新银合欢种子的萌发检验

通过用4个不同恒温、1个变温及用80 ℃热水、98%的浓硫酸不同时间分别浸种对新银合欢Leucaena leucocephala种子进行发芽试验,研究不同处理水平和不同处理组合对新银合欢种子萌发的影响.结果表明:在不同处理水平下,新银合欢种子发芽率、发芽势的最佳温度分别为18 ℃16 h/28 ℃8h 变温和20 ℃恒温,发芽率、发芽势的最佳热、酸蚀处理分别为酸蚀20和45 min;在不同处理组合下,新银合欢种子发芽率、发芽势最佳处理组合均是18 ℃16h /28 ℃8h 变温与98%浓硫酸浸种45 min的组合.     

银合欢生态适应性研究

１９９０年引入１１个种源的银合欢，在南亚热带云南景东育苗栽培试验，结果表明银合欢有较强的生态适应性，其中勐腊、元谋、元法种源生长较好，东扑硅Ｋ×１、Ｋ×３Ｃ显示了抗逆性强的杂交优势，为我国热带、南亚热带地区推广栽培银合欢提供了科学依据。     

水分胁迫对银合欢种子萌芽的影响

采用配置不同浓度的PEG(聚乙二醇)溶液,对银合欢种子萌芽进行人工水分胁迫处理。结果表明:银合欢种子发芽过程的水势范围为0~-0.4 Mpa;随着水分胁迫加剧,种子发芽率、发芽速度、芽长、发芽指数、活力指数呈下降趋势;当水势为-0.6 Mpa时,种子不能发芽。表明,银合欢在轻度干旱胁迫时,具有一定的耐旱性。     

脱毒银合欢饲喂小白鼠的安全利用研究

选取平均体重18~21 g左右,雌雄各半的N IH系小白鼠50只,随机分为5组,每组10只,进行5周饲养试验。A组为对照组,饲喂小白鼠基础日粮。B、C、D、E组为试验组,在小白鼠基础日粮上分别添加20%、30%的晒干银合欢叶粉和20%、30%经过1.2%F eC l3处理的银合欢叶粉。试验结束时,全部扑杀,采血检查血常规血清,剖检,取下脏器称重,计算心、肝、脾、肺、肾的脏器系数。结果表明:所有银合欢叶粉替代部分基础日粮饲喂小白鼠,适口性好,小白鼠正常采食。用经过1.2%F eC l3处理的银合欢叶粉替代20%的基础日粮饲喂小鼠,小白鼠在最后平均体重、平均日增重、料重比方面相近于对照组(P>0.05),优于用经过F eC l3处理的银合欢叶粉替代30%的基础日粮组。各组的心、肝、脾、肺、肾系数之间无显著差异(P>0.05),内脏器官正常。B、C组的血红蛋白(HGB)、红细胞(RBC)、白细胞(W BC)与对照组差异显著(P<0.05)。D、E组的血红蛋白(HGB)、红细胞(RBC)、白细胞(W BC)、淋巴细胞(LYM PH)与对照组没有显著差异(P>0.05)。各组的尿素氮(BUN)、肌酐(CRE)、谷丙转氨酶(ALT)、谷草转氨酶(A ST)均无显著差异(P>0.05)。     

Paraiso (Melia azedarach var. “Gigante”) woodlots: an agroforestry alternative for the small farmer in Paraguay

This paper describes the salient aspects and analyses the potential of the Paraiso Woodlot System, which is becoming popular as an agroforestry alternative to land use in the degraded acid sandy soils of the humid sub-tropical Guayaybi area of Paraguay. The system consists of a combination of paraiso (Melia azedarach var gigante) with other trees, especially Leucaena leucocephala, and annual crops.The fast growth habit, deep root system, addition of large quantities of organic matter through leaf and litter fall, compatibility with agricultural crops, high value of the sawlogs and production of substantial quantities of poles and firewood make paraiso an excellent species for agroforestry combination. Preliminary results of the trials indicate that the woodlots are successful and with increasing efforts of the extension agencies, they are being accepted as a viable alternative to traditional agricultural systems.Besides discussing the potential of these woodlots based on initial results, the paper identifies the constraints of the system and highlights the priority research areas.     

Effects of salt stress on nitrogen fixation,oxygen diffusion,and ion distribution in soybean,common bean,and alfalfa

The exposure of legume nodulated‐roots to 100 mM NaCl resulted in a rapid decrease in plant growth associated with a short‐term inhibition of both nodule growth and nitrogenase activity (C₂H₂ reduction=ARA). However, these NaCl effects varied among species, common bean being more sensitive than soybean and alfalfa. The higher sensitivity of common bean was associated with a higher accumulation of sodium (Na) and chlorine (Cl) in the nodules and only a small difference between salt‐treated and control plants of common bean in their responses of ARA to raising rhizosphere pO₂. By contrast, soybean and alfalfa plants showed a higher stimulation of ARA by pO₂ for the salt‐treatment than for the control. It is concluded that the intraspecific variation in short‐term inhibition of ARA by salt may involve the regulation of O₂ diffusion and the distribution of ions in nodules.     

