垄沟覆膜集雨系统垄宽和密度效应对玉米产量的影响

通过大田试验研究了垄沟覆膜集雨系统中,垄宽和密度效应对玉米产量和水分利用效率的影响。垄沟覆膜集雨系统有30、60 cm 2种垄宽,低、中、高3种玉米种植密度。结果表明,垄沟覆膜集雨能提高土壤含水率和土壤微生物量碳质量分数。随着玉米密度的增加,同一垄宽的垄沟集雨系统中,玉米株高和单株生物量逐渐下降,玉米单位面积生物量逐渐增加。降雨量较少的情况下,60 cm垄宽的垄沟覆膜集雨能显著提高玉米的叶绿素质量分数,但其在高密度条件下却显著降低玉米叶绿素质量分数。高密度条件下,30 cm垄宽的垄沟覆膜集雨处理,由于玉米种内竞争较激烈而导致有机物质向籽粒输入减少,从而引起产量降低。在所有的处理中,高密度、60 cm垄宽的垄沟覆膜集雨种植的玉米产量和水分利用效率最高。     

覆盖材料和沟垄比对燕麦产量和水分利用效率的影响

为改善半干旱地区土壤水分状况和提高降雨资源利用率,在中国气象局兰州干旱气象研究所定西干旱气象与生态环境试验基地布置田间试验,采用完全随机设计,以无覆盖平作为对照,研究不同覆盖材料垄作(普通地膜、生物可降解地膜和无覆盖土垄)及垄作不同沟垄比(60 cm∶30 cm、60 cm∶45 cm和60 cm∶60 cm)对燕麦土壤贮水量、干草产量、籽粒产量、水分利用效率和经济效益等的影响。结果表明,就同一覆盖处理的平均值而言,土壤贮水量的排列次序为普通地膜≈生物可降解地膜土垄平作,在同一覆盖处理下,土壤贮水量随沟垄比减小而增加。土垄燕麦的干草产量、籽粒产量和水分利用效率比平作分别降低12%、18%和27%;生物可降解膜垄燕麦的干草产量、籽粒产量和水分利用效率比平作分别提高5%、4%和14%;普通膜垄燕麦的干草产量、籽粒产量和水分利用效率比平作分别提高7%、9%和23%。就大多数情况而言,燕麦干草产量、籽粒产量和水分利用效率随沟垄比减小而减小。对垄宽和实际籽粒产量的回归分析表明,当沟垄比为60 cm∶38 cm时,普通膜垄的燕麦实际籽粒产量达到最大值2 213 kg·hm-2;当沟垄比为60 cm∶34 cm时,生物可降解膜垄的燕麦实际籽粒产量达到最大值2 114 kg·hm-2。平作、土垄、生物可降解膜垄和普通膜垄燕麦经济效益分别为5 194元·hm-2、4 557元·hm-2、4 889元·hm-2和5 637元·hm-2。从燕麦籽粒产量、水分利用效率和环保等方面考虑,在我国半干旱黄土高原区沟垄集雨种植燕麦,覆盖材料应采用生物可降解膜,沟宽∶垄宽为60 cm∶34 cm。     

