Watermelon is grown all over the world at 3.5 million ha with production of a 117 million tons, tons, most of which is in Asia (82.6 %) and only 5.7 % in Europe. Watermelon prefers dry, warm climate and is very sensitive to frost. It is grown for its fruit peponis, which is mostly consumed fresh. In the chapter Overview of previous research presented studies show how nitrogen has a key role in all meristem functions, photosynthesis and protein synthesis in all plant organs. Nitrogen fertilization is necessary to obtain high crop yields, however. There is a strong possibility of nitrogen leakage and ground water contamination especially in karst regions like Istria. Fertirrigation is a widely used technology of vegetable production which provides water and nutrients necessary for plant growth. Common agricultural practice for intensive watermelon productions based on soil mulching with black PE-film and fertirrigation. Straw mulch or bare ground is usually used in organic agriculture. Effects of soil mulching with polyethylene (PE) mulches, especially with black PE-film, are higher early growth and yield, higher number of fruits and total yield, better water and mineral uptake and crops pest resistance. Depending on material characteristics, various polymer or plant mulches have different impacts on crops, which could be seen as effects on plants microclimate: temperature and available photosynthetically active radiation (PAR). Studies show how the most influential microclimate factor is the root zone temperature (RZT), which rises under black PE-mulch, but decreases under straw mulches, compared to bare ground. Enhanced RZT stimulates root growth, water and minerals uptake and results in a higher growth degree day’s sum. In the chapter Material and methods the course of research and data processing is presented. The aim of the research was to determine nitrogen rate and mulch type impact on watermelon early vegetative growth, yield, fruit quality and watermelon microclimate conditions. Two-year field trial was set up in Valtura (44°52’52.7”N; 13°53’52.8”E), south Istria as two factorial experiment according to split–plot scheme with three replications. The first factor was additional nitrogen rate: 0 – control, 60, 120 and 180 kg N ha-1 and the second factor was mulch type: bare ground, straw and black PE-film. Data was collected on vegetative growth parameters (main vine length, diameter and number of leaves, number of secondary vines longer than 2.5 cm), total leaf nitrogen, HNT index, photosynthesis parameters, yield components fruit physical parameters and soluble dry matter, and also fruit panel sensory evaluation. Microclimate data was collected: RZT was measured with temperature sensors placed under mulches, 5 cm below the soil surface, also air temperature 5 cm above the soil and mulches and PAR reflected from the soil and mulch surface. The obtained results of the research showed that higher nitrogen doses didn’t increase vegetative growth, total yield and yield components, fruit soluble dry matter, but increased fruit sensory ratings in both years. Black PE-film increased early vegetative growth, higher HNT index, early yield and yield components in 2010. Straw mulch had the highest marketable fruit yield and number in late harvests of 2010. Black PE-film had higher growing degree days sum (GDD) and higher weekly average temperature 5 cm below the surface than straw mulch and bare ground. Highest reflected PAR was recorded on straw mulch. Black PE-film and nitrogen fertilization of 42 kg ha-1 is enough for high early vegetative growth results, early yield and fruit physical parameters. Black PE – film with nitrogen fertilization of 60 kg ha-1 is enough for achieving the highest organoleptic fruit quality. The best microclimate conditions for watermelon growth: highest weekly average temperature and GDD, was achieved with usage of black PE –film as mulch.