Agronomic effectiveness of rock phosphate combined with nitrogen sources in spot application: A pot experiment

Rock phosphate (RP) shows reduced dissolution in soils amended with limestone and when applied through spot application. A simple way to improve RP efficiency under these unfavorable conditions may be the combination with nitrogen (N) fertilizers which can increase the solubilization of apatite minerals and/or stimulate P uptake. In this context, we evaluated the agronomic effectiveness of a RP from Bayóvar, Peru (BY), combined with different N sources in spot application, in a clayey Oxisol (Typic Hapludox). The pot experiment consisted of a factorial scheme (3 × 2 × 2+4) in randomized block design with four replications. Treatments consisted of BY combined with three N sources (ammonium sulfate–BY+AS; urea–BY+U; potassium nitrate–BY+KN), in two forms (granulated or powdered), and in two N : P molar ratios (0.5 : 1.0 or 1 : 1) and four additional treatments [control: without P; monoammonium phosphate (MAP); powdered BY; granulated BY]. The products were incorporated into a 50 cm³ cylindrical soil volume (central and upper position in the pot: diameter 17 cm and height 15 cm) with three maize plants (Zea mays L.). Above‐ground biomass was sampled after 42 d after sowing, analyzed for N and P concentrations to calculate N and P uptake. Soil samples were taken from the cylindrical soil volume and measured for RP dissolution (ΔCa index), P availability (P‐resin index), and soil pH. Application of MAP increased soil P availability about 11 times compared with BY treatments. As a result, maize plants grew 3.8 times and absorbed 7.3 and 3.3 times more P and N compared to those fertilized with BY combined with N fertilizers. Compound fertilizers BY+AS and BY+KN had the same effect on N and P uptake, presenting an effectiveness about 12 and 19% greater than pure BY, respectively. Compound fertilizers with BY+AS were more effective in powdered form (with no N/P ratio effect), while BY+KN was more effective in granulated form and in 1 : 1 N : P ratio. BY+U combinations were less efficient in promoting plant P bioavailability than the other N sources. We conclude that Bayóvar RP has a low agronomic effectiveness for spot application, even when combined with N.     

Modeling of Soil-Plant-Fertilizer Relationships for Optimizing Fertilizer Doses for Different Levels of Finger Millet Yield under Semi-Arid Alfisols

Experiments were conducted to test the superiority of treatment combinations of nitrogen (N; 0, 50, 100, 150, 200 kg ha^?1), phosphorus (0, 30, 60, 90 kg ha^?1) and potassium (0, 30, 60 kg ha^?1) for finger millet during 2005–2007. Application of 200-90-60 kg ha^?1 gave maximum yield of 1666, 1426 and 1640 kg ha^?1 in 3 years, respectively. The yield regression model through soil and fertilizer nutrients gave predictability of 0.98, 0.97 and 0.98, with sustainability yield index (SYI) of 50.4, 49.4 and 52.5 in 2005, 2006 and 2007, respectively. Optimum nitrogen, phosphorus and potassium (NPK) doses for attaining yields of 800 and 1200 kg ha^?1 were derived at soil nitrogen, phosphorus and potassium of 75–400, 10–70 and 150–750 kg ha^?1. Fertilizer nitrogen, phosphorus and potassium ranged from 30–128, 3–19, 13–25 kg ha^?1 and 105–203, 4–32, 27–39 kg ha^?1 for attaining 800 and 1200 kg ha^?1 yield, respectively. The doses could be adopted for attaining sustainable yields under semiarid Alfisols.     

Role of Some Plant Growth Promotory Bacteria on Enhanced Fe Uptake of Wheat

The quest for plant growth promotory bacteria that can help in sustainable agriculture has increased in the recent years owing to increasing cost of fertilizers. In the present study, the potential of three isolated bacteria having plant growth promotory effects in mobilizing the indigenous soil iron (Fe) in two different varieties of wheat was evaluated. Three bacterial isolates belonging to the genera Burkholderia and Acinetobacter were evaluated singly and in combinations for Fe uptake of wheat in a net house study. Results showed that bacterial isolates when used in combination performed better in comparison to their individual use. These isolates significantly increased the mean Fe concentration in grains and straw by 34.0% and 52.4% over the uninoculated controls and also increased the total Fe uptake per pot in comparison to uninoculated controls. The bacterial inoculation also showed a positive impact on the bioavailability of diethylenetriaminepentaacetic acid (DTPA) extractable Fe in soil.     

