Effects of Gliricidia sepium (Jacq.) Steud and Leucaena leucocephala (Lam.) de Wit on growth and development of Imperata cylindrica (L.) Raeuschel.

Field studies carried out in a forest transition site on a tropical Alfisol in southwestern Nigeria, show that shading by gliricidia (Gliricidia sepium (Jacq.) Steud) and leucaena (Leucaena leucocephala (Lam.) de Wit) hedgerow species reduced density of speargrass (Imperata cylindrica (L.) Raeuschel) by 67% and 51%, respectively. Shoot biomass of speargrass decreased by 81% and 78% in gliricidia and leucaena hedgerows, respectively. Reduction in speargrass rhizome biomass in gliricidia plots was 96% while rhizome reduction in the leucaena plots was nearly 90%. Rhizome mortality was significantly higher in gliricidia plots than in leucaena and control plots. The bulk of rhizomes was found between 10 cm and 20 cm of soil depth but rhizome did not penetrate further than 30 cm depth in the Alfisol in which this study was carried out. Gliricidia was better than leucaena hedgerow species in suppressing speargrass.     

丝茅入侵对高羊茅根系及土壤性状的影响

针对南方地区丝茅(Imperata koenigii (Retz.) P. Beauv.)入侵对冷季型草坪造成严重危害的实践生产问题,通过模拟高羊茅(Festuca arundiacea L.)草坪建植时丝茅入侵形成的混生群落,连续测定群落中根长密度、根干重密度和根体积密度等根系性状指标,土壤容重、土壤含水量及pH等土壤性状指标,分析丝茅入侵对高羊茅草坪根系及土壤性状影响的动态变化。结果表明:丝茅入侵对高羊茅草坪根长密度、根干重密度和根体积密度均有极显著影响(P<0.01);丝茅入侵60 d起影响根长密度,90 d起影响根干重密度,150 d起影响根体积密度;侵入持续时间对高羊茅根系指标影响排序为根体积密度>根干重密度>根长密度;丝茅对草坪分层土壤的含水量、容重和pH均有极显著影响(P<0.01);入侵60 d起首先影响高羊茅根系主要分布的10~20 cm层的土壤性状,影响逐渐向上、向下扩展;持续时间对土壤性状的影响排序为土壤含水量>容重>pH;丝茅入侵使高羊茅根系分生和更新能力下降,使其根系分布土壤层的含水量降低、透气性变差、酸度增高,从而降低高羊茅根系活性与吸收能力,使其竞争力降低而逐渐退化。本试验结果将为草坪中丝茅的防治提供基础数据。     

Effect of method of Imperata cylindrica management on maize grain yield in the derived savanna of south-western Nigeria

Field studies were conducted in 1991 and 1992 on a sandy loam soil in the derived savanna zone of south-western Nigeria to assess the effect of the underground organs of Imperata cylindrica (L.) Raeuschel on maize grain yield. Total dry matter of I. cylindrica in abandoned arable land averaged 16 t ha⁻¹ and rhizomes contributed 56% of this. Rhizome removal from soil before planting maize significantly increased maize yield relative to hoe tillage or slashing of I. cylindrica shoots before planting maize. Digging up rhizomes before planting maize and weeding the crop twice gave a yield reduction of only 23% compared with weed-free crops with rhizomes removed. Grain yield reduction was 51% in plots where rhizomes were only fragmented by hoe tillage and the crop was weeded twice. Grain yield was 62% less when maize was grown in slashed plots with intact rhizomes that were weeded four times (farmers' practice). Slashing without additional weeding resulted in crop failure in maize.