Effect of PGPR,Phosphate sources and vermicompost on growth and nutrients uptake by lettuce in a calcareous soil

In order to study the effect of plant growth promoting rhizobacteria (PGPR), vermicompost and phosphate sources on the growth and nutrients uptake by lettuce, a greenhouse experiments was conducted. Treatments consisted of PGPR (Pseudomonas fluorescens) (with and without inoculation), vermicompost (0 and 1% w/w) and phosphate sources (control, rock phosphate (RP), tricalcium phosphate and triple super phosphate (TSP) at 25 mg P kg^?1 level). Biological fertilizers, RP and TSP significantly increased shoot dry matter (SDM) and some measured nutrients uptake. Co-application of PGPR and RP, in non-vermicompost treatments significantly increased SDM, shoot nitrogen, phosphorus (P), potassium, zinc and manganese uptake rates. Shoot P uptake had no significant difference between TSP and RP treatments. Co-application of PGPR, vermicompost and TSP significantly decreased SDM, which may be due to the P toxic levels in the plant aerial parts and/or the inhibition of the bacterial activities in the rhizosphere soil.     

Effect of liming on the availability of three rock phosphate sources in two West African Ultisols

Abstract

The relative effectiveness of two African rock phosphate (Morocco rock, MR and Togo rock, TR) was compared with the more reactive North Carolina rock phosphate (NCR) and with Triple superphosphate (TSP) in greenhouse using two strongly acidic Ultisols from southern Nigeria with and without application of lime.

Without liming, the relative effectiveness of the four P sources is in the order of NCR>TSP>MR>TR; while with liming, the sequence becomes: TSP≥NCR>MR>TR.

Liming soils to pH near 5.5 depressed P uptake by plant from the rock P sources but increased P uptake from TSP.

Morocco and Togo rocks are poor sources of P for direct application under both limed and unlimed conditions.     

Sorghum and soybean response to natural and modified phosphate rock on acid soils in Venezuela

Abstract

An agronomic evaluation of phosphate rock (PR) on acid soils of Guarico and Anzoategui States was conducted to measure the effect on soil available phosphorus (P), grain yields of sorghum (Sorghum bicolor (L.) Moench) and soybean [Glycine max (L.) Merr.], and P absorption by these crops. Field experiments were established using a complete randomized block design with three replications. The treatments used were: triple superphosphate (TSP), North Carolina phosphate rock (NCRPR), compacted NCRPR with TSP at 60–40% and 70–30% (NCRPR 60/40 NCRPR 70/30), compacted Venezuelan Monte Fresco phosphate rock 60–40% and 70–30% (MFPR 60/40, MFPR 70/30), finely ground Monte Fresco phosphate rock (MFPR), finely ground Navay phosphate rock (NPR), and a check plot with no P source added. Five rates were applied, 0, 50,100,150, and 200 P₂O₅/ha, broadcasted and incorporated prior to planting. A basic fertilization of N, K, S, Mg, and Zn was uniformly applied to ensure an adequate supply of these nutrients. Soybean seeds were inoculated with Bradyrhizobium japonicum. Soil samples were taken before planting and at harvest, and plant samples taken at critical growth stage (flowering) for tissue analysis, Crop grain yields were measured at 12% moisture content. The relative agronomic effectiveness (RAE) was calculted by the formula: RAE (%( = Yield of the rock ? Yield of check plot/Yield of TSP ? Yield of check plot × 100 Maximum yields in all cases were obtained with TSP, however, in most cases there were no statistically significant differences between TSP and NCRPR as received or compacted (60/40 and 70/30). The compacted Venezuelan phosphate rocks also gave significantly higher yield and RAE responses showing the potential of these P sources for annual crops in the country. The finely ground Venezuelan phosphate rocks increased yields and RAE as compared to the check plot, but they gave the lowest response of all P sources. Soil available P after harvest had a tendency to increase where any source of P was applied or when the rates increased. The increment in soil available P was more evident when TSP and NCRPR as received and compacted were used. The lowest increments were reached with finely ground Navay phosphate rock. Leaf P concentration values were between the sufficiency range, except for those treatment where Monte Fresco and Navay finely ground phosphate rocks were applied at the rate of 50 kg P₂O₅/ha and for the check plot.     

