Trumpų sėjomainos rotacijų agrobiologinis įvertinimas ; Agrobiological Assessment of Short Rotations
LITHUANIAN UNIVERSITY OF AGRICULTURE LITHUANIAN INSTITUTE OF AGRICULTURE Vytautas Seibutis AGROBIOLOGICAL ASSESSMENT OF SHORT ROTATIONS Summary of doctoral dissertation Biomedical sciences, agronomy– (06 B) Akademija, 2005 2 This doctoral dissertation was prepared at the Lithuanian Institute of Agriculture in 2000 – 2004. Chairperson of the doctoral committee and scientific supervisor: Dr. Algimantas Magyla to 2004 (Lithuanian Institute of Agriculture, biomedical sciences, agronomy – 06 B) Scientific supervisor: Dr.Virginijus Feiza from 2004 (Lithuanian Institute of Agriculture, biomedical sciences, agronomy– 06 B) Scientific advisor: Prof. Dr. Habil. Leonas Kadžiulis from 2004 (Lithuanian Institute of Agriculture, biomedical sciences, agronomy– 06 B) This dissertation will be defended in the Counsil of Agronomy Sciences at the Lithuanian University of Agriculture: Chaiman: Prof. Dr. Habil. Petras Lazauskas (Lithuanian University of Agriculture, biomedical sciences, agronomy– 06 B) Members: Dr. K ęstutis Armolaitis (Lithuanian Institute of Forestry, biomedical sciences, ecology and environmental sciences – 03 B). Dr. Habil. Juozas Benediktas Staniulis (Institute of Botany, biomedical sciences, biology– 01 B) Dr. Habil. Benediktas Jankauskas (Lithuanian Institute of Agriculture, biomedical sciences, agronomy– 06 B) Assoc. Prof. Dr.
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LITHUANIAN UNIVERSITY OF AGRICULTURE LITHUANIAN INSTITUTE OF AGRICULTURE
Vytautas Seibutis AGROBIOLOGICAL ASSESSMENT OF SHORT ROTATIONS
Summary of doctoral dissertation Biomedical sciences, agronomy (06 B)
2 This doctoral dissertation was prepared at the Lithuanian Institute of Agriculture in 2000 2004. Chairperson of the doctoral committee and scientific supervisor: Dr. Algimantas Magyla to 2004 (Lithuanian Institute of Agriculture, biomedical sciences, agronomy 06 B) Scientific supervisor: Dr.Virginijus Feiza from 2004 (Lithuanian Institute of Agriculture, biomedical sciences, agronomy 06 B) Scientific advisor: Prof. Dr. Habil. Leonas Kadiulis from 2004 (Lithuanian Institute of Agriculture, biomedical sciences, agronomy 06 B) This dissertation will be defended in the Counsil of Agronomy Sciences at the Lithuanian University of Agriculture: Chaiman: Prof. Dr. Habil. Petras Lazauskas (Lithuanian University of Agriculture, biomedical sciences, agronomy 06 B) Members: Dr. Kęstutis Armolaitis (Lithuanian Institute of Forestry, biomedical sciences, ecology and environmental sciences 03 B). Dr. Habil. Juozas Benediktas Staniulis (Institute of Botany, biomedical sciences, biology 01 B) Dr. Habil. Benediktas Jankauskas (Lithuanian Institute of Agriculture, biomedical sciences, agronomy 06 B) Assoc. Prof. Dr. Vaclovas Boguas (Lithuanian University of Agriculture, biomedical sciences, agronomy 06 B) Oponentai: Prof. Dr. Habil. Vida Stravinskienė the Great University, biomedical sciences, (Vytautas ecology and environmental sciences 03 B). Dr. Stasys Bernotas (Lithuanian Institute of Agriculture, biomedical sciences, agronomy 06 B) Defense of doctoral dissertation will take place at the public meeting of the Council of Agronomy Science on the 28th of October, 2005 at 11 a.m. in the room No. 322, Central building of the Lithuanian University of Agriculture. Address: Lithuanian University of Agriculture, Studentųst. 11, LT-53361 Akademija, Kauno d., Lithuania. E-mail: e.patas: email@example.com The summary of the doctoral dissertation was distributed on the 27thof September, 2005. The doctoral dissertation is available in the libraries of the Lithuanian University of Agriculture and the Lithuanian Institute of Agriculture.
