1036

Bulgarian Journal of Agricultural Science, 22 (No 6) 2016, 1036–1042Agricultural Academy

FIELD INVESTIGATION OF THE PERFORMANCE OF ROTAVATOR UNDER HEAVY STRAW CONDITION

H. FANG1,2, Q. ZHANG2, S. JIAN1, C. JI2,*, A. A. TAGAR3, C. ARSLAN2,4 and M. S. MIEMON2,3

1 Shandong Academy of Agricultural Machinery Sciences, Jinan 250100, China2 Nanjing Agricultural University, College of Engineering, Nanjing 210031, China3 Sindh Agriculture University, Faculty of Agricultural Engineering, Tandojam 70060, Pakistan4 University of Agriculture, Department of Structures and Environmental Engineering, Faisalabad 38000, Pakistan

Abstract

FANG, H., Q. ZHANG, S. JIAN, C. JI, A. A. TAGAR, C. ARSLAN and M. S. MIEMON, 2016. Field investigation of the performance of rotavator under heavy straw condition. Bulg. J. Agric. Sci., 22: 1036–1042

The incorporation of straw into the soil increases soil organic carbon storage and reduces soil erosion. Straw is rich in organic material and soil nutrients, thus it is increasingly considered as an important natural organic fertilizer. The present study investigated the physio-mechanical properties of soil, displacement and burial of straw under heavy straw conditions at three rotational speeds (180, 230 and 280 rpm). Soil and straw displacement were measured using tracer technology, soil shear properties were determined by direct shear box, penetration resistance was measured with a hand-held penetrometer (OK-JS1, Zhengzhou Oukeqi Instrument Manufacturing Co., Ltd). Results revealed that the lateral and forward displacements of both straw and soil increased with the rotational speeds. Forward displacement of both soil and straw was signifi cantly larger than that of lateral displacement. The addition of straw increased the cohesion and internal friction angle of soil, thus strengthened the soil. The penetration resistance of soil decreased with the increasing rotational speeds. The mean clod diameter was smaller at higher rotational speeds, while the rate of soil breakage increased with increasing rotational speeds. The rate of straw burial increased with the increasing rotational speeds. It is concluded that the fi elds should be cultivated at the rotational speed of 280 rpm to achieve the better soil conditions, displacement and burial of straw.

Key words: C-type rotary blade, soil and straw displacement and burial, physio-mechanical properties, soil break-age, mean clod diameter

*Corresponding author: chyji@njau.edu.cn

Introduction

Rice and wheat are the two main cereal crops; their pro-duction accounts for 80% of the total grain production in China (Yang et al., 2000). After harvesting of these crops, the residues (straw) are incorporated into soil to increase soil organic carbon storage (Zhang et al., 2014) and to reduce soil erosion (Foltz et al., 2012). Straw is rich in organic material and soil nutrients, thus it is increasingly considered as an im-portant natural organic fertilizer (Tan et al., 2007). Incorpo-ration of straw into soil either directly or indirectly promotes

the soil environment or maintains the physicochemical con-dition of the soil (Li et al., 2002).

The degree of straw incorporation into the soil depends on the tillage (Lal, 1997) and the implement types (Hanna et al., 1995). Mari et al. (2014) used single disc tool in a soil bin under controlled conditions, while Farid Eltom et al. (2015) used moldboard plow in a fi eld. Liu et al. (2007, 2010) used sweep tool in both soil bin and in a fi eld. Munir et al. (2012) used furrow opener in untilled fi eld condition. In contrast rotary tiller is widely used in Jiangsu province of China, which accounts for 75.8% of all tilling land ma-

1037Field Investigation of the Performance of Rotavator under Heavy Straw Condition

chines (China machinery industry yearbook, 2013). Chen et al. (2015) found a gentle soil surface and better straw burial with mini-powered rotary tiller. Sirisak et al. (2008) concluded that the rate of straw burial increased with the increase in the rotational speed of rotary tiller. Tillage with rotary tiller can obtain better mechanical stability and fa-vorable environment for plants (Horn, 1986). Moreover Ji et al. (2012) pointed out that the working quality of rotary tiller could meet the requirements of national standard of China. Many studies have explored straw displacement and burial with stubble only and with different amounts of straw, but a little information is currently available on the straw displacement and burial under heavy straw condition after harvesting of a crop.

