The Modification of Humus Content in Moldova Chernozems Under the Process of Explotation in Agriculture.
Serafim V. Andriesh V, Inst for Soil Science, Ialoveni,100, Kishinau, Morocco
Humus is one of the primary indexes of soil fertility. This fundamental component of soil represents a reservoir of nutritive elements for plants, and largely determines its physical, physico-chemical, chemical and biological particularities. The organic substance consists of approximately 96 to 98% of the total amount of soil nitrogen, 60 to 80% of sulphur, 30 to 60% of phosphorus and other macro and microelements.The amount of organic material in soil depends on the processes of synthesis (accumulation) and humification (loss) of humus. For recent millenniums, in natural plant formations, the whole synthesized organic substance was returning into soil. It was estimated, that in steppe conditions, in which the chernozems were formed, annually, 12 to 15 t/ha of dry organic matter are returning into soil. The processes of synthesis were dominant upon the processes of mineralization, and as a result, the humus was accumulated in soil. According to the researches made by the founder of genetic pedology, V. Docuceaev, who about 120 years ago had studied the soils of our lands, the content of humus in chernozems was constituting 5-6% or 200 t/ha. Including the lands into the agricultural circuits, everything what the soil was producing was exported as the primary and secondary product. The biological circuit became unclosed and the dehumification processes were dominant upon the processes of synthesis. As a result, the quantity of organic substance in soil started to decrease. Till 1965, the content of humus decreased to 3,5-4,0%, or 130 t/ha. At the end of the 90s of the last century, the reserves of humus had constituted about 3,1%, or 110 t/ha. The rapidity of mineralization and organic substance loss in various periods of chernozem exploitation in agriculture was different. Generalizing the experimental results obtained by different researchers on various subtypes of chernozem, the following things can be mentioned:For the first 5-10 years after the utilization of virgin soils, the rate of mineralizing the organic substance is high and constitutes 0,03-0,035% or about 1,1-1,3 t/ha per year.In 10-30 years of chernozem utilization on arable, annually 0,025-0,030% or 0,9-1,1 t/ha of organic substance is mineralizing. The loss of humus under the processes of dehumification constitutes 10-20% from the primary reserves. For the next 30-50 years after virgin chernozem utilization and its utilization on arable, the speed of mineralizing the organic substance is of only 0,020-0,025% or 0,7-0,9 t/ha annually. During 50-100 years, only 0,018-0,020% or 0,5-0,7 t/ha of organic substance is being mineralized. Humus losses, in a period of 100 years, constitutes about 30-40% from the primary quantity (till the uncultivated land). In a period of time longer than 100 years (from 100 till 300), humus losses constitutes 40-47% from the primary amount. Annually, about 0,015-0,018% or 0,4-0,5 t/ha of organic substance are mineralizing. Concomitantly, with the decrease of mineralization speed of humus from 1,1-1,3 t/ha, the amount of nutritive elements is also decreasing, especially nitrogen and phosphorus, which are accessible for culture plants. The decrease of humus content in soil on the account of biological and erosion processes leads to the worsening of agrophysical, physico-chemical, microbiological particularities, and as a result, the production capacity of soils decreases, and law and bad quality harvests are obtained. Key words: accumulation, chernozem, humus, mineralisation, soil, synthesis.