Abstract
Various effects of the dry deposition of soot on maize were investigated in Keszthely (Hungary) in two consecutive years. In order to be able to study a wider range of weather conditions, some of the plants were placed in a Thornthwaite-Matter type evapotranspirometer and given ad libitum water supplies. Pollution with airborne black carbon was simulated throughout the season by distributing rates of 3 g?m–2 a week using a motorised dust sprayer. Among the plant growth parameters, the leaf area index was increased by 3% - 14%, depending on the year, suggesting that the plants were able to absorb the carbon settling on the leaves. The black carbon reduced the albedo of the canopy by 17.5% - 21.8%, depending on the year, forcing the polluted maize to absorb more energy. Part of this surplus energy was utilised for increased evapotranspiration (3.9% and 11% in the two years) and to raise the surface temperature of the canopy by 1℃ - 2℃ during the mid-day hours. The effect of the contamination on maize was more intense in the hot, dry year. The unfavourable effect of soot on maize fertilisation could be observed as a significant increase in the number of deformed ears, leading to a reduction in grain dry matter. The reduction in dry matter yield for polluted maize grown with irrigation in the evapotranspirometer was far less severe than that on non-irrigated plots, suggesting that irrigation was the most obvious solution for mitigating the negative effects of contamination with airborne soot.
Highlights
Black carbon (BC) is one of the end products of incomplete combustion, but due to the multiplicity of techniques used to determine its composition, various definitions are to be found in the literature [1]
The black carbon reduced the albedo of the canopy by 17.5% - 21.8%, depending on the year, forcing the polluted maize to absorb more energy
While 2010 had average temperatures but rainfall supplies 51% higher than the long-term mean, the growing season in 2011 was 1.2 ̊C warmer than average, with less than half the normal rainfall quantity (–56%). This year was drier than any recorded during the period 1901-2000 (Figure 1). In both years the differences from the long-term mean were least pronounced in July, which coincides with the most sensitive developmental phase of maize, so this may have been favourable for plant growth
Summary
Black carbon (BC) is one of the end products of incomplete combustion, but due to the multiplicity of techniques used to determine its composition, various definitions are to be found in the literature [1]. A combustion-generated carbonaceous compound, is absorbed by and stored in the soil, influencing its properties, fertility and water retention [3,4,5,6]. Some of the BC arising from burning remains in the soil, enriching its carbon content, the process of forest burning may have negative effects. A further disadvantage of soot in the soil could be its high adsorption capacity, which may bind heavy metals and pesticides [2,10]. If these enter the food chain, they have a negative effect on all the links in the chain, and especially on humans, at the end of the chain. BC has a significant effect on the global carbon cycle [11], acting as a carbon sink from the more rapid bioatmosphere carbon cycle to the slower (long-term) geological carbon cycle [12]
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