Provedena su istraživanja uzroka kloroze krušaka sorti Pastorčica, Jakovka, Gellertova i Viljamovka na podlozi sjemenjaka Pyrus communis u voćnjacima na obroncima Zagrebačke gore (lokaliteti: Šestine, Šestinski kraljevac, Gračani, Pustike i Dolje). Kruške su uzgojene u području humidne klime na antropogeniziranom smeđe karbonatnom tllu koje je razvijeno na podlozi lapora miocenske geološke formacije. Ustanovljeno je da se fero-kloroza javlja zbog poremećaja u primanju željeza na tlu koje sadrži više od 20 do 22% aktivnog vapna, a ima alkalnu reakciju tla s pH od 8,0 do 8,5. Zdrava stabla istih sorti postižu dobru vegetativnu razvijenost na tlu alkalne reakcije s pH od 7,5 do 7,9 i količinu aktivnog vapna od 15 do 18%. Lišće klorotičnih stabala sadržavalo je znatno niže koncentracije Fe ili imalo nepovoljan omjer P/Fe od klorotičnog lišća. Osim toga klorotično lišće je sadržavalo signifikantno više P, K i imalo nepovoljniji omjer K/Ca od zdravog lišća. Koncentracija N, Mg i Mn bila je podjednaka u zdravom i klorotičnom lišću.The research was carried out on the cause of chlorosis of pears of the varieties Vicar of Wingfield, Jacobs, Beurre Hardy and Williams on rootstock seedling Pyrus communis in the orchards on the hillsides of Zagrebačka gora (localities: Šestine, Šestinski kraljevac, Gračani, Pustike and Dolje). The pears were grown in an area of humid climate on anthropogenised brown calcareus soil developed on marly soil of the Miocene geological formation. It was found that iron chlorosis occurred due to disturbance in getting iron in the soil containing over 20 to 22% of active lime and having alkaline soil reaction with pH from 8.0 to 8.5. Healthy trees of the same varieties achived good vegetative development in the soil of alkaline reaction with pH from 7.5 to 7.9 and the amount of active lime from 15 to 18%. Leaves of the chlorotic trees contained significantly lower Fe concentrations and had unfavourable P/Fe ratio of chlorotic leaves. Besides, chlorotic leaves contained significantly higher P and k and had more unfavourable K/Ca ratio than the healthy leaves. The N, Mg and Mn concenttration was equal in healthy and chlorotic leaves
