Soil organic carbon and phosphorus availability regulate abundance of culturable phosphate-solubilizing bacteria in paddy fields

Low availability of phosphorus(P) is a major constraint for optimal crop production, as P is mostly present in its insoluble form in soil. Therefore,phosphate-solubilizing bacteria(PSB) from paddy field soils of the Indo-Gangetic Plain, India were isolated, and their abundance was attempted to be correlated with the physicochemical characteristics of the soils. Ninety-four PSB were isolated on Pikovskaya's agar medium, and quantitative phosphate solubilization was evaluated using NBRIP medium. The isolates solubilized P up to a concentration of 1 006 μg mL~(-1) from tricalcium phosphate with the secretion of organic acids. These isolates were identified by 16 S rRNA gene sequence comparison, and they belonged to Gammaproteobacteria(56 isolates),Firmicutes(28 isolates), Actinobacteria(8 isolates), and Alphaproteobacteria(2 isolates). Phylogenetic analysis confirmed the identification by clustering the isolates in the clade of the respective reference organisms. The correlation analysis between PSB abundance and physicochemical characteristics revealed that the PSB population increased with increasing levels of soil organic carbon, insoluble P, K~+, and Mg~(2+). The promising PSB explored in this study can be further evaluated for their biofertilizer potential in the field and for their use as potent bio-inoculants.     

Application of low‐phosphorus‐containing legume residues reduces extractable phosphorus in a tropical Ultisol

Application of legume green manure (GM) is suggested to be effective in increasing the availability of native soil phosphorus (P) and the dissolution and utilization of phosphate rock (PR)‐P by food crops. Experiments were conducted to study the dynamics of extractable P (P extracted by Bray‐1‐extracting solution) of an Ultisol amended with or without GM residues of contrasting P concentrations in the absence of growing plants. In two separate experiments, GM residues of Aschynomene afraspera (a flood‐tolerant legume) and of Crotalaria micans (upland) with varying P concentrations were added to an acidic soil amended with PR‐P or triple superphosphate (TSP) in plastic bottles. Soil moisture was brought to field capacity of the soil in the upland experiment and saturated with distilled water in the lowland setup. This was done to simulate aerobic upland and anaerobic lowland soil conditions in the relevant plastic bottles. Only P concentration of the residues added varied, while lignin and C : N ratios were similar. A temperature of 25°C was maintained throughout the experiment. Changes in soil extractable Bray‐1‐P were measured at the end of the incubation period (60 or 80 d). In the aerobic soils, extractable P in the combined PR+GM or TSP+GM treatments was significantly lower than in the PR‐ or TSP‐ treated soils. The amendment with GM residues alone significantly increased Bray‐1‐P over the unamended control in the case of the inorganic P‐fertilized GM residues. The trend in extractable P was similar in the soils incubated under anaerobic conditions. However, in the case of PR, concentrations of P extracted by Bray‐1 solution did not significantly change in the presence or absence of GM. The results suggest that the incorporation of GM residues with low P concentration does not lead to a net P release in upland or lowland soils. These results have implications for nutrient cycling in farming systems in W Africa as most of the soils are poor and very low in available P.     

Making modern agriculture sustainable: Fam research network on agroecosystems

All forms of agriculture cause changes in the balances and fluxes of preexisting ecosystems, thereby limiting self-regulatory ecosystem (resiliency) functions. The intensive agriculture of the past, with its strong reduction of landscape structures and vast decoupling of energy and matter cycles, has caused stress and degradation of the production base; massive influence has also been exerted on neighboring compartments. This has resulted in the well known problems of pesticide loads, high phosphate loads to surface waters via over-fertilized soils or erosion as such. To overcome the economic, social and political inadequacies leading to ecological degradation, the demand for sustainable agricultural management needs to be transposed into knowledge-based practical instructions and political regulations on a regional scale. Thus, applied research for a sustainable and ecologically compatible land use aimed at sufficient food production is ever so important. In the FAM, thirty German research institutes have merged to perform research on this topic.     

