The Photosynthetic Activity of Crops and Atmospheric Carbon Sequestration in Red Clover and Spring Wheat in Crop Rotation

The objective of this research was to assess the intensity of light energy absorption by rotational crops during the growing season and to determine the amount of atmospheric carbon absorbed during the process of photosynthesis. In a long-term stationary experiment, we studied the absorption of photosynthetically active radiation (PAR) by the red clover crops of 2 years of use and spring wheat in variants without fertilizers and with the application of N₆₀P₆₀K₆₀. To assess the intensity of light energy absorption, we used indicators of the content of chlorophyll A, chlorophyll B and carotene, which serve as photoreceptors-pigments of photosynthesis in higher plants. The most active period of PAR absorption by red clover leaves was noted from the stem phase to flowering; the sum of chlorophyll A and B in the leaves was 11.08–14.32 mg/g dry weight, carotene, 2.2–3.3 mg/g dry weight. During photosynthesis, the carbon content in clover leaves varied in the range of 40.4–45.5%. The content of the main products of photosynthesis, sugars, decreased from 9.8% in the stemming phase to 3.4% during seed formation. The most intensive process of photosynthesis of spring wheat occurred in the period from the tillering phase to the beginning of ripening; the chlorophyll content was 9.14–11.90 mg/g dry weight and the carotene content was 2.5–4.3 times lower. Most of the sugars were noted at the beginning of stem elongation: without fertilizers sugar content comprised 15.3%, with NPK applied at 60 kg ai/ha it was 17.2%. The amount of carbon absorbed by the red clover crops during photosynthesis in the growing season, depending on the experimental options, was 2.26–2.42 t/ha (8.09–8.66 t/ha CO), while for spring wheat it was 1.49–1.93 t/ha (5.33–6.90 t/ha CO).