Plant availability of two phosphate rock materials in acid Malaysian soils

Abstract

The amount of phosphorus (P) dissolved in a closed‐incubation system, in soils receiving Christmas Island grade‐A phosphate rock (CIPR), Gafsa phosphate rock (GPR), and triple superphosphate (TSP), as measured by extraction with 0.5M NaHCO₃ (APb) or 0.5M NaOH (AP) and expressed as ?Pb/?P*100 (PDP) was compared to P uptake (?Ps) by Setaria in a glasshouse experiment. There was no direct relationship between APs and PDP for CIPR, GPR, and TSP added at 50 and 150 mgP/kg soil to three Malaysian soils (Bungor, Kundor, and Segamat) during a 10‐month period. Averaged across soils, rate of addition, and P sources, ?Ps was 17% higher than PDP. Overestimation of PDP by ?Ps could be due to the ability of the roots of Setaria to use more of the P which is dissolved from the three P sources and then chemisorbed, than can be extracted by the NaHCO₃ reagent. The chemisorbed P pool is extractable using 0.5M NaOH. There was a close relationship between ?Ps and ?P, with a correlation coefficient of 0.85**. Residual P, determined by Pb method after each harvest, successfully predicted Ps by Setaria in the subsequent harvest with correlation coefficients varying between 0.74* and 0.99** for CIPR, GPR, and TSP in five soils (Bungor, Durian, Kundor, Segamat, and Tok Yong). The critical Pb values ranged from 5 for Durian to 10 mgP/kg soil for Kundor.     

Phosphorus Sources and Rates Associated with Nitrogen Fertilization in Mombasa Grass Yield

Nitrogen (N) and phosphorus (P) deficiency is one of the important causes of degradation of cultivated pasture under tropical conditions. The aim of this study was to evaluate phosphate rates and sources, and N rates on the concentration and uptake of N and P, and shoot dry mass (SDM) yield of Megathyrsus maximum grass cv Mombasa in an Ultisol. The trial was carried out in a greenhouse in pots with 4.0 dm^?3 of soil. The experiment was arranged in a completely randomized design with four replicates. The 3 × 3 × 3 factorial treatments consisted of phosphorus sources [reactive rock phosphate from Morocco (RPM), reactive rock phosphate from Algeria (RPA) and triple superphosphate (TSP)], three phosphorus rates (0, 150, and 300 mg kg^?1), and three N rates (0, 250, and 500 mg kg^?1). The SDM and tillering of Mombasa grass were significantly influenced with the TSP, RPM, and RPA application associated with N fertilization. The RPM, RPA, and TSP met the nutritional demands of Mombasa grass. The three P sources showed the same effect on the total N uptake by Mombasa grass. The P use efficiency (PUE) when fertilizer-P sources were added alone by Mombasa grass was <12% of the added P, and PUE decreased as follows: TSP > RPA > RPM. When P and N-fertilizer were added together, the fertilizer-N use efficiency (NUE) was 62%. The reactive phosphate (RPM and RPA) is an efficient P sources for Mombasa grass, but requiring higher rate of application compared to TSP source.     

Effectiveness of Panda Hills phosphate rock compacted with triple superphosphate as source of phosphorus for rape,wheat, maize,and soybean

Abstract

Greenhouse experiments were conducted to evaluate the agronomic effectiveness of Panda Hills phosphate rock (PPR) from southwest Tanzania, its mixture with triple superphosphate (TSP), and a compacted mixture of Panda PR and TSP (PPR+TSP) for wheat, rape, maize, and soybean on two United States soils (Hiwassee and Windthorst). The mixture of Panda PR and TSP was prepared by mixing ground TSP with Panda PR in proportions such that 50% of the total phosphorus (P) in the final mixture was from TSP. The compacted product (PPR+TSP) was prepared by compacting some of the blended mixture of Panda PR and TSP into pellets using a laboratory scale Carver press followed by crushing and screening. The P rates applied to Hiwassee soil were 0, 25, 50, and 100 mg P kg^‐1 for each P source and test crop while on Windthorst soil only one rate of application (50 mg P kg^‐1) was applied to one test crop (rape). A lime treatment was also included on the Windthorst soil to enable evaluation of rape response to the different P sources under calcareous conditions. Wheat and rape were allowed to grow to maturity while maize and soybean were grown for six weeks only. The performance of the P sources as reflected by yield, P uptake and relative agronomic effectiveness (RAE) followed the order TSP>>(PPR+TSP)>(PPR)+(TSP)>>PPR for wheat, rape, maize, and soybean on Hiwassee soil. Panda PR was very ineffective in increasing grain or dry‐matter yields of the test crops on this soil. The mixture of Panda PR and TSP as well as the compacted product increased wheat, maize, and soybean yields and P uptake significantly. The increases in yields were, however, largely attributed to the TSP component of the (PPR)+(TSP) mixture or its compacted product with little or no contribution from PPR. On the alkaline Windthorst soil, the performance of the P sources as reflected by rapeseed yield and RAE followed the order TSP= (PPR+TSP)>(PPR)+(TSP)>PPR. Remarkably compacted PPR and TSP was at par with TSP while PPR alone was 50% as effective as TSP in increasing rapeseed yield. Addition of lime drastically reduced the effective‐ness of Panda PR, but it had little or no effect on the agronomic effectiveness of the (PPR)+(TSP) mixture or its compacted product.     