3 LIETUVOS EMĖSŪKIO UNIVERSITETAS LIETUVOS EMDIRBYSTĖS INSTITUTAS Vytautas Seibutis TRUMPŲSĖJOMAINOS ROTACIJŲLOGINIS RGA OIBO ĮAM SVERTINI
Daktaro disertacijos santrauka Biomedicinos mokslai, agronomija (06 B)
4 Disertacija rengta 2000 2004 metais Lietuvos emdirbystės institute. Doktorantūros komiteto pirmininkas ir darbo vadovas: Dr. Algimantas Magyla iki 2004 (Lietuvos emdirbystės institutas, biomedicinos mokslai, agronomija, - 06B) Mokslinis vadovas: Dr.Virginijus Feiza nuo 2004 (Lietuvos emdirbystės institutas, biomedicinos mokslai, agronomija 06 B). Mokslinis konsultantas: Prof. habil. dr. Leonas Kadiulis nuo 2004 (Lietuvos emdirbystės institutas, biomedicinos mokslai, agronomija 06 B). Disertacija ginama Lietuvos emėsūkio universiteto Agronomijos mokslo krypties taryboje: Pirmininkas: Prof. habil. dr. Petras Lazauskas (Lietuvos emėsūkio universitetas, biomedicinos mokslai, agronomija 06 B). Nariai: Dr. Kęstutis Armolaitis (Lietuvos mikų biomedicinos mokslai, ekologija ir institutas, aplinkotyra 03 B). Habil. dr. Juozas Benediktas Staniulis (Botanikos institutas, biomedicinos mokslai, biologija 01 B). Habil. dr. Benediktas Jankauskas (Lietuvos emdirbystės institutas, biomedicinos mokslai, agronomija 06 B). Doc. dr. Vaclovas Boguas (Lietuvos emėsūkio universitetas, biomedicinos mokslai, agronomija 06 B). Oponentai: Prof. habil.. dr. Vida Stravinskienė(Vytauto Didiojo universitetas, biomedicinos mokslai, ekologija ir aplinkotyra 03 B). Dr. Stasys Bernotas (Lietuvos emdirbystės institutas, biomedicinos mokslai, agronomija 06 B). Disertacija bus ginama vieame Agronomijos mokslo krypties tarybos posėdyje 2005 m. spalio mėn. 28 d. 11 val. Lietuvos emėsūkio universiteto centriniųrūmų322 auditorijoje. Adresas: Lietuvos emėsūkio universitetas, Studentųg. 11, LT-53361 Akademija, Kauno raj., Lietuva. e.patas: firstname.lastname@example.org Disertacijos santrauka isiuntinėta 2005 rugsėjo mėn. 27 d. Disertacijągalima periūrėti Lietuvos emėsūkio universiteto ir Lietuvos emdirbystės instituto bibliotekose.