Thus, the present study was designed to investigate the straw displacement and burial, shear properties of soil, pen-etration resistance, mean clod diameter and soil breakage at different rotational speeds under heavy straw condition.

Materials and Methods

Experiments were conducted at Jiangpu Experimental Farm of Nanjing Agricultural University, Jiangsu Province of China during 2015. It is located at 32°01′-32°03′N lati-tudes and 118°36′-118°38′E longitudes. The average pre-cipit ation is 1000 mm, average humidity is 76%. Prior to the experiments both straw and stubbles were cut by smashed machine (4J-180B, Henan Haofeng Machinery Manufactur-ing Co., Ltd), and the total amount of residues on soil surface after smashing was 6.3 t per hectare. The soil was composed of 39.4% sand, 32.7% silt, and 27.9% clay and was classi-fi ed as clay loam and the organic matter content was 4.2%. The average dry bulk density of soil was 1.57 g cm-3 and cone index was 1106, 17 58, 3286 kPa at 5, 10, 15 cm depth, respectively.

Rotary tiller (1GQN-200H, Henan Hao feng machinery manufacturing Co., Ltd) with 2 m working width was used in the experiments. The C-type rotary blade (58 IT245), with 245 mm radius and 50 mm tilling width were installed in double helix on the rotor shaft. The blade was operated at three different rotational speeds corresponding to 180, 230, and 280 rpm, while the tractor speed (0.5 m s-1) and working depth (100 mm) were kept constant during tests. Figure 1 depicts the fi eld conditions.

Physical and mechanical properties of soilMoisture contentThe undisturbed soil and soil-straw cores (61.8 mm d i-

ameter and 20 mm long) were procured from the fi eld, while straw samples were collected in the aluminum boxes (70 mm diameter and 35 mm long). The aluminum boxes, soil and soil-straw cores were labeled, packed and brought to the laboratory. The moisture content of soil and straw mixture was determined by gravimetric method (Blake and Hartge, 1986). The moisture content of straw was 19.6%, the mois-ture of soil was 24.6%, while the moisture content of soil straw mixture was 23.3%.

Soil and straw displacementTracer technology was used for measuring soil and straw

displacement in fi eld experiment, similarly as done by Liu et al. (2007, 2010) and Chandio et al. (2013). Seven tin alloy cubes (2 cm) were marked and then inserted into soil perpen-dicular to the direction of rotary tiller to track the movement of surface soil. Straw pieces used as tracers, were colored, labeled and laid fl at on the surface at designated spots later-ally and longitudinally. The longitudinal tracers were placed parallel to the travel direction, and the lateral ones were po-sitioned perpendicular to the direction of tool travel (Figure 2). Soil and straw displacements were then calculated by the

Fig. 1. Field conditionFig. 2. Schematic view of soil and straw tracer

placements in the fi eld

1038 H. Fang, Q. Zhang, S. Jian, C. Ji, A. A. Tagar, C. Arslan and M. S. Miemon

absolute difference between the original positions and fi nal positions.

Straw burialThe rate of straw burial was measured following meth-

od adopted by Dursun et al. (1999) using a square frame (500 × 500 mm2) as shown in Figure 3.

(A1 – A2)B = ––––––––, A1

whereas:B = Burial straw, %A1 = Total weight of straw before tillage, gA2 = Buried weight of straw after tillage, g

Shear properties of soilSoil samples were taken with no straw burial before the

incorporation of straw and with straw burial after the incor-poration of straw (Figure 4). Shear properties of soil and soil-straw samples were determined using direct shear box (SDJ-1 strain-controlled, Nanjing Soil Instrument Co., Ltd,

Nanjing, China) at Soil Mechanics Laboratory, Department of Agricultural mechanization, College of Engineering, Nan-jing Agricultural University, Jiangsu, China.

Penetration resistanceThe penetration resistance (cone index) was measured at

5 different locations in each plot at the depths of 0-15 cm with a hand-held penetrometer (OK-JS1, Zhengzhou Oukeqi Instrument Manufacturing Co., Ltd).

