Tuesday, 11 July 2006

Agrochemical Aspects of Long-term Systematic Fertilization in the Agroecosystems of Siberia.

Gennady P. Gamzikov and Olga Gamzikova. Novosibirsk State Agrarian Univ, Dobrolyubova 160, Novosibirsk, Russia

Agricultural land use is known to change a range of their properties, the most important being the decrease of soil organic matter and nutrients content. The quantitative parameters of these changes are determined by both soil formation condition and agrotechnical practices (Turin, 1966; Aleksandrova, 1980; Tate III, 1991 and others). Under specific climatic conditions of Siberia with very short both vegetation and soil biological activity period, intensive agricultural land use leads to more rapid and profound undesirable changes of soil properties. These changes can be prevented or slowed down only by employing agrotechnical practices aimed specifically at preserving and maintaining soil fertility: strip agriculture, crop rotations, soil tillage practices, etc. Of special importance, as showed the results of long-term field experiments, are mineral and organic fertilization practices (Cooke, 1972; Lykov et al., 2004). We monitored changes in the agrochemical properties of soddy podsolic, grey wooded, chernozemic and chestnut soils in the long-term (15-25 years) field fertilization experiments. Manure and mineral fertilizer application rates were 10 t and 30-40 kg per hectare of crop rotation area. The results shown that systematic fertilization under crop rotation helps not only to prevent the losses of organic matter from soils, but also to maintain its content on the higher level (by 10-18% under mineral and 19-38% under manure fertilization), as compared to the unfertilized control. The observed increase in soil organic matter content could be attributed to the increase in soil microbial biomass, root and crop phytomass residues after harvesting, which form the organic C pool for humification and mineralization. The increase is accompanied by changes in humus quality, i.e. the increased share of humine and more labile fractions of humus acids. The long-term fertilization also had a stabilizing effect on the soil nitrogen pool by increasing total and labile nitrogen content as well as the number of its mineral forms. In all soil types fertilization had a common effect: the relative content of phosphates increased in all mineral groups. The biggest increase in residual phosphate content was observed in the first two groups, thus increasing the labile form content and the fertilizers efficiency under crop rotation. Long-term systematic application of only nitrogen and phosphorus fertilizers as a rule resulted in the decreased content of exchangeable potassium. The decrease depended on the initial content of the element and the length of the experiment, i.e. how long the element was taken out of the soil ecosystem with crop yields. Potassium fertilization optimizes plant mineral nutrition and maintaining soil potassium pool. The long-term fertilization was shown to increase crop yields by 2.4-3.6 t∙ha-1 due to the marked increase in crop production (by 23-59%) and mineral fertilizer cost efficiency (1 kg of effective nutrient is equivalent to 7-12 grain units). Thus, systematic long-term fertilization in the agroecosystems of Siberia serves as an important factor of potential and effective soil fertility and crop production intensification. Moreover, no negative effect of fertilization on environment was observed.

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