Comparison of effects of phosphorus sources on soil acidity,available phosphorus and maize yields at two sites in western Kenya

The effects of farmyard manure (FYM), Tithonia diversifolia (tithonia) and urea when applied alone or in combination with Minjingu phosphate rock (MPR), Busumbu phosphate rock (BPR) or triple superphosphate (TSP) on soil acidity, P availability, maize yields and financial benefits were evaluated at Bukura and Kakamega in western Kenya. A reduction in exchangeable acidity and Al was observed in most tithonia- and FYM-treated soils, but not with inorganic P sources when applied in combination with urea. The effectiveness in increasing available soil P followed the order; TSP > MPR > BPR among inorganic P sources, and FYM > tithonia among organic materials at both sites. At Bukura, a site higher in both available P and Al saturation compared with Kakamega, maize did not respond to inorganic P sources applied in combination with urea. Maize, however, responded when inorganic P sources were applied in combination with FYM or tithonia at this site. At Kakamega, maize responded to TSP but not to MPR or BPR when applied with urea. Application of TSP in combination with tithonia gave the highest maize yields at both sites. Of the tested technologies, only FYM when applied alone at Bukura was economically attractive.     

Comparative Efficiency of Phosphorus Sources for Upland Rice Production

Rice (Oryza sativa L.) is a staple food for more than 50% of the world’s population, and phosphorus (P) is one of the most yield-limiting nutrients for rice production in tropical acidic soils worldwide. A greenhouse experiment was conducted to evaluate efficiency of six P sources for upland rice production. The P sources used were simple superphosphate (SSP), polymer-coated SSP (PSSP), triple superphosphate (TSP), polymer-coated TSP (PTSP), monoammonium phosphate (MAP), and polymer-coated MAP (PMAP). There were four P rates [50, 100 200, and 400 mg phosphorus (P) kg^?1] applied with four sources plus one control treatment [0 mg phosphorus (P) kg^?1]. Plant height, straw yield, grain yield, panicle density, root dry weight, maximum root length, and 1000-grain weight were significantly increased with increasing P rates in the range of 0 to 400 mg P kg^?1. However, P-use efficiency (mg grain produced per mg P applied) was decreased with increasing P rate. Based on regression equation, overall maximum plant height was obtained with the application of 235 mg P kg^?1, maximum straw yield with the application of 265 mg P kg^?1, and maximum grain yield at 227 mg P kg^?1. Based on maximum grain yield, the P source were classified as PMAP > SSP = MAP > PSSP > TSP > PTSP in the upland rice production efficiency. Overall, maximum panicle density was obtained with the addition of 231 mg P kg^?1 and maximum 1000-weight was obtained with the addition of 226 mg P kg^?1. Similarly, overall root dry weight and maximum root length were achieved with the application of 261 and 298 mg P kg^?1 of soil. Most of the growth and yield components had a significant positive association with grain yield. Optimum soil acidity indices such as pH; exchangeable calcium (Ca), magnesium (Mg), and potassium (K); Ca, Mg, and K saturation; base saturation; and acidity saturation were established for maximum upland rice grain yield.     

