The role of organic matter content and humus quality in the maintenance of soil fertility and in environmental protection
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Landscapeand Urban Planning, 27 (1993) 161-167 Elsevier Science Publishers B.V.. Amsterdam
The role of organic matter content and humus quality in the maintenance of soil fertility and in environmental protection
L. Hargitai Department of Soil Science and Agrochemistry, University of Horticulture and Food Industry, Vilkinyi u. 35-43,
H-l I18 Budapest, Hungary
The role of organic matter in soil fertility has been well known for hundreds of years, but the role of humus quality and its environmental functions has been discovered only during the last 30 years. We outlined in an earlier study our equiva- lent humus parameter for the characterization of humus content and humus quality, EH,= H, ha-~ K, where H, hs-~ is the humus content in tonnes per hectare at a depth of 1 m and K is the humus quality parameter calculated from extinction ratios of 1% NaF and 0.5% NaOH soil humus extracts. K values vary greatly; soils with raw organic materials show values around 0.0 1, whereas soils with the best humus quality (chemozems) have values of about 10. In investigations in recent years, we started from our genera1 database of about 4000 sampling sites and extended the research with particular humus quality investigations over many hundreds of soil profiles for equivalent humus values. Compared with their humus status expressed in our results in log EH, values, podzols have the lowest values ( 1.50-1.70), brown forest soils are in the medium range ( 1.90-2.50) and chernozems have the highest values (3.00-3.20). The results represent 8 1.14% of the cultivated area of Hungary. As K values increase as a result of humification, which produces long-chain humic acids, and their C/N values decrease, we express at the same time the polyfunctionality of humic substances, by a genera1 environ- mental protection capacity, EPCo= D, Hz K, and a special environmental protection capacity, EPCs=D, H* R, where D, is the thickness of the soil layer in centimetres, H is the humus percentage and R = K/ (C/N). This system is suitable for evaluation of the humus status in landscape planning, in land use and in the maintenance of soil fertility. Because of the important role of humus in binding toxic elements and xenobiotics, the results are of value for sustainable land use.
The role of organic matter in soil fertility has been known for centuries. Recently, the role of humic substances has become much more im- portant than in the past because it has been re- alized that, in addition to their role in soil fer- tility, they are extremely important in environmental protection. The use of organic manures and composts is an ancient tradition, connected with the practical experience that the dark-coloured material of soils, the humus, is responsible for soil fertility. Allison ( 1973) mentioned in his fundamental book on or- ganic soil matter that the most ancient agricul- tures in history used organic waste materials of animal and human origin 4000 years ago for
the maintenance of soil fertility. The words compost and humus are of Roman origin and are connected with laws passed by the Caesars that all the city wastes in Rome should be collected and transported to the fields of Latium for composting and for use in the maintenance of soil fertility. Although the im- portance of humus was recognized very early, knowledge of the role of humus in soils was de- tected only in stages from the eighteenth cen- tury, step by step. From the classical work of Berzelius ( 1839) to the end of the nineteenth century, about 50 years were needed until sci- entists could declare that the most important factor in the role of humus in soil fertility was the N content of the humus. This finding was first declared by Hermann ( 184 1)) but a great
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162 L. Hargttar /Landscapeand Crban Plannmg27/1993) 161-167
deal of time passed before this fundamental knowledge became generally accepted.
About 50 years later, in the middle of the twentieth century, the extremely important question of the chelate character of humic sub- stances was studied. Schatz et al. ( 1964a,b), in particular, investigated the chelate character of humic substances, which plays an outstanding role in binding toxic elements and heavy met- als in the soils. At present, in addition to the role of humus in soil fertility, many interesting results have been published on humic sub- stances as important compounds in the total environment and biosphere. The manifold di- versity of their involvement in environmental processes forms the background of their out- standing importance in the biosphere. In con- nection with this, there is a new concept that in our opinion, may be of interest. This con- cept is the new theory of chemical speciation known mainly through fundamental research papers by Bernhard et al. ( 1986).
