Mineral uptake and growth of sorghum colonized with VA mycorrhiza at varied soil phosphorus levels

Mineral nutrient uptake can be enhanced in plants inoculated with vesicular‐arbuscular mycorrhizal fungi (VAMF). The effects of the VAMF Glomus fasciculatum on uptake of P and other mineral nutrients in sorghum [Sorghum bicolor (L.) Moench] were determined in greenhouse experiments for plants grown on a low P (3.6 mg kg^‐1) soil (Typic Argiudolls) with P added at 0, 12.5, 25.0, and 37.5 mg kg^‐1 soil. Enhancements of growth and mineral nutrient uptake because of the VAMF association decreased as soil applications of P increased above 12.5 nig kg^‐1 soil. Root colonization with VAMF without added soil P resulted in increased dry matter yield equivalent to 12.5 mg P kg^‐1 soil (25 kg P ha^‐1). Total root length colonized with VAMF decreased as soil P level increased. Regardless of P added to the soil, mycorrhizal plants had higher leaf P concentrations and contents than did nonmycorrhizal plants. Enhanced contents, but not necessarily concentrations, of the other mineral nutrients were noted in shoots of mycorrhizal compared to nonmycorrhizal plants. Mycorrhizal plants had enhanced shoot contents of P, K, Zn, and Cu which could not be accounted for by increased growth. The VAMF associations with sorghum roots enhanced mineral nutrient uptake when P was sufficiently low in the soil.     

Upland rice genotypes evaluation for phosphorus use efficiency

Phosphorus (P) deficiency is one of the most important yield‐limiting factors in acid soils in various parts of the world. The objective of this study was to evaluate the growth and P‐use efficiency of 20 upland rice (Oryza sativa L.) genotypes at low (0 mg P kg^‐1), medium (75 mg P kg^‐1), and high (150 mg P kg^‐1) levels of applied P on an Oxisol. Plant height, tillers, shoot and root dry weight, shoot‐root ratio, P concentration in root and shoot, P uptake in root and shoot, and P‐use efficiency were significantly (P<0.01) affected by level of soil P as well as genotype. Shoot weight and P uptake in shoot were found to be the plant parameters most sensitive to P deficiency, suggesting that these two parameters may be most suitable for screening rice genotypes for P‐use efficiency under greenhouse conditions.     

The competitive vs. complementary bacteria‐fungi interactions promote microbial release of Fe(III)‐fixed phosphorus: the roles of exogenous C application

The phosphorus deficiency is very common in Fe(III)‐rich soil, and one of the key point is to clarify the condition in release or desorption of phosphorus from the Fe(III)‐rich minerals. The present study was to explore the effect of labile carbon on microbial reduction of Fe(III) and release of phosphorus in root‐free sub‐tropical soil. A two‐compartment microcosm was collected, in which the roots of Medicago sativa L. cultivar ‘Aohan' were confined within one compartment by a barrier of 30‐μm nylon mesh, while mycorrhizal hyphae could penetrate to the second compartment. Arbuscular mycorrhizal fungi (Funelliformis mosseae) were added to the root compartment and iron‐reducing bacteria (Klebsiella pneumoniae) were added to the hyphal compartment. Hyphal compartments were provided with two levels of additional carbon (0 and 23 mg C kg^?1 soil as sodium acetate) and eight levels of inorganic phosphorus (0 to 35 mg P kg^?1 soil as KH₂PO₄). At low phosphorus levels (< 5 mg P kg^?1 soil), shoot biomass, and total biomass phosphorus were substantially less with added carbon in the presence of iron‐reducing bacteria. Carbon had little effect without iron‐reducing bacteria. At higher phosphorus levels (> 15 mg P kg^?1 soil), the effect of added carbon was reversed; that is shoot biomass and total biomass phosphorus were greater with added carbon. Available soil phosphorus showed a similar response to added carbon—less at low levels of phosphorus and greater at higher levels of phosphorus. Microbial phosphorus in the presence of iron‐reducing bacteria was always higher with added carbon at all corresponding levels of soil phosphorus. Taken together, these results show that some phosphorus mobilized by iron‐reducing bacteria was converted into microbiological phosphorus, but there was an obligatory requirement for labile carbon for this to happen—reducing the amount of phosphorus that was absorbed by the mycorrhizal hyphae. Iron‐reducing bacteria and mycorrhizae showed a competitive interaction at lower levels of available soil phosphorus, and a complementary, or possibly a carbon‐dependent synergistic function at higher levels of available phosphorus. These results demonstrate that phosphorus released from ferralsols by iron‐reducing bacteria is positively mediated by both phosphorus and labile carbon and, hence, that phosphorus release and mobilization by iron‐reducing bacteria is likely to be enhanced by additions of exogenous carbon.     

