Agricultural Development and Environmental Research: American and Czechoslovak Perspectives: Proceedings of a Bilateral Workshop (1987)

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Protection of Soil Organisms and Improvement of Biological Properties of Soil JOSEF RUSEK Institute of Soil Biology (CSAV) Soil without life is no longer soil. It is a dead substrate which does not meet any of the important functions of soil in ecosystems. This postulate is not quite as obvious as it would seem. There are many famous pedologists in the world who consider the role of biota in soil as a marginal factor. There are even more who treat soil in practice as a substrate able to bear any mechanical or chemical impact. However, the development and the existence of soil are inseparably connected with the development and existence of life on earth. Soil develops together with the whole ecosystem, and its devel- opment has its own laws of succession. Soil organisms have an active role in the development of soils and entire ecosystems. The richness and variability of life in soil can be compared perhaps only with the life richness on coral reefs. Table 1 illustrates the various groups and densities of organisms living in soil. The large diversity, biomass, and number of soil organisms not only concentrate an enormous amount of biogenic elements and energy but also result in properties of soil for which there are no substitutes. Man's activities have affected directly or indirectly most ecosys- tems on earth, including soils and their biotic components. The influence has not always been negative. For instance, in meadow soils man has influenced some components of soil organisms in a favorable way while he has suppressed others completely. But the deepest negative impact on soil biota has been in arable soils. 89

90 TABLE 1 Density and biomass of soil organisms Specimens on m 2 Biomass in gm/m Group Average Optimum Average Optimum Microflora (bacteria, aktinomycetes, fungi, algae) 1014 1016 320 2,350 Microfauna 108 1010 5 150 Mesofauna Rotatoria 104 106 0.01 0.3 Nematoda 106 108 5 50 Tardigrada 10S 105 0.01 0.5 Acarina 7 x 104 4 x 105 0.6 4 Entognatha 5 x 104 4 x 105 0.5 4 Macrofauna Enchytraeidae 3 x 103 3 x 104 5 50 Gastropoda 50 1,000 1 30 Aranea 50 200 0.2 1 Isopoda SO 200 0.4 1.5 Myriapoda 230 2,800 4.45 13 Insecta 350 16,600 3.5 50 Megafauna Lumbricidae 100 500 SO 200 Vertebrata 0.01 0.1 0.1 10 TOTAL 375.17 2,914.3

91 To understand the role of soil organisms in agroecosystems a ba- sic question must be answered first: What is the role of organisms in soil? Soil organisms can be divided into two groups: soil microflora (bacteria, actinomycetes, micromycetes, and algae) and soil animals (ranging from protozoans to vertebrata). The functions of the groups are different. Soil microflora (except for algae) decompose dead or- ganic matter into simpler chemical compounds and mineral nutrients accessible to higher plants, while soil animals reduce dead organic matter mechanically to smaller pieces and mix them with mineral particles. Zooedaphon takes part in soil microstructure formation— through its excrements, through its active burrowing, and by its transport of particles of organic matter to deeper levels and mineral particles from lower layers toward the surface. Soil microflora are functionally connected with soil animals, and the web of mutual re- lations among soil organisms is one of the most intricate in terrestrial ecosystems. For example, the functional unity of soil microflora with soil fauna is very important in the humus-forming processes which it accelerates. There is one other important function of soil organisms which is not sufficiently appreciated. Their large biomass—which averages six tons per hectare—binds all biogenic elements necessary for plant growth. In steppe soil this represents 500 kg of nitrogen, 40 kg of phosphorus, and 45 kg of potassium per hectare. Of course, these nutrients are bound in the living organisms for a longer or shorter part of the year. Soil organisms differ in the length of their life cycles. Edaphic biota can be divided by size into four groups: micro-, meso-, macro-, and megaorganisms. Microorganisms—including bacteria, actino- mycetes, micromycetes, algae, protozoans, and smaller representa- tives of nematodes—have life cycles ranging from several hours to sev- eral days. Mesoorganisms—including animals such as microarthro- pods, enchytraeids, and nematodes—have life cycles from several weeks to several months. The life cycles of soil macroorganisms last from several months to four years. Finally, the duration of the life cycle of megafauna is several years. In the course of these cycles there is an intensive cycling of soil nutrients. Part of the nutrients is taken by plant roots, and part passes to other cycles of soil organisms. In this light, soil organisms appear to be the most natural fertilizer not only in agriculture, but in all ecosystems. This high diversity of soil organisms and their functions illustrates their important role in soil. Man affects soil organisms, particularly in agricultural practices.