沟覆盖材料对垄沟集雨种植土壤温度、作物产量和 水分利用效率的影响

为寻求半干旱地区垄沟集雨环保的沟覆盖材料,改善土壤水分和温度状况,提高降雨资源利用效率,采用完全随机设计大田试验,以玉米和高粱作为供试作物,以沟无覆盖作为对照,研究垄沟集雨不同沟覆盖方式(无覆盖、液体地膜覆盖、秸秆覆盖和生物可降解地膜覆盖)对土壤温度、土壤水分、作物产量、水分利用效率等的影响。结果表明,与沟无覆盖相比,液体地膜和生物可降解地膜覆盖种植玉米的沟中作物全生育期表层(0~25 cm)土壤温度分别提高0.2℃和1.0℃,种植高粱的沟中表层土壤温度分别提高0.2℃和1.1℃,秸秆覆盖种植玉米和高粱的沟中表层土壤温度分别降低1.1℃和1.3℃;液体地膜覆盖、秸秆覆盖和生物可降解地膜覆盖0~140 cm土壤贮水量种植玉米分别提高0.4 mm、21.5 mm和8.6 mm,种植高粱分别提高2.3 mm、21.0 mm和10.9 mm。液体地膜覆盖和生物可降解地膜覆盖玉米青贮产量分别提高增加0.4%和10.4%,玉米籽粒产量分别增加1.6%和11.3%,玉米地上生物量分别增加0.7%和7.3%;高粱青贮产量分别增加0.2%和10.9%,高粱籽粒产量分别增加1.1%和11.8%,高粱地上生物量分别增加1.6%和9.4%;秸秆覆盖的玉米青贮产量、玉米籽粒产量、玉米地上生物量、高粱青贮产量、高粱籽粒产量和高粱地上生物量分别减少2.9%、2.2%、1.9%、0.7%、1.4%和1.0%。液体地膜覆盖、秸秆覆盖和生物可降解地膜覆盖种植玉米的水分利用效率分别提高0.9 kg·hm~(-2)·mm-1、0.5 kg·hm~(-2)·mm-1和4.9 kg·hm~(-2)·mm-1,种植高粱分别提高0.3 kg·hm~(-2)·mm-1、0.4 kg·hm~(-2)·mm-1和2.7 kg·hm~(-2)·mm-1。综合分析表明,生物可降解地膜适宜作为半干旱黄土高原区垄沟集雨沟覆盖材料。     

基于修正SCS-CN模型集雨垄径流预测

为了探寻半干旱区垄沟集雨种植控制水土流失和增产的机理,利用前2年(2012—2013年)日降雨量、实测径流和修正SCS—CN模型,率定集雨垄的径流模型参数CN、λ和α,然后利用后3年(2014—2016年)日降雨量和实测径流资料检验该模型有效性,预测不同覆盖材料(土壤结皮、生物可降解地膜和塑料地膜)和不同垄宽(30,45,60 cm)集雨垄的径流量。结果表明,土壤结皮覆盖集雨垄、生物可降解膜覆盖集雨垄和塑料地膜覆盖集雨垄的CN取值范围分别为82.0~82.9,97.9~98.8,98.3~99.9,λ取值范围分别为0.045~0.071,0.251~0.327,0.189~0.213,α取值范围分别为2.35~2.89,4.21~4.82,3.32~3.99。通过对模型有效性进行评价,土壤结皮覆盖集雨垄、生物可降解膜覆盖集雨垄和塑料地膜覆盖集雨垄的平均相对误差取值范围分别为1.36%~3.41%,1.21%~3.42%,2.48%~5.42%,纳什效率取值范围分别为0.97~0.98,0.97~0.98,0.96~0.98。日降雨量等级对修正SCS—CN模型参数CN、λ和α的影响不明显,不同覆盖材料之间的CN、λ和α差异远大于不同垄宽之间的CN、λ和α差异。修正SCS—CN模型集雨垄径流预测的相对误差满足要求(≤20%),可信度较高(纳什效率≥0.95),可以用于半干旱区集雨垄的径流预测,为控制水土流失和提高降水利用效率提供科学方法。     

垄沟集雨对紫花苜蓿草地土壤水分、容重和孔隙度的影响

在旱作条件下, 将垄沟集雨措施应用于紫花苜蓿种植, 研究沟垄宽比和覆膜方式对2年龄紫花苜蓿草地土壤水分状况、土壤容重及孔隙度的影响。结果表明: 全越冬期, 膜垄和土垄处理0~120 cm土壤水分平均散失量分别低于CK(平作)28.43 mm和13.61 mm。膜垄处理整个集雨期的蓄墒增加率为59.03%~99.27%, 产流效率为53.43%~91.72%; 2009年集雨前期(4月上旬~6月上旬)土垄处理的蓄墒增加率、产流效率分别为1.92%~2.74%和1.71%~2.55%, 2009年集雨中后期(6月中旬~9月下旬)土垄处理的蓄墒增加率、产流效率较集雨前期显著升高, 分别为8.85%~36.77%和8.01%~35.82%; 膜垄和土垄处理的蓄墒增加率、产流效率均随垄面宽度增加而显著增加, 且膜垄的蓄墒增加率、产流效率显著高于土垄处理。垄沟集雨种植能够显著降低0~40 cm土壤层容重, 且0~20 cm土壤层容重降幅表现为膜垄大于土垄。垄沟集雨种植也能够显著增加0~40 cm土壤层孔隙度, 且0~20 cm土壤层孔隙度增幅表现为膜垄大于土垄。     