米氏凯伦藻生长对磷的响应及其吸收动力学研究

研究了3种不同无机磷水平培养条件下对米氏凯伦藻(Karenia mikimotoi)细胞密度、体积的影响以及米氏凯伦藻的磷吸收动力学行为。结果表明:不同无机磷水平培养条件对米氏凯伦藻的生长有显著影响。在整个实验期间,磷浓度越高,米氏凯伦藻细胞密度越高,而且从第12天开始到实验结束,高磷组中米氏凯伦藻细胞密度均显著高于中磷组和低磷组(P0.05);与之相反,低磷组中米氏凯伦藻细胞体积从第6天开始显著大于中磷和高磷组(P0.05),而中磷组中米氏凯伦藻体积与高磷组差异不显著(P0.05)。利用米氏方程可较好地拟合米氏凯伦藻对无机磷的吸收速率和初始磷浓度之间关系,其中米氏凯伦藻对无机磷的最大吸收速率(ρ_(max))为18.587 fmol/(cell·h),半饱和常数(K_s)为0.490μmol/L。鉴于东海赤潮高发区的海水中无机磷含量偏低的事实(0.10μmol/L左右),米氏凯伦藻对无机磷的较强亲和力以及低磷条件下的持续增长潜力表明在低磷条件下甲藻对营养盐的吸收比硅藻更具有竞争力,从而驱动东海区硅藻赤潮和甲藻赤潮演替。     

The Use of Coal Gangue as a Cultivation Bed Conditioner in Forage Maize Inoculated with Arbuscular Mycorrhizal Fungi

A greenhouse pot experiment was conducted to investigate the effect of application of coal gangue (CG) at different rates (0, 5, 10, 20, and 50%) and inoculation with two arbuscular mycorrhizal (AM) fungi Glomus intraradices and Glomus mosseae, as mediating plant adaptation to soil amended with CG, on the nutrient content of forage maize. The results showed CG amendment at all levels and both AM fungi significantly improved the nutrient content of the plant as compared to control. In general, the highest shoot dry weight and nutrient phosphorus, iron, and zinc (P, Fe, and Zn) were obtained with 10% CG and G. intraradice treatments, which were 49.68, 30.49, 16.72, and 75.71% higher than those of the control plants, respectively. Therefore, 10% dose of CG may be considered as a suitable dose for amendment in the corn cultivation bed in terms of providing nutrient contents for this plant as well as AM fungi root colonization.     

Simultaneous Dynamics and Kinetics of Soil Phosphorus Under Different Fertilizer Systems During Two-Growth Seasons of Maize

This study investigated phosphorus (P) dynamics and kinetics in calcareous soil under inorganic, organic, and integrated (inorganic+organic) fertilizer systems during two growing seasons of maize in two soil depths (0–0.15 and 0.15–0.30 m). A field experiment was conducted with 150, 300, and 400 kg ha^?1 triple superphosphate (TSP), 7.5 and 15.0 ton ha^?1 (on dry matter basis) farmyard manure (FYM), and integrated systems. In order to analyze Olsen P, soil samples were collected in 30-day-intervals after planting. The results showed that at the end of the two growing seasons of maize, the lowest magnitudes of Olsen P_0–0.15 m were 6.0, 6.8, 7.4, and 7.6 mg kg^?1 for the control, 7.5 FYM, 15 FYM, and 150 TSP, respectively. The highest magnitudes of Olsen P_0–0.15 m were 12.4, 11.5, 11.4, and 11.1 mg kg^?1 for 300 TSP+15 FYM, 400 TSP+7.5 FYM, 400 TSP+15 FYM, and 300 TSP+7.5 FYM, respectively. The same trends were observed for Olsen P_{0.15–0.30 m}. Heterogeneous diffusion model demonstrated that Elovich equation could best describe the experimental data (mean; R² = 0.98, SE = 0.29). The highest P supply rates (PSR) were 4.73, 3.91, and 3.86 mg kg^?1day^?1 (days after application) for 400 TSP, 400 TSP+15 FYM, and 300 TSP, respectively. The models of P supply capacity of soil could estimate P supply of soil under different fertilizer systems (R² = 0.84–0.95). The present study improved the understanding of the capacity and rate of P supply by considering P uptake by grain maize. Fertilizer recommendations depend on the accessibility of fertilizer types suggested to help choose the best fertilizer systems.     