Agronomic evaluation of phosphate rock and slag on an upata acid soil in Bolivar State,Venezuela

Abstract

An agronomic evaluation of phosphate rock and slag on the acid soils of Upata, Bolivar State was conducted to measure their effect on the chemical properties of the soil and growth of Brachiaria decumbens. A field experiment was established using a split plot design with three replications. The treatments were, i) three sources of phosphate rock (Riecito and Lizardo of Falcon State and Monte Fresco of Tachira State) at four rates of P₂O₅/ha (0, 50, 100, and 200), ii) one source of high‐solubility P [triple superphosphate (TSP) at the same rates], and iii) three levels of calcium applied as basic slag from the Orinoco Steel Company (0, 300, and 600 kg Ca/ha). A basic fertilization was applied to all plots (217 kg/ha Urea, 50 kg/ha KCl, and 78 kg/ha magnesium sulphate). The pasture species used was Brachiaria decumbens. Pasture and soil samples were taken at 2, 3, 5, 7, 12, 14, 16, 17, 24, 27, and 31 months after planting. The pasture samples were analyzed for dry matter production (DM), and percentage content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg). Soil samples were analyzed for pH, cation exchange capacity (CEC), and available calcium (Ca) and phosphorus (P). The relative agronomic effectiveness (RAE), calculated using the formula: RAE (%) = DM of the rock ‐ DM of the check plot/DM of TSP ‐ DM of check plot × 100 was applied for each harvest time. The best RAE values at each sampling time were obtained with the Monte Fresco phosphate rock at the rate of 200 kg P₂O₅/ha and 600 kg Ca/ha as slag. There was a tendency for the RAE value to improve with each sampling apparently due to the slow release of phosphorus from the phosphate rock and its residual effect. There are also values of RAE that show better dry matter production than the high soluble source of TSP.

Soil available P and Ca increased with phosphate rock and slag application from 5 and 200 mg/kg to 25 and 400 mg/kg, respectively, after 2.5 years of the experiment. Phosphorus uptake changed from 0.1% in the check plot, which is insufficent to supply the P requirement of grazing cattle in the tropics to a value higher than 0.2%, depending on the sampling time. Soil pH increased slightly from 5.2 to 5.6 with phosphate rock, and to 6.2 when basic slags were applied.     

AM真菌对田间山银花生长、矿质营养及绿原酸含量的影响

Lonicera confusa, a traditional Chinese medicine herb for treating cold, flu, acute fever, and so forth, is often grown artificially in acidic soils and suffers from phosphorus (P) deficiency. A five-year field experiment was carried out to study the colonization rate, growth, nutrition, and chlorogenic acid content of Lonicera confusa seedlings inoculated with arbuscular mycorrhizal (AM) fungi, Glomus etunicatum and Glomus intraradices. Before transplanting into a field, both AM-inoculated and uninoculated control plants were cultured in nursery beds. In the plants inoculated with the AM fungi, the colonization rate decreased linearly with time and a greater decrease was observed in the plants inoculated with G. intraradices than with G. etunicatum, while the AM colonization increased from 0% to 12.1% in the uninoculated control plants 5 years after transplanting. Plant height, crown diameter, number of new branches, and flower yield increased significantly by AM inoculation as compared to the uninoculated control. Phosphorus concentrations in leaves and flowers increased, and plant uptake of nutrients, e.g., nitrogen (N), P, and potassium (K), was also enhanced significantly by AM inoculation. The Lonicera confusa seedlings had a better response to inoculation of G. intraradices than G. etunicatum in both growth and chlorogenic acid content in flowers. In contrast, both plant P uptake and P concentrations in leaves and flowers were similar between two fungal inoculations. The positive responses of Lonicera confusa to AM inoculation in growth, nutrient uptake, flowering, and chlorogenic acid content in flowers suggested that AM inoculation in nursery beds could promote the plant growth and increase chlorogenic acid content in flowers of Lonicera confusa when grown on acidic and P-deficient soils.     

Arbuscular Mycorrhizal Mediated Nutrition in Plants

ABSTRACT

Arbuscular mycorrhizae (AM) are the symbiotic fungi that predominate in the roots and soils of agricultural crop plants. The most recognized beneficial effect of these fungi is to enhance host plant uptake of relatively immobile nutrients, in particular phosphorus (P), and several micronutrients. The AM fungi absorb inorganic P either from the soluble P pools in the soil, or from insoluble forms such as rock phosphates as well as from insoluble organic sources. Recent studies show that mycorrhizal fungi would have access to rock phosphate through localized alterations of pH and/or by the production of organic acid anions that may act as chelating agents. The AM colonization also improves plant N nutrition. Generally mycorrhizal symbiosis more influences on nitrogen (N) uptake and translocation if ammonium (NH₄ ⁺) rather than nitrate (NO₃ ^?) is the nitrogen source. However, under drought stress the role of mycorrhizae in NO₃ ^? transport to the root surface may be significant as the NO₃ ^? mobility is severely restricted due to its low concentration and diffusion rate under such circumstances. However, as yet little is known about the mechanism of N uptake by the AM fungi. Uptake of micronutrients is also influenced by mycorrhizal colonization.     