Short‐term effects of application of different rates of inorganic P and residue P on soil P pools and wheat growth

Phosphorus (P) can be added to soil as inorganic P or crop‐residue P, but little is known about how these two forms of P addition affect soil P pools and how their effect changes with the rate of P addition. A glasshouse experiment was conducted to assess the effect of inorganic P and P added as residues at different rates on (1) soil P pools at two time points: immediately after amendment and 42 d later, and (2) growth and P uptake by wheat at flowering (day 42). Three types of legume residues (faba bean young shoot, chickpea mature shoots with pods, and white lupin mature shoots without pods) were added to a loamy‐sand soil at a rate of 5 or 15 g residue kg^–1. Inorganic P was added at four different rates (3, 10, 30, and 100 mg P kg^–1) to give P‐addition rates corresponding to the total P added with the different residues at the two residue rates. Soil P pool concentrations (microbial P, resin‐P, NaHCO₃‐P, NaOH‐P, HCl‐P, and residual P) and wheat growth and P uptake (shoot and root) were measured after 6 weeks. Compared to inorganic P addition, P added with residues led to a 10%–80% greater increase in shoot biomass at the two highest P‐addition rates. Wheat P uptake was positively correlated with resin‐P and microbial‐P concentrations in residue‐P‐amended soil, but with resin‐P and NaOH‐P_i concentrations in soil amended with inorganic P. The concentration of HCl‐P decreased by up to 30% from day 0 to day 42 in the residue treatments and that of residual P decreased by about 20% in all treatments during this period suggesting that these nonlabile P pools are quite dynamic and could serve as P source for plants.     

The combination of localized phosphorus and water supply indicates a high potential for savings of irrigation water and phosphorus fertilizer

Water and phosphorus (P) are often unevenly distributed in the soil profile, thus limiting water and P uptake and plant growth. A soil column and a split‐root experiment were conducted to quantify the effect of localized water and P supply on shoot growth, root morphology, specific P uptake (SPU), P‐use efficiency (PUE), and water‐use efficiency (WUE) of maize (Zea mays L.). Our results indicate that roots preferentially grow in the layer or compartment with both adequate water and P supply, subsequently stimulating SPU, PUE, and WUE, and enhancing shoot growth. Compared with the treatments in which both layers and compartments were supplied with adequate P and/or water, the growth of maize was maintained or minimally affected. SPU, PUE, and WUE were increased when both P and water were supplied in one layer or one compartment only. These findings show that normal plant growth with an adequate P uptake was achieved even if part of the roots were supplied with 2/3 (soil column experiment) and 1/2 (split‐root experiment) of the phosphorus and water supplied in the full‐phosphorus and full‐water treatment. Changes in root morphology under water stress conditions induced by the application of phosphorus and water in deeper soil layers or to a part of the roots may have substantial practical implications for agricultural production and environmental protection.     

Biotic strategies to increase plant availability of sewage sludge ash phosphorus

Sewage sludge incineration‐ash (FB‐I) represents a potential alternative phosphorus (P) fertiliser with a high concentration of P, although with relatively low crop availability. In this study, we investigated two P‐solubilisation approaches (acidification and P mobilisation by citrate) to enhance plant P uptake from the FB‐I ash in a pot study by using various biotic strategies: (1) a pre‐treatment of ash with a Penicillium bilaiae inoculum, (2) an isogenic line of wheat that excretes citrate from the root tip, (3) nitrogen (N) provided as combined with nitrification inhibitor dicyandiamide (DCD). All strategies were tested combined with each other and with different methods for ash application: (1) completely mixed within the top one third of soil in a pot, or (2) applied as distinct band at 10 cm depth. Triple super phosphate (TSP) at a rate of 15 mg P kg^?1 soil per pot was sufficient to support maximum shoot growth. Ash mixed into the first top third part of soil in the pot at a rate of 180 mg P kg^?1 soil (equivalent to 60 mg P kg^?1 soil throughout the pot) significantly increased the soil water‐extractable P and the subsequent shoot P uptake and shoot biomass for both wheat lines and microbial pre‐treatment to support maximum plant performance. Shoot P concentration in these treatments was further enhanced when the plants received and DCD, although not leading to a significant increase in shoot biomass. The citrate secretion by the root tips and pre‐inoculation with P. bilaiae of the ash did not influence plant growth. In conclusion, root‐zone soil acidification by nutrition is regarded as a promising strategy to improve the fertilising effect of such alternative P fertilisers originating from urban waste streams.     