The term species refers to the molecular form of an element or cluster of atoms from different elements, which plays an important role in processes in the environment. Accord- ing to this concept, humic acids can play an outstanding role in forming and influencing some chemical species which are important in environmental protection and also in pro- cesses influencing human health. Starting from the background of this concept, we applied some of our knowledge of chemical speciation to environmental reactions of humic sub- stances, and developed a new line of research on this topic. In environmental processes, the functional groups of humic acids (the COOH and amino-N groups) play the most important role in binding toxic elements and compounds.
Based on our earlier investigations, we have outlined a new complex evaluation for char- acterizing polyfunctionality in humic sub- stances. The evaluation system deals with the length of humic chains connected with more functional groups in humic substances. This feature of humic substances provides a great
possibility for environmental reactions. In the present work, we have summarized the general consequences of our parameter system for the characterization of the humus status of soils. This system expresses the role of humus prop- erties in plant nutrition, in the maintenance of soil fertility and in environmental protection.
Materials and methods
In line with our fundamental methodical concept, we outlined much earlier a new method for evaluation of humus quality (Har- gitai, 195 5 ) . According to this method, we can evaluate the rate of real, long-chained and well- humified organic substances to the raw, non- humified organic materials. This is expressed as the K value, which is the ratio of the extinc- tion of humus extracts divided by the total hu- mus content of the soils:
where ENaE and ENaOH are the extinction val- ues of 1% NaF and 0.5% NaOH extracts of humic substances and H is the total humus content of soils, as a percentage. The method is very simple. The extracts are prepared at room temperature, left for 48 h, and then, after simple filtering (on filter paper), the extracts are investigated in the visible spectrum for ex- tinction values. To obtain exact basic values for K we determine the K values at nine wave- lengths in the visible spectrum and calculate their average as the characteristic K value. K values are very low in raw humic materials (0.0 1); those in soils with poor humus quality are greater than in raw humic materials (O.l- 1 .O), and the highest values are obtained in soils with the best humus quality, for instance in chernozems (around 10).
In 1980-1982 we outlined a new practical system for the characterization of soil fertility and plant nutrition of soils. We introduced the concept of equivalent humus value (Hargitai, 1982 ) , with which we can characterize the hu-
L. Hargitai / Landscapeand Urban Plannmg27(1993) 161-167 163
mus content and humus quality by a single pa- rameter. This so-called equivalent humus value expresses the amount of humus in the soil at a depth of 1 m and records the humus quality in K values. We can express the equivalent hu- mus value as follows: EH,=H, ha- 1 K. This value is suitable for characterization of our main soil types and regions, for general infor- mation on their humus status. To obtain more information on the role of humus quality in environmental processes, we introduced new parameters, which give the environmental protection capacity of soils (Hargitai, 1982). In the fundamental values of environmental protection capacity we considered the humus content as well as the humus quality, particu- larly at a depth of 60 cm. After determining the environmental protection capacity values of the sampling sites from layers at depths of O- 20,20-40 and 40-60 cm, the summary for the whole 60 cm surface layer is a characteristic value from the point of view of environmental protection. (For the definition and calculation of EPCo values, see Table 1. )
To obtain a better special parameter for the humus status of soils from the point of view of compensation for and binding of toxic ele- ments and xenobiotics, the N contents of soils based on their C/N values were considered (Hargitai, 1983 ). This series of values is in fact the special environmental protection capacity, represented by EPCs and EPCs, values. The EPCs is calculated by considering the C/N val- ues of soils, and EPCs, takes into considera- tion the hydrolysable N content of soils. These two types of values take into consideration the forms of N that are most active in environ- mental processes.
Results and conclusions
Based on our outlined methodical back- ground we started, in 1986, long-term investi- gations of the humus status of the main Hun- garian soil types. We were able to use, in addition to general information on soil condi-
tions, the database of the Centre of Plant Pro- tection and Soil Control, Budapest, from which we used the general values of humus content at a depth of 1 m of 4000 sampling sites all over Hungary. The particular investigations in many hundreds of soil profiles of Hungarian soil types were carried out with our special method, and as background data the tonnes per hectare humus values were used from the database. The investigations carried out for the determina- tion of our special parameters have provided the opportunity to characterize the most im- portant Hungarian soil types through their equivalent humus values, and the results are summarized in Table 2. In addition to the equivalent values we also calculated the loga- rithmic values; these express general proper- ties much better because the ranges of equiva- lent humus values are wide ( l-l 000), and therefore logarithmic values are more conve- nient, for comparisons of the humus status in soil types, as the comparison and evaluation are continuously changing in the same range with characteristic values (Hargitai, 1986a,b). If we had more information on special aspects of soil properties in environmental protection, we could calculate the environmental protection capacity. In that case, we could express the variation in humus quality from layer to layer throughout the soil depth. From the calcula- tion of the equivalent humus values we have only total average values for a 1 m depth.
