A. Singh, A. Baoule, H. Ahmed, A. Dikko, U. Aliyu, M. Sokoto, J. Alhassan, M. Musa and B. Haliru, “Influence of Phosphorus on the Performance of Cowpea (Vigna unguiculata (L) Walp.) Varieties in the Sudan Savanna of Nigeria,” Agricultural Sciences, Vol. 2, No. 3, 2011, pp. 313-317. http://dx.doi.org/10.4236/as.2011.23042
 P. J. White, M. R. Broadley and P. J. Gregory, “Managing the Nutrition of Plants and People,” Applied and Environmental Soil Science, Vol. 2012, 2012, pp. 1-14.
 A. Bationo, B. Ntare, S. Tarawali and R. Tabo, “Soil Fertility Management and Cowpea Production in the Semiarid Tropics,” In: C. A. Fatokun, S. A. Tarawali, B. B. Singh, P. M. Kormawa and M. Tamo, Eds., Challenges and Opportunities for Enhancing Sustainable Cowpea Production, IITA, Ibadan, 2002, pp. 301-318.
 E. Ndor, N. Dauda, E. Abimuku, D. Azagaku and H. Anzaku, “Effect of Phosphorus Fertilizer and Spacing on Growth, Nodulation Count and Yield of Cowpea (Vigna unguiculata (L) Walp) in Southern Guinea Savanna Agroecological Zone, Nigeria,” Asian Journal of Agricultural Sciences, Vol. 4, No. 4, 2012, pp. 254-257.
 W. X. Han, J. Y. Fang, P. B. Reich, F. Ian Woodward and Z. H. Wang, “Biogeography and Variability of Eleven Mineral Elements in Plant Leaves across Gradients of Climate, Soil and Plant Functional Type in China,” Ecology Letters, Vol. 14, No. 8, 2011, pp. 788-796.
 M. Govindaraj, P. Kannan and P. Arunachalam, “Implication of Micronutrients in Agriculture and Health with Special Reference to Iron and Zinc,” International Journal of Agricultural Management and Development, Vol. 1, No. 4, 2011, pp. 207-220.
 C. Bowen, I. Cakmak, S. Eker, H. Erdem, G. J. King and P. J. White, “Shoot Zinc (Zn) Concentration Varies Widely within Brassica oleracea L. and Is Affected by Soil Zn and Phosphorus (P) Levels,” Journal of Horticultural Science & Biotechnology, Vol. 85, No. 5, 2010, pp. 375-380.
 P. Arunachalam, P. Kannan, J. Prabhaharan, G. Prabukumar and Z. Kavitha, “Response of Groundnut (Arachis hypogaea L.) Genotypes to Soil Fertilization of Micronutrients in Alfisol Conditions,” Electronic Journal of Plant Breeding, Vol. 4, No. 1, 2013, pp. 1043-1049.
 P. J. White and M. R. Broadley, “Biofortification of Crops with Seven Mineral Elements Often Lacking in Human Diets—Iron, Zinc, Copper, Calcium, Magnesium, Selenium and Iodine,” New Phytologist, Vol. 182, No. 1, 2009, pp. 49-84.
 J. H. Makoi, S. Bambara and P. A. Ndakidemi, “Rhizobium Inoculation and the Supply of Molybdenum and Lime Affect the Uptake of Macroelements in Common Bean (P. vulgaris L.) Plants,” Australian Journal of Crop Science, Vol. 7, No. 6, 2013, pp. 784-793.
 K. Okada, M. Kondo, H. Ando and K. I. Kakuda, “Phosphorus Application Affects Root Length Distribution and Water Uptake of Upland Rice in a Column Experiment,” Soil Science and Plant Nutrition. Vol. 50, No. 2, 2004, pp. 257-261.
 P. A. Ndakidemi and F. D. Dakora, “Yield Components of Nodulated Cowpea (Vigna unguiculata) and Maize (Zea mays) Plants Grown with Exogenous Phosphorus in Different Cropping Systems,” Australian Journal of Experimental Agriculture, Vol. 47, No. 5, 2007, pp. 583-589.
 M. F. Baqual and P. K. Das, “Influence of Biofertilizers on Macronutrient Uptake by the Mulberry Plant and Its Impact on Silkworm Bioassay,” Caspian Journal of Environmental Science, Vol. 4, No. 2, 2006, pp. 98-109.
 M. Zafar, M. Abbasi, N. Rahim, A. Khaliq, A. Shaheen, M. Jamil and M. Shahid, “Influence of Integrated Phosphorus Supply and Plant Growth Promoting Rhizobacteria on Growth, Nodulation, Yield and Nutrient Uptake in Phaseolus vulgaris,” African Journal of Biotechnology, Vol. 10, No. 74, 2011, pp. 16793-16807.
 W. M. W Othman, T. Lie, L. Mannetje and G. Wassink, “Low Level Phosphorus Supply Affecting Nodulation, N 2 Fixation and Growth of Cowpea (Vigna unguiculata L. Walp),” Plant and Soil, Vol. 135, No. 1, 1991, pp. 67-74.
