,days after emergence)逐渐超过棉花的,茎直径于18—70 DAE逐渐大于棉花的。在棉花成熟期,反枝苋株高比棉花高35.6—128.2 cm,反枝苋茎直径比棉花粗9.9—24.8 mm。反枝苋在株高和生物量上对棉花具明显优势。随着反枝苋密度增加,棉花株高变化不明显,茎直径明显减小;棉花单株铃数、果枝数和单铃重显著减少,衣分也有一定程度减小。1株/m的杂草密度导致棉花单株果枝数减少4.63%—69.18%,铃数减少20.81%—84.98%,单铃重减少3.04%—20.36%,衣分减少1.54%左右。引起子棉产量显著减产的反枝苋密度分别是0.125株/m(2013年)和0.25株/m(2014年和2015年),导致子棉减产14.0%—33.7%;子棉产量损失率与反枝苋密度符合双曲线模型,据此可预测子棉减产50%的反枝苋密度为0.2—2.8株/m。在反枝苋与棉花竞争91 DAE,0.125—0.5株/m反枝苋可显著减少棉花单株果枝数和铃数。在部分年份,棉纤维的上半部平均长度、马克隆值及断裂比强度随反枝苋密度增加有减小的趋势,且差异显著。【结论】在安徽省沿江棉区,当反枝苋与棉花全生育期竞争时,对反枝苋及棉花的株高影响不明显,对两者的茎直径产生显著影响;随着竞争时间的延长,反枝苋的株高和茎直径逐渐大于棉花的;因而反枝苋在株高和生物量上对棉花具有竞争优势。反枝苋苗期是其防治关键期。当反枝苋密度逐渐增加时,其种内竞争逐渐增强。反枝苋生物量易受环境条件影响,随着反枝苋密度增加,单位面积反枝苋生物量增加,对棉花生长和产量的抑制作用明显增强。反枝苋竞争主要通过影响棉花单株铃数和单铃重而减少棉花产量。推测本地区导致子棉减产5%的反枝苋密度为0.011—0.090株/m。

The Influence of Redroot Pigweed (Amaranthus retroflexus) Density on Cotton (Gossypium hirsutum)

【Objective】Amaranthus retroflexus is one of the worst agricultural weeds in the world, and it is a major weed in cotton belt along Changjiang River in Anhui Province. Cotton is very sensitive to the competition of weeds. The objective of this study is to clarify the interference impact of A. retroflexus in cotton field, and to provide useful information for weed control programs. 【Method】Field additive series experiments were conducted to evaluate the influence of 8 A. retroflexus densities on growth, yields and yield components, fiber properties of cotton with full-season interference of A. retroflexus during 2013-2015 in Anqing test plot of Anhui Province, with cotton density no changing. The weed densities employed were 0 (the check), 0.125, 0.25, 0.5, 1, 2, 4 and 8 plants/m of row. 【Result】With the increase of weed density, plant height and stem diameter of A. retroflexus gradually decreased, and the plant stem diameter reduced obviously by 12.0%-18.6% at the density of 1 plant/m of row (2013 and 2014) and 0.5 plant/m of row (2015) than that at the density of 0.125 plant/m of row, respectively. The plant height reduced significantly by 24.2% at the density of 0.5 plant/m of row than that at the density of 0.125 plant/m only in 2015. The per unit area biomass of A. retroflexus increased from 1 156.9 kg·hm^-2 at density of 0.125 plant/m of row to 7 524.0 kg·hm^-2 at the density of 8 plants/m of row over the average of three years. Intraspecific competition among A. retroflexus plants was observed at the higher weed densities. With the increasing interference between A. retroflexus and cotton, A. retroflexus remained taller and thicker than cotton after 52-83 DAE and 18-70 DAE, respectively. At the maturity stage of cotton, the plant stem height of A. retroflexus was 35.6-128.2 cm higher than that of cotton, and the plant stem diameter of A. retroflexus was 9.9-24.8 mm thicker than that of cotton. A. retroflexus had more obvious advantages than cotton in plant height and biomass. The interference of A. retroflexus density had no significant influence on cotton height, but cotton stem diameter reduced obviously at higher weed densities. With the increasing of weed density, per plant bolls, fruit-branch numbers, single boll weight of cotton reduced significantly; and lint percentage of cotton also decreased to some extent. Bolls, fruit-branch number per plant and single boll weight reduced by 20.81%-84.98%, 4.63%-69.18% and 3.04%-20.36% at the density of 1 plant/m of row, respectively; and lint percentage reduced by about 1.54% at this density. The interference of A. retroflexus affected significantly on seed cotton yield at the density of 0.125 plant/m of row (2013) and 0.25 plant/m of row (2014 and 2015), respectively, and the seed cotton yield reduced by 14.0%-33.7% at these densities. The relationship between cotton yield loss rate and the density of A. retroflexus was described by the hyperbolic regression model, which estimated that a density of 0.2-2.8 weed plant/m of row would result in 50% seed cotton yield loss from the maximum yield. Boll and fruit-branch numbers per plant of cotton were reduced obviously at the density of 0.125-0.5 plant/m of row of A. retroflexus after 91 DAE. In some year, the fiber length, Micronaire and fiber strength of cotton fiber significantly decreased with increase of weedy densities.【Conclusion】 The full-season interference of A. retroflexus had no significant influences on plant height, and obvious impacts on plant stem diameter of cotton and A. retroflexus in cotton belt along Changjiang River in Anhui Province. With the increase of interference time between A. retroflexus and cotton, A. retroflexus surpassed cotton in plant height and stem diameter. It was concluded that A. retroflexus had competitive advantages over cotton in plant height and biomass and A. retroflexus should be controlled at its seedling stage critically. Intraspecific competition among A. retroflexus plants was enhanced with increasing weedy density. The biomass of A. retroflexus is easily affected by environmental conditions. The per unit area biomass of A. retroflexus increased with increase of weed density, and the impact on cotton development and yields were enhanced obviously. The cotton yields were reduced by the interference of A. retroflexus through decreasing boll numbers per plant and single boll weight of cotton. It was inferred that a density of 0.011-0.090 plant/m of row of A. retroflexus would result in a 5% seed cotton yield loss from the maximum yield.