Soil breakageAfter tillage, the resulting soil clods were sampled from

an area of 500×500 mm2 at the depth of 100 mm, and then rate of soil breakage was determined using following rela-tion (Lee et al., 2003):

m1 – m2Rsb = ––––––––, m1

whereas:Rsb = The rate of soil breakage, %, m1 = The mass of total soil of the area, g, m2 = The mass of soil with a diameter of 20 mm or more

of the area, g.

Soil clod diameterThe mean clod diameter was determined using following

equation (Sirisak et al., 2008):

5A + 15B + 27.5C + 37.5D + 45E + 55FScd = –––––––––––––––––––––––––––––––––, M

whereas&Scd = The mean soil clod diameter, mm, M = The mass of total soil, g,A–F = The weight of soil retained on the next smaller sieve.

Statistical analysisThe experiments were arranged in a randomized com-

plete block design (RCBD) with three replications. One way ANOVA and Duncan’s multiple range tests (DRMT) were carried out to assess differences between means at 5% prob-ability level using SPSS software (ver. 20, SPSS, Inc., Chi-cago, IL, USA).

Results and Discussion

Soil and straw displacementThe lateral displacement of the straw was 87.30, 132.50

and 203.90 mm at 180, 230 and 280 rpm, respectively; while forward displacement of the straw was 273.72, 365.80 and 446.90 mm at 180, 230 and 280 rpm, respectively (Figure

Fig. 3. Measurement of straw burial

Fig. 4. Soil samples: (a) with no straw and (b) with straw burial

1039Field Investigation of the Performance of Rotavator under Heavy Straw Condition

5a). Similarly the lateral displacement of soil was 76.00, 85.56 and 126.67 mm at 180, 230 and 280 rpm, respectively; while the forward displacement of soil was 305.67, 353.39 and 418.17 mm at 180, 230 and 280 rpm respectively (Figure 5b). It was found that the lateral and forward displacements of both straw and soil increased with the rotational speeds. This is consistent with Liu et al. (2010), who concluded that straw displacement increased with the increase in speed. Mari et al. (2014) concluded that with the increase in the speed of disc tool, the lateral and forward displacements of straw increased. Rahman et al. (2001, 2005) found that the slight increase in the forward speed led to larger soil move-ment. Also Hendrick and Gill (1971) concluded that increas-ing rotational speed resulted in a greater movement of soil particles.

It was also found that the forward displacement of soil and straw was larger than that of lateral displacement. This is consistent with Liu et al. (2010), who concluded that the for-ward displacement of both soil and straw were larger com-pared to the lateral displacement. The displacement of straw was larger than that of soil, possibly due to straw dragging (Liu et al., 2010). This is consistent with Eltom et al. (2015) who found that the straw displacement was larger compared to the soil displacement. However the forward displacement of soil was larger than that of straw at 180 rpm.

The statistical analysis of the data (ANOVA) showed signifi cant differences among the lateral displacements of straw at the rotational speeds of 180, 230, 280 rpm. Similarly non-signifi cant differences were found among the forward displacements of straw at the rotational speeds of 230 and 280 rpm, while the signifi cant (p < 0.05) differences were observed at the rotational speed of 180 rpm. The non-signif-icant differences were obtained among the lateral displace-ments of soil at the rotational speeds of 180, 230 and 280 rpm as well as among the forward displacements at 180 and 230 rpm rotational speeds, while signifi cant differences were experienced at the rotational speed of 280 rpm.

Shear propertiesThe cohesion of soil before tillage was 40.7 kPa, while

after tillage operation, the cohesion was 75.64 kPa. Internal friction angle of the soil before tillage was 7.12°, while af-ter tillage operation, the internal friction angle of soil was 13.44°. The cohesion and internal friction angle of soil after tillage operation signifi cantly increased compared to that of the before tillage operation. The results revealed that the ad-dition of straw increased the cohesion and internal friction angle of soil, which strengthens the soil. Thus it will require additional forces to till the soil compared to the soil with no straw (Mckyes, 1985; Subrata et al., 2014). This is consistent with Farid Eltom et al. (2015), who found that the draught

Fig. 5. Lateral and forward displacements at different rotational speeds: (a) straw and (b) soil

Fig. 6. Cohesion and internal friction angle of soil before and after tillage operation

Dis

plac

emen

t, m

mD

ispl

acem

ent,

mm

Rotary speed, rpm

Rotary speed, rpm

1040 H. Fang, Q. Zhang, S. Jian, C. Ji, A. A. Tagar, C. Arslan and M. S. Miemon

force of moldboard plough was larger in dense straw cover (Figure 6).