旱作农田沟垄微型集雨结合覆盖玉米种植试验研究

田间沟垄微型集雨结合覆盖技术有效地利用了膜垄的集水和沟覆盖的蓄水保墒功能,改变了降雨的时空分布,使降雨集中富集在种植沟中,显著地提高了降水的利用效率,特别是小雨的利用率。研究结果表明:土垄的平均集水效率为7% ,而垄上覆膜后集水效率为87% ,膜垄能产生径流的最小降雨量为0 8mm。田间沟垄微型集雨结合覆盖技术能提高土壤贮水量,增加玉米的产量。垄上覆膜结合沟覆盖处理玉米产量比平地增加2 339～5 2 97kg/hm2 (44 %～14 3% ) ,水分利用效率基本都在2kg/m3 以上。     

坡地打结垄沟集雨对水土流失、紫花苜蓿干草产量和水分利用效率的影响

为寻求半干旱区控制水土流失和提高降水资源利用率的最佳坡地垄沟集雨种植方式,以传统平作为对照,在坡度5°和10°的坡地布置大田试验,研究打结方式(无打结垄和打结垄)对土壤贮水量、小区径流效率、径流量、泥沙流失量、紫花苜蓿干草产量和水分利用效率(WUE)的影响。结果表明:在坡度5°时,与平作相比,无打结垄和打结垄的紫花苜蓿全生育期土壤贮水量分别增加9.3,15.0mm,紫花苜蓿实际干草产量分别提高20.4%,8.9%,WUE分别提高4.78,4.58kg/(hm2·mm),而径流量分别降低21.9%,41.2%,泥沙流失量分别降低80.8%,83.3%。在坡度10°时,与平作相比,无打结垄和打结垄的紫花苜蓿全生育期土壤贮水量分别增加11.2,16.2mm,紫花苜蓿实际干草产量分别提高22.4%,9.0%,WUE分别提高4.89,4.06kg/(hm2·mm),而径流量分别降低24.8%,36.4%,泥沙流失量分别降低74.5%,82.0%。采用平均径流法,坡度5°时,平作、无打结垄和打结垄的小区径流效率分别为11.6%,9.2%,6.7%;坡度10°时,平作、无打结垄和打结垄的小区径流效率分别为14.1%,10.0%,7.8%。就紫花苜蓿全生育期平均值而言,坡度5°的平均土壤贮水量比坡度10°增加4.3mm,坡度5°的净干草产量、实际干草产量和WUE与坡度10°相差不明显。坡度10°的径流量、泥沙流失量和小区径流效率均是坡度5°的1.2倍。无打结垄和打结垄集雨种植具有较好水土保持和增产效果,其中无打结垄增产效果最为明显,打结垄水土保持效果最为明显。     

垄覆膜集雨对苜蓿草地土壤水分动态及利用效率的影响

我国西北黄土高原干旱半干旱区年降雨稀少和土壤水分周期性亏缺, 导致人工草地生产力低下、水分利用效率低。本试验在旱作条件下, 将垄覆膜集雨措施应用于紫花苜蓿种植, 研究了沟垄宽比和覆膜方式对2 年龄苜蓿草地土壤水分动态及水分利用效率的影响。结果表明: 垄覆膜集雨在集雨前期(4 月中旬至6 月上旬)显著提高0~20 cm 土层土壤含水量, 在集雨中后期(6 月中旬至9 月下旬)显著提高0~120 cm 土层平均含水量,越冬期增加土壤水分入渗能力, 提高20~120 cm 土层平均含水量; 且垄覆膜处理的集雨效率高于土垄处理。随着生育时期的延伸, 垄覆膜处理0~120 cm 土壤平均贮水量呈先降后升的趋势, 土垄处理0~120 cm 土壤平均贮水量呈由高到低的趋势; 在苜蓿生长后期垄覆膜处理的蓄墒能力显著高于土垄处理。垄覆膜处理的平均水分利用效率为34.91 kg·mm^-1·hm^-2, 为对照(平作, CK)的2.25 倍, 土垄处理的平均水分利用效率为28.47kg·mm^-1·hm^-2, 为CK 的1.83 倍, 垄覆膜相对土垄处理平均水分利用效率提高22.62%; 垄覆膜处理以沟垄宽比为60 cm∶60 cm 和60 cm∶75 cm 的水分利用效率最高。     