Effect of seed phosphorus and soil phosphorus applications on early growth of rice (Oryza sativa L.) cv. IR66

Abstract

The vigour and size of rice seedlings in the nursery are generally correlated with final grain yield. The present study examined the possibility that increasing seed phosphorus (P) concentration would stimulate early growth of rice seedlings and therefore would have the potential to increase rice yield. Rice seeds with a uniform size and three levels of P concentration (0.115, 0.173, and 0.240% on a dry weight basis) were sown in pots on a P deficient soil with three levels of P supply (0, 7.75, and 38.8 mg P kg^?1 soil) to investigate their effect on root and shoot dry weight and P accumulation at three harvest times, 10, 20, and 30 d after sowing (DAS). The effect of seed P concentration on plant growth was greatest at a low soil P concentration and it was less pronounced with increasing soil P concentration and with time at all levels of soil P. At 10 DAS, shoot dry weight was 15% higher at a high seed P concentration (0.240%) (p < O.O1) than at a low seed P concentration (0.115%) at each level of soil P supply whereas at subsequent harvests (20 and 30 DAS) the effect of seed P concentration was observed only when the soil P supply was deficient. In contrast with its effects on shoot dry weight, high seed P concentration increased root dry weight only at the latest harvest (30 DAS). The fact that high seed P increased P concentrations in shoot tips, and in roots at 10 DAS suggests that improved P nutrition of seedlings in the first 10 DAS may be the mechanism by which high seed P concentration stimulates early growth, especially in soils with low P concentration. Sowing rice seed with high P concentration may be beneficial for increasing farmer's rice yields, in P deficient soil, and requires further field investigations.     

Evaluation of common bean genotypes for phosphorus use efficiency

A greenhouse experiment was conducted to evaluate phosphorus (P)‐use efficiency of 10 promising genotypes of common bean (Phaseoius vulgaris L.) with short and normal growth duration. The genotypes were grown on an Oxisol at 25 mg P kg^‐1 (low P) and 150 mg P kg^‐1 (high P) of soil. Shoot and root dry weight, root length, P concentration in the shoot, and P uptake in the shoot were significantly (P<0.01) affected by soil P concentration and genotype. However, P level did not effect root length and genotype had no effect on root dry weight. On the basis of P‐use efficiency (mg dry weight of shoot/mg P accumulated in the shoot) genotypes were classified as efficient and responsive (ER), efficient and nonresponsive (ENR), nonefficient and responsive (NER), and nonefficient and nonresponsive (NENR). From a practical point of view, genotypes which produce a lot of dry matter in a soil with a low P level, and respond well to added P are the most desirable because they are able to express their high yield potential in a wide range of P environments. Novo Jalo and Pérola genotypes fall into this group. Genotypes Irai, Jalo Precoce and L93300166 fall into the ENR group. Genotypes Carioca, Rosinha G‐2, and Xamengo were classified NER, whereas, genotypes L93300176 and Diamante Negro were classified as NENR. There were no differences between short and normal growth duration genotypes in P‐use efficiency.     

Effect of one phosphorus rate placed in different soil volumes on p uptake and growth of wheat

Abstract

The volume of soil treated with P fertilizer affects P uptake by the crop. Earlier studies have shown that the stimulation of root growth in P‐fertilized soil was similar for both corn (Zea mays L.) and soybean (Glycine max L. Merr). The objective of this research was to determine the effect of fertilizer P placement on P uptake and shoot and root growth of spring wheat (Triticum vulgare L.). Wheat was grown for 34 days in Raub silt loam (Aquic Argiudolls) in a controlled climate chamber. One rate of phosphate per pot, 150 mg P per three kg of soil, was mixed with 2, 5, 10, 20, 40 and 100% of the soil in the pot. The P was equilibrated with moist soil for 5 days at 70°C followed by 21 days at 25° C before transplanting 8‐day‐old wheat plants into each 3 L pot. The P stimulation of root growth in the P‐treated soil was similar to that for corn and soybeans. The effect could be described by the equation y = x^0.7 where y is the fraction of the root system in the P‐fertilized soil where P is mixed with x fraction of the soil. The greatest P uptake and plant growth occurred when added P was mixed with 20% of the soil.     

