Significance of Mn and Fe for growth of coastal marine diatom <Emphasis Type="Italic">Thalassiosira weissflogii</Emphasis>

The significance of Mn and Fe for the growth of a coastal marine diatom Thalassiosira weissflogii was investigated by performing culture experiments containing macronutrients with either Mn or Fe, or both. Only the addition of both Mn and Fe induced the highest growth rates and maximal cell yields. Maximal growth was maintained in continuous culture media, which were repeatedly prepared by an inoculation of pre-culture and the addition of both Mn and Fe to the control culture medium containing macronutrients. In particular, it was found that the full growth recovery in Mn-sufficient medium (without added Fe) is accomplished by the addition of Fe even after several days’ incubation. On the contrary, there was no sufficient growth recovery by the addition of Mn after a long incubation time in Fe-sufficient medium but without additional Mn. These results suggest that T. weissflogii in Mn-sufficient waters retains the ability for full physiological recovery for a long time, probably resulting from the decrease in the oxidative stress of phytoplankton by the production of antioxidant enzyme Mn superoxide dismutase during a long incubation period.     

《植物育种学》教学质量提升探索

根据社会发展对植物育种人才的要求,分析了《植物育种学》教学中存在的问题,总结了华南农业大学《植物育种学》教学团队在教学开展中的一些经验,提出了进一步改进的建议。     

种衣剂在小麦上的应用效果初报

就17%多·克·酮小麦种衣剂对幼苗生长的调控作用以及田间防治甘肃省小麦主要病害的实际应用效果进行了试验研究。盆栽试验结果表明,17%多·克·酮种衣剂安全的药种比为1:50,在此包衣比例下,不仅可提高出苗率,对植株生长无不良影响,而且能使植株根系活力显著增强,叶片叶绿素含量明显提高,生长后期抗倒伏能力增强;田间小区试验结果表明,对早期小麦条锈病的防效可达76.2%、小麦白粉病可达77.0%,对土传性小麦全蚀病的防效可达到82.1%,冬麦区小麦产量提高6.8%,春麦区小麦产量提高10.9%。     

城市近郊菜地不同耕作模式对土壤养分的影响

研究了不同种植模式下土壤养分的变化.试验结果表明,土壤碱解氯含量与有机质含量的变化呈正相关,土壤碱解氮含量可以反映土壤近期氮素供应情况.因此增加土壤有机质含量是提高土壤肥力的一种重要手段.化肥的施用是土壤速效钾的重要来源之一,农作物秸秆肥田对提高缺钾型土壤的速效钾含量有显著的效果.长期的蔬菜连作会加重土壤的负担,不利于城市近郊菜地的可持续利用,实行123种植模式(RVCs)有利于减轻土壤速效磷的富集.     

Deficit irrigation as an on-farm strategy to maximize crop water productivity in dry areas

Deficit irrigation (DI) has been widely investigated as a valuable and sustainable production strategy in dry regions. By limiting water applications to drought-sensitive growth stages, this practice aims to maximize water productivity and to stabilize - rather than maximize - yields. We review selected research from around the world and we summarize the advantages and disadvantages of deficit irrigation. Research results confirm that DI is successful in increasing water productivity for various crops without causing severe yield reductions. Nevertheless, a certain minimum amount of seasonal moisture must be guaranteed. DI requires precise knowledge of crop response to drought stress, as drought tolerance varies considerably by genotype and phenological stage. In developing and optimizing DI strategies, field research should therefore be combined with crop water productivity modeling.     

研究作物群体结构及生态因子时空分布的新方法——三维切片法

本文介绍了三维切片法的原理，用于切片的框架制作 ，操作方法和资料处理及表达方法。     

Evaporation from a Clay Soil Covered with a Surface Mulch - Three Lysimeter Studies

Cultivation systems with mulching have been successfully tested in spring cereals for several years in Sweden. The water conserving effect of the mulch was considered to be important in these field experiments. Three experiments with lysimeters were conducted in this study to investigate the effect on evaporation of a) different amounts of mulch, b) different types of mulch and c) different frequencies of rain in combination with mulching. The lysimeters contained undisturbed soil cores from a heavy clay soil. The protection against evaporation was largest at the beginning of soil drying. It increased with increasing amounts of mulch, but there were no differences in protection between the various kinds of mulch tested. Accumulated evaporation was 12, 14 and 30% lower in the mulched compared to bare soil after 28 days with no rain, infrequent rain and frequent rain respectively. The implications for designing a cultivation system with mulching are discussed as well as its potential in different weathers.     