5 INTRODUCTION The area sown with the chief grain crops, winter wheat and spring barley, has been on a steady increase in Lithuania recently: in 2005 winter wheat production area amounted to 298.5 thousand ha and barley production area amounted to 340.1 thousand ha (Lithuanian Department of Statistics). As a result, poorer preceding crops have to be inevitably employed. A large part of them are continuously grown or sown after other cereals. On some farms cereals are grown as the third or fourth cereal crop in succession. An excessively large area of the same agricultural crops in a crop rotation exerts a negative effect on the phytosanitary state of crops /Monstvilaitė, 1996/. Phytosanitary role of a crop rotation - weed, disease and pest control, open up much wider chances for the specialisation of a crop rotation and for continuous growing of valuable crops /Lazauskas, 1990/. Adequately chosen preceding crops in a crop rotation are an effective means of weed control and suppression /Könnecke,1967, Rubenis, 1975/. Weeds are very sensitive to mechanical (tillage), chemical (herbicide application) and agronomic (crop rotations) control measures applied /Blackshaw et al., 1994/, as well as to individual crops grown, soil type, moisture content which have a direct effect on weed community /Hume et al., 1991/. Consequently, weeds are justly considered to be indicators of the degree of crop production intensification. Crop rotation is deemed to be an effective means for the reduction of weed incidence, since individual crops grown in a crop rotation suppress weeds under competitive conditions or on the basis of allelopathic effect. This fact has been demonstrated by the research evidence generated from the studies on weed control in crop rotations /Doucet et al., 1999/, that suggest that a greater weed density is formed when crop rotation is disregarded. The prevalence of weed species occurring in different crop cultivation systems is determined by the interactions between crop rotation crops, intensity of weed control and soil tillage /Legere, Samson, 1999/. Some sources of research literature suggest that the incidence of weeds, especially that of perennial weeds, is more markedly affected by the crop rotation and weed control rather than soil tillage /Legere et al., 1993/. Proper alternation of crops not only reduces weed incidence, but also enables cut down of costs intended for weed control. Alternation of winter cereals with spring cereals provides up to 25 % reduction in weed density and biodiversity of individual weed species /Hald, 1999/. An appropriate crop alternation tends to improve soil agrochemical and physical properties. Experiments conducted in Dothuva indicate that ploughing-in of straw and beet tops in a crop rotation tended to increase soil pH /Magyla, 2003/. Sugar beets are attributed to the crops that deplete soil humus reserves, and cereals offset humus balance only in the case when straw is left in the soil after harvesting / Freyer, 2003/. Increment of beneficial soil fauna is a guarantee of soil fertility maintenance and improvement. Earthworms improve soil aggregate stability /Yeates et al., 1998/, increase water infiltration, incorporate organic matter, generate nutrients more readily available to plants, increase soil porosity /Zachman et al., 1987/, accelerate growth of plant underground part, and reduce plant disease occurrence /Bohlen et al., 1995/. 1.1 Relevance of the subject. agricultural reform resulted in significant Lithuanias changes in land use, i.e. in the emergence of small individual farms /Antanavičius, Atkocevičienė, 2002/. As a result, the formerly most popular 7, 8, 9-course crop rotations, or even 5-6-course crop rotations became inapplicable on small farms, especially on those not involved in animal production and cultivation of grass forage. Multiple-course crop rotations would disperse the same crops over several places, and the fields would not be unacceptably small. This is especially problematic for market farms, where it is intended to have 1-2-3 main crops and adequately alternate them. In foreign countries short rotations are a common practice in similar cases /Heenan
