小黑杨防风固沙林土壤物理性质研究

通过烘干法和环刀法,对嫩江沙地不同林龄小黑杨防风固沙林的土壤容重、孔隙度和持水量进行了研究。结果表明:小黑杨防风固沙林对土壤物理性质有一定的改良作用,主要集中在0~20cm土层中;随着林龄的递增,土壤田间持水量、毛管持水量、最大持水量、非毛管孔隙度、毛管孔隙度、总孔隙度0~40cm土层表现出降低再升高的趋势,而容重表现则相反;40cm土层以下物理性质变化不明显。     

不同恢复时期马尾松次生林土壤养分与微生物的演变

为了探讨牯牛降国家级自然保护区不同恢复时期（10年、20~30年、50年以上）马尾松次生林下土壤养分、微生物特征及其相互关系,采用稀释平板法和常规化学分析法进行测定。结果表明：（1）不同恢复时期马尾松次生林土壤铵态氮含量无显著差异(P＞0.05),土壤有机碳、全氮、有效磷和硝态氮含量主要集中在0~20 cm土层内差异显著(P＜0.05),但含量峰值点分布有所不同。（2）不同恢复时期马尾松次生林土壤微生物的总数量为：恢复50年以上＞20~30年＞10年,均呈显著差异(P＜0.05)。细菌是土壤微生物的主要类群,数量最多,为20.11×10⁴~521.11×10⁴ cfu/g,占全部微生物比例的50.25%~89.43%;放线菌次之,真菌数量最少。（3）恢复50年以上马尾松次生林土壤微生物量碳、氮、磷含量均显著高于其他恢复时期的(P＜0.05)。（4）相关分析表明,不同恢复时期马尾松次生林土壤微生物量碳、氮与土壤全氮、有效磷呈显著或极显著正相关,说明土壤全氮和有效磷是影响土壤微生物量的重要因素。     

Absorption of potassium,sodium, calcium,and phosphorus by two date palm cultivars and the effect of Gibberellin treatment

Experiments were conducted to avaluate the K, Na, Ca, and P uptake by seedlings of two date palm (phoenix dactylifera L.) cultivars, Khedhri and Sekkeri as well as the effect of gibberellin (GA₃) treatment, Khedhri cultivar showed a typical hyperbolic curve of absorption of K,N, end low concentration of Ca (up to 5mM) but at higher Ca concentration, there seems to be another phase of absorption. Sekkeri cultivar exhibited similar but lower absorption rate of K and Ca while Na seems to be extruded at lower substrate concentration. The rate of P uptake by Sekkeri was irregular. Applied GA₃ slightly stimulate Na uptake by Sekkeri cultivar but at 10^–4M GA₃ enhancement of both Ca and P accummulation in both cultivars was observed.     

Nodulation Productivity and Nutrient Uptake of Cowpea (Vigna unguiculata L. Walp) with Phosphorus and Potassium under Rainfed Conditions

Low availability of phosphorus (P) and potassium (K) in acidic soil is a major constraint for crop production. Therefore, a field study was conducted to determine the effects of K and P on nodulation, productivity, and nutrient uptake of cowpea (Vigna unguiculata L. Walp) under rainfed conditions. The K and P were subjected to main and subplots, respectively with 100, 75, and 50% of fertilizer application. The growth and yield attributes were better using 100% K with 100% P. However, 100% K resulted in 20.9 and 16.9% greater green pod and stover yield than 50% K. Similarly, 100% P recorded 20.2 and 15.6% greater green pod and stover yield than 50% P. Uptake of nutrients such as nitrogen (N), P, and K followed the trend of greater to lower, 100% > 75% > 50%, in order for K and P. Similarly, nutrient-use efficiencies and production efficiency followed the trend of nutrient uptake.     

The influence of root hairs on the uptake of phosphate

Abstract

The uptake of phosphate from stirred solution by roots was not affected by root hairs. In contrast to this, root hairs appreciably increased the uptake of phosphate from a clay soil.     

