Influence of Fertilization Systems on Physical and Chemical Properties of the Soil

OANA MARIA MUSCALU (PLESCAN)1,2, VALENTIN NEDEFF1,3, ALEXANDRA DANA CHITIMUS1*, IOAN GABRIEL SANDU4,5, ELENA PARTAL6, EMILIAN MOSNEGUTU1, ION SANDU5,7*, DRAGOS IOAN RUSU1 1 Vasile Alecsandri University of Bacau, Department of Environmental Engineering and Mechanical Engineering, 157 Calea Marasesti, 600115, Bacau , Romania 2 Romanian Waters National Administration of Siret Basin, 1 Cuza Voda Str., 600274, Bacau, Romania 3 Gheorghe Ionescu Sisesti, Academy of Agricultural and Forestry Sciences Bucharest, 61 Marasti Blvd., 011464, Bucharest, Romania 4 Gheorghe Asachi Technical University of Iasi, Faculty of Material Sciences and Engineering, 69 Dumitru Mangeron Str., 700050, Iasi, Romania 5 Romanian Inventors Forum, 3 Sf. Petru Movila St., Bl. L11, III/3, 700089, Iasi, Romania 6 National Agricultural Research and Development Institute of Fundulea, Calarasi, 1 Nicolae Titulescu Str., 915200, Fundulea, Romania 7 Alexandru Ioan Cuza University of Iasi, ARHEOINVEST Interdisciplinary Platform, 22 Carol I Blvd., 700506, Iasi, Romania

Natural (organic) fertilizers are a source of nutritive mineral elements for plants, thus contributing to the improvement of physical and biological features of the soil. Farmyard manure has a complex effect on plants and soil. It is applied in summer and autumn and it is embedded in soil by ploughing. Higher doses are recommended for low fertility soils and on irrigated surfaces, for intensive culture [1][2][3][4][5][6][7][8][9][10].
The purpose of this research has been to determine the influence of soil fertilizations systems on the physical properties (penetration hardness) and chemical properties (humidity, metals: chrome, manganese, nickel, copper, zinc, arsenic, lead, cadmium).

Experimental part
When choosing the sampling point in order to determine the heavy metal content and physical properties of the soil, the research team took into account the topo-pedological base of the agrochemical cropping plots, updated with all necessary elements to identify and locate the plots.
The study has been carried out in the experimental field of National Agricultural Research and Development Institute-Fundulea, Romania, for a wheat monoculture. The researches at INCDA have been carried out following a two-factor experience, stationary and multiannual, mounted in 1968 and up to date, with reference to emphasizing the differentiation of soil's properties as an effect of fertilization sequence, i.e: -nitrogen (90 kg N/ha active matter -active matter);   Figure 2 shows soil sampling method used to determine the soil heavy metal content.
Moreover, in the filed have been determined: -soil penetration hardness, by the penetrologger (fig.  3); -soil humidity, by the in situ direct reading moisture sensor ( fig. 4). and an atomic absorption spectrometer (AAS), ZEENIT AAS version. Through the inductively coupled plasma mass spectrometry, the following metals have been detected: chrome, nickel, copper, arsenic, lead, and cadmium. Through atomic absorption spectrometry, zinc and manganese content has been detected [28,29]. Tables 2 and 3 show the experimentally determined values for the soil samples taken on the unfertilized wheat parcel (control sample) for eight heavy metal and for the in physical properties measured in situ. Table 3 shows the experimentally determined values for eight metals in soil in which a wheat monoculture has been embedded, with fertilization sequence in 2016.

