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2015, N 6 (22) |
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ECOLOGY |
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Sokolov O., Chernikov V., Vasenev I. |
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Agroecological assessment of nitrogen losses in conditions of erosive agricultural landscape (results of long-term research with 15N) |
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Global climate change and their consequences for agroecosystem functioning in different soil-geomorphic and bioclimatic conditions actualize issues of integrated agroecological assessment of current and predicted nitrogen losses in conditions of representative erosive agricultural landscapes. Damage from erosion is increasing with the agricultural technologies intensification and is determined significantly by direct economic and indirect environmental impacts from the nitrogen unproductive losses resulting from the use of agro-ecologically unreasonable doses or application technologies of nitrogen fertilizing in conditions of particular agricultural landscape. The paper includes the results of long-term agro-ecological research using the indicating isotopic (15N) method on the evaluation of the fertilizer and soil nitrogen gaseous losses level, its spatial differentiation and principal factors in the conditions of typical crops cultivation at the various elements of the representative for the Central region of Russia erosive agro-landscape with long-term cultivated sod-podzoluvisols. Field research has been done in the long-term micro-plot experience (with plot size 0.5 m x 1.0 m), conducted since 2002 on the concave-convex slope of South-Eastern exposition with changing gradient from 2-3o at the top to 4-5o at the medium and 5-7o – at the bottom of the slope. Experience includes the annual application of 15N-labelled nitrogen fertilizer to the rotated crops: winter rye – oats – barley – grass-legume grasses (clover, Timothy) 1st year of use – legumes-grasses of the 2nd year use. Nitrogen fertilizer (ammonium sulfate, with 20ат% 15N) was applied under cereal crops in the dose of N50 and under herbs in dose of N30 in spring by scattering and by band-directing at a depth of 10 cm. Cultivated soils are sod-podzoluvisols medium loamy on carbonate moraine loam: lightly eroded at the top of the slope with 2-3o gradient and moderately ones – in the slope middle of 4-5o and in the lower part of the slope of 5-7o. The conducted research has shown the close links of the nitrogen main fluxes intensity in the long-term cultivated lightly and moderate eroded sod-podzoluvisols on the investigated erosive agro-landscape slope with the concrete mesorelief form, crop and method of nitrogen fertilizer application that should be considered into attention during planning the fertilizing effectiveness and for assessment of its agro-ecological consequences. The intensity of the fertilizer, soil nitrogen and symbiotic nitrogen main fluxes, directed to the crop use and soil immobilization is significantly reduced from the watershed to the bottom of the concave-convex slope with bigger pools of mobile phosphorus and potassium, that essentially decrease the efficiency of their use by plants. According to the obtained results the band localization of nitrogen fertilizer application in case of lightly and moderate eroded sod-podzoluvisols at the erosive agro-landscape provides a significantly better (in 1.2-1.3 times) nitrogen fertilizer use by crops – compared to broadcast application of the same doses of fertilizer. This contributes to considerable reduction in the nitrogen compounds emission into the atmosphere and to increase of sustainable biological productivity of the field agro-ecosystems. Immobilization of fertilizer nitrogen, soil nitrogen and symbiotic nitrogen has been significantly increased in case of perennial legume-cereal grasses growing: in 1.2-1.5 times compared to grain crops at the different elements of the slope. The intensity of the nitrogen gaseous compounds fluxes is significantly increasing from the upper to the lower part of the slope, but they are essentially reduced (in 1,5-2,5 times) in case of perennial legume-cereal grasses. Stabilization of nitrogen balance in the long-term cultivated sod-podzoluvisols at the erosive agro-landscapes are accompanied by normalization of their gas-regulatory environmental function in the Central region of Russia and creates favorable conditions for con-prevent the characteristic for XXI century Global climate and biota changes.
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