Penetration resistanceThe average penetration resistance before tillage opera-

tion was 114.16 N, while after tillage operation, it reduced to 63.21, 40.60 and 32.14 N, at the rotational speeds of 180, 230 and 280 rpm, respectively (Figure 7). The penetration resistance signifi cantly decreased (p < 0.05) after tillage, but the differences of penetration resistance among differ-ent rotational speeds were non-signifi cant (p > 0.05). Unger et al. (1998) found lower values of penetration resistance in stubble mulch tillage plots than no-tillage plots due to soil losing by tillage. Osunbitan et al. (2005) found a signifi -cant (p < 0.05) decrease in penetration resistance with the soil manipulation during tillage. Salokhe and Ramalingam (2001) also concluded that the penetration resistance sig-nifi cantly decreased (p < 0.05) after the tillage.

Soil breakage and clod diameterFigure 8 shows the mean clod diameter and rate of soil

breakage at different rotational speeds. The mean clod di-ameter of soil was 37.23, 29.67 and 23.69 mm at the rota-tional speeds of 180, 230 and 280 rpm, respectively; while the rate of soil breakage was 22.43, 32.53 and 42.98% at the rotational speeds of 180, 230 and 280 rpm, respectively. The results showed that the rotational speeds had signifi cant effects on the mean clod diameter and rate of soil breakage. Higher rotational speed leads to the smaller bite length. This is consistent with Matin et al. (2015), who concluded that at higher rotational speeds, blades cut a smaller soil slices in each bite, which break into smaller clods. Tsuchiya (1965) concluded that at higher rotational speeds the mean clod di-ameter would be very small. Indeed Sirisak et al. (2008) also found a decrease in mean clod diameter with the increase in rotational speeds. Meanwhile, the soil breakage rate in-creased with the increase in the rotational speeds. Duncan test showed signifi cant differences (p < 0.05) among the val-

ues of mean clod diameter at three rotational speeds, while in case of soil breakage rate signifi cant differences (p < 0.05) were found at the rotational speeds of 180 and 280 rpm, how-ever non-signifi cant differences (p > 0.05) were observed at the rotational speed of 230 rpm.

Straw burialStraw burial rates were 82.09%, 84.13%, and 90.50% at

the rotational speeds of 180, 230 and 280 rpm, respectively (Figure 9). It showed that rotational speeds have positive impacts on the straw burial. This is consistent with Mari et al. (2014), who reported the increase in straw burial rate

Fig. 7. Penetration resistance at different rotational speeds

Fig. 8. Mean clod diameter and rate of soil breakage at different rotational speeds

Fig. 9. Straw burial rates at different rotational speeds

1041Field Investigation of the Performance of Rotavator under Heavy Straw Condition

with increasing speed. Liu et al. (2010) also obtained more straw burial at higher speeds. Sirisak et al. (2008) concluded greater straw burial with increasing rotational speed of rotary tiller. Duncan test showed signifi cant differences (p < 0.05) among straw burial at the rotational speeds of 180 and 280 rpm. However non-signifi cant differences (p > 0.05) were found at the rotational speed of 230 rpm.

Conclusions

The study has shown signifi cant effects of rotational speeds on the physio-mechanical properties of soil, displace-ment and burial of straw under heavy straw conditions after harvesting of a crop.

The lateral and forward displacements of both straw and soil increased with the rotational speeds. Forward displace-ment of soil and straw was signifi cantly larger than that of lateral displacement. The addition of straw increased the co-hesion and internal friction angle of soil, thus strengthened the soil. The penetration resistance decreased signifi cantly (p<0.05) after tillage operation with increasing rotational speeds. The mean clod diameter was smaller at higher rota-tional speeds, while the rate of soil breakage increased with increasing rotational speeds. The study has also shown that the rotational speeds had positive effects on the straw burial. The rate of straw burial increased with the increasing rota-tional speeds.

