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The purpose of this research has been to determine the influence of soil fertilizations systems (fertilization with: nitrogen, phosphorous, nitrogen and phosphorous, farmyard manure) on the chemical properties (pH, humus, aluminium and phosphorous content) of the soil. The experiments have been carried out in the experimental field of National Agricultural Research and Development Institute � Fundulea, Romania, for: wheat monoculture, 2-year crop rotation (wheat-corn), 3-year crop rotation (wheat-pea-corn), and 4-year crop rotation wheat-sun-flower-pea-corn. The lowest values of the phosphorous content in soil have been recorded for 3-year experimental variant (wheat-pea-corn), unfertilized (a3b1), and the lowest aluminium content in soil 596 mg/kg d.m.) has been recorded for the a4b5 experimental variant (4-year crop rotation wheat-sunflower-pea-corn) � fertilized with N90P75 kg/ha a.m., working depth: 15-30 cm.

In Romania, over 40 % of the population lives in rural areas where wastewater infrastructures are poor or missing. Development of infrastructure in water supply and sewerage is essential for improving living conditions and human health. To solve the problem of domestic wastewater treatment in the areas where only decentralized sewage treatment systems can be implemented, compact installation that operating as a Sequencing Batch Reactor (SBR) process can be used. Unlike the conventional biological mechanical wastewater treatment systems, in which the process is divided into several basins, the treatment system that uses the SBR process segregates the treatment process by working times. Therefore, the compact installation that uses SBR process is among the most effective alternatives to the conventional wastewater treatment with low flow. To ensure a high degree of treatment in small treatment plants which operates by SBR process, it is essential to identify the correlations among some parameters, such as: qualitative and quantitative characteristics of the influent, construction characteristics of the treatment system and operating factors. The main direction of this research aims at identifying the mathematical model able to describe the heat balance for a SBR used in a small municipal wastewater treatment plant. Moreover, the theoretical model was correlated with the numerical values obtained during 30 days of measurements and monitoring of a small wastewater treatment plant used to treat real municipal wastewater. The installation used in this research was used in real condition to obtain the values as close to reality for the component of the heat balance.

The purpose of this research have been to determine the influence of soil main works systems (no tillage, fall tillage, spring tillage, discing in) on the physical properties (penetration hardness, air speed in soil) and chemical properties (humidity, humus, total nitrogen, calcium, chlorides) of the soil. The experiments have been carried out in the experimental field of National Agricultural Research and Development Institute - Fundulea, Romania, for a corn monoculture. The highest values of the soil penetration hardness have been recorded for the corn monoculture for which the spring tillage system had been applied (4.9 MPa, working depth 15-30 cm). The lowest values of total nitrogen and chlorides content have been recorded for the corn monoculture for which the fall tillage system had been applied (1.37 mg/kg d.s., working depth 15-30 cm) in the case of the total nitrogen and for the corn monoculture - discing in system (4.43 mg/100g sol, working depth 0-15 cm).

The industrial development, the demographic growth and the limitation of the natural regions have determined a continuous degradation of the water quality due to high concentrations and complexity of pollutants from the wastewater. The centralized and decentralized treatment systems apply treatment procedures and techniques which can be complementary in solving the environmental pollution problems due to wastewater. In the present paper a three-dimensional mathematical model was elaborated based on the experimental data obtained in a wastewater treatment plant with sequential operation, correlating the treatment degree with independent variables such as the temperature of the wastewater and the treatment duration, respectively. The mathematical model was developed and verified by using a specialized software, Table Curve 3D .The model was based on experimental data obtained by using a low capacity treatment plant, with a sequential operation, in a Sequencing Batch Reactor (SBR) type and the real domestic wastewater.