氮磷肥配施促进半干旱区沟垄集雨种植谷子节水增产

沟垄集雨种植是西北旱作农田广泛运用的高效节水栽培模式,为优化施肥配置,进一步提升其增产效能,该研究在沟垄集雨和平作2种种植模式下分别设置不施肥、低量（N 93 kg/hm2+ P2O548 kg/hm2）、中量（N 186 kg/hm2+ P2O596 kg/hm2）和高量（N 279 kg/hm2+ P2O5144 kg/hm2）共4个施肥量水平,对宁南旱区连续4 a（2012—2015年）施肥梯度处理下谷子产量及水肥利用效率进行了研究。结果表明,沟垄集雨种植较平作可有效降低土壤水分蒸发,谷子全生育期总耗水量减少了18.3~26.8 mm;同一施肥水平下,沟垄集雨种植在2012、2013年（丰水）呈减产趋势,在2014、2015年（平水）显著增产,较平作增加了穗粒数和收获指数,提高了谷子的水肥利用效率。在各降雨年份下,随施肥量的加大,沟垄集雨种植下谷子干物质积累量、产量和水分利用效率均呈增加趋势,当超过中肥后增幅不显著,肥料农学利用效率呈下降趋势,经济收益在中肥下达到最大。综合产量和经济效益分析,中肥是半干旱区谷子沟垄集雨种植模式的适宜施肥量,较平作种植在平水年型下可增产7.6%,水分利用效率和肥料农学利用效率分别提高了14.9%和9.9%。     

半干旱地区沟垄微型集雨种植马铃薯最优沟垄比的确定

采用沟垄微型集雨种植马铃薯，垄作为集水区，沟作为种植区，采用三种沟垄比和两种下垫面材料。在2001～2002年的试验中，膜垄种植马铃薯平均水分利用效率分别是对照的2.8倍(2001)和2.4倍(2002)，土垄种植马铃薯水分利用效率和对照相差不大；由于降雨量和降雨高峰期出现时段的不同，虽然使2001～2002年度沟垄微型集雨种植马铃薯产量有所差异，但在两年试验中，马铃薯增产趋势基本一致,膜垄种植马铃薯产量分别比对照平均提高231%(2001)和153%(2002)，土垄种植马铃薯产量分别比对照平均提高58%(2001)和23%(2002)。通过直线回归分析，在半干旱地区膜垄种植马铃薯最佳沟垄比为60 cm∶40 cm，当沟垄比为60 cm∶40 cm马铃薯产量的期望值可以达到最大，该技术是适合于半干旱地区的能较好提高降水利用率和产量的一种种植方式。     

Genetic similarities among Spanisch populations of Agropyron, Elymus and Thinopyrum, using PCR-based markers

Arbitrary oligonucleotides were used as primers to amplifygenomic DNA of 48 wild Spanish populations of Agropyroncristatum, Elymus hispanicus,E. caninus,E. repens,Thinopyrum curvifolium, Th.junceum and Th.intermedium. Genetic diversity was analysedusing nineteen primers. The number of amplified products ranged from8 to 18 per primer and a total of 240 markers were scored. Differentlevels of intraspecific genetic diversity were found, the allogamousspecies E. repens andTh. intermedium being themost variable. Jaccard's similarity coefficients for internalmeasure within and between populations were used to produce a clusterdiagram. The results demonstrate differences in the degree ofsimilarity between taxonomic units. Interpopulational variability andinterspecific genomic relationships of these species arediscussed.     

