STUDYING THE RESEARCH RESULTS REGARDING FERTILIZERS USED IN THE REPUBLIC OF MOLDOVA

Abstract. This paper represents an analysis of the research concerning the use of fertilizers and nutrients balance in the soils of the Republic of Moldova. The nature and effectiveness of fertilizers, their influence on the agrochemical properties of soils, the protection of the environment from the pollution by nutrients in addition to the regulatory normatives of our country developed in order to determine the necessary in fertilizers for obtaining the expected crops have been as well discussed.

The presented data shows that the share of farmlands is inadmissible large (73.8%) and for forest is of 2 -3 times less than optimal ones.The imbalance between natural and anthropogenic ecosystems causes the amplifi cation of the various forms of land degradation.

The nature and effectiveness of fertilizers
The territory of the Republic of Moldova is characterized by a rugged relief.Thus, the predominance of the slopes on 80% of the territory creates favorable conditions for the expansion of erosion processes.The average absolute altitude of the surface of the Republic of Moldova is 147 m, the maximum altitude is 429 m, and the minimum one is 5 m.The soil eroded area, which missed from 20 up to 70% of their initial fertility, is about 36% [2].
The climate of the Republic of Moldova is temperate continental [3], with a mild and short winter (the average temperature of January is -3 ÷ -5 0 C) and a warm and long summer (the average temperature of July 20 ÷ 22 0 C).In relation to the climatic indices, the territory of Moldova was divided into three areas, which are at the same time and agro-pedoclimatic areas: North, Center and South.
The quantity of atmospheric precipitation varies within the limits of 500-630 mm in the North area and 450-500 mm in the South area [4].The sum of temperatures higher than 10 0 C constitutes 2750-2850 0 C in the North zone and 3100-3350 0 C in the South zone.The hydrothermal coeffi cient (K after Ivanov -Vîsoţchi) is 0.7-0.8 in the North zone and 0.5 -6 in the South zone of the country.The frequency of droughts in ten years is: once in the North zone, 2-3 times in the Centre zone and 3-4 times in the South zone.
The soil structure is quite complex.The main soil types and subtypes are: chernozems ("black earth"), occupying 70%; brown and grey soils -10.2%; alluvial soils -10.2% and the delluviale soils -4,0% [5][6][7].Soils with a high fertility coupled with the thermal favorable regime allow cultivating a wide range of valuable crops: vines, etherooleaginous plants, fruits, nuts, vegetables, sunfl ower, etc. to yield the production with a high quality taste.The current state of the quality of soil is shown in Table 1.The soils with the note of creditworthiness between 80 and 100 points occupy approximately 27% of the total area of the agricultural lands [7].On these soils with a high productivity, presented as a general rule by the typical chernozems and landfi ll leachate (standard soils) containing organic matter of 3.6-4.5%,can be achieved at the expense of actual fertility 3.2-4.0t/ha for the autumn wheat.The class II and III of the lands contained within the note of creditworthiness of 60-80 points is 36% or 918 thousand ha.The