What is chemical reactions of watermelon …

Watermelon (Citrullus lanatus (Thunb.) Matsum. et Nakai) is a species cultivated in many parts of the world. The height of watermelon fruits production in 2012 amounted 105.3 million tons that is almost 10% of word total vegetable production [1]. The watermelon crop in Poland still takes place rather on the amateur scale, because the country is influenced by a temperate climate, which significantly reduces the cultivation of this vegetable. Nevertheless, the popularity of watermelon from year to year is growing, so in the Polish National List of Vegetable Plant Varieties already placed four cultivars that are well adapted to grow on Polish territory [2]. Among the factors that influenced the development of watermelon cultivation, water and nitrogen deserve special attention. Watermelon plants have a well-developed root system, so irrigation of this species in the Polish climate has a complementary function during periods of low precipitation, notably in the stage of intensive vegetative growth and flowering, as well during the formation and growing of the fruits [3]. However, in view of the increasing popularity of watermelon in Poland, so there is a need to develop knowledge of its cultivation. Generally, researchers consider that the irrigation and fertilization of watermelon plants are important determinants of high fruit yield and quality. Morais et al. [4] using four irrigation levels and four levels of nitrogen fertigation reported increasing of watermelon fruit yield, but interaction between factors was invisible, nevertheless the sugar content was influenced by the depth of irrigation, depths of nitrogen and by its interaction. According to study published by Hendricks et al. [5] with increasing of fertilizer and soil moisture content rising total biomass, as well as yield and dry weight of watermelon fruits, but at the same time soluble solids content and hollowheart ratings were not affected by treatments. In the experiment carried out by Araújo et al. [6] increasing nitrogen doses resulted in better watermelon plant growth, higher fruit yield, as well as dry matter content, but not influenced the fruits pH, and reduced sugar content. Souza et al. [7] noticed that nitrogen and phosphorus fertigation has a positive effect on watermelon yield, because it allows avoiding deficiency of macronutrients such as N, P, K, Ca, Mg, Fe and Mn. Santos et al. [8] also noted better watermelon fruit yield and quality with nitrogen fertigation doses increasing, but at the same time it leads to the stronger infestation by diseases such as gummy stem blight and the downy mildew. On the other hand, rising potassium doses applied by Santos et al. [9] did not result in the development of these diseases, as well as did not increase the number, weight and quality of watermelon fruits, instead irrigation influenced the progress of downy mildew and significantly raised the total and marketable yield. While Oliveira et al. [10] reported a beneficial effect of potassium fertigation and irrigation on the yield of watermelon fruit. Silva et al. [11] testing the production of components and the soluble solids content of watermelon fruits in relation to the nitrogen and potassium fertigation, also stated that potassium did not cause the variables. In turn, Cecílio Filho et al. [12] did not record the effects of different doses of nitrogen and potassium fertigation on the yield of watermelon, but they found that reducing plant spacing decrease the fruit number and yield. Supplemental irrigation of watermelon plants clearly improves the root distribution and fruit yield [13]. According to Wakindiki and Kirambia [14] watermelon plants irrigation increases the number of fruits and yield, as well as the fruit weight, but it can also contribute to a reduction of soluble solids in fruits. Díaz-Pérez et al. [15] also noted decrease of watermelon fruit soluble solids concentration with increasing rate of irrigation, while fruits yield and weight were not visible affected by irrigation rates. Kuşçu et al. [16] testing different deficit irrigation strategies recorded maximum marketable watermelon fruit yield when the full irrigation level was used, which at the same time decreased the values of soluble solids, sugar, vitamin C and lycopene. Kirnak and Dogan [17] reported that watermelon canopy dry weights, leaf water and chlorophyll content, as well as fruit yield were considerably reduced by water stress. Melo et al. [18] analyzing different irrigation levels of watermelon plants observed positive effects of high doses of water on vegetative growth, stomatal resistance, photosynthetic efficiency and fruit yield. The irrigation of the watermelon plants is especially important when the cultivation is carried out on a very light and sandy soil like a sand dune upland fields tested by Maruyama et al. [19]. Fernandes et al. [20] growing watermelon plants in semi-arid regions, in soil of sandy texture with low retention capacity of water and nutrients noticed a good influence of daily irrigation and nitrogen fertigation on the growth performance. Rolbiecki et al. [21,22] reported a notably beneficial effect of irrigation and fertigation on the yielding of watermelon cultivated on fine sand. Additionally, Rolbiecki et al. [22], Wakindiki and Kirambia [14], Costa et al. [23] and Souza et al. [7] comparing the effect of irrigation and fertilization on the yield characteristics of different watermelon cultivars have observed a significant influence of genetic factors on the studied traits. The objective of this experiment was to evaluate the effect of nitrogen fertigation applied three times a growing season on the watermelon fruits yield characteristics. As the control drip irrigation and traditional fertilization were used. The marketable yield, the single fruit weight and the number of fruits per plant of two watermelon cultivars: Bingo and Sugar Baby were evaluated. The field experience was conducted in the central region of Poland, which is characterized by high irrigation needs [24,25,26]. The use of nitrogen fertilization can be beneficial for crops and environment (decreased fertilizer and water use for irrigation) as well as for farmers (increased income).