Determination of Lands with Optimal Soil and Climate Conditions for Growing Potatoes (Solanum tuberosum L.) in Pazardzhik Region

Determination of Lands with Optimal Soil and Climate Conditions for Growing Potatoes (Solanum tuberosum L.) in Pazardzhik Region Georgi Dimitrov1, Zornitza Mitreva2 1University of Forestry, Faculty of Agronomy, 10 Kliment Ohridski Blvd., 1797 Sofia, Bulgaria 2 - N. Poushkarov Institute for Soil Science, Agrotechnology and Plant Protection, Agricultural Academy, 7 Shosse Bankya Str., 1331 Sofia, Bulgaria Corresponding Author: Georgi Dimitrov,e-mail: [email protected] Received: 4 March 2025 Accepted: 25 June 2025 Abstract Information from databases on soil diversity in Pazardzhik district was used for the report. On the basis of Large-scale soil mapping (M 1:10000 and 1:25000 - Fund ISSAPP "N. Pоushkarov"), 671 soil differences have been identified, which cover the lands of all settlements in the district. Based on the soil properties and taking into account the climate conditions, relative evaluation was made for potatoes (Solanum tuberosum L.) by applying the "Methodology for working with the Cadastre of agricultural lands in the Republic of Bulgaria". The field ratings for the crop for all soil differences have been calculated. From the database, only soil differences, which receive 65-100 evaluation rating ("good" and "very good" lands) for growing potatoes are presented. The field ratings are under non-irrigated conditions. The name of soils, the physico-chemical properties and the settlements, in which they are distributed, are presented. Optimal conditions for growing potatoes are available in the municipalities of Batak, Belovo, Bratsigovo, Panagyurishte, Rakitovo, Velingrad. Keywords: Pazardzhik region, soil characteristics, potatoes, land evaluation, natural conditions Introduction Due to the high taste and nutritional value, potatoes (Solanum tuberosum L.) are used in a wide variety of forms for human and animal food. According to their purpose, they are: dining, feed, industrial, and universal. Potato tubers contain about 25% dry matter, 18-22% of which starch and about 2% protein. The culture is rich in vitamins B1, B2, C, P and K. Therefore, for some people it is indispensable source of these vitamins in the winter months of the year (Gorbanov, 2010). In our country, potatoes have been grown since the end of the 19th century. The average yield per hectare in the 80s of the last century was 1000 kg. In 1990, the sown areas with potatoes were 41.2 thousand hectares, in 2012 -14.9 thousand hectares. The occupied area with potatoes for 2023 in the country is 7019 ha (Agrarian Report for 2024 of the Ministry of Agriculture and Food). Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 93 Bulgarian potato production ranks among the last places in the European Union, according to „Eurostat“(2023) statistics. Our country produced less than 119135 tonеs in 2023 (20.1% of total vegetable production), followed by tomatoes (Solanum lycopersicum L.) - 115.7 thousand tonеs (19.5%), watermelon (Citrullus lanatus Sch.), - 80.1 thousand tones (13.5%), pepper (Capsicum annuum L.) - 52 thousand tonеs (8.8%), cucumber (Cucumis sativus L.) - 50.1 thousand tonеs (8.4%) and head cabbage (Brassica oleracea var. capitata L.) - 45 thousand tonеs (7.6%). By comparison, Germany, the country with the largest potato production in the EU, produced almost 10 times more. In our country, there is a trend of steady decline in production. In 2022, 172,200 tones were reported, and in 2021 this volume was almost 196 thousand tones. Within two years, the potato harvest has decreased by more than 76 thousand tones. Germany is the largest producer of potatoes in the EU in 2023, with a harvest of 11.6 million tones for the period tones. This is 24% of the total amount in the EU. France ranks second, and the Netherlands ranks third. Together, these three countries account for the majority (55.4%) of the EU's potato harvest in 2023. The aim of the study is to determine the most suitable lands for growing potatoes in the Pazardzhik region through the values of the field ratings (65-100 evaluation rating), as well as to indicate the lands, in which these soils are located. Materials and Methods The relative evaluation for potatoes growing is determined on the basis of an assessment of soil and climate conditions. The culture requires loose, sand-clay soils (physical clay (<0,01 mm) 20-30%), with slightly acid reaction (pH in H2O 5.0-6.5). Clayey, compacted soils with alkaline reaction and high level of groundwater are unsuitable. Table 1, part 1. Indicators of soil conditions and assessment (field rating) for potatoes Indicators Degree Parameters Evaluation (field rating) note Mechanical composition in arable soil layer (physical clay,%) - Loose sand 0-5 0 The values of the indicator are doubled Bonded sand 5,1-10 30 clay-sandy 10,1-20 50 Slightly sandy-clayey 20,1-30 100 Medium sandy-clayey 30,1-45 80 Heavy sandy-clayey 45,1-60 60 Slightly clayey 60,1-75 30 Clay over 75 1 Dimitrov & Mitreva, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 94 Table 1, part 2. Indicators of soil conditions and assessment (field rating) for potatoes Indicators Degree Parameters Evaluation (field rating) note Humus horizon thickness(cm) 0-20 80 21-30 90 over 30 100 Soil thickness (cm) 0-30 1 Only for soils developed on hard rocks 31-50 30 Texture factor under 1 100 1,01-1,3 90 1,31-2 85 over 2 60 Soil reaction (pH in H2O) over 7,5 20 The values of the indicator are doubled 6,5-7,49 60 5,0-6,49 100 under 5 90 Humus content (%) under 1 20 1,01-2 40 2,01-3 80 over 3 100 Groundwater level (cm) 0-50 0 Only for soils with groundwater level of 0-150 cm. For layered meadow, gravel and sandy soils with groundwater level deeper than 100 cm, the indicator should not be evaluated. The following indicators are included in the assessment of soil conditions for potatoes: mechanical composition (physical clay content in % (particles <0,01 mm) of the arable land; thickness of the humus horizon (cm); soil thickness (depth) in cm (applies only to soils formed on hard rocks); texture coefficient (the ratio of the amount of silt clay fraction from horizon B to its amount from horizon A); soil reaction of plough soil layer (рН in Н2О); humus content in arable soil layer (%); groundwater level (in cm from the soil surface). In the assessment of soil conditions for development of the crop, importance is given to two indicators - mechanical composition of the soil and soil reaction (their assessments are doubled). For assessment of climate conditions (Table 2) the Selyaninov Hydrothermal Coefficient (HTC) was used. The developments were made on the basis of the heat and moisture requirements of varieties with medium-long and long growing season for the period June-August (during tuber formation). For moisturizing, HTC with optimal values of 1.4-2.0 was used. Areas with such humidification receive rating of 1 (the maximum assessment of climate suitability for growing the crop). For tubers formation, the presence of suitable, not very high temperatures is important. The assessment also includes the indicator of average Dimitrov & Mitreva, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 95 daily temperature for the same period, with the optimal being 14-18°C. Due to the use of both indicators, climate regions 2 and 3, although identical in terms of HTC values, differ in temperature conditions and therefore have different estimates for the production of late potatoes (Table 2). The HTC values are calculated on the basis of 40-50 annual averaged data from meteorological sources of National Institute of Meteorology and Hydrology (Climate Guide for the People's Republic of Bulgaria, 1979; Climate reference book for the People's Republic of Bulgaria, 1983; Koleva & Peneva. 