Results and discussions
The manganese content value ( fig. 5) registered in the nitrogen fertilized parcel (90 kg N/ha) was 9.02 % lower than the value registered in the unfertilized soil parcel for the 0-15 cm depth, respectively by 14.79 % lower than the control sample for the 15-30 cm depth. Fig. 2. Soil samples preparation methods to determine heavy metals through inductively coupled plasma mass spectrometry, and atomic absorption spectrometry respectively [27][28][29][30]. Experiments have been carried out for the content of eight metals in the soil: chrome, manganese, nickel, copper, arsenic, lead, cadmium.
The metal content in the soil samples has been determined by using inductively coupled plasma mass spectrometer (ICP-MS) [17], Agilent 7500cx ICP-MS version  In the case of the phosphorous fertilized parcel (75 kg P/ha) the soil manganese content was 517.87 % higher than the value registered on the unfertilized soil parcel for the 0-15 cm depth, respectively 309.55 % higher for the 15-30 cm depth; The nickel content value ( fig. 6) on the nitrogen fertilized parcel was 112.22 % higher than the control sample value for the 0-15 cm depth. For the 15-30 cm depth the nickel content was 77.73 % of the control sample value.
In the case of the phosphorous fertilized parcel, the copper content was 190.18 % higher than the value registered for the unfertilized soil parcel for the 0-15 cm depth, respectively 27.31 % lower than the control sample, for the 15-30 cm depth.
The copper content for the experimental wheat variants -fertilized with nitrogen and phosphorous N90P75 kg/ha (a 1 b 4 ) was: -0-15 cm: 25.833 % of the soil control sample value; -15-30 cm: 11.33 % of the soil control sample value. For the soil parcel fertilized with farmyard manure (b 5 ) the copper content was 180.36 % higher than the control sample value, for the 0-15 cm depth, respectively 18.64 % lower than the control sample, for the 15-30 cm depth.
Zinc content ( fig. 8)   For the soil parcel fertilized with 75 kg P/ha (b 3 ) factor, the nickel content was 121.14 % higher than the control sample value, for the 0-15 cm depth, respectively 46.62 % lower than the control sample value for the 15-30 cm depth.
The nickel content for the experimental wheat variants -fertilized with nitrogen and phosphorous N90P75 kg/ha (a 1 b 4) and wheat-fertilized with farmyard manure (a 1 b 5 ) was: -wheat -fertilization with nitrogen and phosphorous N90P75 kg/ha (a 1 b 4) : Ï% 0-15 cm: 14.46 % of the soil control sample value; Ï% 15-30 cm: 7.37 % of the soil control sample value; -wheat-fertilization with farmyard manure (a 1 b 5 ): Ï% 0-15 cm: 123.11 % lower than the valued registered in the soil sample with no fertilization sequence; Ï% 15-30 cm: 41.34 % lower than the valued registered in the soil sample with no fertilization sequence.
The copper content value ( fig. 7) registered for the soil parcel fertilized with nitrogen was 109.22 % higher than the value registered for the unfertilized soil parcel for the 0-15 cm depth, respectively 30.79 % lower than the control sample, for the 15-30 cm depth. Arsenic content value ( fig. 9) registered for the soil parcel fertilized with nitrogen was 129.65 % higher than the control sample value for the 0-15 cm depth. For the 15-30 cm depth the nickel content was 83.63 % of the control sample value.
For the soil parcel fertilized with phosphorous (b 3 ), the arsenic content was 125.93 % higher than the control sample value for the 0-15 cm depth, respectively 32.07 % lower than the control sample, for the 15-30 cm depth.
The arsenic content for the experimental variants wheat -fertilization with nitrogen, and phosphorous N90P75 kg/ ha (a 1 b 4 ) and wheat-fertilization with farmyard manure (a 1 b 5 ) was: The lead content ( fig. 10) registered for the soil parcel fertilized with nitrogen was (90 kg N/ha) was 116.34 % higher than the value registered for the unfertilized soil parcel for the 0-15 cm depth, respectively 151.73 % higher than the control sample, for the 15-30 cm depth.
In the case of the soil parcel fertilized with phosphorous (75 kg P/ha) the soil lead content was 179.21 % higher than the value registered for the unfertilized soil parcel for   For the soil parcel fertilized with farmyard manure (b 5 ), the lead content was 166.52 % higher than the value registered for in the soil control sample, for the 0-15 cm depth, respectively 11.95 % lower than the value registered for in the soil control sample, for the15-30 cm depth.
