Productivity of Pear Plantings Depending on the Content of Main Macroelemants (n, p, k) in the Soil after Optimized Fertilization

It is important to ensure the optimal nutrition with all elements in particular, with the main macro elements (nitrogen, phosphorus and potassium) in order to maintain the most productive relationship between the growth of vegetative organs and tree fruiting in fruit plantations. During many years of growing of fruit planting there are significant changes in soil fertility in accordance with peculiarities of soil-forming processes under its cover and rather intensive application of agrochemical means for protection against harmful organisms, as well as the significant use of nutrients by trees which significantly differs in different periods of growing apples and pears. This is due to the uneven removal of nutrients that are digested for the creation of biomass of vegetative and generative organs of trees. Ergo, according to the research data (Kopytko et al., 2018), 30-year-old apple and pear trees has extracted nitrogen (N) 385 and 214 kg ha^-1, phosphorus (P₂O₅) 126 and 120 kg ha^-1 and potassium (K₂O) 470 and 270 kg ha^-1 from the soil, including fruit harvest - 286 and 111, 104 and 78 and 397 and 270 kg ha^-1 and localized in trees - 96 and 163, 22 and 42 and 76 and 124 kg ha^-1. Accordingly, an apple compared to a pear removed much more nitrogen and potassium from the soil and almost the same amount of phosphorus. Most of all elements were used for fruit harvest. These were trees on the seed rootstock which began to bear fruit after harvesting at different ages and their total fruit yield was 263 and 157 t, respectively. Therefore, there is another ratio of indicators of the removal of fertilizer elements in terms of one ton of crop: nitrogen was 1.10 kg, phosphorus 0.40 kg and potassium 1.51 kg in one ton of apples; it was 0.71 kg, 0.50 and 1.72 kg in pear fruits, respectively. The total removal per one ton of fruits was 1.46 kg, 0.48 and 1.79 kg, respectively and 1.75, 0.76 and 2.51 kg, respectively. Due to significant differences in the mineral nutrition of apples and pears, there is a need for pear optimization based on appropriate studies in its plantations. This is especially true for the cultivation of its new high-yielding plantings on logged-off gardens as a result of certain soil depletion for the long previous cultivation of the plot which was solved in our experiment.
       
Optimum fertilization is one of the main components of intensive growing technology for fruit planting. It promotes activation of photosynthesis, differentiation of fruit buds which in turn provides regular high yield and improvement of fruit quality (Kopytko, 2001; Kopytko et al., 2018; Fura 2009; Wawrzynczak and Wojcik, 2012; Zygmuntowska and Jadczuk-Tobjasz, 2008). Sufficient mineral nutrition of fruit crops provides the positive effect on the entire agricultural phytocoenosis and increases economic efficiency of growing horticultural products after the rational use of fertilizers (Maliuk 2009; Salash and Kobelush, 2015; Jarocinski, 2012). Rational fertilization also increases the yield of other crops  (Medhi et al., 2007; Sharma et al., 2000; Dhinesh and Santhiet 2016). Due to reduced fertilizer application, optimized fertilizing also contributes to the introduction of environmentally friendly technologies in horticulture and getting high quality fruits (Jarocinski, 2012; Chen et al., 2017). The aim of the research is to obtain stable high yield of pears using optimal parameters of mineral nutrition with nitrogen, phosphorus and potassium on dark gray podzolized soil in Right-bank Forest-Steppe of Ukraine.

