Phosphorus is one of the seventeen essential nutrients required for plant growth. Despite its importance, it is limiting crop yield on more than 40% of the world's arable land. Moreover, global P reserves are being depleted at a higher rate and according to some estimates there will be no soil P reserve by the year 2050.This is a potential threat to sustainable crop production. Most of the P applied in the form of fertilizers may be adsorbed by the soil, and is not available for plants lacking specific adaptations. Available soil P and hence crop yield can, however, be increased through applying P containing fertilizers to feed the ever increasing world population. The P contained in crop residues if left in the field can be recycled by incorporating the residues into the soil whereas part of P in crop residues fed to livestock can be returned back to the soil in the form of manure and as bone meal. Additionally, plants have evolved a diverse array of strategies to obtain adequate P for their growth under P limiting conditions (a term called as P-efficiency mechanisms). Plant P-efficiency mechanisms include both improved uptake efficiency (the ability of a plant to take up more P under P limiting condition) and improved utilization efficiency (the ability of a plant to produce higher dry matter yield per unit P taken up). Uptake efficiency mechanisms include modification of root architecture, development of large root system, longer root hairs and thinner roots, exudation of low molecular weight organic acids, protons and enzymes such as phosphatases and phytases, association with mycorrhiza, production of cluster roots and expression of high affinity P transporters all of which contribute to increased P uptake efficiency of the plant. Other mechanisms include the use of alternative P-independent enzymes and glycolytic pathways, efficient cytoplasmic P homeostasis and higher ability to remobilize P from other plant parts all of which are part of enhanced P utilization efficiency. Traits related to the above morphological, physiological, biochemical and molecular adaptation mechanisms under P stress can be utilized in improving cultivated crops for P efficiency through breeding programs.

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Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P-efficient genotypes. Two efficient and two inefficient genotypes were investigated for P-efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P-uptake rate of roots but decreased root-to-shoot ratio, root-hair length, and P-utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot-dry matter yield and relative shoot-growth rate at low P supply, and therefore can be considered as P-efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P-utilization efficiency and that of CIP 384321.3 to both higher P-uptake efficiency in terms of root-to-shoot ratio and intermediate P-utilization efficiency. Phosphorus-efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P-utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P-utilization efficiency. Simulation of P uptake revealed that no other P-mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described.

cropping seasons to investigate the response of tomato cultivars varying in growth habit to rates of Nitrogen (N) and Phosphorus (P) fertilizers and plant spacing. The treatment consisted of factorial combination of two cultivars (Margelobe and Melka shola), three NP fertilizers rates (50 kg N + 60 kg P 2 O 5 /ha, 80 kg N + 90 kg P 2 O 5 /ha and 110 kg N + 120 kg P 2 O 5 /ha) and three spacing (100 cm x 30 cm, 80 cm x 30 cm and 60 cm x 45 cm) arranged in a Randomized Complete Block Design. Results revealed that fertilizer rates and spacing significantly affected the total and marketable fruit yields as well as % marketable fruit yield. Similarly, plant vigor (plant height), number of fruits per cluster and 10 fruit weight were significantly influenced by all of the main factors. Besides the main factors effect, fertilizer rate*spacing and cultivar*spacing interaction effects were also observed on % marketable fruit yield and 10 fruit weight, respectively

A field experiment was conducted to assess the effect of farmyard (cattle) manure (FYM) and inorganic nitrogen (N) phosphorus (P) fertilizers on growth and tuber yield of potato (Solanum tuberosum L.). The treatments consisted of factorial combination of 4 levels of FYM (0. 10, 20 and 30 t h -1 ) and three levels of inorganic NP fertilizers (0, 33.3%, 66.6% recommended rates) laid out in a Randomized Complete Block Design (RCBD) replicated three times. Results demonstrated that the application of 20 or 30 t ha -1 FYM + 66.6% of the recommended inorganic NP fertilizers significantly increased total tuber yield over the application of full dose of inorganic NP fertilizers without FYM in vertisol whereas in nitosol, the highest level of FYM (30 t ha -1 ) + 66.6% of the recommended inorganic NP fertilizers significantly improved total tuber yield over the application of full dose of inorganic NP fertilizers without FYM. The application of 10 t ha -1 FYM + 66.6% of the recommended inorganic NP fertilizers and 20 or 30 t ha -1 FYM + 33.3% of the recommended inorganic NP fertilizers gave a total tuber yield, which was on par with the tuber yield obtained due to the application of full dose of inorganic NP fertilizer alone, in both soils. Thus, the application of 10 t ha -1 and 20 or 30 t ha -1 FYM resulted in a saving of 33.3% and 66.6% of the recommended NP fertilizers, respectively without significantly reducing the total tuber.