干法灰化—石墨炉原子吸收法测定面制食品中铝含量

建立了面制食品中铝残留量的石墨炉原子吸收测定方法。通过干法灰化样品,筛选最佳石墨炉原子吸收分析条件,并对面制食品中铝进行测定。结果显示,该法在质量浓度20～50μg/L内呈线性关系,相关系数R=0.9998,回收率96.4%～98.5%,RSD为1.46%～3.32%;定量限下限7.35μg/L,最低检出质量浓度3.50μg/L。该方法结果符合要求,操作简便、快速、准确、干扰小、检出限低,适用于面制食品中铝含量的测定。     

中性氧化铝作为吸附剂对土霉素薄层层析的效果测定

通过以中性氧化铝为吸附剂，０．５％ＣＭＣ－Ｎａ为粘合剂，在展开剂分别为９５％乙醇－１ＮＨＣｌ、正丁醇－１ＮＨＣｌ、正丁醇－１ＮＨＣｌ－水、甲醇－１ＮＨＣｌ和甲醇－１ＮＨＣｌ－水中对土霉素的层析效果研究，结果表明：中性氧化铝在上述５种展开剂中均不能使土霉素达到有效分离。故不能用中性氧化铝单独作为吸附剂对土霉素进行层析分离。     

黑糯玉米面粉磷酸单酯制备及性质的研究

研究了制备黑糯玉米面粉磷酸单酯的最佳工艺条件，并测试了其主要特性。试验结果表明：在pH值6．5、NaH2PO4与面粉配比为0．19、反应温度为130℃，反应时间为1h的工艺条件下制备的产品效果最好，粘度最高。糊粘度和冻融稳定性达到了黑糯玉米淀粉的水平。     

土壤磷素Langmuir等温吸附特性与磷肥效果的关系

应用Langmuir等温式解释土壤磷吸收附等温线,具有良好的适合性。在24个供试土壤中,有21个土壤的相关系数达到极显著水准,3个达显著水准。通过Langmuir等温式可获得土壤吸磷参数——最大吸磷量(Xm)和吸附平衡常数(K)。Xm值可以衡量土壤磷库的大小,K值反映了土壤吸磷反应自由能下降的程度。Xm和K与磷肥利用率呈极显著负相关,其相关系数分别为-0.7146、～0.6233。不同性质的土壤,适宜作物生长的土壤平衡溶液磷浓度差异不大。当土壤平衡溶液磷浓度为0.1ppm P时,水稻产量可达最高产量的95％以上。因此,可根据Langmuir方程计算出满足水稻正常生长所需要的磷肥施用量。     

南方森林土壤溶解有机碳与土壤因子的关系

采用TOC-5000A总有机碳仪测定了福建主要森林类型土壤溶解有机碳(DOC)的含量，分析了土壤溶解有机碳与土壤因子的关系。结果表明：南方酸性森林土壤中，DOC与有机碳总量、全氮、全磷、碱解氮、有效磷和速效钾等养分因子之间呈极显著或显著的正相关关系，因而可以作为评价土壤肥力性状的生物学指标。土壤DOC与土壤中有机络合态铁、有机络合态铝和活性轻基铝之间呈权显著或显著的正相关。土壤中有机碳是影响土壤中铝和铁的溶出及迁移的一个重要因子。土壤DOC与pH值之间在一定的范围内呈权显著的负相关关系，因而土壤中铝的吸附、保持及溶解铝的排出受到溶液中DOC的强烈控制。土壤DOC与交换性铝之间无显著相关性。表2参14     

活化磷矿粉在砖红壤上的施用效果

砖红壤酸性强和活性铁、铝含量高，对磷固定强烈，磷肥有效性低．为了提高磷肥利用率，将高分子有机化合物与磷矿粉混合加工制成活化磷矿粉，分别施用于种植甘蔗的新垦砖红壤和种植大白菜的严重侵蚀砖红壤以及种植花生的水旱轮作熟化砖红壤，结果表明：施用活化磷矿粉的肥效至少与过磷酸钙相当，甚至优于过磷酸钙．因此，为了节省生产成本和改良土壤，活化磷矿粉值得在砖红壤区推广应用。     

土壤铝对林木根系的影响

采用孔洞根系生长法、进行铝对杉木和湿地松根系生长影响的研究，结果表明：土壤中加入铝离子后，活性铝含量明显增加，PH值下降；孔洞中根系生物量与对照比较，虽无明显差异，但均表现出铝毒害症，根中铝含量降低，但钙含量继续升高。这说明铝对杉木和湿地松根系有抑制作用，而钙对铝有拮抗作用。表3参7