productivity of these soils is also quite high and constitutes 2.4-3.2t/ha for the autumn wheat.These two classes of soils of the note of creditworthiness are often affected by the processes of humifi cation, their diminuation in nutrient contents, destructuration and compactisation, biologycal degradation and the partial surface erosion.The soils of classes IV, V and VI of the note of creditworthiness occupy 30% from the total surface and have a note of creditworthiness of 20-60 points and a low productivity of 0.8-2.4t/ha of the autumn wheat respectively.These soils are weak, moderately and severely degraded, especially by the erosion processes.
At present, according to the Land Cadastre of the Republic of Moldova on 01.01.2011 [2] the note of creditworthiness is 63 points.The effi cient fertility of the soil assures the formation of 2.5 t/ha of winter wheat.
In the conditions of the Republic of Moldova, the soil moisture (rainfall) is one of the factors determining the formation of high and stable yields.The calculations carried out by the Institute of Pedology, Agrochemistry and Soil Protection "Nicolae Dimo" [14] shown that in a multiannual cycle the average potential harvest of the winter wheat formed from precipitations constitutes 4.3 t/ha.The difference in yield, obtained in function of the amount of rainfall and the note of creditworthiness is great and constitutes (4.3-2.5 t) 1.8 t/ha.In the conditions of insuffi ciency of nutritive elements, the unsatisfactory state of physical and biological characteristics of the soil, plants consume unproductively the moisture reserves accumulated in the soil fot the organic compound synthesis and as a result, harvests are small and of low quality.Those were confi rmed by the research carried out in fi eld experiences of long periods of time.It was established that for the variants fertilized optimally, the crop plants consumed 20-25% less water compared to the nonfertilized version [8].Krupenikov I. [9] by analyzing the main forms of soil degradation (total for the 11 forms) arranged under number 1 the humic degradation and under number 2 -the agrochemical degradation agrochimică (the reduction of nutritive elements in soil).These two forms of degradation occur continuously and for all the farmlands.
The results of the multiannual fi eld experiences have shown that in the conditions of the Republic of Moldova the use of fertilizers in the optimal doses provide a harvest enhance of 66% for sugar beet, 48% for the winter wheat and 35% for the cultivation of maize for grain and sunfl ower (Table 2).The productivity of the plants for the fertilized variants was 4.3 t/ha of the winter wheat, 5.4 t/ha maize for grains, 2.0 t/ha of sunfl ower seeds and 34.8 t/ha of sugar beets [8].In the Republic of Moldova the regulatory normatives were developed in order to determine the necessary in fertilizers for obtaining the expected crops [10].It was established that the use of the optimal doses of fertilizers gave a raise in the harvest of 1.2 t/ha for the winter wheat, 1.4 t/ha of maize for grains, 13.8 t/ha of sugar beets and 0.5 t/ha for sunfl ower seeds.From the presented data that soil fertilization and mineral nutrition of plant optimization of culture is an important factor for obtaining high crops.

