Sweet potato or bathe [Ipomoea batatas (L.) Lam], a drought-tolerant plant, originates in Central America and now cultivated on large areas in China, India, Japan, Africa, the US, Mediterranean areas of Europe in a soil having moderate fertility. In Romania there are about 439,000 ha of sandy areas and due to more and more frequent changes of climate, it is necessary to find some species and varieties, which can withstand the thermohydric stress. In this respect, during the period 2015-2017, at Dăbuleni, located in southern Oltenia, Romania we have studied five sweet potato varieties of Korean origin, with different growing seasons, (Yulmi, Juhwangmi, Hayanmi, KSP 1 and KSC 1), in order to determine the plant's reaction to the color of the mulch used to protect the soil and the time of harvesting. The results showed that most of the genotypes had reached a maximum production potential at 120 days from the planting of the shoots in the field (24232.1-37746.1 kg / ha, in the variants with transparent mulch and 22327-38587.7 kg / ha, in the variants with smoky mulch). The exception is the Juhwangmi variety, which, being earlier, achieved the maximum yield when the harvest was carried out 110 days after planting, irrespective of the color of the mulch (47044,4-48285 kg / ha). Harvesting sweet potato varieties outside the optimal age of the plant maturity, results in the reduction of production and the depreciation of its quality, having negative repercussions in winter storage.

In order to solve and clarifying certain aspects of the clay content (particles [0.002 mm) sands and sandy soils, humus, respectively, the process of bioaccumulation and mineralization the organic matter of the land, in the Research and Development Centre for Plant Growing on Sand Dabuleni, have initiated research aimed at finding methods and means for accumulating and thus the increase in the content of clay in the soil, respectively humus.Therefore, to improve radical of sandy soils, we found it necessary to resort to what is called loess process. It consists in enriching the horizon the surface soil (20-25 cm) the fraction with 8-10% clay, to 1.5-5%, as currently it contains. It is primarily intended to influence various amounts loess material on physical, hydro- physical and chemical properties of soils, then the plant response to changes products in the soil, increasing the guaranteed potential fertility of these soils, which will result in production high and constant.Obtaining appropriate agricultural production on sandy soils (eutric psamosol) it is limited not only by the soil, but also other factors such as relief, drainage and even climate. Because coarse texture, water-holding capacity in the case of sandy soils it is very low in all soils, the clay content below 5% production capacity of soils it is particularly low in the absence of agropedoameliorative measures and especially irrigation. Wind erosion occurs in all perimeters sandy soils, with higher intensity is observed in Oltenia Plain (Dabuleni Field).

Sweet potato Ipomoea batatas (L)Lam is a drought resistant species with vigorous growth and high productivity adapted to the conditions of sandy soils (Iamandei Maria et al., 2014, Diaconu Aurelia et al., 2016. In terms of Romania, sweet potato are reproduces by shoots obtained under solar. In this respect, the research carried out at CCDCPN Dabuleni between 2016-2017 aimed at obtaining sweet potato shoots in a trifactorial experience, as follows: Factor A -Planting time in the solar (15 March, 25 March), Factor B -Variety (KSP 1 and KSC 1), Factor C -Diameter of tubers (2, 3, 4 cm). The results obtained on the monitoring of solar microclimate influence on growth and development of sweet potato shoots and plant physiological processes (photosynthesis, perspiration, chlorophyll content) underline the importance of the planting period and the quality of the biological material planted in the solar. Observations and determinations of growth rate they have a slow pace in April, when climatic factors have fluctuated greatly from night to day, which increased in the first decade of May, when the shoots saw the optimal planting size of 35-40 cm. The best results were obtained by planting in the solar on March 25, using tuberous roots 3-4 cm in diameter, when there was an intense physiological activity and a large number of shoots on the tuber (9.125-9.980 shoots).

Potato production is very high performing culture, but also very demanding environmental conditions (climatic) and technological (fertilization, protection). Potato yields are influenced by a complex of biological factors, environmental and technological. The strongest factor limiting production is drought period from May to September, when training and intense accumulation of tubers that occurs with great frequency in all areas of the country's culture. Potato varieties tested in 2008-2010 to the Research-Development Station for the Culture of the Plants on the Sandys Soils Dăbuleni, Dolj County, Romania, regarding the dynamics of accumulation in tubers showed that the variety is an important factor in culture technology. Choosing the right variety of potato crop leads to success. To highlight the ability of potato cultivars to accumulate as early substances in tuber harvesting were done at 45 days of vegetation at 55 days after physiological maturity vegetation and potato plants. Production of tubers in the trade conditions of the area by plain ranged greatly depending on the variety grown and harvest time. Determinations on quantitative accumulation and nutritional quality of potato tubers were performed according to the variety and amount of fertilizer applied to sandy soils in climatic conditions in southern of Oltenia.

Climate change has led to drought, the expansion of desertification, loss of wetlands, loss of biodiversity, declining agricultural output and productivity. In the area of sandy soils in the southwest of Romania, where, compared to the multiannual average, the average air temperature in the May-August period increased by 1.010C and the precipitations recorded insignificant increases (5.97 mm), being very low (227. 82 mm) and unevenly distributed in relation to plant requirements. In these conditions, it is necessary to cultivate some species of plants resistant to drought and to preserve and improve some genetic resources adapted to the arid climate. For the efficient use of the microclimate in the sandy soils areas at the Dabuleni Research & Development Station for Plant Culture on Sands, three genotypes of Aura 26, Ofelia, Doljana were developed, which were studied in a comparison comparative culture with Jiana variety. The production potential of the new varieties (2120-2706 kg / ha) was clearly superior to the control variety, the production differences being significant and very significant.