6 et al., 1994, Schmidt, 1997, Shparet al., 2000/. However, in Lithuania short rotations have hardly been investigated, except for the sporadic research cases, therefore it is rather complicated to judge the feasibility of market crops growing in short rotations. When the area of cereals is increased in a crop rotation, it is more difficult to choose preceding crops, and continuous growing of crops becomes inevitable. It is of special relevance here to maintain soil fertility, moreover, the adverse effects of crops concentration manifest themselves much more severely than in any other system, namely, heavy occurrence of weeds, diseases and pests, soil depletion and fatigue /Vasinauskas, Klimavičiūtė, 1967, Baker, 1997, Legere, Samson, 1997, Krupinsky et al., 2002, Freyer, 2003/. 1.2 Research hypothesis. On cultivated Central Lithuanias soils shortening of rotations and proper choice of preceding crops make it feasible to produce profitable, high quality agricultural production without depleting soil and without increasing weed and disease incidence. 1.3 Experimental objective and tasks. experimental objective was to carry out 10 The crop rotations (including 2-4 course ones) and 2 monocrops by ploughing in by production as green manure and to perform agrobiological assessment of these practices on Central Lithuanias light loam Cambisol. The following tasks were set for the agrobiological assessment of short rotations. To determine: 1 the effect of the number of rotation courses on soil agrochemical and physical properties and on pedobiology; 2 the effect of shortening of the rotation and preceding crops on biometrical indicators of winter wheat, spring barley and pea crops; 3 the effect of shortening of the rotation and choice of preceding crops on weed incidence in winter wheat, spring barley, pea, and sugar beet crops; 4 the damage done by root diseases spread with the crop rotation in cereal crops; 5 the effect of shortening of the crop rotation and choice of preceding crops on the productivity and quality of the main production of winter wheat, spring barley, pea, sugar beet, and winter and spring oilseed rape. 1.4 Novelty of the research work.Up till now no comparative short rotation agrobiological research has been done in Lithuania on the number of rotation courses, preceding crops, plant species and time of cultivation of the same crop in the same place when all by-production is ploughed in as green manure. Moreover, there was a great need for research on the feasibility of winter and spring oilseed rape cultivation in short rotations. 1.5 Practical relevance of the research.Unique crop rotation research is carried out on Central Lithuanias loamy Cambisol which is oriented towards the already existing or newly emerging farms that intend to be involved solely in crop production, i.e. in the cultivation of commercial crops. The tasks set in this research will help for the first time to look into the feasibility of application of short rotations with 4, 3 and 2 courses and 2 monocrops with a view to producing high yield of agricultural crops of high quality, free from diseases and weeds. 1.6 Approval of the research work. Experimental findings were published in the proceedings of doctoral students conferences The youth strive for progress 2001 and The youth strive for progress 2003, in the international scientific practical conference Reorganisation of agricultural structures and cooperation arranged at LUA in 2002, and in 2 articles in the refereed Lithuanian publication Agriculture . 1.7 Volume of work. The dissertation is written in Lithuanian. It consists of the introduction, review of literature, experimental methods and conditions, experimental results, conclusions, list of publications on the subject of the dissertation, list of references. The dissertation is comprised of 140 pages, 43 tables, 40 figures, 179 literature references.
7 EXPERIMENTAL METHODS AND CONDITIONS A field experiment designed to investigate short rotations was started at the Lithuanian Institute of Agriculture in Dotnuva in 1997. The experiment was set up by dr. A.Magyla, and from the autumn of 2000 the experiment was jointly carried out with a LIAs doctoral student V. Seibutis. The experiment consists of 10 crop rotations with short (24 - course) rotations and 2 monocrops, altogether 30 members (courses) (Table 1). Monocrops (sugar beet and spring barley) were continuously grown for four years. Afterwards, for another 4-year cycle the plots of monocrops were changed places former sugar beet plots were allocated for spring barley continuous growing, and spring barley plots were allocated for sugar beet. Table 1.Experimental design No. o cNroo.p o No. of rotation course cNroo.p o No. of rotation course crop No. of rotation course rotation rotation rotation 1. Pea 1. Pea 1. Pea I 23.. SWuignatre rb eweht e at IIiWtn2 .bngle a ra.t he3r iwSepr yIIIin W2.iW .r e ttnaehewh w 3 rteat 4. Spring barley 1. Sugar beet 1. Sugar beet 1. Sugar beet IV2. Spring barleyV2. PeaVI2. Spring barley 3. Winter wheat 3. Winter wheat 3. Pea 1. Winter rape 1. Pea 1. Sugar beet VII2. Winter wheatVIII2. Winter wheatIXS .r2pS .r3prlbag in ey ing rape 1. Spr eyXISugar beet X tee guS b ra2.ing barl (monocrop)XII )porcoSrp(money barling Plot size (bruto)3 m x 20 m = 60 m2, netto in cereals 45.5 m2, in peas 43.5 m2, in sugar beet 36 m2. Four replications. Treatments in