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The improvement of phosphorus (P) use efficiency (PUE) is a critical problem in crop production because of phosphorus' scarcity. Especially in strongly weathered soil with a high P fixation capacity, a low PUE generally limits plant growth. Here, in a 70-day pigeon pea cultivation pot experiment using Ultisols, we evaluated the effects of Rhizobium inoculation (−I/+I) on the plant growth, rhizosphere, bulk soil P dynamics, and plant root P acquisition characteristics, with or without P fertilization (0P: no P application; 50SSP:50 kg P ha−1 with single superphosphate). The combination of Rhizobium inoculation with P fertilization (50SSP + I) increased the plant growth, P uptake, and organic acid content per pot by 63%, 41%, and 130%, respectively, but not without P fertilization (0P + I). The labile and moderately labile inorganic P (NaHCO3-Pi and NaOH-Pi) contents were higher (55% and 44%, respectively) in the rhizosphere soil than those in the bulk soil in the 50SSP + I treatment, indicating the efficient solubilization of the applied P under the 50SSP + I treatment. The fertilized PUE was higher in the 50SSP + I treatment (26%) than that in the 50SSP−I treatment (15%). Thus, these results suggest that Rhizobium inoculation with 50SSP should stimulate plant root P acquisition characteristics, leading to the solubilization of applied P in the rhizosphere and efficient plant P uptake. In conclusion, the 50SSP + I treatment effectively improved the PUE of pigeon peas in strongly weathered soil. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fixation by rhizobia plays an important role in N assimilation of soybean (Glycine max). Nitrogenase, the enzyme responsible for N fixation in rhizobia, contains a large amount of sulfur (S) molecules and requires phosphorus (P) in adenosine triphosphate. Thus, S and P are essential for plant growth and N fixation by rhizobia. However, P in soils forms insoluble PO43 – salts with metals. Plant roots solubilize these PO43- salts by secreting organic acids and absorb solubilized PO43-. In this study, the effects of S application on P solubilization by soybean roots and the involvement of rhizobia were evaluated. Soybean plants inoculated with Bradyrhizobium diazoefficiens USDA110 were grown in vermiculite, and Ca3(PO4)2 was added as the sole P source. A hydroponic solution supplemented with three S concentrations (0, 20, and 1000 µM) was applied, and plants were grown for 5 weeks. Root fresh weight, the soil-plant analysis development (SPAD) values, and shoot and root S concentrations increased significantly with S application, but root nodule numbers and nitrogenase activity were not significantly affected. Organic acid secretion by roots was drastically increased by S application, and shoot P concentration and content also increased significantly. These results indicated that S application can promote P solubilization by increasing the secretion of organic acids by roots and increase in N fixation is not involved in this promotion at least in early vegetative growth period. [ABSTRACT FROM AUTHOR]

Intercropping with cereal and phosphorus (P)-mobilizing leguminous crops is a traditional agricultural practice in Sub-Saharan Africa. It is essential to evaluate the effect of intercropping (i.e., rhizosphere sharing) on fractionated rhizosphere soil P dynamics under the various soil P conditions and legumes, to improve the soil-plant P dynamics in this region. This study aimed to identify the effect of rhizosphere sharing of maize (MZ)/P-mobilizing legumes intercropping on fractionated rhizosphere soil P dynamics and plant P uptake under different P fertilization rates in strongly weathered cropland soil of Tanzania. We conducted 60-day MZ and P-mobilizing legumes intercropping pot experiments under different P-fertilized conditions (0, 50, and 100 kg P ha−1) with two legumes (pigeon pea (PP) and groundnut (GN)) by using three different root-separation treatments (no separation (NS) for rhizosphere sharing, nylon mesh separation (MS), and complete separation (CS)), to compare the effect of rhizosphere sharing in one pot. We evaluated the Hedley-fractionated P of rhizosphere soil and plant P uptake in each pot. We found that both P-efficient legumes did not clearly decrease the less labile P (NaOH-P) of rhizosphere soil in no P treatment, while these clearly decreased the less labile P in 100 kg P ha−1 treatment. It indicates that P-efficient legumes can solubilize the fertilized P but not native less labile P of the soil. The NS treatment increased the labile P of rhizosphere compared with CS by solubilizing the fertilized P, except for MZ/GN intercropping at 50 kg P ha−1. Relative to CS, MZ/PP intercropping increased the total plant P uptake per pot (20%–40%) under P-fertilized conditions, whereas MZ/GN intercropping decreased it (17%) at 50 kg P ha−1 or showed no change at 100 kg P ha−1. MZ/PP intercropping improved P fertilizer recovery efficiency, whereas MZ/GN intercropping did not. Enhanced P use efficiency through intercropping with P-mobilizing legumes is dependent on P-solubilizing characteristics of each P-mobilizing legume. [ABSTRACT FROM AUTHOR]

