Land use affects the distribution of soil inorganic nitrogen in smallholder production systems in Kenya

 We hypothesized that the integration of trees and shrubs in agricultural landscapes can reduce NO₃ ^– leaching and increase utilization of subsoil N. A field survey was conducted on 14 farms on acid soils in the subhumid highlands of Kenya, where there is little use of fertilizers, to determine the effect of vegetation types (VT) on soil NH₄ ⁺ and NO₃ ^– to 4 m depth. The VT included maize (Zea mays) with poor growth and good growth, Markhamia lutea trees scattered in maize, natural weed fallow, banana (Musa spp.), hedgerow, and eucalyptus woodlot. The effect of VT on NH₄ ⁺ was small (<1 mg N kg^–1). NO₃ ^– within a VT was about constant with depth below 0.25 m, but subsoil NO₃ ^– varied greatly among VT. Mean NO₃ ^–-N concentrations at 0.5–4 m depth were low beneath hedgerow and woodlot (<0.2 mg kg^–1), intermediate beneath weed fallow (0.2–0.7 mg kg^–1), banana (0.5–1.0 mg kg^–1) and markhamia (0.5–1.6 mg kg^–1), and high beneath both poor (1.0–2.1 mg kg^–1) and good (1.9–3.1 mg kg^–1) maize. Subsoil NO₃ ^– (0.5–4 m) was agronomically significant after maize harvest with 37 kg N ha^–1 m^–1 depth of subsoil beneath good maize and 27 kg N ha^–1 m^–1 depth beneath poor maize. In contrast, subsoil NO₃ ^– was only 2 kg N ha^–1 m^–1 depth beneath woodlot and hedgerow. These results demonstrate that the integration of perennial vegetation and the rotation of annual and perennial crops can tighten N cycling in agricultural landscapes. Received: 8 July 1999     

桉树采穗母株和采穗年限的选择

桉树丰产林能否获得速生、高产，除了气候、温度和土壤等立地条件和造林措施以及种苗品种等因子外，苗木扦插繁育技术也是重要因素，其中采穗母株和采穗年限的选择是关键环节．近几年，对湛江市桉树林进行了测定和调查．结果表明：与扦插苗作母株相比，组培苗作母株能扦插的穗条产量增产100-216．6％。组培苗造林后年平均生长量增加28．5％；组培苗的苗龄超过3a后．穗条产量和丰产林的年平均生长量均明显下降．采穗母株的采穗年限应控制在3a以内，3a后必须更新．     

黄芩水提液对肠炎模型小鼠空肠损伤修复的作用

本文旨在探讨黄芩水提液对肠炎模型小鼠空肠损伤的作用机理。将30只小鼠随机分为对照组、模型组和黄芩水提液低、中、高剂量组,每组6只小鼠。通过连续3 d给小鼠灌胃0.4 mL·d^-1产肠毒大肠杆菌（3×10⁸ CFU·mL^-1）建立肠炎模型,黄芩水提液组每只小鼠在攻菌前预灌服0.2 mL黄芩水提液（低剂量组0.3 g·d^-1,中剂量组0.6 g·d^-1,高剂量组1.2 g·d^-1）,连续灌胃6 d。结果显示,相比于对照组,模型组小鼠空肠炎性因子IL-6 mRNA表达量极显著升高（P<0.01）,空肠绒毛结构受到严重破坏,但参与肠道损伤修复的MAPK mRNA表达量未发生显著变化;相比于模型组,黄芩水提液各剂量组的小鼠空肠IL-6 mRNA表达量极显著下降（P<0.01）,空肠JNK/ERK mRNA表达量显著下降（P<0.05）,且绒毛结构得到显著改善。综上所述,在小鼠肠炎模型中,黄芩水提液可通过降低炎症反应和下调JNK/ERK mRNA的方式促进空肠的损伤修复。     

Effects of different agricultural treatments on narrowing winter wheat yield gap and nitrogen use efficiency in China

Under the limited cultivated land area and the pursuit of sustainable agricultural development,it is essential for the safety of grain production to study agricultural management approaches on narrowing the winter wheat yield gap and improving nitrogen use efficiency (NUE) in China.In this study,DSSAT-CERES-Wheat Model is used to simulate winter wheat yield under different agricultural treatments,and we analyze yield gaps and NUE with different management scenarios at regional scales and evaluate the suitable approaches for reducing yield gap and increasing NUE.The results show that,the potential of narrowing yield gap ranges 300–900 kg ha~(–1) with soil nutrients increase,400–1 200 kg ha~(–1) with sowing date adjustment and 0–400 kg ha~(–1) with planting density increase as well as 700–2 200 kg ha~(–1) with adding nitrogen fertilizer.Contribution rates of management measures of soil nutrients,sowing date adjusting,planting density,and nitrogen fertilizers are 5–15%,5–15%,0–4%,and 10–20%,respectively.Difference in nitrogen partial productivity ranges 3–10 kg kg~(–1) for soil nutrients,1–10 kg kg~(–1) for sowing date adjusting,1–5 kg kg~(–1) for planting density increase,and–12–0 kg kg~(–1) for adding nitrogen fertilizers,respectively.It indicates that four treatments can narrow yield gap and improve the NUE in varying degrees,but increasing nitrogen fertilizer leads to the decrease of NUE.     