AcknowledgmentsThis study was fi nancially supported by National Key

Research and Development Plan of China (Grant No. 2016YFD0300800) and National Natural Science Founda-tion of China (Grant No. 51275250).

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Received March, 16, 2016; accepted for printing November, 1, 2016

1043

BULGARIAN JOURNAL OF AGRICULTURAL SCIENCE - VOLUME 22Author index

AAbid, M. – 415Abui , O. A. – 1006Adamczyk, F. – 165Adamowski, J. – 655Akhtar, S. – 470Aksoylu, Z. – 324Aktas, M. – 303Aladjadjiyan, A. – 857Alavikia, S. S. – 426Aleksieva, K. – 1010Alexandrov, V. – 485 Alexieva, I. – 857Al-Ghzawi, A. L. A. – 897Al-Kofahi, S. D. – 897Al-Rawashdeh, I. M. – 897Altarawneh, M. – 10Altunlu , H.- 665 Antova, G. – 857Apostolov, A. – 144Apostolov, A. – 293Arabska, E. – 527Arslan, C. – 1036Arsoy, D. – 303Atanasov, S. S. – 1014Atanasov, S. S. – 1027Atanasov, V. – 566Atanasova, B. – 125Atanassov, A. – 272Atanassov, A. – 368Atanassov, I. – 584 Atyhanov, A. K. – 318Aydin, L. – 303Ayranci, Y. – 665

BBachar. Kh. D. – 415Baciu, A. – 391 Badjakov, I. – 46Bakhsh, Kh. – 358Balabanova, T. – 643Ballesteros, C. – 548Banov, M. – 573Banov, M. – 912

Banov, М. – 368Baranova, E. N. – 987Barłog, P. – 197Bashir, M. A. – 358Batchvarov, V. – 849 Batchvarova, R. – 437Baudoin, J.-P. – 447 Bazitov, R. – 245Bazitov, V. – 245Beloev, H. – 318Ben Khaled, A. – 415Ben Yahya,V. – 415Bendlin, L. – 691Bernal, H. – 548Bezdiček, J. – 821 Bibbal, D. – 505Bicoku, Y. – 339Biel, W. – 604 Bistrichanov, S. M. – 794Blasco, M. – 40Bojkova, M. – 144Bonfi m, B. L. S. – 869Borisova, A. – 465Boudjerda, D. – 505Boyaci, M. – 151Boyadzhiev, D. – 857Bozadjiev, B. – 331Bozhilova-Sakova, M. – 315Bozhilova-Sakova, M. – 482 Bozhinova, R. – 16Bozhinova, R. – 386 Bres, Wl. – 401Brugère, H. – 505Bruni, M. – 1Bsoul, E. Y. – 897 Buhalova, D. – 857

CCagindi, O. – 324Canestrari, G. – 906Catapan, A. – 869Catapan, M. F. – 869Changying, J. – 655Chincarini, M. – 906

Christov, N. – 437 Christov, N. K. – 987Christova, P. – 437Ciğdem, Z. – 772Cilev, G. – 829DDa Veiga, C. P. – 691Dashchenko, A. – 108Daskalov, H. – 308Daskalov, P. – 318Daskalov, P. I. – 1014Daskalov, P. I. – 1027Daskalova, N.- 262Deshev, M. – 982Dessev, Tz. – 331Dhanushkodi, S. – 627Di Mola, I. – 942Di Vaio, C. – 942Dikova, B.- 108Dimitrov, D. – 216Dimitrov, D. S. – 30Dimitrova, I. – 315Dimitrova, I. – 482Dimitrova, V. – 705 Dimov, K. – 1010Dimova, D. – 114Dincheva, I. – 46Dincheva, Ts. – 91Dinkov,V. – 492 Dolijanović, Ž. – 52Doneva, S. – 262Duclós, L. C. – 691 Dumitru, M. G. – 391Dunich, A.- 108Durakova, A. – 331Dushkova, M. – 492Dyavolova, M. – 999Dyulgerova, B. – 114Dzhamburshyn, A. Sh. – 318