Bromine Accumulation in Some Crops and Grasses as Determined by Neutron Activation Analysis

Till now information on bromine (Br) in the environment is still incomplete. The purposes of this research were the following: to study accumulation of Br in plants grown under different environmental conditions and to assess the factors controlling Br uptake by different plant species when the plants grow in soil uncontaminated with Br. For the determination of Br and other elements, neutron activation analysis was used. This method allows for determining a wide range of elements in various samples with high sensitivity and accuracy. Model tests and greenhouse experiments demonstrated different abilities of plants to uptake Br from various media and transfer it from roots to upper plant parts. It was shown that the main source of Br for a plant was soil. As a result of the plant growth concentration of Br in the rhizosphere soil decreased. The characteristics of soil have a pronounced effect on the Br uptake by plants.     

Silicon influences cadmium translocation by altering subcellular distribution and chemical forms of cadmium in peanut roots

Effects of silicon (Si) on subcellular distribution and chemical forms of Cd in two contrasting peanut cultivars, Qishan 208 (low seed Cd cultivar) and Haihua 1 (high seed Cd cultivar), were investigated by a hydroponics experiment at low Cd level (0.2 μM CdCl₂). Two cultivars differ in Cd translocation, subcellular distribution and chemical forms. In comparison to Qishan 208, Haihua 1 shows higher translocation factors (TFs); this may be resulted from higher Cd in the soluble fraction, and a larger proportion of inorganic Cd (extracted by 80% ethanol) and water-soluble Cd (extracted by d-H₂O) in roots. Pretreatment with Si decreased Cd in the cell wall, and enhanced Cd in the soluble fraction for both cultivars. However, effects of Si on chemical forms and TFs are cultivar dependent. Si enhances Cd translocation and the d-H₂O extractable Cd in Haihua 1. Positive correlations were observed between TF and Cd in the soluble fraction (r = 0.71, P < 0.05), and between TF and d-H₂O extractable Cd in root (r = 0.89, P < 0.001). Therefore, larger proportion of d-H₂O extractable Cd may be responsible for high TF in Si pretreated plants of Haihua 1.     

Phosphorus desorption affected by drying and wetting cycles in Ferralsols and Luvisols of Brazilian Northeast

Semiarid soils are subjected to wetting and drying cycles which influence sorption and desorption of applied phosphorus fertilizer. Phosphorus desorption was determined in soils from toposequences of two soil groups (Ferralsol and Luvisol) from a semiarid area, subjected to wetting and drying cycles. Samples from surface and subsurface horizons of upslope, midslope, and downslope positions were incubated for 4 months with phosphorus doses corresponding to 0, 5, 10, 25, 50, 75, and 100% of the maximum adsorption capacity, under constant moisture (80% water retention capacity) or 12 cycles of wetting and drying. Phosphorus desorption was lower in the Ferralsol than in the Luvisol, and lower in the subsurface than in the surface horizons, probably due to greater clay, Fe, and Al oxides contents, but they were similar among slope positions, of same mineralogy. Desorption tended to be greater in samples submitted to wetting and drying cycles but differences were small. P recovery reached 40–50% in the Luvisol, and 30–40% in the Ferralsol. The relatively low P retention capacity suggests a high residual effect of the P applied. Therefore, in relation to P losses, water retention techniques are less important than those that prevent soil erosion.     

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.