地衣芽孢杆菌与3种微藻生长的相互影响

为弄清水产养殖中常用的有益菌--地衣芽孢杆菌和3种常见的浮游微藻的相互关系,本文采用陈海水配制的无机培养液和对虾养殖池水,分别研究了地农芽孢杆菌对微绿球藻、隐藻和颤藻的影响以及这几种微藻对地衣芽孢杆菌的反作用.以通径分析法分析微绿球藻、隐藻和地衣芽孢杆菌对颤藻直接和间接影响力的大小.结果发现,地衣芽孢杆菌对微绿球藻有一定的抑制作用,对隐藻的促进作用明显,而对颤藻的作用效果不明显;在与微绿球藻和隐藻混合培养时,地衣芽孢杆菌生长正常,仅在藻细胞密度较大时受到一定程度的抑制;在与颤藻混合培养时,地衣芽孢杆菌受到明显的抑制作用.通径分析结果发现,地衣芽孢杆菌与微绿球藻协同时颤藻产生抑制作用,而隐藻对颤藻的作用较弱.     

2CM-2型起垄式木薯种植机机架的模态分析及拓扑优化

以2CM-2型起垄式木薯种植机机架为研究对象,采用UG软件建立了机架的有限元模型,利用NX NASTRAN解算器进行了机架的模态特性分析,确定了机架前6阶模态振动固有频率范围、振动位移最大值和主要振型特征,明确了机架发生共振的情况,并进行机架拓扑优化。研究结果表明:优化后木薯种植机机架的前6阶模态固有频率为30.778～120.965 Hz,避免了路面激振频率与固有频率发生重叠共振,机架优化合理,动态特性良好。本研究为2CM-2型起垄式木薯种植机机架的优化改进提供理论参考依据,对提高木薯种植机机架的使用寿命具有重要意义。     

两种生长调节剂对大豆叶片昼夜同化物生理代谢及产量的影响

为探究两种不同类型植物生长调节剂对大豆叶片昼夜同化物生理代谢的影响,以两个大豆品种合丰50和垦丰16为试验材料,于始花期叶面喷施烯效唑(S₃₃₀₇)和2-N,N-二乙氨基乙基己酸酯(DTA-6),在鼓粒期的一昼夜内依次选取9∶30、17∶30、21∶30和5∶30(次日)4个时间点,测定功能叶片中蔗糖含量、淀粉含量、淀粉转化率、蔗糖代谢关键酶活性,并于成熟期测产。结果表明:S₃₃₀₇和DTA-6处理均能促进两品种叶片蔗糖和淀粉在白天的积累和夜间的降解,且S₃₃₀₇对两品种叶片蔗糖的调控效果优于DTA-6,DTA-6调控两品种叶片淀粉的作用效果优于S₃₃₀₇。在不同时间点S₃₃₀₇和DTA-6处理均能够提高两品种叶片夜间蔗糖和淀粉转运率。S₃₃₀₇和DTA-6处理能够提高两品种叶片蔗糖合酶和蔗糖磷酸合酶活性,且均在17∶30达最大值;S₃₃₀₇和DTA-6在整个昼夜变化中提高两品种蔗糖转化酶的活性。S₃₃₀₇和DTA-6能够有效调控两品种的单株荚数和单株粒数,提高产量,S₃₃₀₇和DTA-6处理后合丰50产量与对照相比分别增加17.76%和37.67%,垦丰16产量与对照相比分别增加11.34%和32.49%。综上所述,S₃₃₀₇和DTA-6处理均能通过促进叶片昼夜同化物代谢,提高合丰50和垦丰16大豆品种产量。     

论湛江茶文化与旅游业的互动发展

在倡导旅游业可持续发展的今天,旅游与文化呈现出相互依存、相互促进的良性循环态势,茶文化旅游也不例外。基于事实和推理,本文认为湛江的茶文化与旅游业之间正是呈现出良好的互动发展关系,一方面,茶文化可以丰富湛江旅游资源、提升旅游品位,进而提高旅游者的旅游体验,推动湛江旅游业发展;与此同时,旅游不仅促进茶产业的发展,同时可以有效继承和传播湛江茶文化。因此,加强湛江茶文化与旅游业的互动结合,不仅能在一定程度上推动湛江茶文化旅游的发展,而且是实现湛江旅游持续发展的可行举措之一。