EEskhozhin, K. – 862Etropolska, A. – 98

1044

FFalcone, G. – 517Falta, D. – 796Famiani, F. – 942 Fang, H. – 1036Farahani, L. – 228Farina, V. – 497Farokhzad, A. – 73Fartzov, K. – 368Ferchichi, A. – 415 Firincioğlu, H. K. – 756Fomin, D. – 381Fomin, D. – 921Formigoni, A. – 906 Frąckowiak, P. – 165Fusaro, I. – 906Fusaro, L. – 906Fustini, M. – 906

GGacovski, Z. – 829Galluzzo, N. – 347Galluzzo, N. – 536Gandev, S. – 600Ganeva, D. – 961García-Martínez, Y. G. – 548Genova, K.- 140Georgieva, D. – 857Georgieva, L. – 745Georgieva, M. – 46Georgieva, M. – 745Georgieva, S. – 374Georgieva, St. – 188Ghanbar, T. – 73Ghoudsi, M. – 976 Giammarco, M. – 906Giannetto, C. – 705Gjeci, G. – 339Gogova, Ts. – 331Gospodinov, I. – 245Gramenzi, A. – 906Grcević, M. – 297Grzebisz, W. – 197Gubatov, T. – 927Gudev, D. – 999 Gulisano, G. – 517Guneri, M. – 591Gunes, N. – 303Gurova, E. – 308

HHadzhy, A. – 673Hajiyev, N. G.-O. – 875 Hamidi, A. – 836Hanif, Ch. M. Sh. – 470Hanuš, O. – 286Hanuš, O. – 796Hashmi, M. S. – 358Hasoňova, L. – 796Hosseini, B. – 73Hosseini, N. M. – 936Hossienbor, Z. – 955Humbatova, S. İ. – 875

IIantcheva, A. – 783 Iantcheva, A.- 253Igras, J. – 752 Ijaz,V. – 470 Imami, D. – 339Inglese, P. – 497 Irene De Luca, A. – 517Isfendiyaroglu, M. – 772Ishpekov, St. – 982Isuf, E. – 600Ivanov, A. – 368Ivanov, G. – 643Ivanov, M. – 442Ivanov, M. – 968Ivanova, M. – 643Ivanova, S. – 135Ivanova, S. – 849Ivanova, T. – 158Izambaeva, A. – 331

JJabbarzadeh, Z. – 73Jarausch, B. – 98Jarausch, W. – 98Jestrovic, Z. – 119Ji, C. – 1036Jian, S. – 1036Jiménez- García, D. – 548 Jiménez-García, L. – 548Jomantas, Z. – 477 Juhos, K. – 209Jukna, V. – 627Juma’a, K. A. – 897

KKakabaev, N. – 862 Kalchev, R. – 485Kalcheva, H. – 485Kamenova, I. – 267Kamenova, I. – 465 Kamran, M. A. – 358Kanev, D. – 135Kaneva, Kr. – 176Kapchina-Toteva, V. M. – 767 Karadjova, O. – 619Karaivanov, D. – 862Karatoteva, D. – 580Karatoteva, D. – 728 Karatoteva, D. I. – 26Karsznia, M. – 752Kaya, I. – 995Khaliluev, M. R. – 987Khan, Gh. A. – 513 Khodshenas, M. A. – 228Kistanova, E. – 815Koleva, A. – 331Kondakova, V. – 46Kondakova, V. – 745 Kornov, G. – 600Kose, E. – 324Kosolapova, A. – 381Kosolapova, B. – 921Kostadinova, G. – 566Kostova, D. – 961 Кoteva, V. – 245 Koutev, V. – 397Kowalewska-Łuczak, I. – 131Kozludzhova, S. – 492Kračmar, S. – 286Kralik, I. – 297Kralik, Z. – 297Krasteva, А. – 331Krusteva, H. – 619Krzebietke, S. – 722Krzymińska, A. – 79Krzyżaniak, M. – 65Kudlawicz-Franco, C. – 691Kukusheva, А. – 948Kulig, H. – 131Kulynych, M. – 182Kurenina, L. V. – 987Kurzawińska, H. – 458