Dynamics of phosphatase activities in a cork oak litter (Quercus suber L.) following sewage sludge application

As part of a study of the processes involved in litter biodegradation following sewage sludge (SS) addition, the variations over 14 months of phosphatase activities in a cork oak litter (Quercus suber L.) were investigated. A field experimental design was carried out using the litter-bag method on both a fertilized plot receiving SS applications (twice ) and a control plot. Acid (APH) and alkaline (BPH) phosphatases were measured, along with several biotic and abiotic variables potentially involved in the regulation of these enzymes. These included moisture, temperature, pH, water-extractable inorganic P (P_W), culturable heterotrophic bacteria and fungi. Sludge addition had significant effects on all the variables measured. Indeed, sludge increased significantly BPH activities, available P_W, microbial densities (i.e. bacteria and fungi) and pH in the fertilized plot. In contrast, APH activities decreased significantly following sludge addition. As a consequence, the BPH/APH ratio increased markedly and immediately in the fertilized plot, but only after the 1st amendment. Following the 1st preconditioning SS amendment, the 2nd fertilization had fewer effects on biological variables, because of summer dryness. The different properties examined varied significantly with incubation time, and most were significantly related to the seasonal patterns of litter moisture in this Mediterranean forest ecosystem. Hence, sewage sludge application modified the intensity of microbial responses to environmental factors, but biological patterns regulating P turn-over were maintained.     

NITROGEN HARVEST INDEX AND ITS ASSOCIATION WITH CROP YIELDS

Nitrogen (N) is one of the most yield-limiting nutrients in crop production around the world. The main reasons of N deficiency are low recovery efficiency (RE) of applied N fertilizers. The RE efficiency of N by most crop plants is lower than 50%. The lower RE of this element is associated with losses by volatilization, leaching, denitrification, and soil erosion. Some part of N is also immobilized in undecomposed organic materials and by soil microbial population. Nitrogen harvest index (NHI) is a ratio between N accumulated in grain to N accumulated in grain plus straw. The NHI is an important index in determining crop yields because it is positively associated with grain yield. Relationship between GHI and crop grain yield may be positive linear or quadratic depending on crop genotypes and soil and crop management practices adopted. In cereals retranslocation of previously assimilated N in the vegetative parts is the predominant source of N for the grain. The most important practices that can improve NHI are liming acid soils, use of adequate N rates, source and timing, planting N efficient crop species or genotypes within species, and use of appropriate crop rotation.     

Biochemical aspects of nitrogen use efficiency: An overview

Crop productivity relies heavily on nitrogen (N) fertilization. N is an essential macronutrient limiting the growth and development of plants in agriculture. Both organic and inorganic forms of N are metabolized in plants; nitrate and ammonia are common forms of inorganic N that can be metabolized in all plants. In the last 40 years the amount of synthetic N applied to crops has risen dramatically, resulting in significant increases in yield but with considerable impacts on the environment. Production and application of N fertilizers consume huge amounts of energy, and excess is detrimental to the environment. A requirement for crops that require decreased N fertilizer levels has been recognized in the call for a ‘Second Green Revolution’ and research in the field of nitrogen-use efficiency (NUE) has continued to grow. Nitrogen-use efficiency is inherently a complex trait, as each step-including N uptake, translocation, assimilation, and remobilization-is governed by multiple interacting genetic and environmental factors. The limiting factors in plant metabolism for maximizing NUE are different at high and low N supplies, indicating great potential for improving the NUE of present cultivars. Decreasing environmental losses and increasing the productivity of crop-acquired N requires the coordination of carbohydrate and N metabolism to give high yields. This has prompted a search to identify genes that improve the NUE of crop plants, with candidate NUE genes existing in pathways relating to N uptake, assimilation, amino acid biosynthesis, carbon (C)/N storage and metabolism, signaling and regulation of N metabolism and translocation, remobilization and senescence. In this review, we present the over view of N metabolism, relation of C/N metabolism and future prospects of improving NUE in crops using various complementary approaches.