Soil acidity is one of the major factors limiting soil fertility and crop production in large areas of Ethiopia. A two-month incubation experiment was conducted to evaluate the effects of lime, vermicompost (VC), and chemical phosphorus (P) fertilizer on selected chemical properties of Dystric Nitisols in Ebantu District, Western Ethiopia. The treatments comprised of three rates of lime (2, 4, and 6 tons CaCO3·ha−1), VC (2.5, 5, and 7.5 tons·ha−1), and mineral P fertilizer (20, 40, and 60 kg·P·ha−1) each applied alone and in various combinations. The experiment was laid down in a completely randomized design with two replications. The results showed that the highest increment of pH from 4.83 at the control to 6.05 and reduction of exchangeable Al from 1.70 to 0.09 cmolc·kg−1 were obtained from combined application of lime at 4 tons CaCO3·ha−1 and VC at 7.5 tons·ha−1. The most significant decrease in exchangeable acidity (0.17 cmolc.kg-1) was observed in soil that was treated with 6 tons CaCO3·ha−1 lime applied alone (93%) and combined application of lime at 4 tons CaCO3·ha−1 with VC at 7.5 tons·ha−1 by (81%). The highest contents of OM (4.1%) and total nitrogen (0.29%) were obtained from combined application of lime at 4 tons CaCO3·ha−1 and VC at 7.5 tons·ha−1. Integrated application of chemical P (60 kg·P·ha−1) with lime (2 tons·ha−1) plus VC (7.5 tons·ha−1) resulted in Bray-II P increased by 45% relative to control. The various combinations of the treatments also improved exchangeable Ca2+ and Mg2+. The results indicate that integrated use of lime, vermicompost, and chemical P fertilizer can improve soil acidity and availability of nutrients. However, the real potential of the amendments used in this experiment should be further assessed under field conditions using a test crop.

A field experiment was conducted during the summer season of 2000-2001 at the Vegetable Research Farm of Indian Agricultural Research Institute (I.A.R.I.), New Delhi (India) to test the efficacy of three Azotobacter strains as a potential supplement to nitrogenous fertilizer in improving growth and yield of onion cv. Pusa Madhvi. The treatments consisted of factorial combination of four levels of nitrogen (0, 25, 50 and 75 kg N ha-1) and three Azotobacter strains (CBD-15, AS-4 and M-4) with two uninoculated controls one with full dose of N (100 kg ha-1) and the other without NPK. Application of 75 kg N ha-1 along with inoculation of CBD-15 was found to have significantly increased most of the growth and yield parameters, soil available nitrogen, and nitrogen content in the bulb followed by M-4 inoculation as compared to application of full dose of nitrogen without the inoculation. Days to bulb initiation were significantly reduced due to inoculation with CBD-15 or M-4 along with 50 kg N ha-1 whereas days to bulb maturity were significantly reduced due to inoculation with any of the strains along with the same N rate (50 kg ha-1) as compared to application of full dose of nitrogen without the inoculation. The finding demonstrated a saving of 50 kg N ha-1 without significantly affecting yield and an average increase of 13.5% marketable yield due to Azotobacter inoculation in the presence of 75 kg N ha-1 .

Potato (Solanum tuberosum L.) has high phosphorus requirement for optimum growth and yield. Thus, under P deficiency, growth and yield are considerably reduced. An experiment was conducted in a controlled growth chamber on the effect of P supply on morphological and physiological plant parameters of three potato genotypes having contrasting P efficiency. The genotypes were CGN 17903, CIP 384321.3 and CGN 18233. They were grown under two P levels [100 mg P kg-1 soil (low P) and 700 mg P kg-1 of soil (high P)]. Treatments were arranged in a completely randomised block designs with six replications. Low P supply reduced shoot dry matter yield, relative growth rate, leaf number, whole plant relative leaf expansion rate, total leaf area per plant, plant height and net assimilation rate of P-inefficient genotype, more than that of the P-efficient genotypes. However, low P supply did not affect net photosynthetic rate per unit leaf area, leaf dark respiration rate, chlorophyll fluorescence rate and electron transport rate of both P-efficient and inefficient genotypes. P-efficient genotype CGN 17903 allocated more dry matter yield to the leaf which might have enabled higher light harvesting, hence contributing to high biomass accumulation of this genotype.