1045

LLak, M. R. – 228Lakis, Ch. – 733Łakomy, P. – 131Lanfranchi, M. – 705Lazarova, Ts. – 91Lehouel, M. – 505Liguori, G. – 497Lodhi , T. E. – 513Loncarić, Z. – 297MMadarasz, B. – 209Malard, J. – 655 Malinov, I. – 205Malinova, L. – 21Malinova, L. – 580Malinova, L. – 728Mambetnazarov, A. B. – 250Mansour, E. – 415Marchev, Y. – 144Marchev, Y. – 815Marcheva, M. – 452Marcheva, M. P. – 778 Marinova, G. – 849Markova, D. – 91Masheva, S. – 91Mashhadi, H. R. – 936 Matouke, M. M. – 1006Mazur, S. – 458Medvedkov, Е. B. – 840 Mehmedov, T. – 140Miemon, M. S. – 1036 Mihajlov, L. J. – 125Mihaylova, G. – 566Mikos-Szymańska, M. – 752Milošev, D. – 52Mishchenko, L. – 108Miteva-Petrova, M. – 492Mitova, I. – 912Mitova, Iv. – 573Mitrofanova, E. – 381Mitrofanova, E. – 921Mokreva, T. – 234Moneva, P. – 999Mpokos, P. – 733Muhammad, Sh. – 513Mutlu , Z. – 756

NNacheva, I. – 1010Nadziakiewicz, M. – 458 Najgebauer-Lejko, D. – 1021 Nakev, J. – 815Nanev, I. – 600Nawrocki, J. – 458 Naydenov, M. – 91Nedeva, R. – 135Nedeva, R. – 144Nedeva, R. – 815Nedeva, V. I. – 1014Nedeva, V. I. – 1027Němečkova, I. – 796Nenov, M. – 397 Nenova, L. – 912 Nikolić, L. J. – 52Nikolic, O. – 119Nikolova, K. – 857Nocerino, S. – 942Nukeshev, S. – 862

OOgunremi, J. B. – 543Otávio Senff, C. – 691Ozeker, E. – 772Ozubek, S. – 303Ozuicli, M. – 303

PPacinovski, N. – 829Palmonari, A. – 906Papanikolaou, K. – 733 Papazafeiriou, A. Z. – 733Pasari, B. – 955Pasev, G. – 961Pavlovic, M. – 119Penchev, P. – 144Pepliński, K. – 197Peteva, Zl. – 188Peteva, Zl. – 374Petrov, G. – 673Petrov, S. – 492, Petrovska, B. – 829Phan, T. D. – 286Pitacas, F. I. – 40Politycka, B. – 401Popova, T. – 815

Popova, T. P. – 103Pourmohammad, A.- 426 Pozdišek, J. – 286Pronina, Yu. – 840Prusevichus, V. – 627Pużyński, S. – 604

QQishuo, D. – 655

RRadeva–Ivanova, V. – 961Radišić, Ž.- 297Ramazani, S. H. R. – 976Raycheva, E. – 158Reis, C. M. G. – 40Revalska, M. – 253Revalska, M. – 783Ribikauskas, V. – 477Ribikauskienė, D. – 477Řiha, J. – 821Rodrigues, A. M. – 40Rogova, M. A. – 767Rokhzadi, A. – 955 Roubal, P. – 286Roubal, P. – 796Roukos, Ch. – 804 Rousseva, S. – 205Roversi, Al. – 171Roychev, V. – 234Roychev, V. – 442 Roychev, V. – 968 Rusek, P. – 752Russo, R. – 942

SSabet, M. – 936Sabkov, H. – 158Saffari, M. – 60Sagheer,V. – 470Sagyndykova, A. Zh. – 318Saleem, Sh., – 470Samkova, E. – 796Sankibaev, T. – 862Santucci, F. M. – 1Saray, M. – 995 Sarsu, F. – 447Sarsu, F. – 91