The use of fertilizers and nutrients balance in the soil
Moldovan soils are characterized with a high fertility [6, 7, 11-13, 15, 16].The research carried out in the 1950-1960 yrs.demonstrated that the chernozems of Moldova contained in that period 340 t/ha of humus in the layer of 100 cm.In the composition of organic matter was contained 20 t/ha of nitrogen and 5 t/ha of phosphorus.The total quantity of P 2 0 5 the plowed layer was approximatively 160-180 mg and to the depth of 90-100 cm -up to 100 mg in 100 g of soil.The reserve of the total phosphorus in the layer of 1 m was 17 t/ha.Moldovan soils are rich in minerals containing potassium [17].The total content of these soils is 10-15%.The reserve of the total potassium in the layer of 1 m of chernozems constitutes 170-290 t/ha.
In the period 1950-1960 the plant crop harvests were modest and constituted: 1.6 t/ha of winter wheat, 2.8 t/ha maize for grains, 1.5 t/ha of sunfl ower seeds and 11.9 t/ha of sugar beets (Table 3).Obtaining the high crops was limited by two natural factors: 1) the insuffi ciency of moisture and 2) the low level of nutrients in the soil.The possible harvests calculated according to the degree of humidity were by 60-70% higher than those obtained of that time (Table 4).These data allowed presuming that of limitative factors the fi rst place belonged to the insuffi ciency of nutrients in the soil.
Generally, the effectiveness of fertilizers [E] is expressed by the equation: , where R w.s.-the harvest quantity is limited by the extent of water supply; R n. -the harvest quantity is determined by the contents of nutrients in the soil.
By the 1965 year, the input of fertilisers in the agriculture of Moldova was insignifi cant.According to the statistic data, in the period of 1961-1965 yrs. on the 1 ha of arable land and perennial plantations 6.2 kg/ha of N, 8.7 kg/ha of P 2 O 5 and 3 kg/ha of K 2 O that were introduced with mineral fertilizers.The average dose of organic fertilizers was 1.3 t/ ha (Table 5).The export of nutrients from the soil by crops was signifi cant.As a result, in the agriculture of Moldova was formed a deeply defi cient of nutrients.During the considered period the defi cit of nutrients per hectare was annualy: 59 kg of N, 14 kg of P 2 0 5 and 80 kg of K 2 0 (Table 6).The research carried out in the 1955-1970 years showed that fertilizers were effective for all the cultures and for all the soils [13,18].That conditioned the accelerate rhythms of the agriculture chimization.The volume of mineral fertilizers applied to the arable lands and the perennial plantations grew rapidly.In 1970 the agrarian sector of the Republic of Moldova received fertilizers by 2.5 times more in comparison with the 1963 year.The dose of used fertilizers accounted for 62.7 kg/ha NPK.As a result, the balance of nutrients was rapidly improved.
In the period of 1981-1988 yrs for the fi rst time in the history of Moldova's agriculture the nutrient balance became positive.
During this period per a hectare of the arable lands and plantations of fruits, with mineral and organic fertilizers, 100 kg N, 66 kg P 2 O 5 and 87 kg K 2 O were applied.The average dose of manure applied in the agriculture was 6.0-6.6 t/ ha.As a result the productivity of crop plants increased signifi cantly.The average harvest of the winter wheat amounted to 3.8 t/ha, of the maize for grains was 2.4 t/ha and for sunfl ower was 2.0 t/ha.During the period of chimization, which lasted for 25 years (1965-1990) there were applied 1200 kg of nitrogen, 960 kg of phosphorus and 860 kg of potassium.The accumulation of nutrients in the soil was relatively small in comparison with their export throughout the entire history of agriculture.Just for 100 years on each arable land with the harvest there were exported 2300 kg of nitrogen, 1000 kg of phosphorus and 5000 kg of potassium [20].
After the 1998 year, the volume of fertilizers increased substantially, reaching the minimum level in the period of 1996-2005 yrs.During that period, there were applied about 4-6 kg of nitrogen, 0.3-0.4kg of phosphorus and 0.3-0.9kg of potassium per hectare.The nutritional balance again became deeply negative (Table 4), of minus 30 kg of nitrogen, 21 kg of phosphorus and 83 kg of potassium.As a result, the productivity of crop plants dropped to the level of the 60 years of the last century (Table 3).
In the recent years (2006-2012) the volume of mineral fertilizers has increased in comparison with the 1996-2006, but it has not been touched even the 1961-1965 years.Currently the fertilizers with nitrogen are preponderently applied.Practically, the fertilizers with phosphorus are not applied -the fi rst necessary element in soils.In the last 10-12 years the dose of the applied manure in Moldova's agriculture constitutes 0.02 t/ha, the optimal rule being about 10 t/ ha [13][14][15]18].
The largest quantities of fertilizers are applied to the production of potatoes, sugar beets and vegetable crops -193, 70 and 52 kg/ha, respectively.The insuffi cient quantities of NPK fertilizers is applied to the cultivation of winter wheat (27 kg), maize and sunfl ower (7-12 kg/ha) (Table 7).The soil nutrient balance is negative (Table 6), the chemical degradation of the soil takes place and as a result the harvests are small and of low quality.