1990; Sabev & Stanev, 1963; Hershkovich, 1984). Calculation of the HTC is made according to the formula: HTC = Sr / 0.1 x St, where: HTC - Selyaninov's hydrothermal coefficient; Sr - amount of precipitation for a period with average daily temperatures > 10 °C; 0.1 - equalization coefficient; St - amount of average daily air temperatures > 10 °C for the period. HTC values < 0.5 indicate drought and > 2 – waterlogging. Table 2. Assessment of climate conditions for growing potatoes. (Hydrothermal coefficient and average temperature for the tuber formation period). District № Indicators and their values Climate coefficients 1 1,4-2,0 1.0 2 1,1-1,4 0,8 3 1,1-1,4 (in adverse temperature conditions) 0,5 4 0,8-1,1 0,2 5 Places with an altitude of more than 1800-2000 m 0 The relative evaluation for potatoes in the surveyed sites (characterized by the presented soil differences) was carried out according to the "Methodology for working with the cadastre of agricultural lands in the Republic of Bulgaria" (by assessing the indicators presented in Table 1 and Table 2), (Petrov et al., 1988). The determination of field ratings is calculated on the basis of aggregated data on the soil difference. If it is characterized with more soil profiles, averaged data are used. The same approach is applied to physical and chemical properties of soil diversity, relief, soil-forming materials, climate, and the biological requirements of the crop.. The soil names are presented in accordance with the World Reference Base for Soil Resources – WRB (IUSS Working Group WRB, 2022). Dimitrov & Mitreva, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 96 Field rating The field rating is a final estimate and is the sum of the estimates of each indicator (for each soil difference) presented below in the equation. The assessments of the individual indicators and the complex assessment of the EBN are with values from 0 to 100, under nonirrigated conditions. Optimal conditions receive a score of 100 ball, and unfavorable conditions, depending on the severity of the indicator, receive a lower score, and in certain cases 0 (unfavorable conditions). The land evaluation is made by the following equation (Georgiev, 2006): FRx = 2RTX+ RTHH+ RTSP+ RCCR+ 2RpH+ RHC+ RGWT kEA kSA kST kFL kCL nR where: FRX – Field Rating for a particular crop. Ratings (from 0 to 100) for: RTX - soil mechanical composition; RTTHH -thickness of the humus horizon; RTSP - soil profile thickness; RCCR - texture profile differentiation; RpH - soil reaction; RHC - content of organic matter (humus); RGWT - groundwater level. Correction coefficients for: k EA - soil erosion or accumulation; k SA - soil salinity/alkalinity; k ST - stoniness of the arable soil layer; k FL - swamping; k CL - climate; nR - number of characteristics involved (R ...). The climate conditions are evaluated by the indicator HTC (according to Selyaninov, 1958) and average temperature for the period of tuber formation. Results and Discussion This section presents the results of land evaluation for potatoes. Only sites with "good" and "very good" growing conditions for the crop are selected. There are the soil differences, which receive 65-100 evaluation rating. Dimitrov & Mitreva, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 97 Table 3, part 1. Settlements, main physical and chemical indicators of the suitable soils for growing potatoes, field rating values. Municipality Land Soil (WRB, 2014) Physic al clay arable soil, % Physic al clay under arable soil, % Thickn ess humus horizo nt, cm Thick ness soil profile , cm Texture coefficie nt pH / H2 O Humu s, % Groundwa ter level, cm Field rating for potatoes Batak Fotinovo Umbrisol s, no erosion 30 29 88 110 1.7 4.8 13.0 deep 95 Batak Batak, Nova mahala Cambiso ls, low erosion 29 26 30 70 1.4 4.8 3.8 deep 75 Batak Batak, Nova mahala Fluvisols – Aluvial, Fulvisols - Deluvial 19 14 20 80 0.9 5.2 4.0 deep 83 Batak Batak, Nova mahala Fluvisols – Deluvial 18 19 50 100 0.9 5.6 1.1 