replications arranged randomly. According to LTDK-99, the soil of the experimental site ishydoglpoarlcEni-nEacodyeci Cambisol, content in the ploughlayer 2.28 %, pH humusKCl7.2, mobile phosphorus (P2O5) and potassium (K2O) 142 and 180 mg kg-1soil, respectively. The following crops were grown in the trial: winter wheat (Triticum aestivumL.) irvinta (seed rate 4 million ha-1viable seed), spring barley(Hordeum vulgareL.)Alsa (3.5 million ha-1), pea(Pisum sativumL.)Profi (1 million ha-1), sugar beet(Beta vulgarisvar.SacchariferaAlef.) Manhatan (1.3 seed unit ha-1), winter rape(Brassica napusL. var. oleifera DC.)Kazimir (4.5 kg ha-1), and spring rape(Brassica napusL.)Maskot (7 kg ha-1). Conventional crop cultivation technology linked with sustainable fertilisation of agricultural crops was applied in the trial. By production, i.e. chopped cereal straw, pea vines, oilseed rape stems, and sugar beet leaves, were spread on soil surface as a green fertiliser. To accelerate straw mineralization, 10 kg of nitrogen per 1 ton of cereal and rape straw (D.M.) was applied after harvesting, and shortly afterwards stubble was cultivated at 10-12 cm depth. Two-three weeks after stubble breaking the soil was ploughed at 20-22 cm depth. Pre-sowing soil tillage for all crops was identical shallow loosening by a cultivator with a light harrow at 5-8 cm depth, the operation was performed twice. After cereal sowing, and for rape also before sowing, the soil was rolled by a Cambridge roller. No farmyard manure was used in the trial, only mineral fertilisation was applied. Fertiliser rates: for wheat N80P40K30, barley N70P40K30, 7
8 pea P40K40, sugar beet N150P60K120 N, winter rape120P60K90, spring rape N90P60K60. PK fertilisers were broadcast before primary tillage, nitrogen was applied to winter cereals upon resumption of vegetative growth, and to spring crops soon after post-emergence. Herbicides were applied in all crops: winter wheat and spring barley were sprayed by a mixture of Granstar (0.015 kg ha-1) and Starane (0.4 l ha-1), pea was sprayed by Bullet 1.5 l ha-1, sugar beet by a mixture of Betanal Expert (1.5 l ha-1) and Goltix (1.5 l ha-1). Winter wheat and spring barley were applied with a fungicide Tango Super (1.5 l ha-1). Insecticides were used according to the need. Experimental analyses and methods Plough layers characteristics were determined before trial establishment in 1996, 2000, 2003 after harvesting of all plots (by making 15-20 bore holes walking diagonally): pHKCl; P2O5, K2O (by A-L method), humus after Tyurin, total nitrogen by Kjeldahl method. Besides, annually in all winter wheat plots in spring (03 04 2001, 03 04 2002, 16 04 2003), and like in barley, pea or sugar beet crops two weeks after nitrogen application (05 06 2001, 24 04 2002, 15 05 2003) and after spiked crops harvesting (07 08 2001, 30 07 2002, 08 08 2003) we measured nitrogen content in 0-20 cm depth for treatments. N-NO3analysis in freshly taken samples was done ionometrically, and that of N-NH4 a colorimeter. For agrochemical analyses (pH byKCl, P2O5,K2O), humus, total nitrogen measurement composite samples from all replications were made. Mobile phosphorus (P2O5) and potassium (K2O), and Nmin.determined at the LIAs agrochemical research centre,were humus at LIAs laboratory of chemical tests. Soil structure for all crop rotations was determined in spring at barley tillering stage and at the end of growing season in two replications by digging two holes. Soil aggregate stability in water was estimated by Savinov method, and coefficient of structurality was determined according to the formula: K=C : B, where C content of soil aggregates 0.25-7 mm in size, B content of all soil aggregates (>7 + 0.25-7 + <0.25 mm) /Nerpin,Čiudnovskij, 1967/. Soil bulk density was measured by Katchinski method, total and air-filled porosity by calculation method from bulk density, solid phase density and moisture /Vadiunina, Korčagina, 1986/, soil moisture in a thermostat by drying the samples at constant +105oC temperature to a constant weight. Soil samples for physical analyses were taken at the end of the growing season from two replications (II and III), in 2001, 2002, 2003 in two places of each plot at 0-5, 5-10, 10-15, 15-20 cm depths. Physical analyses were performed at LIAs laboratory of soil and crop production department. Earthworms were studied during 2001-2003 in April before soil tillage, on an area of 0.25 m2of each treatments two replications at 0.25 cm depth in two places of the plot. The dug soil in the field was placed on 2 mx2 m polyethylene film, the earthworms were thoroughly collected by hand and were transferred to boxes. In the laboratory the earthworms were washed, blotted, counted and weighed /Gilerov, 1965, soil sampling and methods of analysis, 