Evaluation of Paecilomyces lilacinus,chitin, and cellulose amendments in the biological control of Aspergillus flavus fungi

This study was undertaken to investigate the feasibility of using Paecilomyces lilacinus NRRL 13 866, chitin, and cellulose amendments, in order to reduce survival and prevent germination of sclerotia from Aspergillus flavus NRRL 6556, NRRL 13 048, and A. parasiticus NRRL 13 005, NRRL 13 539 buried in sandy soil in Georgia and Illinois (April–October, 1990). The number of sclerotia that germinated sporogenically in moist chambers following burial in Illinois was twice that of sclerotia buried in Georgia and varied among the four sclerotium-producing Aspergillus spp. strains. Sclerotium viability, as measured by Aspergillus spp. colony formation on potato dextrose agar, was high (>84%) for all strains and treatments (e.g. amendment, location). Even so, A. parasiticus NRRL 13 539 sclerotia were apparently more susceptible to P. lilacinus colonization than sclerotia from other strains. Treatment with Paecilomyces sp. caused a small but significant reduction in germination among sclerotia buried in Georgia.     

Ontogenic variation in nitrogen fixation and accumulation of nitrogen in mungbean,blackgram, cowpea,and groundnut

Ontogenic variations in N₂ fixation and accumulation of N by the mungbean (Vigna radiata L. Wilczek), blackgram (Vigna mungo L. Hepper), cowpea (Vigna unguiculata L. Walp.), and groundnut (Arachis hypogaea L.) were studied by a ¹⁵N-dilution technique. Pots filled with 7 kg of red yellow podzolic soil were used. Samples were taken 20, 40, 60, and 80 days after emergence which approximately corresponded to preflowering, flowering, early/mid-pod filling and late pod filling stages, respectively. During early growth (up to 40 days after emergence), the carryover of seed N accounted for a considerable fraction of the total plant N in the legumes, the highest being in the groundnut. With a correction for carryover, the groundnut derived over 45% of its N content from the atmosphere 20 days after emergence whereas the corresponding figures were 33% for the blackgram and about 28% for the cowpea and mungbean. Between flowering and early pod fill, there was a rapid increase in N₂ fixation in all legumes except in groundnut which showed highest fixation from 60 to 80 days after emergence. In the mungbean, N₂ fixation and uptake of soil N were insignificant 60 days after emergence while in other legumes these processes continued beyond this time. All legumes derived about 90% of their N from atmosphere by 80 days after emergence. However, due to considerable interspecific differences in total N yield the final amount of N₂ fixed showed an appreciable variation among legumes. It was highest in the groundnut (443 mg N plant^-1) followed by the cowpea (385), blackgram (273), and mungbean (145), respectively. The groundnut maintained nodules until the late pod filling stage while in other legumes, nodules senesced progressively following the mid-pod filling stage. During pod filling there was a net mobilization of N from vegetative tissues to developing pods in the mungbean, which amounted to about 20% of N in seeds. This mobilization was not evident in other legumes.     

Agricultural potential of Mediterranean grain and forage legumes: Key differences between and within Vicia species in terms of phenology, yield, and agronomy give insight into plant adaptation to semi-arid environments

