* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Survey
Document related concepts
Total organic carbon wikipedia , lookup
Arbuscular mycorrhiza wikipedia , lookup
Soil horizon wikipedia , lookup
Surface runoff wikipedia , lookup
Soil erosion wikipedia , lookup
Plant nutrition wikipedia , lookup
Crop rotation wikipedia , lookup
Soil respiration wikipedia , lookup
Soil compaction (agriculture) wikipedia , lookup
Soil salinity control wikipedia , lookup
Canadian system of soil classification wikipedia , lookup
Terra preta wikipedia , lookup
Human impact on the nitrogen cycle wikipedia , lookup
No-till farming wikipedia , lookup
Soil food web wikipedia , lookup
Soil microbiology wikipedia , lookup
Transcript
1.3.3. Soil biota There is a positive correlation between soil fertility, on the one side, and diversity and abundance of the soil biota, on the other side. Thus, the number of soil invertebrates varies between 110-135 ex/m2 in the rich chernozems in the North of Moldova, and 42-64 ex/m2 in the South; where the soils are, generally, less fertile. The same tendency has been recorded for fungi (53,000-68,000 and 15,000-22,000 per one gram of soil, respectively). During the last decades, the anthropic activity resulted in a substantial deterioration of the soil biota. Both diversity and total biomass of the soil organisms decreased. For example, the Sorenson diversity index for invertebrates diminished to 0.582, and presently only five species from the Lumbricidae family can be found in Moldovan soils compared to nine species 40 years ago. This was accompanied by a succession of species that resulted in slowing down the natural processes of accumulation of organic substances in soils. The activity of microbiological processes of humus mineralization has increased while the biomass and activity of saprophagous invertebrates, contributing to humus accumulation, fell sharply. According to last data, the activity of saprophytes decreased 4-10 times, and the coefficient of humus accumulation, 1.7-3.3 times. Besides, the fixation of atmospheric nitrogen in soils decreased sharply. In the same time, the number of toxic species (Penicillium purpurogenum, Aspergillus ustus, Penicillium funiculosum etc.) increased dramatically. All these reduce the biological productivity and ecological stability of the soils. Data on several indicators of the anthropic impact on the status of soil organisms are presented in Table 1.14. Table 1.14 Dynamics of soil organisms in different types of chernozems subject to agriculture use Year Humus Microorganisms Invertebrates content, Chernozem % Ammoni ActinoFungi Total Biomass of Subtype ficators micetes number Lumbricidae 2 million/g soil thousand/ org/m g/m2 g soil Typical 1958 5.18 5.0 3.4 39 227 25.0 1994 4.00 4.3 2.2 31 135 17.1 Levigated 1958 4.24 3.6 1.8 50 88 13.0 1994 3.30 3.1 1.4 25 76 8.3 Common 1958 4.30 5.5 5.6 60 72 10.0 1994 3.30 3.3 2.5 15 62 6.7 Carbonated 1958 3.70 3.2 4.3 14 47 8.0 1994 2.92 2.2 2.0 30 44 5.8 After 1994, there were no systematic investigations on the microbiological diversity of the soil biota. Under such circumstances, indirect methods of qualitative and quantitative evaluation of the status of soil organisms like carbon balances can be applied. The emissions of CO2 are an indirect indicator of the soil biota status. The factors causing carbon losses from the topsoil have been intensified during the last decades while the inputs of carbon – mainly from vegetal residues and organic fertilizer - have diminished (Table 1.15). In general, a positive carbon balance sustains higher biomass and diversity while a negative carbon balance causes the suppression of soil organisms. Table 1.15 Emissions of carbon dioxide from arable soils in the Republic of Moldova Carbon inputs Anul 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 Vegetal residues 699 653 497 644 352 478 350 553 397 516 Organic fertilizers 242 215 132 77 35 37 20 - Carbon outputs*, thousand tons Total 941 868 629 721 387 515 370 553 397 516 Inorganic carbon 40 40 31 10 4 5 6 - Orga nic carbon 6 5 3 2 1 1 0,5 - Symbiotic carbon 12 10 11 5 3 3 1 2 2 3 Car- Carbon bon from from humus vegetal rezidues 17 18 14 16 11 14 11 15 12 15 77 72 52 104 58 82 62 102 75 98 Carbon balance CO2 emissions ,000 tons (Gg) t/ha 1629 998 1479 1299 2323 1649 2099 1,18 0,81 1,16 1,01 1,77 1,57 1,61 Carbon export, total Carbon outputs ,000 tons (Gg) t/ha 152 145 111 137 77 105 80 119 87 113 862 789 570 1165 659 918 724 1886 845 1129 79 79 59 -444 -272 -403 -354 -633 -448 -613 0,050 0,051 0,043 -0,321 -0,221 -0,316 -0,277 -0,483 -0,348 -0,440 * Calculated according to the C:N ratio and the amount of N released as a result of biochemical degradation of organic matter from the soil. Erosion processes have a deleterious effect on the soil organisms. In the low, moderate and highly eroded soils, their number and biomass may be reduced by 20-30%, 30-60% and over 60%, respectively. In eroded soils the biodiversity suffers a sharp reduction, many species disappear. Per total, the changes mentioned above lead to more intense dehumification, loss of soil texture and soil self-purification capacity. Therefore, the recovery of the invertebrates and microorganisms diversity and functions is a precondition for resolving the problem of soil conservation and enhancement of soil fertility. The excessive use of mineral fertilizers herbicides and pesticides is just another important factor that led to essential changes in the soil biota structure and functions. The herbicides are an essential source of soil pollution with mutagenic substances. The indicator microorganisms from the soils processed with herbicides show a mutagenic level increased by 10-20 times compared to the level of spontaneous mutations. The presence of pesticides with mutagenic potential leads to changes in the populations of soil microorganisms. The microflora is now less abundant and diverse, the species communities have been restructured and presently are less stable. The communities of nitrogen fixing bacteria were particularly affected by the use of herbicides. This hampered the nitrogen cycle in soils and limited soil productivity. The rehabilitation of the soil biota is possible through more active introduction of organic agriculture approach and through reduction of agrochemicals use.