To clarify parameters of optimized mineral nutrition soils set by the problematic research laboratory of Uman NUH for apples and recommended for pears (Kopytko, 2001), we conducted an experiment on studying pear productivity grown on such optimized soils applying fertilizer norms for an apple in comparison with the norms proposed for planting pear in zonal recommendations (production check variant) and with variants after additional fertilization to the optimized soil. The experimental garden with ‘Conference’ and ‘Osnovianska’ pear varieties planted in 2007 on an area of logged-off old pear tree garden with tree placement of 5x3 m and in 2010 the experiment was carried out according to the following scheme: 1. Without fertilizers (check variant);2. N₉₀P₆₀K₉₀ (production check variant); 3. Estimated fertilizer rates (background); 4. Soil + N₃₀; 5. Soil + N₃₀K₃₀; 6. Soil + N₃₀P₃₀K₃₀. There were three replications with randomized placement of plots and on each of them there were five record trees. Starting the experiment the provision level of nitrate nitrogen (according to the nitrification capacity) was insufficient (N-NO₃ content in the layer of 0-40 cm was 16.5 mg/kg of soil which is less than the optimal level (23.5 mgkg^-1 at 7 mgkg^-1 and the provision level of phosphorus mobile compounds was higher and the provision level of potassium forms was within the sufficient level in the layer of 0-60 cm (P₂O₅ content was 166 mg/kg comparing with the optimal one of 70-100 mgkg^-1and K₂O content was 250 mgkg^-1 comparing with the optimal one of 230-280 mgkg^-1 in the soil). Therefore, in order to have the optimal mineral nutrition with main macro elements N, P and K for the pear in relevant agrochemical analyzes, in accordance with relevant recommendations (Kopytko, 2001), the norm of nitrogen fertilizer was calculated to bring N-NO₃ content to the soil to the optimal level of 35.5 kg N per hectare. The soil was analyzed annually. Based on the results of the analysis, nitrogen fertilizer rates were calculated to maintain the optimal content of N-NO₃ in the rooting soil layer (0-40 cm). In different years they were within 35-55 kg N per 1 hectare of the garden. According to the results of agrochemical analyzes in 2012, it was found that the level of moving forms of potassium in the layer of 0-60 cm was lower than the optimal one. Therefore, in order to have the optimal content level in this layer of soil on fertilized areas, such quantities of potassium fertilizers were calculated and applied: background variant – 230-260 kgha^-1; soil + N₃₀ – 275-330 kgha^-1; soil + N₃₀K₃₀ – 115-320 kgha^-1; soil + N₃₀P₃₀K₃₀ – 200-330 kgha^-1 K₂O. These amounts of K₂O used with potassium fertilizers are to maintain its optimal content in the soil during a 3-4-year period.
       
In the fertilized areas of variants, phosphorus and potassium fertilizers were introduced in autumn during plowing and disk harrowing and nitrogen fertilizers were applied in spring during soil cultivation in row spacing. The soil in the non irrigated experimental was kept by fallowing system. The studies were performed according to generally accepted methods (Bolotina and Abramova, 1968; Egner et al., 1960; Yeshchenko, 2014).

Studied various fertilizer variants did not have the same effect on the content of main macro elements of mineral nutrition in the rooting soil layer (Table 1). The most widely available nitrogen, phosphorus and potassium forms were for the annual application of N₉₀P₆₀K₉₀ recommended fertilizer norm where their content exceeded corresponding indicators in check variant non-fertilized areas by 10.6, 27.8 and 63.0 mg/kg of soil. When fertilizing with nitrogen and potassium norms calculated on the basis of agrochemical analysis of soil, the content of N-NO₃ (under nitrification capacity of soil) and K₂O was maintained within the optimum levels throughout the eight-year study period. In case of additional fertilization there were slightly more nutrients in the soil but increasing the content of N-NO₃ and K₂O was negligible, respectively, by 2,2-2,9 and 4-5 mgkg^-1 and P₂O₅ increasing was more noticeable (by 10,6 mgkg^-1 of soil). These differences, respectively, were conditioned by large needs of the pear in nitrogen and potassium nutrition, so there were less of them remained in the soil not used by trees.
 

 
This is confirmed by data from other researchers (Popova, 2004; Pilipenko and Melnyk, 2014). Phosphorus compounds added with fertilizers for less use of plants replenish soil phosphates more.
       
According to the results of the study of fruiting indicators, it is found that ‘Conference’ pear variety has the largest number of flowers (256-314 flowers/tree) during the period of growth and fruiting (in 2010-2012) (Table 2). Most of them were in the variant with the addition of N₃₀ to the optimized mineral nutrition soil with calculated fertility rates where their number significantly exceeded the number of flowers in the check variant without fertilization and with indicators in other variants did not differ significantly. Trees of ‘Osnovianska’ variety were less blooming. The number of flowers was significantly higher on plots of all experimental variants with fertilizers than on check variant plots without fertilization.
 
  
 
The number of flowers significantly increased on trees of both varieties during the period of fruiting and growth (in 2013-2017) which was due to the increase of crown habit and fertilizer influence. Trees of ‘Osnovianska’ variety blossomed the most in variants with calculated fertilizer rates and with the additional application of N₃₀K₃₀ where there were flowers by 278 and 280 more than in the check variant without fertilization. Trees of ‘Conference’ variety blossomed less intensively with the number of flowers from 1083 to 1227 flowers/tree. Most of them were in the soil + N₃₀K₃₀ and soil + N₃₀P₃₀K₃₀, respectively, by 44 and 40 flowers/ tree more than in the check variant without fertilization.
       
The degree of fruit setting depended on age, variety and fertilizer variants. During the period of growth and fruiting (in 2010-2012) they setting on trees of ‘Conference’ variety the most in the variant the soil + N₃₀K₃₀ (20.9%) and
 
‘Osnovianska’ variety had the most in the soil + N₃₀ (23.5%).
       