Phosphorus efficiency of ornamental plants in peat substrates

A pot experiment was conducted to investigate factors contributing to phosphorous (P) efficiency of ornamental plants. Marigold (Tagetes patula) and poinsettia (Euphorbia pulcherima) were cultivated in a peat substrate (black peat 80% + mineral component 20% on a volume basis), treated with P rates of 0, 10, 35, 100, and 170 mg (L substrate)^–1. During the cultivation period, plants were fertigated with a complete nutrient solution (including 18 mg P L^–1) every 2 d. Both poinsettia and marigold attained their optimum yield at the rate of 35 mg P (L substrate)^–1 and the critical level of P in shoot dry matter of both crops was 5–6 mg g^–1. After planting, plant‐available P increased at lower P rates to a higher level for poinsettia than for marigold, but no significant change was observed at higher P rates. Balance sheet calculations indicated that at lower P rates more P was fertigated than was taken up by the plants. Root‐length density, root‐to‐shoot ratio, and root‐hair length of marigold were doubled compared to that of poinsettia. Root‐length density increased with crop growth, and 10 d after planting the mean half distance between roots exceeded the P‐depletion zone around roots by a factor of 3 and 1.5 for poinsettia and marigold, respectively. Thus, at this early stage poinsettia exploited only 10% of the substrate volume whereas marigold utilized 43%. Later in the cultivation period, the depletion zones around roots overlapped for both crops. Taking into account P uptake via root hairs, the simulation revealed that this was more important for marigold compared to poinsettia especially at low P‐supply levels. However, increase of P uptake due to root hairs was only 10%–20% at optimum P supply. For the two lower P levels, the P‐depletion profile around roots calculated for 10 d after planting showed that after 2 d of depletion the concentration at the root surface was below the assumed K_m value (5 μM) and the concentration gradient was insufficient to fit the demand. A higher content of plant‐available P in the substrate was observed for poinsettia compared to marigold in the treatment with P application adequate for optimum growth, because more fertigated P was accumulated during early stages of cultivation due to lower root‐length density of poinsettia. The observed difference of root morphological parameters did not contribute significantly to P‐uptake efficiency, since P mobility in the peat substrate was high.     

Effects of early mycorrhization and colonized root length on low‐soil‐phosphorus resistance of West African pearl millet

Phosphorus (P) deficiency at early seedling stages is a critical determinant for survival and final yield of pearl millet in multi‐stress Sahelian environments. Longer roots and colonization with arbuscular mycorrhizal fungi (AMF) enhance P uptake and crop performance of millet. Assessing the genotypic variation of early mycorrhization and its effect on plant growth is necessary to better understand mechanisms of resistance to low soil P and to use them in breeding strategies for low P. Therefore, in this study, eight pearl millet varieties contrasting in low‐P resistance were grown in pots under low P (no additional P supply) and high P (+ 0.4 g P pot^?1) conditions, and harvested 2, 4, 6, and 8 weeks after sowing (WAS). Root length was calculated 2 WAS by scanning of dissected roots and evaluation with WinRhizo software. AM infection (%) and P uptake (shoot P concentration multiplied per shoot dry matter) were measured at each harvest. Across harvests under low P (3.3 mg Bray P kg^?1), resistant genotypes had greater total root length infected with AMF (837 m), higher percentage of AMF colonization (11.6%), and increased P uptake (69.4 mg P plant^?1) than sensitive genotypes (177 m, 7.1% colonization and 46.4 mg P plant^?1, respectively). Two WAS, resistant genotypes were infected almost twice as much as sensitive ones (4.1% and 2.1%) and the individual resistant genotypes differed in the percentage of AMF infection. AMF colonization was positively related to final dry matter production in pots, which corresponded to field performance. Early mycorrhization enhanced P uptake in pearl millet grown under P‐deficient conditions, with the genotypic variation for this parameter allowing selection for better performance under field conditions.     