In order to identify key adaptive traits which affect productivity in Mediterranean grain and forage legumes and simultaneously determine the agricultural potential of a wide range of Vicia species, germplasm collected from the wild throughout the eastern Mediterranean was grown under semi-arid conditions in Tel Hadya, Syria (313 mm growing season rainfall). These included species currently in use in Mediterranean agriculture, such as V. sativa L., as well as those more widely used in the past-such as V. ervilia L., but also a broad selection from Section Narbonensis (B. Fedtsch. ex Radzhi) Maxted, including V. narbonensis L, V. johannis Tamamsch., V. hyaeniscyamus Mout., V. serratifolia Jacq., and V. kalakhensis Khattab et al. V. faba, a near relative of the taxa in Section Narbonensis, was included as a domesticated control. Where applicable, a representative range of subspecies was used. Accessions were chosen from a wide range of habitats in terms of latitude (31.02–40.72 decimal^o), longitude (27.1–43.17 decimal^o), altitude (20–1510 m), rainfall (180–1700 mm/yr) and soil depth (5–50 cm) in order to maximise diversity within species. Agricultural potential was determined by measuring seed, hay and biological yield, as well as agronomic traits such as harvest index, standing crop height, and seed size. The comparative influence of phenology and key agronomic traits such as plant habit and seed size on productivity varied tremendously between species, depending on their reproductive strategies. In V. sativa and V. ervilia, the smaller seed species which rely on long vegetative phases and growing seasons to accumulate sufficient biomass to set seed, and in which there was comparatively little agronomic variation, phenology had a large impact on yield. In early emerging taxa such as V. ervilia and V. s. subsp. sativa, with built-in long vegetative phases and growing seasons, seed yield was negatively correlated with flower ing (r = –0.86 to –0.88), whereas the opposite was the case for later emerging taxa such as V. s. subsp. nigra (L.) Ehrh. (r = 0.95). Within V. narbonensis and relatives, the larger seeded Vicia species which rely on more conservative reproductive strategies where high seedling vigour associated with large seeds enables the species to enter reproductive phases relatively early, phenology had a much smaller impact on yield than did variation of key traits such as seed weight, plant habit and pod shattering. Among the undomesticated germplasm harvest indices ranged from 0.09–0.31, hay yields from 0.1–3.4 t/ha, seed yield from 0–2.0 t/ha, and dry matter at maturity from 1.6–6.5 t/ha. Sub-specific taxonomy was crucial in determining agronomic potential. V. narbonensis var. aegyptiaca Kornhuber ex Asch. et Schweinf. showed the most potential, combining an upright habit, large seeds (212 mg) and tendency to retain intact pods after maturity, with the highest yield, harvest index and crop height of all the wild Vicia species. V. sativa subsp. sativa, V. ervilia and V. narbonensis var. narbonensis were less productive, but still showed agricultural potential. The smaller seeded V. narbonensis, var. affinis, var. jordanica H. Schäf. and var. salmonea (Mout.) H. Schäf., and their close relatives V. johannis, V. hyaeniscyamus, V. serratifolia and V. kalakhensis have little to offer Mediterranean agriculture on the basis of poor agronomy.     

Nitrogenase activity associated with leaf,root, and rhizosphere soils in an Indian tropical forest

Summary N₂ fixation (acetylene reduction assay) by phylloplane microorganisms was measured in dominant and co-dominant plant species growing in a tropical rain forest. No significant acetylene reduction was recorded with intact leaf samples. Azotobacter sp., Beijerinckia sp., Derxia sp., and Klebsiella pneumoniae were isolated as phylloplane N₂-fixing bacteria. Azospirillum lipoferum was only isolated from soil samples containing the roots of Poaceae. Nitrogenase activity was recorded in culture derived from the roots and rhizosphere soil samples, although low acetylene reduction activity indicates that these associations did not provide large amounts of N to the systems studied.     

In situ net N transformations in pine,fir, and oak stands of different ages on acid sandy soil, 3 years after liming

Summary The effect of liming on in-situ N transformations was studied in two stands of different ages of each of Scots pine (Pinus sylvestris L.), Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and common oak (Quercus robur L.). The stands were located on acid sandy soils in an area with high atmospheric N input. The organic matter of the upper 10-cm layer of the soil, including the forest floor, had a relatively high N content (C: N ratio <25) in all stands. Using a sequential core technique, N transformations were measured in both control plots and plots that had been limed 3 years previously with 3 t ha^-1 of dolomitic lime. Limed plots had a higher net NO _inf3 ^sup- production and a higher potential for NO _inf3 ^sup- leaching than the controls in all stands except that of the younger oak. Net N mineralization did not differ significantly between limed and control plots in oak stands and younger coniferous stands but was significantly lower in the limed plots of the older coniferous stands. It is concluded that long-term measurements of net N mineralization in limed forest soils are needed to evaluate the effect of liming with respect to the risk of groundwater pollution.     