The general value of environmental protec- tion capacity (EPCG) is extended with the EPCs values. These latter values are extremely interesting, not only from the point of view of soil fertility but also because of the special role of humic substances in binding toxic elements and xenobiotics. A higher N value by the same other soil parameters such as humus content and K values expresses much better the prop- erties of soils in connection with compensa- tion of dangerous environmental contamina- tions. With this complex system of three parameters - equivalent humus value, and general and special environmental protection
164 L. Hargrtm /Landscape and Urban Planning 27 (1993) 161-167
Table 1 The main parameters of humus quality, equivalent humus values and environmental protection capacity of soils
K= E NaF
E H NaOH where His the total humus content (O/o), and ENaF and ENaOH are extinction values of humus extracts (in 1% NaF and 0.5% NaOH)
where C, is the total C content
where Nt,ydr. is hydrolysable N in 0.25 M H,S04
Environmental protection capacity values of soils: General environmental protection capacity: EPCG=D,H2 K Special environmental protection capacity: EPCs=D, H= R Special environmental protection capacity considering mobile N content: EPCs,=D,Hz R, where D, is the thickness of the soil layer (in cm)
Parameters of equivalent humus value and logarithmic values: Equivalent humus value: EH,=H,,,-I K where H t ha-l is the total humus in 1 m depth Logarithmic value: logEH,
Table 2 The humus status of soils
Soil type Area (ha)
H K EH,= H, ha-l K log EH, (t ha-)
Brown forest and pseudogleyic brown forest soils
Brown forest soils (Ramann) Brown forest soils
(with kovirvany ) Chernozem brown forest soils Illuvial chemozem Sand with chernozem character Meadow chernozem Chernozem (salt affected) Typical chemozem (lime coated) Alluvial meadow soils Meadow soils Meadow solonetz Steppe meadow solonetz
1429000 2.00 197 0.236 46 1.6628 929000 2.76 157 0.631 99 1.9956
213000 0.62 88 1.600 140 2.1461 599000 2.42 344 0.804 275 2.4393 31000 1.75 240 1.38 331 2.5198
250000 2.54 140 3.29 460 2.6628 578000 2.91 336 2.52 846 2.9274 274000 2.51 372 3.71 1400 3.1461
1030600 2.99 300 5.71 1713 3.2338 595000 2.95 341 0.600 207 2.3160 713000 3.38 348 0.895 312 2.4942 211000 2.63 205 0.150 31 1.4914 256000 2.67 205 0.677 138 2.1399
The area of investigated soils was 7 108 600 ha, compared with a total agricultural cultivated area in Hunary of 8 260 000 ha. The investigated soil types are 8 1.14% of the total cultivated area of Hungary. The table does not include special areas such as wind-blown sandy soils, rendzinas, very hydromorphic soils, peats and soils with extreme and rapidly changing humus status. Kovarvany is a special local Hungarian name of a soil type. It is a slightly acidic sandy brown forest soil with a B horizon distributed in l-2 cm thick red-brown sesquioxide accumulation strips periodically in the soil profile.
L. Hargilai /Landscapeand Urban Plannrng 27(1993) 161-167 16.5
capacity - the opportunity is provided for evaluation of the humus status of soils in land- scape planning, rational use of different soil types and reasonable maintenance of soil fer- tility. At the same time, these values give out- lines for sustainable land use from the point of view of organic farming. Table 3 shows the dif- ferences in the general and special environ- mental protection values in the Environmen- tal Protection Model Area Altaler (in West Hungary).
