Veska Georgieva

Fruit growing is a traditional component of Bulgarian agricultural production. According to the latest statistical data, the share of areas planted with cherries is 10.5% of the total orchard area, and with apples, 7.2%, totaling 67,800 ha. This article presents the results of ground and remote (satellite) measurements and observations of cherry and apple orchards, along with the methods for their processing and interpretation, to define the current state and forecast their expected development. This research aims to combine the capabilities of the two approaches by improving and expanding observation and forecasting activities. Ground-based measurements and observations consider the dates of a permanent transition in air temperature above 5 °C and several cardinal phenological stages, based on the idea that a certain temperature sum (CU, GDH, GDD) must accumulate to move from one phenological stage to another. The obtained data were statistically analyzed, and by means of classification with the Random Forest algorithm, the dates for the occurrence of the stages of bud break, flowering, and fruit ripening in the development of cherry and apple orchards were predicted with an accuracy of −6 to +2 days. Satellite studies include creating a database of Sentinel-2 digital images across different spectral bands for the studied orchards, investigating various post-processing approaches, and deriving indicators of developmental phenostages. Ground data from the 2021–2023 experiment in Kyustendil and Plovdiv were used to determine the phases of fruit bursting, flowering, and ripening through satellite images. An assessment of the two approaches to predicting the development of the accuracy of the models was carried out by comparing their predictions for bud swelling and bursting (BBCH 57), flowering (BBCH 65), and fruit ripening (BBCH 87/89) of the observed phenological events in the two selected orchard types, representatives of stone and pome fruit species.

A world problem of increasing importance is the continuous increase of greenhouse gases and the accompanying global warming. Growing global industries, excessive use of fossil fuels, along with deforestation and agriculture, which are major greenhouse gas polluters, are cited as the main causes. Of the greenhouse gases with the largest share, but also the possibility of control is CO2. This gas is vital for the growth and development of plants and, through them, is included in the continuous carbon cycle. On this basis, strategies for sustainable development in agriculture are built since this is one of the main sectors contributing to the increase in carbon emissions. The present study tracked the seasonal dynamic of CO2 uptake by natural grasslands positioned at two altitudes by measuring photosynthesis and plant and soil respiration. A significant variation in CO2 uptake capacity was observed depending on the climatic conditions.

Serious economic damages in many regions of the world were caused by the changes in agroclimatic resources during the last 2–3 decades. The Balkan Peninsula is much affected by the temperatures rising, changes in the distribution of precipitation, and the increasing frequency of extreme events—basically, droughts and frosts. Bulgarian agriculture is developed under various agrometeorological conditions. The climate of the country is characterized by the atmosphere and soil moisture deficit in the time of active crop vegetation and yield formation. The aim of this research is to assess the changes in agrometeorological conditions for the growth of the main grain crops and the possibilities for reaction through agro-technologies. Furthermore, the features of contemporary varieties and hybrids of spring and autumn cereals will be taken into account. The next important factor is the specific requirements for hydro-thermal conditions at different phenological phases of agricultural crop development, i.e., sums of the temperatures and precipitations. Agro-technologies react to tendencies in changing agrometeorological conditions. For the adaptation of agro-technologies, the maximum use of natural agroclimatic resources should be included in activities for overcoming unfavorable conditions, as well as the increased frequency of extreme events. A detailed assessment of the agrometeorological conditions is necessary to choose the suitable agro-technology activity. The analysis of the main meteorological elements—temperatures, precipitations, air humidity, wind speed, and solar radiation for thirty years (1986–2015) was used to assess the changes in agrometeorological conditions on agricultural lands in Bulgaria. Appropriate agro-technical activities for growing the main grain crops are proposed in accordance with the observed changes.

The contemporary climate is characterized by dynamic weather conditions and the observation of non-standard for the seasons of our region events. We observe frequently and sudden - winter warming and cooling in the summer; long periods with dry spells and droughts and intense rainfall with catastrophic floods; of late spring and early autumn frosts; of devastating storms and hailstorms in the spring, all of them causing a severe reduction or total compromise of crop yields. The described phenomena pose many questions connected with the provision of food supply and subsistence to the population. Successful solving of these questions is part of the main issue of our society, that of national security. The proposed report presents the achievements in the field of agrometeorology over the last years and closely related to the implementation of a modern agrometeorological forecasting system, agrometeorological observations, and the assessment of agro-climatic resources in various administrative structures - from region to separate farm. In connection with these results recommendations are made for a necessity to restructure agriculture by regions, both according to the type of agricultural production and the ways of subsidizing agricultural production.