Water retention and hydraulic conductivity of a loamy sand soil as influenced by crop rotation and fertilization

Measurements are reported of soil organic carbon content, dry bulk density, water retention characteristics, and saturated hydraulic conductivity of a sandy loam soil with two different crop rotations and two levels of fertilization. The water retention characteristics were fitted to the van Genuchten equation. Values of unsaturated hydraulic conductivity were estimated by calculation. It was found that crop rotation has much larger effects on these soil physical properties than fertilization. Water retention and hydraulic conductivity are greater when mustard, and clover with grass are included in the crop rotation, but only at water contents greater than 0,10 and 0, 13 kg kg^?1respectívely.     

化肥减施下土壤改良剂DK-1对设施丝瓜生长及土壤性状的影响

为研究DK-1型土壤改良剂对设施蔬菜生长及土壤性状的影响,进行了本次田间试验。本研究共设置4个处理,分别为:T1(不施用任何肥料)、T2(常规施肥处理)、T3(常规施肥处理配施土壤改良剂)和T4(化肥减施20%并配施土壤改良剂)。试验结果表明,土壤改良剂的施用具有促进丝瓜产量提升的潜力,T3较T2处理丝瓜产量增加9.89%;T3处理作物茎粗也有所增加,较T2和T4处理分别增加了13.22%和14.56%;各处理对丝瓜SPAD值的影响不大;土壤改良剂的添加可以显著促进土壤pH值的增加,T3和T4处理土壤pH值分别比T1处理土壤pH值增加了4.79%和5.39%;同时DK-1的添加可以显著降低土壤EC值,T3和T4处理土壤EC值均显著小于T2处理,分别降低了32.26%和23.66%。综上所述,化肥减施并配施DK-1型土壤改良剂,促进丝瓜植株生长、产量的提升和土壤理化性质的改善,均具有较强的可操作性,是设施蔬菜连作障碍防控的有效手段之一。     

Seasonal variations in sap flow and soil evaporation in an olive (Olea europaea L.) grove under two irrigation regimes in an arid region of Argentina

The emergence of intensively managed olive plantations in arid, northwestern Argentina requires the efficient use of irrigation water. We evaluated whole tree daily transpiration and soil evaporation throughout the year to better understand the relative importance of these water use components and to calculate actual crop coefficient (Kc) values. Plots in a 7-year-old ‘Manzanilla fina’ olive grove with 23% canopy cover were either moderately (MI) or highly irrigated (HI) using the FAO method where potential evapotranspiration over grass is multiplied by a given Kc and a coefficient of reduction (Kr). The Kc values employed for the MI and HI treatments were 0.5 and 1.1, respectively, and the Kr was 0.46. Transpiration was estimated by measuring main trunk sap flow using the heat balance method for three trees per treatment. Soil evaporation was measured using six microlysimeters in one plot per treatment. Both parameters were evaluated for 7-10 consecutive days in the fall, winter, mid-spring, summer, and early fall of 2006-2007. Maximum soil evaporation was observed in the summer when maximum demand was combined with maximum surface wetted by the drips and evaporation from the inter-row occurred due to rainfall. Similarly, maximum daily transpiration was observed in mid-spring and summer. Transpiration of MI trees was 30% lower than in HI trees during the summer period. However, this difference in transpiration disappeared when values were adjusted for total leaf area per tree because leaf area was 28% less in the MI trees. Transpiration represented about 70-80% of total crop evapotranspiration (ETc) except when soil evaporation increased due to rainfall events or over-irrigation occurred. We found that daily transpiration per unit leaf area had a positive linear relationship with daily potential evapotranspiration (r² = 0.84) when considering both treatments together. But, a strong relationship was also observed between transpiration per unit leaf area and mean air temperature (r² = 0.93). Thus, it is possible to predict optimum irrigation requirements for olive groves if tree leaf area and temperature are known. Calculated crop coefficients during the growing season based on the transpiration and soil evaporation values were about 0.65-0.70 and 0.85-0.90 for the MI and HI treatments, respectively.