This paper was peer-reviewed for scientific content. Pages 632-636. In: D.E. Stott, R.H. Mohtar and G.C. Steinhardt (eds). 2001. Sustaining the Global Farm. Selected papers from the 10th International Soil Conservation Organization Meeting held May 24-29, 1999 at Purdue University and the USDA-ARS National Soil Erosion Research Laboratory. The Impact of Deep Rooted Plants on the Qualities of Compacted Soils Jaan Kuht and Endla Reintam* ABSTRACT on root development, runoff etc.; 3) chemical effects of soil Deterioration of arable soil properties as a result of compaction; 4) effect of soil compaction on soil biota and the use of heavy agricultural machinery, improper consequences on the physical and chemical properties of cultivation and crop rotations have brought about the soil. It is first and foremost the biota of soil and the growing deterioration of soil quality and decline in crop yields. plants that suffer the most as a result of the negative There is a wide amount of compacted soil in Estonia, biological effects of soil compaction. However, researchers while deep tillage to loosen compacted soil is expensive, have paid too little attention to reverse studies – to the energy consuming and cannot be applied to large areas. impact of biological organisms on the properties of The effects of soil loosening by means of biological compacted soils. So far, most of the studies have been factors are more durable. Data to verify the given confined to their impact on the plough layer (epipedon) assumption have been collected in the course of field and (Bakken et al., 1987; Kooistra et al., 1992; Lindstrom and laboratory experiments carried out on sandy clay soil Voorhees, 1994). (Stagnic Luvisol) at Eerika (County of Tartu, Estonia). The impact of biological organisms on subsoil has The purpose of the present research was to determine the primarily been studied as a phenomenon accompanying the suitability of the use of plants with various types of root former. While in the subsoil that is not cultivated the systems to improve soil quality and increase the negative effects of compaction become permanent. One durability of the positive effects on the physical should pay greater attention to studies aimed at improving properties of degraded soils. The measurements taken the properties of subsoil, especially those utilizing natural during the experiment showed that the horizontal and and biological methods. vertical roots of Canadian thistle (Cirsium arvense (L.) In 1989 – 1994, a group of Estonian researchers Scop.) had remarkable capacity to penetrate deep developed and conducted a field trial to study the impact of compaction caused by heavy tractor traffic. The average deep and exuberant rooted plants on the properties of penetration resistance of soil in the fields where compacted soil. Although the crops used in the field trial Canadian thistle was planted was 10–35% lower in (Galega orientalis L., Brassica napus L. and Trifolium epipedon and 15–25% lower in subsoil compared to the pratense L. (coll.)) did not eliminate all the deformations of fields where only grain was grown. The plants induced excessively compacted soils, the results achieved were still the formation of biopores in soil, thus, creating a promising (Kuht and Lopp, 1997). loosening effect. It was the creeping roots that spread Further studies were carried out to study the potential of horizontally and vertically in deep soil that produced the using well-established roots of local natural or semi-natural loosening effect. The deep and extensive root systems of plants to improve the properties of degraded soils. The Canadian thistle made the amelioration of soil properties measurements conducted by the authors of this paper in the possible – by increasing stable porosity and aeration in summer of 1997 showed that the creeping roots of Canadian subsoil. thistle (Cirsium arvense (L.) Scop.) had great capacity to penetrate deep compaction (Kuht and Reintam, 1998). INTRODUCTION However, one should very careful examine the ways of Soil compaction affects all soil properties and processes, using Canadian thistle as a pedocentrically useful plant to sometimes positively but mostly negatively. The main improve the properties of degraded soil, to avoid any problem in compact dry soil is high mechanical resistance to subsequent problems of controlling the thistle (bearing in root growth, while the major problem in compact wet soil is mind the fact that Canadian thistle is a very troublesome poor aeration (Håkansson, 1993; Håkansson et al., 1989; weed). Wood et al., 1991). Numerous sources of literature refer to Since the amount of compacted soil is large in Estonia, the