Interactions between climate, beaver activity, and pond occupancy by the cold-adapted mink frog in New York State, USA

Mink frogs (Rana septentrionalis) are cold-adapted, climate-sensitive amphibians occurring above the 43rd parallel in North America. We conducted repeated night call surveys at 46 ponds near the southern edge of the species’ range to collect presence/absence data and used information-theoretic models to relate pond occupancy to historical climate and habitat factors. Mink frog occurrence was strongly and positively influenced by pond size (>1.5 ha) and the presence of beavers (Castor canadensis). Presence of calling mink frogs decreased sharply at sites with historical mean July air temperatures >19.5 °C. Our results suggest that predicted changes in temperature over the next century might reduce the range of mink frogs in New York, yet we hypothesize that any such reductions could be mitigated by generation of suitable breeding habitat associated with future expansion of beaver populations.     

Influence of humic acids on laurel growth,associated rhizospheric microorganisms,and mycorrhizal fungi

Summary Increasing concentrations of humic acids were tested in order to determine their effects on the microbial rhizosphere and the growth of laurel (Laurus nobilis L.). Plants that were treated with 300 mg kg^-1 of humic acids had the heaviest weights of both fresh and dry shoots; however, doses of 3000 mg kg^-1 were highly phytotoxic and inhibited the growth of laurel. Total aerobic bacteria and actinomycetes were stimulated by doses of 1500 and 3000 mg kg^-1 of humic acids at the first harvest. Nevertheless, at the end of the experiment no significant differences were found among the different doses. The number of fungi living in the laurel rhizosphere was not affected by any concentration of humic acids. Vesicular-arbuscular mycorrhizal (VAM) colonization was only slightly affected by the addition of increasing concentrations of humic substances to the soil, while the hyphal growth of Glomus mosseae was reduced.     

Crossability relationships between the common potato, Solanum tuberosum spp. tuberosum, and its wild diploid relatives S. kurtzianum and S. ruiz-lealii

The common potato, Solanum tuberosum spp. tuberosum (tbr), is a tetraploid species with a narrow genetic base, but with a large number of related species that harbor great genetic diversity for numerous characters of agronomic interest. S. kurtzianum (ktz) and S. ruiz-lealii (rzl) are wild diploid relatives with potential resistance to adverse biotic and abiotic factors. To evaluate if this wild germplasm can be incorporated by conventional crosses into the tbr gene pool, pollen-pistil compatibility relations and seed set in interspecific crosses with tbr were investigated. In 4x tbr × 2x ktz crosses and the reciprocals, 89% and 52.2% of genotypic combinations (respectively) were compatible at the pollen-pistil level. Seeds were obtained from some genotypic combinations in both directions of the cross, suggesting that functional 2n gametes might be produced by particular ktz genotypes. In 2x rzl × 4x tbr crosses and their reciprocals, 35% and 11.7% (respectively) of the genotypic combinations were compatible at the pollen-pistil level, but no seeds were obtained. These results indicate that the reproductive isolation between 4x tbr and 2x ktz is incomplete, and that gene exchange between them is feasible. Moreover, further studies will have to be carried out with rzl to ascertain its crossability with 4x tbr.     

Effects of mulch location on banana weevil,soil and plant nutrients,soil water and biomass in banana fields

Major constraints to banana (Musa spp., genome group AAA) production, a dietary staple for over 70 million people in sub-Saharan Africa, are pest infestations, poor nutrition and inadequate water. Although mulch can improve soil water and nutrient status, many farmers believe it also promotes the proliferation of banana weevil (Cosmopolites sordidus), one of the most serious banana pests. In this study, we evaluated the effects of mulch location (mulch to base of banana pseudostem; mulch recessed 1 m from the pseudostem) on banana weevil, soil and plant nutrient status, soil water, and banana growth and development. After 3 years, the fully mulched plots had significantly more soil Ca and Mg than plots that did not receive mulch. Banana foliar K concentration was significantly higher in both mulch treatments (full and recessed) than in the control (no mulch) plots. The mulched plots had greater recharge after rainfall events and higher soil water contents during dry periods due to increased infiltration in the mulched plots. However, the mulched plots also exhibited significantly higher banana weevil densities and greater plant damage than the control plots. There was no difference in weevil damage with mulch location, although weevil density was higher in the fully mulched plots throughout most of the trial. Despite greater weevil damage, the treatments that were mulched yielded significantly heavier bunches. Hence the effects of the mulch on soil water infiltration and banana foliar nutrient status outweighed the detrimental effects of banana weevil damage.