Čimbenici koji znatno ograničavaju uspješnu poljoprivrednu proizvodnju u svijetu svakako su pristupačnost fosfora, organske tvari u tlu i pH reakcija tla. Iako se značajne količine fosfora nalaze u tlu, većina je prisutna u biljkama nepristupačnim oblicima. Stoga se ulažu sve veći napori u aktiviranje velikih količina biljkama nepristupačnoga fosfora upotrebom mikroorganizama koji otapaju fosfor. Navedena su dva glavna cilja istraživanja. Prvo, utječe li primjena mikrobiološkoga preparata na promatrana svojstva tla (pH, organska tvar, biljci pristupačan P), i drugo, može li primjena mikrobiološkoga preparata utjecati na povećanje razine fosfora u mikrobnoj biomasi tla. Tri neovisna poljska pokusa postavljena su prema principu slučajnoga bloknog rasporeda sa sljedećim tretmanima u četiri ponavljanja: kontrola „C“, kontrola s mikrobiološkim preparatom „CMA“, gnojidba sa smanjenim unosom fosfora uz mikrobiološki preparat „PMA“ i preporučena gnojidba mineralnim gnojivima „RF“. Uzorci tla analizirani su na pH reakciju, biljci pristupačan fosfor, organsku tvar tla i razinu fosfora u mikrobnoj biomasi tla. Vidljiva povećanja s 3,45 na 5,02 mg P u 100 g tla i s 0,53 na 3,42 mg P u 100 g tla zbog primijene mineralnoga gnojiva utvrđena su na dvije lokacije. Nije zabilježen negativan utjecaj primijenjenoga mikrobiološkog preparata na svojstva tla. Međutim, zabilježena je vrlo snažna korelacija (r = 0,9213 u 2016. i r = 0,9508 u 2017.) između biljci pristupačnoga P i razine P u mikrobnoj biomasi tla. Rezultati ukazuju na činjenicu da su unos fosfora i primjena mikrobiološkoga preparata zajedno s količinom biljci pristupačnoga fosfora u tlu utjecali na razinu fosfora u mikrobnoj biomasi tla.The factors limiting a successful agricultural production worldwide are certainly the availability of phosphorus (P), the soil’s organic matter, and a pH reaction in the agricultural soils. The significant amounts of phosphorus are found in the soils, but approximately 95–99% is present as the insoluble phosphates and cannot be utilized by the plants. Therefore, the increasing efforts are invested to activate the large amounts of plant-unavailable phosphorus by improving a crop’s P use efficiency through the use of phosphorus-solubilizing microorganisms (PSM). The two primary research objectives were stated, as follows: first, to assess whether the applied microbial bioagent impacts the observed soil properties (pH, organic matter, and the available P level), and second, to assess whether a microbial bioagent applied enhances the microbial biomass phosphorus (MBP). The three independent field trials were set up as a randomized blok design, with the following treatments in four replicates: a control, “C“; a control with a microbial bioagent, “CMA“; a reduced P fertilizer with a microbial bioagent, ”PMA“; and a recommended fertilization, “RF.“ The soil samples were analyzed concerning a pH reaction, plant-available phosphorus, soil organic matter, and the microbial biomass P. A visible increase from 3.45 to 5.02 mg P and from 0.53 to 3.42 mg P due to an applied mineral fertilizer was noticed at two locations. No negative impact from applied bioagents was recorded regarding the analyzed soil properties. Very strong relationships (r = 0.9213 in 2016 and r = 0.9508 in 2017) between the available P and the microbial biomass P were stated. The results indicate a fact that the P input and the application of microbial bioagent together with the content of the plant-available phosphorus in the soil influenced the MBP pool