Growth,phosphorus uptake,and rhizosphere microbial‐community composition of a phosphorus‐efficient wheat cultivar in soils differing in pH

In a pot experiment, the P‐efficient wheat (Triticum aestivum L.) cultivar Goldmark was grown in ten soils from South Australia covering a wide range of pH (four acidic, two neutral, and four alkaline soils) with low to moderate P availability. Phosphorus (100 mg P kg^–1) was supplied as FePO₄ to acidic soils, CaHPO₄ to alkaline, and 1:1 mixture of FePO₄ and CaHPO₄ to neutral soils. Phosphorus uptake was correlated with P availability measured by anion‐exchange resin and microbial biomass P in the rhizosphere. Growth and P uptake were best in the neutral soils, lower in the acidic, and poorest in the alkaline soils. The good growth in the neutral soils could be explained by a combination of extensive soil exploitation by the roots and high phosphatase activity in the rhizosphere, indicating microbial facilitation of organic‐P mineralization. The plant effect (soil exploitation by roots) appeared to dominate in the acidic soils. Alkaline phosphatase and diesterase activities in acidic soils were lower than in neutral soils, but strongly increased in the rhizosphere compared with the bulk soil, suggesting that microorganisms contribute to P uptake in these acidic soils. Shoot and root growth and P uptake per unit root length were lowest in the alkaline soils. Despite high alkaline phosphatase and diesterase activities in the alkaline soils, microbial biomass P was low, suggesting that the enzymes could not mineralize sufficient organic P to meet the demands of plants and microorganisms. Microbial‐community composition, assessed by fatty acid methylester (FAME) analysis, was strongly dependent on soil pH, whereas other soil properties (organic‐C or CaCO₃ content) were less important or not important at all (soil texture).     

Eucalyptus growth and phosphorus nutritional efficiency as affected by soil compaction and phosphorus fertilization

ABSTRACT

Soil compaction interferes in soil nutrient transport and root growth. The aim of this work was to evaluate eucalypt growth and phosphorus (P) nutritional efficiency as affected by soil compaction and P rates. The treatments were composed of a 3 × 4 factorial scheme (soil bulk densities levels versus P fertilization rates) for two weathered tropical soils, a clayey Ferralsol (F_Clayey) and a sandy Ferralsol (F_Sandy). The soil bulk densities assessed were 0.90, 1.10 and 1.30 g cm^?3 for F_Clayey, and 1.35, 1.55 and 1.75 g cm^?3 for F_Sandy. The P rates were 0, 150, 300 and 600 mg kg^?1 for F_Clayey, and 0, 100, 200 and 400 mg kg^?1 for F_Sandy. Soil compaction reduced root growth, P content in the plant, P utilization efficiency and P recovery efficiency; and increased average root diameter. Phosphorus fertilization increased root length density, root surface area, dry matter, P content in the plant, P utilization efficiency and P uptake efficiency; and decreased P recovery efficiency. It was concluded that P fertilization is not effective to offset the deleterious effects of soil compaction on eucalypt growth and nutrition.

Abbreviations: F_Clayey: clayey Ferralsol; F_Sandy: sandy Ferralsol; R_Dens: root length density; R_Diam: root diameter; R_Surf: root surface area; R_DM: root dry matter; S_DM: shoot dry matter; WP_DM: whole-plant dry matter; R_P: root P content; S_P: shoot P content; WP_P: whole-plant P content; PU_tE: P utilization efficiency; PU_pE: P uptake efficiency; PRE: P recovery efficiency.     

Influence of phosphorus application on growth and cadmium uptake of spinach in two cadmium‐contaminated soils