Phosphorus (P) deficiency is one of the largest constraints to crop production in tropical Africa; so, it is necessary to better exploit soil P resources through increasing labile soil P using P-efficient plants. The aim of this study was to evaluate the effect of various P-efficient legumes on fractionated rhizosphere soil P in two contrasting textured soils of Tanzania, i.e., strongly weathered soils. We conducted a 30-day pot experiment, where white lupin ( Lupinus albus L.; WL), cowpea ( Vignaungui culate L.; CP), and pigeon pea ( Cajanus cajan L.: PP) were grown with and without N application (0 and 50 kg N ha). Plant growth, P uptake, rhizosphere pH, and fractionated soil P were investigated. Plant P uptake decreased in the following order: WL > CP > PP in clayey soil and CP > PP > WL in sandy soil. We observed clear effects of all legumes on the rhizosphere soil P dynamics of all fractions in both soils, except for the labile P fraction in clayey soil. The effect of legume growth on the contents of less labile inorganic P fraction (NaOH-P) was significantly different between legumes; NaOH-P contents of WL was significantly lower than those of CP and PP. All legumes substantially increased the less labile organic P fraction, and its ratio was significantly higher in sandy soil. Our results suggest that WL had different P mobilization characteristics from CP and PP and that the effect of P-efficient legume cultivation on soil P availability should be more important in the inherently P poor sandy soil than in clayey soil. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an essential nutrient for crop production, while most soil P is the less labile P associated with Aluminum (Al) and Iron (Fe) in acidic soils of Japan. The objectives of this study were to evaluate the effects of two contrasting P-efficient legumes (white lupin, WL (Lupinus albus L.); and groundnut, GN (Arachis hypogaea L.)) on rhizosphere soil P dynamics in different soil types of Japan, such as Al-rich volcanic-soil, Fe-rich red-yellow-soil, and sandy-soil, with or without historical fertilization managements (3 soil types × 2 managements = 6 soil samples). We conducted a 56-day pot experiment, and analyzed the plant P uptake and fractionated P of rhizosphere and bulk soils, based on the Hedley-fractionation method. We observed that GN P uptake was generally larger than that in WL in most soil types and managements. WL significantly decreased the labile P in most soils and also decreased the less labile inorganic P (Pi) and organic P (Po) in fertilized Red-yellow-soil, which has much crystalline Fe, though GN did not. In contrast, both WL and GN significantly decreased the less labile Pi in fertilized volcanic-soil, which has much non-crystalline Al. These results indicate that (1) characteristics of less labile P uptake by P efficient legumes were different between the soil types and managements, and (2) WL efficiently solubilized the less labile P than GN in fertilized red-yellow soil, while GN efficiently absorbed the larger amount of P than WL, especially in volcanic- and sandy-soil. [ABSTRACT FROM AUTHOR]

Natural broadleaved forests have been widely converted to plantations with economically valuable trees mainly belonging to the family Pinaceae in temperate regions. Furthermore, mixed natural forests dominated by Pinaceae have been converted into pure cedar plantations involving members of the Cupressaceae in many areas. The objective of this study was to determine the impacts of such conversion with respect to the changes in dominant tree species and tree stand types (i.e. pure vs mixed) on soil properties, including the diversity and community structures of bacteria and fungi colonizing roots, rhizospheres, surface and subsurface bulk soils. Our results showed that vegetation apparently affected the bacterial and fungal community structures, but differently among these compartments. Bacterial alpha diversity was significantly lower in a mixed natural forest than in a pure cedar plantation. In addition, roots in the natural forest supported greater proportions of specific bacteria such as Bradyrhizobiaceae and Burkholderia bryophila , which have been often reported as plant-growth-promoting rhizobacteria. Fungal alpha diversity was not different between vegetation, but ectomycorrhizal (ECM) fungi such as Piloderma olivaceum , Cenococcum geophilum , Tuber pseudosphaerosporum , Sebacina sp. Tomentella sp. and Russula sp. were detected in the natural forest but less than 0.2% in the cedar plantation. The rhizosphere effects on soil pH and bacterial and fungal abundance were observed only in the natural forest, but not in the cedar plantation. Therefore, our results suggested that conversion from mixed natural forest to pure cedar plantation reduces specific bacteria with plant-growth-promoting properties as well as ECM fungi, although it appears to increase bacterial diversity. This has practical implications in that it suggests that specific planting of ECM-associated trees might be an effective strategy when attempting to generate mixed forests from starting points of pure cedar plantations. • Ectomycorrhizal fungi were detected in mixed natural forest dominated by Pinaceae. • The conversion to cedar plantation increased bacterial diversity. • The conversion reduced specific bacteria with plant-growth-promoting properties. [ABSTRACT FROM AUTHOR]