接种丛枝菌根真菌和巨大芽孢杆菌的红三叶草对难溶磷的利用

A pot experiment was conducted to investigate the mobilization of sparingly soluble inorganic andorganic sources of phosphorus (P) by red clover (Trghlium pmtense L.) whose roots were colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and in association with the phosphate-solubilizing (PS) bacterium Bacillus megaterium ACCC10010. Phosphate-solubilizing bacteria and rock phosphate hada synergistic effect on the colonization of plant roots by the AM fungus. There was a positive interaction between the PS bacterium and the AM fungus in mobilization of rock phosphate, leading to improved plant P nutrition. In dual inoculation with the AM fungus and the PS bacterium, the main contribution to plant P nutrition was made by the AM fungus. Application of P to the low P soil increased phosphatase activityin the rhizosphere. Alkaline phosphatase activity was significantly promoted by inoculation with either the PS bacterium or the AM fungus.     

Evaluation of Phosphorus Pools and Fractions in an Acid Tropical Soil Recapitalized with Different Phosphorus Sources

Abstract

Bray 1 phosphorus (B1P) and sequential phosphorus (P) fractions were determined on soils treated with triple superphosphate (TSP), Gafsa (GPR), and Christmas Island phosphate rocks (CIPR), respectively, with and without manure. The fractions extracted in decreasing lability were iron oxide–impregnated paper strip P (Pi‐strip P), inorganic (Pi), and organic (Po) bicarbonate (NaHCO3‐Pi and ‐Po), hydroxide [sodium hydroxide (NaOH)‐Pi and ‐Po], hydrochloric acid (HCl) P, and residual (residue P). The magnitude of B1P was in the order TSP>GPR=CIPR. Average B1P from PRs was two‐fold the amount in TSP, whereas that of the fractions was NaOH‐P>Residue P<sodium bicarbonate (NaHCO₃) P<Pi‐strip P <HCl. Bray 1 extracted mainly the most labile fractions (Pi‐strip P and NaHCO3‐Pi), and plant P uptake was correlated mainly to NaOH‐Po and NaHCO₃‐Pi. Magnitude of various fractions differed between TSP and PRs. Both B1P and the fractions were equally correlated to P uptake (R²=0.38**). Nevertheless, sequential fractionation appears to be a powerful tool to identify the P status and availability in soil.     

Mineral Composition and Dry Mass Production of Corn Plants Affected by Different Phosphate Sources and Different Soil Aluminum Saturation Levels

Abstract

The effects of different commercial phosphate fertilizers [Triple superphosphate (TSP), Tricalcium phosphate (TCP), and ARAD rock phosphate) and soil aluminum (Al) saturation (86, 29, and 0%) on the mineral composition and dry mass production of corn (Zea mays) plants were studied. As soil Al saturation values decreased, pH, calcium (Ca), and magnesium (Mg) levels in the soil increased. High Ca values in the shoot resulted in the reduction in potassium (K) concentrations. The high values of P availability in the soil for the ARAD source of P did not correspond to the high values of dry mass production of corn plants. The high values of corn mass production were noticed for the TSP phosphate source, and the mass productions values were reduced as the soil Al saturation values increased.     