Effect of alley cropping with Leucaena leucocephala and fertilizer application on yield of vegetable crops

Field experiments were conducted to investigate the effect of alley cropping vegetable crops with Leucaena leucocephala (Lam.) de Wit for two seasons on a sandy loam Oxic paleustalf in southwestern Nigeria. Four vegetable crops (Amaranthus cruentus L.; Celosia argentea L.; Okra, Hibiscus esculentus L.; and tomato, Lycopersicon esculentum Mill.) were grown in control plots and in 4-m wide alleys between established Leucaena hedgerows without and with fertilizer (30 N-13 P-24 K kg ha^–1). Leucaena prunings yielded large dry biomass and nutrients during both seasons. Yield of four vegetable crops responded more to fertilizer in control than in alley cropped treatments. Better yield of vegetables in alley cropped plots was in part due to following effect of the Leucaena hedgerows. Fertilizer application increased mean yields of Amaranthus, Celosia, okra and tomato by 325, 164, 47 and 94% in control plots and by 36, 26, 4 and 20% in alley cropped plots, respectively. For both seasons, yields were not significantly different between alley cropped with and without fertilizer and the control with fertilizer treatments. Yield was least in control without fertilizer. Alley cropping with Leucaena can reduce fertilizer requirement for vegetable production. Cost and return analysis using 1988 prices indicated that alley cropping with vegetable crops can be profitable.c/o Miss Maureen Larkin, L. W. Lambourn & Company, 26 Dingwall Road, Croydon CR9 3EE, England     

Diurnal and seasonal variations on soil CO2 fluxes in tropical silvopastoral systems

This study aimed to quantify the dynamics of soil CO₂ fluxes in two silvopastoral systems based on Leucaena leucocephala, one associated with Panicum maximum (L + P) and another with Cynodon plectostachyus (L + C). We measured CO₂ fluxes fortnightly during the dry and rainy seasons in the morning and the afternoon, with an infrared gas analyzer. Simultaneously, we measured soil temperature, soil moisture, ambient temperature, and relative humidity. Soil CO₂ fluxes ranged from 6.0 ± 0.14 to 6.1 ± 0.12 µmol CO₂/m²/s but no statistical differences were observed between systems. Soil CO₂ flux in the L + P was 12.5% higher in the rainy season compared with the dry season but the season did not affect the fluxes in L + C. Regarding the diurnal variation, CO₂ fluxes were 17.6%–34.8% higher in the morning compared with afternoon measurements. Soil moisture and temperature were higher in L + C, but the ambient temperature and relative humidity showed no statistical differences between systems. In both systems, soil temperature was greater in the afternoon, while the soil moisture and relative humidity were greater in the morning. The diurnal variation of soil CO₂ fluxes in silvopastoral systems correlated positively with soil temperature and ambient temperature, but negatively with relative humidity. We concluded that soil CO₂ fluxes did not vary between silvopastoral systems but respond differently to the seasons. The results have important implications on the establishment and management of Leucaena-based silvopastoral systems for the mitigation of soil CO₂ fluxes from extensive livestock production lands.     

蒋家沟泥石流区新银合欢细根固土效应

以蒋家沟泥石流区不同龄级新银合欢根系为研究对象,在分析其垂直分布与构成特征的基础上,运用加筋原理研究其固土效应。结果显示,不同龄级新银合欢根系表聚现象明显,随土层深度的增加呈减少趋势,约80%集中在0—120cm土层范围内;细根（D≤1mm）在整个细根根系中所占比例较大,决定着整个细根的分布趋势;10年生新银合欢D≤1mm细根较5年生增幅明显,15年生1mm     

Nitrogen contribution by leucaena (Leucaena leucocephala) prunings to maize in an alley cropping system

Summary The N uptake of maize was assessed on an Alfisol in a sole crop and in an alley cropping system in southwestern Nigeria. Although the application of prunings increased the maize N content in both sole and alley-cropped maize, the N contributed to the maize by the prunings was low, ranging between 4.4 and 23.8 kg ha^–1. This was equivalent to 3.2% and 9.407% of the N released during decomposition of the prunings. Application of the prunings increased the grain yields of the sole maize by 38% and the maize yield in the alley-cropped plots by 104%, compared with yields in the corresponding plots where prunings were not applied. The results indicate that part of the N from the prunings was retained in the soil organic-N pool. Maize N, dry weights and grain yields were lowest in the alley-cropped plots where prunings were removed, probably because of competition between the maize and the hedgerow trees.