92 However, mechanical soil cultivation has a relatively small negative impact in today's modern agriculture, particularly if heavy machin- ery is not used. Pesticides, inappropriate use of artificial fertilizers, decrease of humus content, and acidification of soils have far greater negative effects on soil organisms. Pesticides are a major factor influencing soil organisms. The impact of insecticides on soil organisms, especially on different com- ponents of soil fauna, is extensive. Recently Edwards (1985) sum- marized knowledge of this problem. Most studies concentrate on the influence of a defined insecticide on a defined species or group of organisms, and there are only limited data concerning the impact on whole communities of soil organisms and on the effect of chemical processes in soil. A positive as well as a negative effect on one species may evoke a set of changes in mutual relations among different soil organisms in the function of the whole soil subsystem. The quantity of insecticides applied in agriculture in the temper- ate zone is substantially lower than the quantity of herbicides. This does not mean that insecticides are not a serious negative pollutant in managed soils in these areas. The CSAV Institute of Soil Biology has a complex research program on herbicide impacts on soil organisms and chemical processes in soil. Some of the results of this research show the complexity of reactions and changes caused by herbicides. In the field as well as in laboratory experiments with the herbi- cide Zeazin 50 (doses 5, 10, 20, and 40 kg/ha), soil organisms were affected to different degrees. Most affected were soil microorganisms and to a lesser extent some groups of soil mesofauna (Oribatei). The changes in the composition and dynamics of soil organism com- munities caused a number of negative reactions in the dynamics of chemical processes in the soil, culminating in such serious changes as the composition and quality of humus and the leaching of phospho- rus, nitrogen, and other nutrients from soil. Toxic and inhibitory properties of herbicides do not disappear by binding with humic acids. Quite the contrary, they remain in the soil as complex compounds, although in this form they are analytically difficult to detect. They have a toxic impact on soil organisms (Rusek and Kunc 1983). The immunity apparatus of soil fauna is affected after herbicide application and results in increased parasitism in earthworms and other groups of soil invertebrates (Pizl 1985). A long-lasting, inten- sive application of herbicides in orchards over 5-10 years caused a complete qualitative as well as quantitative destruction of the soil

93 organism community. Only a few species with very low density were left. No soil-forming processes could be identified in those almost dead soils. On the contrary, serious changes in soil microstructure and podzolization processes as well as severe soil degradation were apparent. Similar effects of five more herbicides were shown in forest soil and in laboratory tests. Apparently, these so-called "harmless" herbicides showed strong negative effects on non-target soil organ- isms and on the soil subsystem as a whole. The ecological stability of most agrocenoses is very low, with the stability of soil subsystems in most cases higher than the above- ground cenoses. Where soil was heavily affected, the stability of the soil organism cenoses was also low. The loss of ecological connections among species and groups of soil organisms—or even disappearance of a number of them—led to pest infestation, diseases in plants, weeds, and general depletion of the soil. This has been proven by the high densities of plant parasitic nematodes, by a set of diseases in underground and above-ground parts of plants (e.g., Streptomyces scabiae and apple scab), and also by the occurrence of different weeds in areas where earthworms were suppressed by insecticides (Edwards 1985, unpublished data). Experiments at the Institute of Soil Biology are directed to the food preference of soil animals. It appears that different species of soil fauna feed on different species of soil microflora, often on a very narrow species spectrum. For instance, the millipede Glomeris hexasticha feeds on the fungus Botrytis cinerea which attacks the roots of trees in nurseries. Currently we know little about mutual relations among different species and groups of soil organisms, but in the future it will be possible to make use of the knowledge referring to these relations in biological and integrated plant control. We know already that there are no serious problems with diseases and plant pests in soils where its biota have not been significantly changed. Over the years we have considered agrotechnics only from the plant-growing point of view. Purposefully, we supported only one component of the agroecosystem—the cultivated plant. The physiol- ogy of mineral nutrition of cultivated plants has been elaborated to the finest detail, and chemicalization of plant production has brought about unexpected possibilities to increase yields through fertilization. For many years organic manures were used in Czechoslovakia in very limited quantities. Recently high levels of energy have been supplied to fields in the form of artificial fertilizers. In addition, the greater part of the aboveground biomass is being taken away with the crop.