The infl uence of fertilizers on the agrochemical properties of soils
Humus is one of the main indices of the soil fertility.This fundamental component of soils determines to a great extent its chemical, physical and biological properties.The preservation of crops and biota with the mineral nutrition depends directly on the organic matter in the soil.It has been experimentally determined that increasing the content of humus with 1% gives 0.5 t/ha of the winter wheat [8].
Since the 1953 year the research institutions and universities have been carried out the agrochemical monitoring.At the same time the balance of humus in the soils has been calculated.It was established that before the period of the intensive chimization  the humus balance was negative (Table 8).Annually 500 kg/ha of organic matter is mineralised [18,19].The systematic use of fertilizers, including 5-7 t/ha of manure, the cultivation of perennial grasses on about 10% of the arable land (180-210 thousand ha) contributed to the formation during the 1975-1990 years to a slightly defi cient balance of humus in soils of about minus 100 kg/ha.
Over the past 10-15 years the insuffi cient quantities of manure (0.01-0.6 t/ha) has been incorporated into the soil.The balance of organic matter is negative, minus 700 kg/ha, while with the losses by erosion is of -1100 kg/ha.

The nitrifi cation capacity
According to the Agrochemical Research Service [24] approximately 39% of farmlands are characterized with a low content of organic matter (less than 2%), 40% with moderate (2-4% of humus) and only 20% with the humus content higher than 3.0% (Table 9).
Chemistry Journal of Moldova.General, Industrial and Ecological Chemistry.2013, 8 (1), [14][15][16][17][18][19][20][21][22]  As a result, about 80% of soils are characterised by a very low and low nitrifi cation capacity.On agricultural lands with the humus content of less than 2% by the nitrifi cation processes in the soil only 50-60 kg/ha of nitrogen is accumulated and the soils with 3.0 -4.5% of organic matter -up to 75 -110 kg/ha of the mineral nitrogen.These quantities of the mineral nitrogen are suffi cient for the formation of 1.7 -2.0 t/ha and 2.5 -3.7 t/ha respectively of the winter wheat [8,23].
At present the content of organic matter in the soils of Moldova is about 3.0%.As a result of the mineralization of organic matter, the soils produce annually about 70 kg/ha of nitrogen.This quantity of nitrogen is suffi cient for the formation of 2.4 t/ha of the winter wheat.
Phosphorus has a special role in the metabolism of plants and in the formation of the elevated harvest.Chernozems as well as the grey soils are characterized by the low content of phosphorus in soil [8,13].The intensity of phosphate regim has been confi rmed by the research results carried out by the State Agrochemical Service [20].In the 1971-1975 years the surface of soils with low phosphorus content was quite large and constituted approximately 68% [8].
In the period of 1965-1990 yrs about 960 kg/ha of phosphorus was incorporated into the soils [22].This agrochemical measure infl uences benefi cially on the phosphorus regime of soils.To the 1990 year the surface of soils with low phosphorus content decreased by 2.0 times, while that with a high phosphorus content increased by 3.0 times.On average per republic the mobile phosphorus content in the soil increased by 2.0 times, as a result the productivity of crop plants has been increased.
In the recent years (2000-2012) in Moldova's agriculture insuffi cient quantities of P 2 O 5 (up to 1 kg/ha) were applied.The export of phosphorus with the harvest is high and constitutes annually about 25-30 kg/ha.The balance of this nutrient element is negative.Currently the postaction with phosphorus fertilizers is practically exhausted.With the natural low background of the mobile phosphorus in soil it is possible to get about 2.5 t/ha of the winter wheat.This level of harvest, usually, has been obtained within the country in recent years.
Potassium The crops for the high harvest formation extract from the soil signifi cant quantities of potassium -100-200 kg/ha.The soils of Moldova are rich in the total potassium.But the main reserve of available potassium for the plants constitutes the exchangeable form.It was found experimentally that the potassium content for 15-20 mg/100 g of soil is suffi cient for the optimal growth and development of plants [13,25].According to data [24], only 13% of the farmlands are characterised with a moderate content (10-20 mg) of exchangeable potassium; 87-95% of the total areawith a high content.
The systematic use of fertilizers in the 1965-2000 years provided an equilibrated balance of potassium in soil.Therefore, the quantity of exchangeable potassium increased average by 2 mg/100 g of soil [24].Currently, the potassic and organic fertilizers are applied in very small doses.The balance of the K 2 O in soil is negative.
The soils of Moldova are rich in accessible potassium to plants, but these reserves in a quite long period (150-200 years) may be exhausted.Hence, it is necessary to maintain an optimal regime of potassium already present in the soil by applying fertilizers.