In the case of the chrome, the values registered for each fertilization sequence have been below the Limit of Quantitation.
Soil humidity has been registered with values between 2 and 9%.
Soil humidity value (table 4) for the soil parcel where a fertilization sequence has been applied was 125 % higher than the value registered on unfertilized soil parcel for the 0-15 cm depth.
For the 15-30 cm working depth, the soil humidity lowered by 28.57 % compared to the soil control sample.
For the experimental wheat variants -fertilization with phosphorous -75 kg P/ha (a 1 b 3 ) and wheat -fertilization with nitrogen and phosphorous -N90P75 kg/ha (a 1 b 4 ), soil humidity for the 10-15 cm working depth was 25 % lower than the soil control sample, and for the 15-30 cm depth it was 114.28 % higher than the soil control sample.
The lowest humidity value (compared to all the other experimental variants) has been registered for the experimental variant wheat -fertilization with farmyard manure (a 1 b 5 ), for the 0-15 cm working depths, respectively 50 % of the soil control sample value.
In the case of the experimental variant wheatfertilization with farmyard manure (a 1 b 5 ), 15-30 cm depth, the highest humidity value has been registered, compared to all the other experimental variants (128. 57 % higher than the control sample value.) Resistance to penetration values varied between 2.70 ÷ 3.70 MPa, meaning that the soil is in the light soil category.
Soil's resistance to penetration (table 4) for the analysed experimental variants was: -wheat-fertilization with nitrogen -90kg N/ha (a 1 b 2 ): Ï% 0-15 cm: 123.33 % higher than the valued registered in the soil sample with no fertilization sequence; Ï% 15-30 cm: 103.7 % higher than the valued registered in the soil sample with no fertilization sequence; -wheat-fertilization with phosphorous -75 kg P/ha (a 1 b 3 ): Ï% 0-15 cm: 120 % higher than the valued registered in the soil sample with no fertilization sequence; Ï% 15-30 cm: 114.81 % higher than the valued registered in the soil sample with no fertilization sequence.
-wheat -fertilization with nitrogen and phosphorous -N90P75 kg/ha (a 1 b 4 ): Ï% 0-15 cm: 3.33 % lower than the valued registered in the soil sample with no fertilization sequence; Ï%15-30 cm: 114.81 %; -wheat-fertilization with farmyard manure (a 1 b 5 ): Ï% 0-15 cm: 90 % of the higher than the valued registered in the soil sample with no fertilization sequence soil control sample value; Ï% 15-30 cm: 103.7 % higher than the valued registered in the soil sample with no fertilization sequence.
The extremely high values of the soil's manganese content are due to its high capacity of metal stabilization by the Triticum aestivum species (wheat) through the phyto-stabilization process.
The lowest metal content values have been registered for the fertilization with nitrogen and phosphorous (b 4 ), for the 15-30 cm working depth, except for the cadmium, where the registered value was much higher than the control sample.

Conclusions
Modern, intensive, high-yielding farming exerts a considerable stress on soil. The numerous crops, diversification of cultures, with or without taking into account the crop-rotation, severe modification of aerohydric regime through irrigation and drainage, increment of ploughing depth, intense traffic very often with high heavy vehicles, fertilization and other technological measures, strictly necessary to obtain a high productivity, exert positive effects but sometimes also negative effects on soil's properties [11].
In the case of the soil parcel fertilized with farmyard manure (a 1 b 5 ) for the 0-15 cm working depth, the lowest manganese content was registered, due to Triticum aestivum's capacity to stabilize metals in soil.
The lowest metal contents in soil (nickel, copper, zinc, arsenic, lead) have been registered for the experimental variant wheat -fertilization with nitrogen and phosphorous -N90P75 kg/ha (a 1 b 4 ), both for 0-15 cm and for 15-30 cm working depths.
Soil's metal contents variations are mainly due to the applied fertilizers sequence (nitrogen, phosphorous, nitrogen and phosphorous, farmyard manure), to Triticum aestivum's capacity to stabilize/assimilate metals in/from soil, as well as to climatic conditions in 2016.