1993/. Weed infestation in crops was investigated in spring before herbicide application (number of weeds) and at early milk ripeness of cereals (BBCH 73), and after beet leaves had covered interrows (weed number, weight, botanical composition)-annually in all plots (for weed assessment we used a 0.25 m2frame, weeds were taken from each replication in 4 places /Stancevičius, 1979/. For the determination of root diseases 10 stems were randomly taken from 10 places in wheat and barley stand at flowering-maturation stage (DK 61-89). Plant density was estimated upon emergence of crops (plants were counted in four places of plots on an area of 0.25 m2). Seedlings of winter wheat were counted twice: upon emergence in autumn and after overwintering in spring. At the end of plant growing season plants were pulled from two 0.25 m2 plots per each plot and sheaves were made from which we determined the
9 number of productive stems, plant height and productivity of eras. For chemical composition and 1000 grain weight determination, 1 kg samples were taken from each plot after grain harvesting and cleaning. Quality assessment indicators of the primary and by production of the crop rotation crops total nitrogen content (N) was determined by Kjeldahl method (LST 1523), P by wet combustion, colorimetrical method usingTechnikoninstrument, K and Ca by flame photometry, gluten content by hand washing (LST 1522), protein content in wheat was calculated according to Ntotal content, measured by Kjeldahl method, by multiplying by coefficient 5.7, for barley by 6.25 (LST 1523), sedimentation by Zeleny method (LST 1498 and LST 1512). All analyses were done at LIAs laboratory of chemical tests. Sugar beet indicators were calculated according to sugar beet quality assessment methodology developed by A.V.Ustimenko-Bakumovski, A.I. Ostroushka, V.A. Makaveck, C.Winner, Carruthers & Oldfield /Winner, 1975./ Processing of experimental data Processing of experimental data.The data presented in this research study were processed by analysis of variance and correlation-regression methods (Stancevičius, Arvasas, 1981). To determine significant differences the data of weed incidence were transformed in the following way: x=x+1 (Tarakanovas, Raudonius, 2003). The content of metabolizable energy accumulated in individual crops of the rotation was calculated according to the yield energy evaluation methodology adapted by the researchers of the Lithuanian Institute of Agriculture /Jankauskas et al., 2000/. Experimental results Soil agrochemical properties.Having measured soil pHKCl, mobile phosphorus (P2O5) and mobile potassium (K2O) contents for individual crops before trial establishment (1996, end of summer) and upon completion of the trial (2003, after harvesting) it was found that soil pHKClfor individual crop rotations varied from 7.0 to 7.9, which suggests that according to the Lithuanian universal classification based on potential exchange acidity the soils were neutral and alkaline. The contents of mobile P2O5varied from 109 mg kg-1to 168 mg kg-1, i.e. the soils were rated as being from moderate to high in phosphorus, according to potassium supply the soils of individual crop rotations were ranked as being from moderate (132 mg kg-1) to high (234 mg kg-1) in potassium. In summary, we can maintain that soils on which crop rotation trials were conducted were sufficiently supplied with potassium, since the dominating content of potassium amounted to over 150 mg kg-1, and moderately supplied with phosphorus (on average 143.6 mg kg-1). According to the data of research continued for seven years, shortening of rotations did not have any effect on the variation in soil pH, and the contents of mobile P2O5 and K2O even increased over the seven experimental years. During the initial 4 experimental years (1996-2000) humus content in the ploughlayer decreased inappreciably (within the 0.06 0.09 percentage unit) for crop rotations I, II, X and VI, while for the rest of the rotations the reduction was even lower 0.01-0.05 percentage unit. Averaged data from all crop rotations indicate that during the final years of the experiment (2000-2003) humus content in the soil tended to slightly decline from 2.24 %, 2.27 %, 2.22 % to 2.17 %, respectively. During the mentioned period the four-course (pea-wheat-sugar beet-barley) crop rotation I and sugar beet monocrop (XI) were distinguished for slightly higher reduction in humus content, where it made up 0.12 percentage unit (5.5 %) and 0.13 percentage (5.6 %), respectively. Total nitrogen content measured at the beginning of the trial varied within the range from 0.129 to 0.151 %. In 2000, compared with the beginning of the trial, the changes in total nitrogen content were inappreciable, varied from 0.003 to 0.02 percentage unit.