Organic and Inorganic P Sources Interacting with Applied Rhizosphere Bacteria and Their Effects on Growth and P Supply of Maize

Plant growth–promoting rhizobacteria (PGPR) may enhance the plant availability of phosphorus (P) in soil. A greenhouse pot experiment was conducted cultivating maize (Zea mays L.) on a P-deficient soil. Three bacterial treatments (control without PGPR and application of either Enterobacter radicincitans sp. nov. strain DSM 16656 or Pseudomonas fluorescens strain DR54) were tested in conjunction with three P treatments [no P addition, inorganic P as triplesuperphosphate (TSP), and organic P as phytin] at two different growth stages of maize (V6 and V9). Amendment with TSP enhanced growth, P uptake, and highly bioavailable P pools in soil to a greater extent than phytin. In contrast, arbuscular mycorrhiza (AM) formation of maize roots after phytin application doubled those for the TSP treatment or the control without P. Application of PGPR was also able to increase AM formation and P uptake of maize, especially when no P source was added. Furthermore, P. fluorescens inoculation resulted in an increase of highly soluble soil P pools at the early growth stage. Greater impacts of phytin on P nutrition of maize may exist in a longer term as a result of slow P release and promotion of AM fungi. Benefits to maize P nutrition derived from PGPR application can be expected under P deficiency.     

Effect of salinity and arbuscular mycorrhizal fungi on growth and some physiological parameters of Citrus jambheri

Arbuscular mycorrhizal (AM) fungi alleviate the unfavorable effects of salinity stress on plant growth. A pot study was conducted to determine the effects of AM fungi and salt on growth and some physiological parameters of Citrus jambheri rootstock. Four levels of salinity (2, 4, 6, and 8 dS m^?1 as NaCl) and three mycorrhizal treatments (Glomus etunicatum, Glomus intraradices and non-mycorrhizal (NM) control) were used. As salinity increased, all measured characteristics of plants after 4.5-month growth except Na uptake, proline content, and electrolyte leakage decreased. Shoot dry weight and K uptake were significantly higher in G. intraradices-colonized seedlings than NM controls at all salinity levels. Root dry weight and shoot P uptake were significantly higher in G. etunicatum-colonized seedlings than NM controls at all salinity levels. G. intraradices-colonized seedlings had significantly higher proline content than NM controls and G. etunicatum-colonized seedlings at salinity levels of 4, 6 and 8 dS m^?1. The electrolyte leakage percentage was significantly lower in G. intraradices-colonized seedlings than NM controls at all salinity levels. The data demonstrated that mycorrhizal citrus seedlings exhibited greater tolerance to salt stress than NM seedlings and the enhanced proline content seems to be one of the mechanisms involved.     

Potential use of rock-phosphate-solubilizing bacteria associated with wild rice as inoculants for improved rice (Oryza sativa)

A study was conducted to isolate P-solubilizing bacteria from the rhizosphere of three wild rice species and to test their ability to mobilize P from rock phosphate (RP). Inoculated seeds or seedlings of eight different strains were grown in soils supplemented with a P fertilizer mixture (PFM) consisting triple super phosphate (TSP) and RP, each providing equal amounts of P₂O₅. Crop growth, NaHCO₃-extractable P, crop P uptake and yield were compared with two uninoculated controls, with either TSP or PFM added. In the pot experiment, P availability varied from 20 to 48 mg P kg^?1 soil. Yields ranged between 4.8 and 6.6 g per pot and were not significantly different between treatments. In the field experiment, shoot P accumulation in inoculated and TSP-control treatments at the heading stage ranged between 79–129 mg and 219 mg per pot, respectively. Dual inoculants comprising Staphylococcus scirui, Bacillus pumilus, Bacillus subtilus and Bacillus cereus increased yield by about 29% over PFM-controls (324 g m^?2) but those yields were 21% lower than TSP-controls (510 g m^?2). Therefore, application of inoculants combined with PFM is not a viable alternative for TSP under the tested conditions because yield was limited by the P availability.     

Agronomic effectiveness and residual effects of Egyptian and Togo phosphate rocks on clover production