In the next period from 2013 to 2017, the degree of fruit fastening decreased markedly. Most of them knitted of both varieties in the soil + N30 variant where the difference with check variant indicators without fertilization was 5.4 and 1.3 %.
       
The loading of fruit trees in all areas of experiment variants with fertilizers substantially exceeded the number of fruits on check variant trees without fertilization. The largest number of fruits was stored in the soil + N₃₀ variant on trees of both experimental varieties they were 38 fruit more than on check variant trees. The close loading indicators of fruit trees were in the soil + N₃₀K₃₀ variant.
       
Depending on flowering, fruit fastening and especially preserving indicators during the period of fruiting start when the vegetative mass of different organs on young trees was still growing, different yield of fruits on plots of the studied fertilizer variants was formed (Fig 1, 2). On average, in 2010-2012, after fertilizering pears of ‘Conference’ variety with calculated fertility rates to create optimal levels of their mineral nutrition (background), it significantly exceeded yields in absolute and production control variants by 1,2 and 0,4 t ha^-1, respectively. Its level was significantly higher after additional addition of N₃₀K₃₀ to the soil. Young trees of ‘Osnovianska’ variety became less fruit bearing intensively and their average yield was in the range of 1,7-2,3 t ha^-1. In fertilizer variants, it was also significantly higher than in non-fertilized areas of absolute check variant.
 

 

       
The excess was not significant in all other experimental variants with fertilizer in comparison with production check variant. In the period of fruiting and growth (in 2013-2017), the yield of ‘Conference’ variety was significantly higher at 3,7-4,7 t ha^-1 in all experimental variants with fertilizers and the yield of ‘Osnovianska’ variety was higher by 3,7-5,3 t ha^-1 compared to its indicators in unfertilized check variant plots.
       
In the period of fruiting and growth of ‘Conference’ and ‘Osnovianska’ experimental varieties, there was a strong direct correlation between their yield and content of N-NO₃ and K₂O in the soil. The correlation coefficient was 0.845 and 0.935 and 0.890 and 0.929, respectively, and with the content of P₂O₅, the correlation was also straight but weak and average (r = 0.302 and 0.547).
       
Qualitative indicators of pears (average weight, total yield of fruits of the highest and first variety grades) also depended on fertilizer variants and varietal characteristics (Table 3).
       
This is confirmed by research Slyusarenko (2018) and other authors (Zygmuntowska and Jadczuk-Tobjasz, 2008; Trunov and Shishkaraev, 1998). Thus, the average weight of fruits of ‘Conference’ variety on young trees at the lowest yield was the largest in plots with the application of calculated fertilizer norms (193 g) and the fruit weight of ‘Osnovianska’ variety on trees of production check variant after N₉₀P₆₀K₉₀ fertilizing. However, its increase was not significant in comparison with fruits in other variants.
       
In the period of fruiting and growth, fruits of ‘Conference’ variety in all studied variants were slightly lower than in the previous period with less yields and by average weight, they did not differ significantly. Fruits of ‘Osnovianska’ variety during this period increased in all variants and the largest were in the plots of production check variant where their average mass significantly exceeded its size in variants without fertilizer and soil + N₃₀K₃₀. There was a direct strong correlation (r = 0.967) between the average weight of fruits and yields during the period of fruiting and growth of ‘Conference’ variety trees.
       
The analysis of indicators of merchantable quality indicates that fruits of the higher and the first commodity grades were the bulk of the harvest. On average, in 2010-2017, there were no significant differences between these quality indicators of fruits in the experimental variants. There was only a tendency to increase fruit commerciality in variants with fertilizer in comparison with check variant without fertilization.

Made by fertilizer of calculated norms of fertilizers on the basis of agrochemical analysis of the soil, such as for apple trees optimal parameters of content and correlation N, P₂Î₅ and K₂Î provide sufficient mineral nutrition for pears trees at additional application of N₃₀K₃₀ which contributes to the greatest increase in yield ‘Conference’ and ‘Osnovianska’ varieties in 37-45%. Therefore, the optimal levels of content in the soil of N and K₂Î should be slightly higher than for apple trees. With annual fertilizer recommended by zonal standards N₉₀P₆₀K₉₀, yield is higher on 36-40%, with a significantly larger amount of fertilizer.
       
Average weight of fruits and their saleable qualities for different fertilizers did not change significantly.
       
The fertilization system with calculated norms of fertilizers which contain only those elements and in such quantities which lack the soil to optimal mineral nutrition of fruit plants without fertilizer application with nutrients which content is equal or higher to the optimum one, is more economical and by the influence on the ecological status of the soil and the environment is more appropriate than the annual introduction of significantly higher fixed norms of all fertilizers based on zonal recommendations.