deep 77 Batak Batak, Nova mahala Fluvisols – Deluvial 28 22 50 100 0.9 5.3 4.4 deep 100 Batak Batak, Nova mahala Fluvisols – Deluvial 39 31 50 100 0.9 5.2 1.5 deep 86 Belovo Belovo, Malko Belovo, Golyamo Belovo, Menenkyov o, Dybravite, Momina Klisura, Gabrovnitsa , Sestrimo Cambiso ls, low erosion 20 21 25 35 1.0 4.9 3.5 deep 65 Dimitrov & Mitreva, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 98 Table 3. part 2. Settlements, main physical and chemical indicators of the suitable soils for growing potatoes, field rating values. Municipality Land Soil (WRB, 2014) Physic al clay arable soil, % Physic al clay under arable soil, % Thickn ess humus horizo nt, cm Thick ness soil profile , cm Texture coefficie nt pH / H2 O Humus, % Ground water level, cm Field rating for potatoes Belovo Belovo, Malko Belovo, Golyamo Belovo, Menenkyov o, Dybravite, Momina Klisura, Gabrovnitsa , Sestrimo Cambiso ls, secondar y grass, no erosion 18 21 30 75 1.0 4.7 4.2 deep 81 Bratsigovo Rozovo Cambiso ls (Leptic) 28 34 35 85 2.2 4.5 1.5 deep 66 Bratsigovo Rozovo Cambiso ls, no erosion 15 18 25 80 0.9 4.6 2.5 deep 79 Bratsigovo Ravnogor Cambiso ls, no erosion 15 19 45 100 1.2 5.2 4.4 deep 84 Panagyurishte Panagyuris hte, Poibrene, Oborishte, Banya, Bata, Popitsa, Elshitsa, Dolno Levski Umbriso ls 16 13 60 90 0.9 5.1 8.0 deep 86 Panagyurishte Panagyuris hte, Poibrene, Oborishte, Banya, Bata, Popitsa, Elshitsa, Dolno Levski Umbriso ls, no erosion – low erosion 21 12 45 95 1.0 5.0 9.5 deep 100 Dimitrov & Mitreva, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 99 Table 3, part 3. Settlements, main physical and chemical indicators of the suitable soils for growing potatoes, field rating values. Municipality Land Soil (WRB, 2014) Physi cal clay arable soil, % Physic al clay under arable soil, % Thick ness humus horizo nt, cm Thick ness soil profil e, cm Texture coeffici ent pH / H2 O Hum us, % Groundw ater level, cm Field rating for potatoe s Panagyurishte Panagyuris hte, Poibrene, Oborishte, Banya, Bata, Popitsa, Elshitsa, Dolno Levski Umbriso ls, no erosion - low erosion 16 14 40 80 1.1 5.0 7.5 deep 76 Panagyurishte Panagyuris hte, Poibrene, Oborishte, Banya, Bata, Popitsa, Elshitsa, Dolno Levski Cambiso ls, (Chromi c - Calcaric ) 50 62 45 110 1.5 6.1 3.7 deep 69 Panagyurishte Panagyuris hte, Poibrene, Oborishte, Banya, Bata, Popitsa, Elshitsa, Dolno Levski Fluvisol s - Deluvial 22 27 110 160 0.9 5.3 2.1 deep 78 Panagyurishte Panagyuris hte, Poibrene, Oborishte, Banya, Bata, Popitsa, Elshitsa, Dolno Levski Fluvisol s - Deluvial 45 54 110 160 1.5 5.6 1.6 deep 67 Rakitovo Rakitovo, Kostandov o, Dorkovo Cambiso l, no erosion 23 31 25 70 1.7 5.3 2.4 deep 75 Dimitrov & Mitreva, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 100 Table 3, part 4. Settlements, main physical and chemical indicators of the suitable soils for growing potatoes, field rating values Municipality Land Soil (WRB, 2014) Physi cal clay arable soil, % Physic al clay under arable soil, % Thick ness humus horizo nt, cm Thick ness soil profil e, cm Texture coeffici ent pH / H2 O Hum us, % Groundw ater level, cm Field rating for potatoe s Rakitovo Rakitovo, Kostandov o, Dorkovo Fluvisol sDeluvial 26 23 60 100 1.0 5.4 6.3 100 68 Velingrad Velingrad (Chepino, Kamenitsa, Lazhene), Dolene, Korovo, Grashevo, Vraninitsi, Dabeva mahala, Draginovo Fluvisol sDeluvial 24 34 40 70 1.4 5.7 2.8 deep 76 Velingrad Velingrad (Chepino, Kamenitsa, Lazhene), Dolene, Korovo, Grashevo, Vraninitsi, Dabeva mahala, Draginovo Fluvisol sAluvial 17 3 30 60 0.9 4.6 4.8 deep 65 Velingrad Sarnitsa, Orlino, Barduche, Krushata, Pepeltsi, Medeni Polyani, Pobit Kamak Cambiso ls 22 17 30 60 0.9 4.6 5.5 deep 96 Velingrad Sarnitsa, Orlino, Barduche, Krushata, Pepeltsi, Medeni Polyani, Pobit Kamak Cambiso l, low erosion 27 20 20 50 0.9 4.6 5.0 deep 75 Dimitrov & Mitreva, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. 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