INTRODUCTION Maize (Zea mays L.) is third most widely cultivated crop, consumed not only for the fulfillment of energy and protein needs, but also for industrial and biofuel production (Cruz- Cárdenas et al., 2019). Given the projected increase in world population by 2050, maize has been foreseen as an economically the most important crop to tackle future food security issue(Jones, 2009).Global dryland ecosystems, arid and semi-arid, cover ~42% of world terrestrial land surface (Bastin et al.,2017),and contribute largely to ensure both subsistence and livelihood benefits in these regions (Sujakhu et al., 2018).Of various soil challenges, impoverished agricultural productivity is one of the major issues of dry land ecosystems, mainly due to historically low organic mattercontent, reduced soil fertility and exacerbated agriculture intensification (Shahzad et al., 2017). Being an important constituent of plant cell structure, K not only activates protein synthesis, carbohydrate metabolism and key enzyme reactions(Chérel, 2004), but also triggers variety of plant adaptive responses under stressful conditions (Anschütz et al., 2014).Many soils of arid and semi-arid regions are increasingly being depleted in soil K fertility, primarily due to the coupled effect of intensive agriculture practices with little or no K application(Ameen et al., 2018). The K availability fluctuates accordingly to the soil types and is mainly governed by nature of clay minerals and organic matter status (Yadav et al.,2016). Cereals are characteristically more efficient K absorber from soil compared to other crop plants, and resultantly cereal based agroecosystems are more likely to experience K deficiency because of negative K balance(Rao et al., 2014).In semi-arid agroecosystem, farmers are paradoxically inclined to the application of N and P fertilizers in large quantities for higher productivity, and neglected altogether the use of K fertilizer in the past three decades(Samra et al., 2008). Because of this incessant imbalanced fertilizer use in semi-arid ecosystem, K deficiency in crop plants has now become widespread and often inflicted crop productivity constraints in high K demanding crops i.e. maize, sugarcane, potato (Mian and Pak. J. Agri. Sci., Vol. 57(4),1045-1055;2020 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/20.9788 http://www.pakjas.com.pk INOCULATION OF POTASSIUM SOLUBILIZING BACTERIA WITH DIFFERENT POTASSIUM FERTILIZATION SOURCES MEDIATES MAIZE GROWTH AND PRODUCTIVITY Muhammad Imran 1 , Sher Muhammad Shahzad 1, *, Muhammad Saleem Arif 2 , Tahira Yasmeen 2 , Basharat Ali 3 and Asif Tanveer 3,* 1 Department of Soil and Environmental Sciences, College of Agriculture, University of Sargodha, Sargodha 10400, Pakistan; 2 Department of Environmental Sciences and Engineering, Government College University, Faisalabad 38000, Pakistan; 3 Department of Agronomy, University of Agriculture, Faisalabad 38040, Pakistan; *Corresponding author’s e-mail: smshahzad_uaf@yahoo.com Potassium (K) deficiency is becoming a major productivity constraint in semi-arid agriculture. It is an essential mineral nutrient that has key role in various plant physiological and biochemical functions. Balanced nutrient application always tends to ensure better plant growth and development. Therefore, in the present study, efficacy of different K fertilizers for mediating maize plant growth and productivity in the presence and absence of KSB inoculant was assessed. A potassium solubilizing rhizobacterial strain, Klebsiella oxytoca KSB-17, was used in a 5 × 2 factorial pot experiment involving maize plant. The treatments comprised of control, waste mica (WM), K chemical fertilizer (KCF), WM-enriched compost (WMEC) and KCF- enriched compost (KCFEC). Compared to control treatment, KCF fertilization increased all plant physiological parameters both in presence and absence of KSB inoculation. From the results obtained, KCFEC followed by CF alone with KSB, demonstrated the most pronounced effect with significant increase in plant height (50% ), shoot biomass (59%), root biomass (73%), root length (92%), plant K uptake (154%), grain starch (16%), protein (31%), oil content (22%) as well as photosynthetic rate (104%), transpiration rate (30%) and water use efficiency (54%) compared to control. Potassium solubilizing bacteria (KSB) prompted down-regulation of plant antioxidant enzyme activities against all K fertilizer treatments. Compared to control treatment, catalase (CAT) activity decreased significantly on application of KCF as well as with KCFEC in the presence of KSB inoculation. Regardless of KSB inoculation, plant growth, physiological, antioxidant and K nutritional traits showed slight improvement with either of WM fertilizers compared to control. Our findings concluded that K enriched compost with efficient KSB inoculant can be used to enhance maize growth and productivity in semi-arid agroecosystems. Keywords: Compost, bio-fertilizer; waste mica; plant nutrition, grain quality, maize.