 P. A. Ndakidemi, S. Bambara and J. H. J. R. Makoi, “Micronutrient Uptake in Common Bean (“Phaseolus vulgaris” L.) as Affected by Rhizobium Inoculation, and the Supply of Molybdenum and Lime,” Plant Omics, Vol. 4, No. 1, 2011, pp. 40-52.
 V. N. Matiru and F. D. Dakora, “Potential Use of Rhizobial Bacteria as Promoters of Plant Growth for Increased Yield in Landraces of African Cereal Crops,” African Journal of Biotechnology, Vol. 3, No. 1, 2004, pp. 1-7.
 R. Dey, K. Pal, D. Bhatt and S. Chauhan, “Growth Promotion and Yield Enhancement of Peanut (Arachis hypogaea L.) by Application of Plant Growth Promoting Rhizobacteria,” Microbiological Research, Vol. 159, No. 4, 2004, pp. 371-394.
 W. Lindsay and W.A. Norvell, “Development of a DTPA Soil Test for Zinc, Iron, Manganese, and Copper,” Soil Science Society of America Journal, Vol. 42, No. 3, 1978, pp. 421-428.
 P. A. Ndakidemi and J. M. R. Semoka, “Soil Fertility Survey in Western Usambara Mountains, Northern Tanzania,” Pedosphere, Vol. 16, No. 2, 2006, pp. 237-244.
 H. Antoun, C. J. Beauchamp, N. Goussard, R. Chabot and R. Lalande, “Potential of Rhizobium and Bradyrhizobium Species as Plant Growth Promoting Rhizobacteria on Non-Legumes: Effect on Radishes (Raphanus sativus L.),” Plant and Soil, Vol. 204, No. 1, 1998, pp. 57-67.
 M. H. Abd-alla, “Phosphatases and the Utilization of Organic P by Rhizobium leguminosarum Biovar Viceae,” Letters in Applied Microbiology, Vol. 18, No. 5, 1994, pp. 294-296.
 S. Bambara and P. A. Ndakidemi, “Changes in Selected Soil Chemical Properties in the Rhizosphere of Phaseolus vulgaris L. Supplied with Rhizobium Inoculants, Molybdenum and Lime,” Scientific Research and Essays, Vol. 5, No. 7, 2010, pp. 679-684.
 H. Rodríguez and R. Fraga, “Phosphate Solubilizing Bacteria and Their Role in Plant Growth Promotion,” Biotechnology Advances, Vol. 17, No. 4, 1999, pp. 319-339.
 A. Goldstein, “Involvement of the Quinoprotein Glucose Dehydrogenase in the Solubilization of Exogenous Phosphates by Gram-Negative Bacteria,” In: A. Torriani-Gorini, E. Yagil and S. Silver, Eds., Phosphate in Microorganisms: Cellular and Molecular Biology, ASM Press, Washington DC, 1994, pp. 197-203.
 K. G. Cassman, A. S. Whitney and R. L. Fox, “Phosphorus Requirements of Soybean and Cowpea as Affected by Mode of N Nutrition,” Agronomy Journal, Vol. 73, No. 1, 1981, pp. 17-22.
 A. Hussain, A. Ali and I. R. Noorka, “Effect of Phosphorus with and without Rhizobium Inoculation in Nitrogen and Phosphorus Concentration and Uptake by Mungbean (Vigna radiata L),” Journal of Agricultural Research, Vol. 50, No. 1, 2012, pp. 49-57.
 Y. G. Zhu, S. E. Smith and F. A. Smith, “Zinc (Zn)-Phosphorus (P) Interactions in Two Cultivars of Spring Wheat (Triticum aestivum L.) Differing in P Uptake Efficiency,” Annals of Botany, Vol. 88, No. 5, 2001, pp. 941-945. http://dx.doi.org/10.1006/anbo.2001.1522
 I. Magani and C. Kuchinda, “Effect of Phosphorus Fertilizer on Growth, Yield and Crude Protein Content of Cowpea (Vigna unguiculata [L.] Walp) in Nigeria,” Journal of Applied Biosciences, Vol. 23, 2009, pp. 1387-1393.
 D. K. Singh and P. W. Sale, “Growth and Potential Conductivity of White Clover Roots in Dry Soil with Increasing Phosphorus Supply and Defoliation Frequency,” Agronomy Journal, Vol. 92, No. 5, 2000, pp. 868-874.
 C. Grant, S. Bittman, M. Montreal, C. Plenchette and C. Morel, “Soil and Fertilizer Phosphorus: Effects on Plant P Supply and Mycorrhizal Development,” Canadian Journal of Plant Science, Vol. 85, No. 1, 2005, pp. 3-14.
 G. Gianquinto, A. Abu-Rayyan, L. Di Tola, D. Piccotino and B. Pezzarossa, “Interaction Effects of Phosphorus and Zinc on Photosynthesis, Growth and Yield of Dwarf Bean Grown in Two Environments,” Plant and Soil, Vol. 220, No. 1-2, 2000, pp. 219-228.
 J. Singh, R. Karamanos and J. Stewart, “The Mechanism of Phosphorus-Induced Zinc Deficiency in Bean (Phaseolus vulgaris L.),” Canadian Journal of Soil Science, Vol. 68, No. 2, 1988, pp. 345-358.