The high cost of conventional, water‐soluble phosphorus (P) fertilizers limits their use by resource‐poor farmers in sub‐Saharan Africa. Phosphate rocks are a low‐cost alternative. We evaluated the effectiveness and residual effects of Egyptian phosphate rock (EPR) and Togo phosphate rock (TPR) relative to triple superphosphate (TSP) applied at 0, 20, 40, 80, and 160 kg P ha^‐1 to annual Trifolium species grown in a P‐deficient Vertisol. The fertilizers were applied once and their effects were followed on seven consecutive annual clover crops. Clover responded to P at all the rates used. Significant (P<0.05) responses to P at the low 20–40 kg P ha^‐1 rates were registered up to the fifth crop after application of P, and responses to higher rates of 80–160 kg P ha^‐1 were significant up to the seventh crop. Critical evaluation of residual effects by comparing the response of clover to these fertilizers with response to fresh applications of TSP in the second and third crops confirmed these observations. Over all the seven crops, EPR was 82% as effective as TSP in increasing clover DM and 83% as effective in increasing P uptake. Its substitution rates were 67% for DM yields and 69% for P uptake. For TPR, the relative responses were 54% and 52% for DM yield and P uptake, respectively, and the corresponding substitution rates were 29% and 27%. In separate experiments, the effects of mixing these phosphate rocks with triple superphosphate (TSP) in various proportions (at 60 kg P ha^‐1) were also investigated. The highest response of clover was observed with TSP applied alone, but the phosphate rocks applied alone also significantly increased yields compared with the controls without applied P. Mixtures of TPR and TSP increased yields only slightly over pure TPR, and mixtures of EPR and TSP had no effect on yields compared with pure EPR, presumably because EPR is more reactive than TPR. It was concluded that EPR is highly effective in these soils, but the effectiveness of TPR is low. The highly reactive EPR could be used to elevate the P status of the P‐deficient Vertisols and increase feed availability and livestock productivity in the Ethiopian highlands. Mixing of these phosphate rocks with TSP cannot be recommended.     

Assessment of maize response to Minjingu phosphate rock and triple superphosphate applied under different P-application strategies in a Ferralsol in Tanzania

Phosphorus undergoes many reactions in acid soils, most of which convert it to less-available forms. There is a need to search for P source and P-application strategies that minimize the unfavourable reactions and optimize the benefits derived from P application. A field experiment was conducted in a Ferralsol for three years (2004–2006) to compare the effectiveness of Minjingu phosphate rock (MPR) with triple superphosphate (TSP) as assessed by maize response. The same experiment compared two P application strategies, i.e. P recapitalization and seasonal P application strategy, and two P rates, namely a standard P rate (SPR) and half of the SPR. The experiment followed a randomized complete block design with nine treatments replicated four times. Both P sources increased yields, nutrient P and Ca uptake significantly (p < 0.05) over the control, but the difference between sources was not significant. Both P sources increased the P concentration in ear leaf to the critical range ≥ 0.2% in all three seasons. Cumulative yields were comparable in the two P-application strategies. Both P sources had high residual effects whereby grain yield increments in the 2006 season ranged from 1 to 2 t ha^?1. Hence, MPR can substitute for TSP without yield reduction in Ferralsols. The seasonal P-application strategy was comparable with the P recapitalization, thus either can be chosen.     

Agronomic Evaluation of Phosphorus Sources in Lowland Rice Production

Phosphorus (P) deficiency is one of the most yield-limiting factors in lowland rice production on Brazilian Inceptisol. The objective of this study was to evaluate eight P sources for lowland rice production. The P sources were simple superphosphate (SSP), polymer-coated simple superphosphate (PSSP), ammoniated simple superphosphate (ASSP), polymer-coated ammoniated simple superphosphate (PASSP), triple superphosphate (TSP), polymer-coated triple superphosphate (PTSP), monoammonium phosphate (MAP), and polymer-coated monoammonium phosphate (PMAP). These P sources were applied in four rates (i.e., 50, 100 200, and 400 mg P kg^?1) + one control treatment (0 mg P kg^?1). Plant height, straw yield, grain yield, panicle number, and root dry weight were significantly increased in a quadratic fashion with increasing P levels from 0 to 400 mg kg^?1 of all the P sources evaluated. However, overall maximum root length and P-use efficiency were significantly less at greater P levels. Based on regression equation, maximum plant height was obtained with 262 mg P kg, maximum straw yield was obtained with 263 mg P kg^?1, maximum grain yield was obtained with 273 mg P kg^?1, and maximum panicle density was obtained with 273 mg P kg^?1. Plant growth and yield components had significant positive association with grain yield, except maximum root length. Based on grain yield and average P rate of maximum grain yield, which is 273 mg kg^?1, P sources were classified for P-use efficiency in the order of PSSP = TSP > PTSP > PASSP > SSP > MAP > ASSP. Soil chemical properties [pH; P; potassium (K); calcium (Ca); magnesium (Mg); hydrogen (H) + aluminum (Al); cation exchange capacity (CEC); base saturation; Ca, Mg, and K saturation; acidity saturation; Ca/Mg, Ca/K, and Mg/K ratios] changed significantly with the addition of different P treatments.