10 Upon full implementation of the crop rotations (2001) the content of total nitrogen increased by on average 5.0 %, compared with that at the beginning of trial establishment (1996), however, at the end of the experimental period (2003), the mentioned content remained on the same level as was before trial establishment. Changes in mineral nitrogen content.Averaged over the 2001-2003 period data suggest that at cereal tillering stage, when shortening rotations from four, three to two courses, Nmin.content per 1 rotation course consistently declined, from 8.23 mg kg-1, 8,04 mg kg-1 7.18 mg kg to-1, respectively. In the three-course crop rotations sugar beet-barley-pea (VI) and sugar beet-barley-spring rape (IX) accumulated slightly more Nmin., 9.19 mg kg-1and 9.06 mg kg-1, respectively. The mentioned changes were most markedly influenced by the inclusion of pea and spring rape into crop rotations. The lowest content of Nmin(6.61 mg kg-1) among the three-course crop rotations was accumulated in the crop rotation III pea-wheat-wheat, consisting solely of cereals, whereas absolutely lowest Nmin.content 6.46 mg kg-1accumulated in the two-course winter rape-wheat crop rotation VII. Averaged over three years data indicate that in spring Nmin.was largely composed of N-NO3 79.2 % in the rotations. Nmin. content in the ploughlayer under sugar beet, grown in the crop rotations, at the beginning of vegetation was the highest 8.34 mg kg-1, where N-NO3accounted for 79 %. During the crop growing season Nmin.content declined by on average 16.9 %. At the end of the mentioned period all the crop rotations contained on average 52 % of N-NO3, and in the three-course (sugar beet-barley-pea) crop rotation VI, N-NO3 for 48.0 %. In the four-course accounted and three-course crop rotations it differed inappreciably and amounted to 6.35 mg kg-1and 6.15 mg kg-1, respectively, and in the two-course crop rotations its content was higher 7.22 mg kg-1. Soil physical properties.Soil bulk density is the parameter which is subject to the greatest variability in response to natural and anthropogenic factors. The best conditions for winter wheat growth are created when soil bulk density is 1.33 Mg m-3/Rasadin, Kačnova, 1980/. For barley, on light loamy soil, bulk density should vary from 1.2 to 1.3 Mg m-3/Zimkuvienė, 1988/. Soil porosity is an important soil property, on which water and air regime and plant growth conditions depend. Optimal total porosity should be 45-50 %. The best aeration is when air in the soil makes up 20-25 % of porosity /Vadiunina, Korčagina, 1986/. Depending on the different weather conditions occurring during the experimental period, (in July of 2001 the rate of rainfall was 102.5 mm, and in July of 2003 54.6 mm) soil physical conditions were diverse. However, the changes in physical soil properties in separate experimental years were also determined by the choice of rotations. Soil bulk density and moisture content in individual crop rotations in 2001 were the highest of all experimental period. In separate crop rotations average soil bulk density varied within 1.36 1.42 Mg m-3, and moisture within 18.2 19.4 % range. The highest soil bulk density (1.44 Mg m-3) was recorded in sugar beet monocrop. A slightly increased soil bulk density was noted for the three-course crop rotations, in the crop structure of which cereals accounted for 2/3 of the area: in the crop rotations III (pea-wheat-wheat) and IV (sugar beet-barley-wheat) soil bulk density was 1.40 and 1.42 Mg m-3reached 19.3 % each. Similar soil bulk, respectively, Soil moisture content density was found for the two course crop rotations VII (winter rape-wheat) and VIII (pea-wheat) 1.40 Mg m-3each, respectively, and the moisture content made up 19.4 and 19.0 %, respectively. The lowest soil bulk density was found in the three-course crop rotations V (sugar beet-pea-wheat) and VI (sugar beet-barley-pea) 1.37 Mg m-3each, respectively and in the two-course crop rotation X (barley-sugar beet) 1.36 Mg m-3Whereas moisture reserves in the plough layer were the lowest. in the crop rotation IX (sugar beet-barley-spring rape) up to 18.2 %. The data from the year 2002 show that similar soil bulk density, compared with the previous years remained in the three-course crop rotation VI (sugar beet-barley-pea), and two-course crop rotations VII (winter rape-whea) and