economic and environmental damages of soil there is a need for a low-cost approved method for the compaction caused by anthropologic factors. Van farmers to restore their compacted soil. Ouwerkerk and Soane (1994), concluding the results of the International Soil Tillage Research Organization (ISTRO) METHODS Melitopol (Ukraine) workshop, have pointed out a number The experiments were conducted on Stagnic Luvisol of trends in the latest studies: 1) environmental (FAO/ISRIC; sandy loamy soil on loamy moraine) at the consequences of soil compaction on a global scale; 2) research station of the Department of Field Crop Husbandry physical effects of soil compaction and their consequences of the Estonian Agricultural University. Stagnic Luvisol is *Jaan Kuht, Estonian Agricultural University, Department of Field Crop Husbandry; Endla Reintam, Department of Soil Science and Agrochemistry, Viljandi Road, Eerika, 51014 Tartu, Estonia, *Corresponding author: [email protected] the arable land in Estonia, of which 70 per cent is cultivated. grown at constant temperature (+23ºC) and high air humidity Since the subsoil of these soils is relatively compacted, (99–100%). Water droplets (guttata) appeared on the periodically saturated conditions may occur when water seedlings in 48-hours time. It is clear that the intensity of forms ponds on the soil surface. These soils are sensitive to gutta secretion depends on the physical conditions of soil compaction as well as chemical contamination of the (moisture, compaction). The soil was compacted in 500 cm3 surface. Temporary excessive water is frequently cylinders where ten seedlings were planted. The height of complicating and hindering field works (Reintam, 1996). the plants was measured when barley (Hordeum vulgare L.) The field trial was carried out using a heavy tractor (14,9 and spring wheat (Triticum vulgare L.) plants were three Mg). A special loader was attached to the front of the tractor days old and Canadian thistle plants four weeks old. The with total weight of 2,5 Mg. The multiple tire-to-tire passing amount of guttation water of barley and spring wheat was method was used. Each tire (23- 1/18-“6 carrying 3,7 Mg or measured on three days. 37 kN) of the tractor passed the field two, four or six times, respectively. RESULTS AND DISCUSSION Canadian thistle plants used for the study were planted at Effects of compaction on soil and its impact on the the density of 9 plants per m-2, to a depth of 15 cm, leaving growth of grain. 50 cm between each patch, on the following four types of The conducted study showed that the compaction of soil soil: 1) non-compacted (control); 2) after 6 times of influenced the properties of both epipedon and subsoil. The compaction (compacted in 1997); 3) compacted 3 times in after-effect of compaction was clearly revealed in the the spring of 1998; 4) after 6 times of compaction uncultivated subsoil. Penetrometric measurement (at 18% (compacted in 1997) and 3 times of compaction in 1998. The water content in soil) showed that double compaction fields of Canadian thistle were compared with the fields of increased the average penetration resistance of subsoil in the barley that had been compacted in the same manner. A 20–40 cm layer by 72.5%, four-times compaction - 84%, hydraulic penetrometer was used to measure the penetration and six-times compaction - 113%, compared to the non- resistance of soil (n=6). compacted areas. When axle loads of vehicles were By laboratory tests using an indicator method (Reppo, increased, the compaction affected deeper soil layers. 1981; Reppo, 1977) the relative guttation (the exudation of With axle loads greater than 6 Mg, compaction water from leaves as a result of root pressure) was predicted. penetrated to depths > 40 cm, where it was very persistent or Following the general principles of the above-mentioned even permanent (Håkansson and Reeder, 1994). method, the graminaceous seeds were put into soil and The bulk density of the subsoil had increased in the area 2 y = -0,21x + 0,65x + 4,34 y = -0,31x2 + 1,82x+ 0,010 2 BARLEY R = 0,72 SPRING WHEAT R2 = 0,75 12 6 12 6 Guttation 10 5 h mg Guttation, 10 5 8 4 8 4 , 6 3 6 3 m g h 4 2 4 2 -1 -1 2 1 2 1 Height of plants, cm 0 0 0 0 Height of plants, cm 2 2 4 4 sprout 6 6 root 8 8 guttation 10 10 1,20 1,29 1,40 1,57 1,65 1,69 1,24 1,48 1,50 1,65 1,71 1,76 Poly. (guttation) 12 12 -3 Bulk density, g cm-3 Bulk density, g cm Total porosity % 53.9 50.4 46.0 39.4 38.5 34.7 52.2 42.8 42.3 36.3 34.2 32.1 Aeration porosity % 25.3 18.7 9.7 4.3 1.9 0.0 23.9 7.1 6.3 0.0 0.0 0.0 Capillary water- 23.9 24.6 25.9 22.4 22.9 20.5 22.7 24.1 24.0 23.6 23.0 21.8 retaining capacity % Figure 1.