A pot experiment was conducted to investigate the influence of phosphate (P) application on diethylene triamine pentaacetic acid (DTPA)–extractable cadmium (Cd) in soil and on growth and uptake of Cd by spinach (Spinacia oleracea L.). Two soils varying in texture were contaminated by application of five levels of Cd (NO₃)₂ (0, 20, 30, 40, and 60 mg Cd kg^–1). Three levels of KH₂PO₄ (0, 12, and 24 mg P kg^–1) were applied to determine immobilization of Cd by P. Spinach was grown for 60 d after seeding. Progressive contamination of soils through application of Cd affected dry‐matter yield (DMY) of spinach shoot differently in the two soils, with 67% reduction of DMY in the sandy soil and 34% in the silty‐loam soil. The application of P increased DMY of spinach from 4.53 to 6.06 g pot^–1 (34%) in silty‐loam soil and from 3.54 to 5.12 g pot^–1 (45%) in sandy soil. The contamination of soils increased Cd concentration in spinach shoots by 34 times in the sandy soil and 18 times in the silty‐loam soil. The application of P decreased Cd concentration in shoot. The decrease of Cd concentration was higher in the sandy soil in comparison to the silty‐loam soil. Phosphorus application enhanced DMY of spinach by decreasing Cd concentration in soil as well as in plants. The results indicate that Cd toxicity in soil can be alleviated by P application.     

Phosphorus Alleviates Aluminum Toxicity in Al-Sensitive Wheat Seedlings

The role of phosphorus (P) in the amelioration of aluminum (Al) toxicity to plants is still unclear. The aim of this study was to examine the amelioration of Al toxicity by P supply. The study involved growing Al-sensitive wheat seedlings for 13 days in an acidic soil [pH 4.5 in calcium chloride (CaCl₂)] with increasing added rates of P (0, 20, 40, and 80 mg P kg^?1 soil) and Al [0, 50, and 150 mg aluminum chloride (AlCl₃) kg^?1 soil]. The results indicated that the effects of Al toxicity in this soil could be fully alleviated by the application of P at 50 mg AlCl₃ kg^?1. The 150 mg kg^?1 AlCl₃ treatment significantly reduced root growth, but this was partially overcome by the 80 mg kg^?1 P treatment. High P significantly reduced the concentration of Al in the apoplast, root, and shoot. It is possible that an insoluble Al-P complex forms in the soil and this decreases Al bound in apoplast as well as uptake into the roots. High P decreased the translocation of Al from root to shoot. This study also concluded that detoxification of Al³⁺ by P mainly occurs in soil but not within the plant tissue.     

Wheat response to combined application of nitrogen and phosphorus in a saline sandy loam soil

Fertilization with nitrogen (N) or phosphorus (P) can improve plant growth in saline soils. This study was undertaken to determine wheat (Triticum aestivum L; cv Krichauff) response to the combined application of N and P fertilizers in the sandy loam under saline conditions. Salinity was induced using sodium (Na⁺) and calcium (Ca²⁺) salts to achieve four levels of electrical conductivity in the extract of the saturated soil paste (EC_e), 2.2, 6.7, 9.2 and 11.8?dS?m^?1, while maintaining a low sodium adsorption ratio (SAR; ≤1). Nitrogen was applied as Ca(NO₃)₂?·?4H₂O at 50 (N50), 100 (N100) and 200 (N200)?mg?N?kg^?1 soil. Phosphorus was applied at 0 (P0), 30 (P30) and 60 (P60)?mg?kg^?1?soil in the form of KH₂PO₄. Results showed that increasing soil salinity had no effect on shoot N or P concentrations, but increased shoot Na⁺ and chlorine ion (Cl^?) concentrations and reduced dry weights of shoot and root in all treatments of N and P. At each salinity and P level, increasing application of N reduced dry weight of shoot. At each salinity and N level P fertilization increased dry weights of shoot and root and shoot P concentration. Addition of greater than N50 contributed to the soil salinity limiting plant growth, but increasing P addition up to 60?mg?P?kg^?1 soil reduced Cl^? absorption and enhanced the plant salt tolerance and thus plant growth. The positive effect of the combined addition of N and P on wheat growth in the saline sandy loam is noticeable, but only to a certain level of soil salinity beyond which salinity effect is dominant.     

Identification of a maize (Zea mays L.) inbred line adapted to low‐P conditions via analyses of phosphorus utilization,root acidification,and calcium influx

