ИСТИНА

The basic hydrological processes on the catchments that effect agricultural production are the surface slope run-off and the soil erosion caused by it during the spring period, and the total evaporation during the warm period of the year. Facing the challenge a lot of countries have turned to soil cultivation agrotechnologies which bring agroecosystems closer to natural geosystems. These agrotechnologies minimise the impact on soil and simultaneously create different kinds of protective, mulching coverings. Such coverings are considered to be top humusessential in natural geosystems. A lot of experimental investigations are devoted to support the soil and water rotection technologies in agriculture, proving their effective role in the crop productivity increase, improvement of the soil structure, its fertility and humidity conditions, reduction of unproductive evaporation and soil erosion intensity. However results of these investigations are received for given physiographic conditions, in case of different schemes of experiments, often very short, not covering all the possible range of hydrometeorological impacts and cannot be applied to forecast the effective role of these agro technologies for the territories with a variety of soil and climatic conditions. The main way to reason the application of these agro technologies aimed at managing hydrological processes on catchments effectively is to develop models of these processes as to natural conditions of their forming and for various scenarios of application of this or that agrotechnology. In this work the impact of a straw mulch of various height on a surface slope run-off during spring snowmelt, depth of the soil freezing at the beginning of snowmelt, run-off coefficient and the structure of water balance in general of a small water catchment in the Central forest-steppe (Kursk region) is considered. The straw mulch efficiency is compared with other traditional agrotechnologies, such as tillage practice, etc. The impact assessments of different agrotechnologies are received with the help of dynamics-stochastic model of spring surface slope run-off development. In this model the slope of a small river catchment is considered as a set of sites with various run-off forming properties. These properties are caused by irregular stochastic nature of snow cover distribution on a slope and water permeability of frozen soils. Spatial heterogeneity of snow cover on a slope depends on weather conditions of the winter period, microrelief, availability of vegetation. The major factors causing water penetration of the soil are the type of a soil cover, depth of soil freezing and thawing, and also humidity of the upper horizons of the soil by the time of the beginning of snowmelt. Process of absorption on the whole slope is substantially caused by frost penetration depth variations as soil humidity along a slope changes slightly. The depth of soil freezing depends on snow cover capacity on a given part of a slope. In this regard it is supposed that spatial distribution of slope sites with various water penetration submits to the same statistical regularities, as the field of snow cover. Input data for calculations of a hydrographer and slope flow volume by this model are: precipitation and air temperature during winter and snowmelt period, the maximal water equivalent of snow cover, values of soil humidity at the beginning of snow melting, and also hydrophysical characteristics of snow and soil. Calculations showed that the model very realistically describes process of surface slope run-off development during the spring snowmelt. In particular, the coefficient of correlation between the calculated and measured values of flow hydrographers averaged Rk = 0.85, and criterion of quality of calculation – s / √ Ds=0.52, where s – mean root square deviation of the calculated and measured volumes of a daily slope flow, Ds – dispersion of the measured values of a daily slope flow. Results of model calculations show a rather high level of adequacy to the data of the actual observations and allow to consider it as a reliable method to assess the effectiveness of various agrotechnical and others melioration (in a broad sense) measures aimed to manage the hydrological processes during the spring period. Results of calculations by dinamics-stochastic model of hydrological processes in a small water catchment in vivo and under the influence of a straw mulch and other agro technologies during the snowmelt period allowed to draw the following conclusions: 1. Fall straw mulching is a very efficient agro technology in the hydrological relation. Its application has significant effect on decrease of soil freezing depth, improves spring water penetration conditions, decreases a spring slope flow as the main factor causing soil erosion, ravines erosion, diffuse pollution of reservoirs and other negative processes on small river catchments. In practice its application is real in the course of a crop rotation within one economy. 2. Influence of a straw mulch on a surface slope run-off development during the winter and spring periods, different in weather conditions, shows not equally, however, on average, the 5-10-centimeter layer of a straw mulch in not frosty winters provides the total absorption of spring water on all types of agrosystems, and in the frostiest winters is capable to bring closer the size of a slope run-off to critical value at which the total absorption of spring water occurs.