Another very important conclusion is that to maintain soil fertility it is not sufficient to re- cycle organic materials, plant residues, organic waste matters, biomass products or composts; we always have to consider the regulation of N status of the soil.
Our long-term experiments in co-operation with the Institute of Soil Fertility, Potsdam, have shown that, comparing a control plot with 200 kg ha- N fertilization and treatment with 100 kg N ha- given in organic manure plus 100 kg N ha- in fertilizers, there is consider- able depression in the equivalent humus val- ues as a result of N fertilization. On the other hand, the most favourable humus status and soil conditions are observed as a result of the application of nitrogen in manure and fertil- izers together. The long-term effects ( 16 years) are shown in Table 4.
environmental protection capacity. This is the result of the extremely thick layer of forest lit- ter in the topsoil and the high humus content of the surface layers (Fig. 1). Very interesting effects of soil erosion can be seen when the main parameters are compared on eroded hill- sides in the Gerecse District. These slopes, one in VCrtesszolBs and the other near Tinnye-Uny, have the same soil conditions on eroded brown forest soils. From the results, it is clear that the Ht ha-l values as well as the EH, and EPCG values do not change in a similar way. This change is the most different in the equivalent humus values and the environmental protec- tion capacity of the soils (Table 5 ) . It can be seen very clearly that, on the tops of hills, EH, values as well as EPCo values are very low in the soils of Tinnye-Uny. These results show the great effect of erosion. On the hillsides, these values may increase near the inflexion point of the slopes, and at the lowest points on these hills, the values decrease again. This result is related to the movement of long-chain humic substances bound in fine soil particles down the hill slopes. Such and similar results are appli- cable with our method for the complex evalu- ation of erosion processes (Hargitai, 1986~).
Our particular investigations within the framework of the Research Project in the Ger- ecse National Wildlife Protection District in Central Hungary have shown that natural for- ests have an outstanding effect in increasing the
We can thus gain data on soil conditions and humus status from the point of view of soil fer- tility, on the maintenance of soil conditions and for landscape planning for sustainable land use. At the same time, the changes in the pa- rameters provide information on the favour- able or unfavourable humus status for the binding of toxic heavy metals and xenobiotics.
Table 3 Characteristic values of general and special environmental protection capacity in the Environmental Protection Model Area Altaltr
Soil type EPCo EPCs
Sandy soils with low humus content 21.77 2.19 Brown forest soil (Ramann) affected by erosion 44.33 3.22 Brown forest soil (sandy, rust-brown) 130.39 11.16 Brown forest soil (Ramann) 393.65 42.82 Chemozemic brown forest soil 659.48 83.93 Chemozem (typical) 2258.42 208.42
166 L. Hargrtai /Landscapeand Urban Plannrng27(1993) 161-167
Table 4 Change in environmental protection capacity of soils in long-term experiments carried out in the framework of international cooperation (Potsdam, Gross Kreutz)
Treatment H ( % ) (total humus content)
K value (humus quality)
EPCo (O-20 cm)
EPCo (O/o of control)
Control 200 kg N ha- in N fertilizers 100 kg N ha- fertilizer plus 100 kg N ha- manure
0.898 0.551 8.88 100 0.992 0.364 7.16 83.6 1.150 0.434 11.84 121.7
? 3 1 5 0 7 0 9 10
Fig. 1. The effect of natural forest on the environmental protection capacity of brown forest soils in the Gerecse Natural Conser- vancy District; 1- 10 are the soil profiles in a series through the district of about 10 km length. (It is clear that the soils covered with natural forest show outstanding environmental protection capacity values.)
Table 5 Changes in relationships between H, ha- I, equivalent humus and environmental protection capacity as a result of erosion in cultivated brown forest soils
Sampling sites H, ha-1 EHG=H,,,,-I K EPCo
VCrtesszBlBs (top of hill) 97.37 42.79 101.5 VCrtessz~lGs (lower point, at foot of hill) 128.40 71.25 88.5 Tinnye-Uny (top of hill, affected by erosion) 83.46 42.75 28.0 Tinnye-Uny (middle of the slope) 158.36 389.45 423.5 Tinnye-Uny (the lowest point of the area) 114.45 171.00 406.0
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