11 VIII (pea-wheat) 1.36 Mg m-3 Ineach, respectively. the mentioned two-course crop rotation VIII and three-course crop rotations III (pea-wheat-wheat) and IX (sugar beet-barley-spring rape) the moisture content was significantly reduced, to 14.6 %, 14.8 % and 14.2 %, respectively, and a significant increase in moisture content was identified for the three-course crop rotation IV (sugar beet-barley-wheat) and for sugar beet monocrop, up to 17.0 % and 18.8 %, respectively. In 2003 the lowest soil bulk density was determined for the two-course crop rotation VII (winter rape-wheat) and the three-course crop rotation III (pea-wheat-wheat) 1.26 Mg m-3as well as for X (barley-sugar -beet) 1.27 Mg m3. Total soil porosity in 2001 varied in separate crop rotations from 44.0 to 49.1 %. However, during the two experimental years it consistently increased and at the end of the trial varied within 47.4 50.4 % range. Soil air-filled porosity varied slightly more during the experimental period. If in 2001 in separate crop rotations air-filled porosity ranged from 16.8 % in the three-course crop rotation IV (sugar beet -barley-wheat) to 23.1 % in barley monocrop, over the next two years it increased. In 2002 it varied from 21.4 % in sugar beet monocrop (XI) to 28.8 % the three-course crop rotation II (pea-wheat-barley) and in 2003 it varied again from 26.3 % in the mentioned sugar beet monocrop to 39.7 % in the three-course crop rotation III (pea-wheat-wheat). Soil aggregate composition.During 2001-2003 to estimate soil structurality of short rotations, separate fractions of soil structure were discriminated by dry and wet sieving methods. Soil structurality is described by soil aggregates whose diameter ranges from 0.25 to 10 mm. Agronomically most valuable are those aggregates that do not break down under the effect of water and maintain their stability for a long time. Water stable soil aggregates >1 mm and > 0.25 mm over the three experimental years (2001-2003) had similar trends of variation. Of all the crop rotations tested the most notable one was found to be the two-course crop rotation VII (winter rape wheat), in which soil aggregates >1 mm during the mentioned period made up 13.86, 15.02 and 22.56%, respectively, i.e. significantly more than in the rest of the crop rotations. In the latter crop rotation there was also found the largest number of aggregates > 0.25 mm, in 2001, 2002 and 2003 they accounted for 62.28, 56.72 and 56.02%, respectively (significant increase). Slightly lower, however, much higher than average for all crop rotations, content of water stable aggregates was found in the three-course crop rotation III (pea-wheat-wheat) where aggregates >1 mm in 2001, 2002 and 2003 accounted for 11.94, 13.22 and 18.13%, respectively, and those >0.25 mm accounted for 59.95, 55.55 and 55.69%, respectively. The lowest content of water stable aggregates >1 mm and > 0.25 mm was found in the sugar beet monocrop (XI). In the mentioned treatment in 2001, when sugar beet was sown after barley monocrop lasting for four years, the following contents of aggregates > 1 mm and 0.25 mm were identified: in the first case slightly higher than average 11.70%, in the second case absolutely highest 63.60%. However, during the next two years the content of water stable aggregates determined in the mentioned monocrop was markedly lower: aggregates > 1 mm in 2002 and 2003 made up 6.72 and 6.49%, respectively, and those larger than 1 mm made up 41.58 and 40.62%, respectively, which was significantly less than on average in the rest of the crop rotations. A slightly higher content of water stable aggregates than in the sugar beet monocrop but much lower than average for all crop rotations, was identified in the three-course crop rotation VI (sugar beet-barley-pea) where aggregates > 1 mm in 2001, 2002 and 2003 made up 8.57%, 9.13%, 11.61%, respectively, and those >0.25 mm made up 57.8, 49.29 and 48.89%, respectively. Occurrence of earthworms in short crop rotations.During the experimental period four earthworm species were found in the trial plots:Aporrectodea caliginosa caliginosaSav., Lumbricus terrestris(Hoffm.), Allolobophora chlorotica chlorotica(Sav.), Eisenia rosea (Sav.). The dissertation provides the data on the total number of earthworms and their weight, not on each individual species.
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