94 If we want to preserve all functions of the soil, we cannot continue this exploitation by depriving it of the produced biomass. Consumed energy must somehow be returned to the soil in an appropriate form. Mineral fertilizers serve as nutrition for plants, but for many soil organisms fertilizers are no source of energy at all. Heterotrophic soil organisms need organic substances for nutrition. To ensure a sufficient development of heterotrophic soil organisms, the extracted plant products must be returned to the soil in the form of farm manure or other organic matter. This is the only way to assure a suitable source of nutrients for soil animals which support the soil microstr ucture. Just as chemical analysis in soil is indispensable in today's agri- culture, biological soil analysis is also necessary. Such analyses are urgent not only for better soil management but also to address the functions of the biological components in soil. We already have methods to assess bioindicators of negative changes in soil. They are operating with changes in whole cenoses, populations, and individual soil organisms. The factors which negatively affect soil organisms can be placed in five main categories: • mechanical soil cultivation; • application of mineral fertilizers in an inappropriate form and at excessively high doses; • pesticide application; • monoculture of the same plant over many years; • incorrect application of irrigation. However, the risks of negative impacts on soil organisms can be restrained by: • eliminating heavy machinery in soil cultivation; • application of mineral fertilizers in combination with organic manures; • introduction of integrated plant control principles; • appropriate crop rotation, including plants supporting develop- ment of soil organisms such as alfalfa; • appropriate application of irrigation which does not lead to salin- ization and compaction of soils. Of course, there are other factors which negatively affect soil biota— such as soil acidification by acid deposition and buildup of heavy metals—but they are not restricted to agricultural soils and the sources of pollutants are outside agriculture.

95 Although much has already been accomplished in soil biology, we are only beginning to understand the various processes and inter- actions in soil. It is clear, however, that the quantity and diversity of soil organisms are directly influencing the function and fertility of every soil type. In recent years there have been many exciting developments in our understanding of how soil physical conditions affect microorganisms (Lynch 1986) and how soil fauna affect nutri- ent cycling and soil microstructure, but there is still a long way to go. Soil biologists must interact closely with soil scientists, plant physiol- ogists, and farmers to develop a more scientifically-based agriculture. Many basic questions in soil biology still remain to be answered. Breeding of earthworms or production of microbial preparations have been explored in different countries with varying degrees of success in increasing the fertility of some plants. From the literature we know about successful introduction of earthworms or coprophageous beetles into soils where their absence had caused problems with soil fertility. At present we have no methodology to increase the density and diversity of soil organisms in agricultural soils. We lack methods for complex soil biological analyses which are useable in agriculture as well as methods for drawing conclusions from these analyses. It is necessary to know the functional relations among dominant groups and species of soil organisms and to consider these relations in agrotechnics and in management of biological pests and plant diseases. Soil biology deals with an enormous quantity of different or- ganisms. Soil microorganisms are sources of streptomicine and other antibiotics, and they produce metabolites with nematicide, herbicide, and insecticide properties. Soil provides a huge source of organisms of industrial significance applicable not only in agriculture but also in other spheres of biotechnology. In soil we must search for compounds applicable as natural pesticides with a minimum of secondary effects on non-target organisms. Soil biologists are thus confronted with the enormous task of transferring results of basic research to practice and assisting in the development of a new industrial branch: the agrobiological industry. REFERENCES Edwards, C.A. 1985. Effects of pesticides on the population dynamics and interactions between soil animals and other organisms. In: Hascoet et al. (edit.) Comportment et effects secondaires des pesticides dans le sol. Versailles. 4-8 juin 1984. Ed INRA Publ. 25-43.

96 Lynch, J.M. 1985. Demands and controls on organisms in soil. Transact. XIII. Congress Intern. Soc. Soil. Sci. Hamburg. Plenary papers I: 45-60 Pill, V. 1985. The effect of the herbicide Ztazin 50 on earthworm infection by monocystid gregarines. Pedobiologia, 28:399-402 Rusek, J. 1985. Soil microstructure contributions on specific soil organisms. Questiones Ent. 21: 497-514. Rusek, J. and P. Kunc. 1983. Synteticka sprava o resenfkontrolovatelne-etapy hlavnfho dkolu SPZU "Vliv herbicidu naedafon a jejich rozklad v pude." Mikrobiologicky ustav CSAV, Praha, 79 pp. (in Ciech).