Phosphorus (P) fertilizers are essential for achieving high crop productivity, but declining soil P reserves and cost of fertilizers suggest that improving crop varieties for improved use efficiency of P be important for sustainability. To explore the possibility of selecting crops suitable for low P conditions, two maize (Zea mays L.) inbred lines, i.e., W22 and W23 were compared for growth, root morphology, and electrophysiological parameters, under hydroponic conditions with either insoluble P source (LP) or soluble P source (HP) in a factorial completely randomized design. Relative shoot biomass of W23 was significantly (38%) greater than that of W22 with LP, while relative root biomass of the two inbred lines did not differ. With LP, the P stress factor was the lowest (25%) and P dissolution in hydroponic solution was the greatest for W23. Root electrophysiological analysis revealed that W23 had 89% greater H⁺ efflux and 225% greater Ca²⁺ influx than W22 with LP. The distant elongation zone (DEZ) of W23 root was significantly longer and more shoot‐ward than W22 with LP. Thus, W23, having significantly greater relative shoot biomass, lower P stress factor, greater P dissolution, greater H⁺ efflux and Ca²⁺ influx, longer and more shoot‐ward DEZ, was better adapted to low‐P condition compared to W22. In the future, the W23 inbred line can be used for developing low‐P stress resistant varieties to utilize native insoluble soil P efficiently or to produce commercially acceptable yields using lower rates of soluble P fertilizers.     

Effects of Arbuscular Mycorrhizal Inoculation and Phosphorus Application on Yield and Nutrient Uptake of Yam

To be sustainable, production in the traditional yam cropping system, faced with declining soil fertility, could benefit from yam–arbuscular mycorrhizal (AM) symbiosis, which can improve nutrient uptake, disease resistance, and drought tolerance in plants. However, only limited information exists about AM colonization of yam. A pot experiment was conducted to collect information on the response of two genotypes (Dioscorea rotundata accession TDr 97/00903 and D. alata accession TDa 297) to AM inoculation (with and without) and phosphorus (P) (0, 0.05, 0.5, and 5 mg P kg^–1 soil). Factorial combinations of the treatments were arranged in a completely randomized design with four replicates. The percentage of AM colonization was significantly lowered at 5 mg P kg^–1 soil rate in mycorrhizal plants of both genotypes. TDr 97/00903 showed more responsiveness to AM inoculation than TDa 297. The greatest AM responsiveness for tuber yield (52%) was obtained at 0.5 mg P kg^–1 soil rate for TDr 97/00903. Mycorrhizal inoculation significantly increased root dry weight and tuber yield of TDr 97/00903 with the greatest values obtained at the 0.5 mg P kg^–1 soil rate. Arbuscular mycorrhizal inoculation did not lead to significant (P < 0.05) changes in root length and area. Phosphorus application significantly increased the shoot dry weight and root diameter of TDa 297. Uptake of P was greatest at 0.5 mg P kg^–1 soil in both genotypes and was significantly influenced by AM inoculation. Nitrogen (N) and potassium (K) uptake were greatest in mycorrhizal plants at 0.05 mg P kg^–1 soil for TDr 97/00903 but at 0.5 mg P kg^–1 soil of nonmycorrhizal plants of TDa 297. The increased tuber yield and nutrient uptake observed in the mycorrhizal plants indicate the potential for the improvement of nutrient acquisition and tuber yield through AM symbiosis.     

Growth,yield and yield components of dry bean as influenced by phosphorus in a tropical acid soil

Phosphorus (P) deficiency is one of the most yield limiting factors for dry bean (Phaseolus vulgaris) production in tropical acid soils. Dry beans are invariably grown as mono-crops or as inter-crops under the perennial tropical crops. Information is limited regarding the influence of phosphorus fertilization on dry bean yield and yield components and P use efficiency in tropical acid soils. A greenhouse experiment was conducted to evaluate the influence of phosphorus fertilization on dry bean growth, yield and yield components and P uptake parameters. Phosphorus rates used were 0, 50, 100, 150, 200, and 250 mg P kg^?1 of soil. Soil used in the experiment was an acidic Inceptisol. Grain yield, shoot dry weight, number of pods, and 100 grain weight were significantly (P < 0.01) increased with phosphorus fertilization. Maximum grain yield, shoot dry matter, number of pods, and 100 grain weight were obtained with the application of 165, 216, 162, and 160 mg P kg^?1 of soil, respectively, as calculated by regression equations. Grain yield was significantly and positively associated with shoot dry weight, number of pods, P concentration in grain and total uptake of P in shoot and grain. Phosphorus use efficiency defined in several ways, decreased with increasing P rates from 50 to 250 mg P kg^?1 of soil. Maximum grain yield was obtained at 82 mg kg^?1 of Mehlich 1 extractable soil P. Results suggest that dry bean yield in Brazilian Inceptisols could be significantly increased with the use of adequate rates of phosphorus fertilization.