The requirement of mineral fertilizers in the Republic of Moldova
In the conditions of Moldova the natural factors which limit the production of high harvests are the insuffi ciency of nutrients in the soils as well the moisture defi cit.In order to achieve the growth rate in harvest of 40-50% it is necessary to compensate the defi cit of nutrients by the use of fertilizers and rational utilization of the soil moisture [8,18,19,22,25].
In determining the amount in fertilizers for agriculture of Moldova, were used the decisions of the Government of For potatoes and vegetable crops will be needed 6.8 thousand tons of nitrogen with the average dose for 1 ha -N 60 .For the fruitful orchard fertilization will be needed 2.0 thousand tonnes of nitrogen, for the fruitful vineyards 1.5 thousand t.The phosphatic fertilizer requirements will constitute 69.9 thousands t for the fi eld crops, 9.0 thousand tonnes for vegetables and potatoes, 1.5 thousand t -for the forfruitful vineyards, 1.2 thousand t for the fruitful orchards.The annual requirement of potassic fertilizers will be 28.3 thousand t for fi eld crops, 6.8 thousand t for vegetables and potatoes and 3.1 thousand tonssuplimentary for the irrigated lands.

The total annual demand of fertilizers for the agriculture of the Republic of Moldova after 2020 will constitute 236.7 thousand tons of the active substance, including 99.9 t of nitrogen, 91.0 thousand t of phosphorus and 45.8 thousand t of potassium. This level of fertilization was reached in the 1976-1985 years by applying annually 243.6-362.0 thousand t (Tabel 5). The use of the optimal fertilization system coupled with other technological links of cultivation of the crop plants will allow to get 4.0-4.2 t of the winter wheat, 3.6 t of grain maize and will form an equilibrated nutrient balance in Moldova's agriculture.
Priority measures for conservation and enhancement of soil's effective fertility 6.
For the conservation and enhancement of soil fertility, the reasearchers of the Institute of Pedology, Agrochemistry and Soil Protection "Nicolae Dimo" developed a complex of fi totechnical, agrotechnical and agrochemical measures, which include [7,8,18,22,25,26]: optimization of crop rotation and their implementation in each pedoclimatic zone; increasing the quota of perennial grasses (alfalfa, sainfoin) in fi eld cropping up to 10-12%; increasing the quota of annual legume crops (peas, beans, soya) in fi eld cropping up to 10-12%.These changes in the structure of the crop rotation will allow to accumulate annually about 40-50 thousand tonnes of nitrogen or 30-35 kg/ha; annual incorporation into soil of 5-6 t/ha of manure; a total of 9-10 million tons; application of 100 thousand t of nitrogen and 90 thousand t of phosphorus; a total of 190 thousand tons; minimizing in the admissible limits of about 5 t/ha of the soil erosion.

Over the past few
years the State Programs have been developed in order to remedy the chemical, physical and biological characteristics of the soil as well as for the protection of soil and water by the pollution with nutrients and substances of plant protection, including: The complex Program of valorifi cation of the degraded lands and improvement of the soil fertility.Part I. Soil improvement approved by the Decision No. 636 of the Government of the Republic of Moldova from 26 May 2003; The complex Program of valorifi cation of the degraded lands and improvement of the soil fertility.Part II.The improvement of the soil fertility approved by the Decision No. 841 of the Government of the Republic of Moldova from 26 July 2003; The Program for the conservation and enhancement of the soil fertility for the 2011-2020 years, approved by the Decision No. 626 of the Government of the Republic of Moldova from 20 August 2011.These documents determine goals, actions (measures), performance indices, the terms of implementation and those responsible for implementation.