1046

Savlak, N. Y. – 324Savov. P. R – 600Selcuk, O. – 303Serbezova, D. – 600 Šeremešić, S. – 52Shafea, L. – 60Shakiba, M. R – 426 Sharafi , A. – 73Shernienė, L. – 627Shimkienė, Al. – 627 Shimkus, Al. – 627Sienkiewicz, S. – 722Sienkiewicz-Cholewa, U. – 752Simeonov, I. – 234Simeonov, M. – 278Simeonovska-Nikolova, D. – 740 Simkus, Al. – 815 Simões, O. A. – 869 Šipalova, M. – 286Škrtić, Z. – 297Šlachta, M. – 796Smirnova, Е. А. – 987 Śnieg, M.- 65Sobolewska, M. – 604Sofkova-Bobcheva, Sv. – 447Sortino, G. – 497Souza, Al. – 691Spada, E. – 517Spasov, D. – 125Spasova, D. – 125Spetsov, P.- 262Stamatov, St. – 982Stancheva, M. – 188Stancheva, M. – 374Stancheva, N. – 315Stanev, St. – 584Stankowski, S. – 604Starzyk, J. – 401 Stefanou, S. – 733Stefanova, V. – 205Stepanov, A. – 948 Sternik, P. – 722 Stillitano, T. – 517Stimbirys, A. – 627Stoilova, A. – 125Stolarski, M. J. – 65Strano, Al. – 517Stratev, D. – 308

Stuogė, I. – 477Suchla, E. G. – 869Sudhakar, K. – 627Sylejmani, D. – 836 Szczepaniak, J. – 165Szczepaniak, W. – 197Szczukowski, St. – 65Szostak, B. – 135Szostak, B. – 293

TTabaszewska, M. – 1021Tagar, A. – 655Tagar, A. A. – 1036Tajalli, H. – 976Terziev, V. – 527Terziyski, D. – 485Teterlev, I. – 381 Teterlev, I. – 921 Thakur, N. – 84Todorov, N. – 278Todorovska, E. G. – 987Tomlekova, N. – 447Tomlekova, N. – 91Tomov, R. I. – 103Toncheva, G. – 857Toorchi, A. – 426Trelka, T. – 401Trenchev, G. – 98Trencheva, K. G. – 103Tsenov, N. – 927 Tsolova, V. – 573 Tsvetkov, I. – 745Tsvetkov, Ts. D. – 673Tsvetkov, Tsv. – 1010 Tuna, A. L. – 591Tworkowski, J. – 65Tzonev, R.- 222Tzonev, T. – 315

UUğurlu, M. – 995Ul-Hasan, M. – 470Ünal, S. – 756

VVatchev, T. D. – 794Valcheva, D. – 114

Valkova, N. – 125Valkova,V. – 566Vashin, I. – 308Vasile, N. I. – 391Vasilev, E. – 222Vasileva, S. – 452Vasileva, V. – 222Vasileva, V. – 573Vasiljević, M. – 52Vassileva, V. – 253Vassileva, V. – 783Vatchev, T. D. – 993Velcheva, N. – 272Velichkova,V. – 566Verter, N. – 713 Vicha, R. – 286Vidinova, E. – 158Vignola, G. – 906Villarreal, O. – 548Vlaseva, R. – 643 Vutov, V. M. – 30Vyletělova-Klimešova, M. – 796

WWalorska, U.-M. – 79Wierzbowska, J. – 722Wilson, V. H. – 627Witkowski, P. – 293Wojdyła, A. T. – 611

YYamaltdinova, V. – 381Yamaltdinova, V. – 921Yanashkov, I. T. – 794 Yanashkov, T. – 993Yanchev, I. – 927Yanchev, I. – 999Yancheva, S. – 46Yankova, V. – 91Yanti, F. – 431Yerenova, B. Ye. – 840Yiakoulaki, M. – 733Yildiz, E. – 278Yildiz, O. – 151Yildiztekin,V. – 591Yokas, I. – 591Yordanova, G. – 815Yordanova, Zh. P. – 767

1047

Yurdugül, S. – 647

ZZagorcheva, Tz. – 584Zaykov, R. – 982

Zehirov, G. – 253Zehirov, G. – 783Zhang, Q. – 1036Živanov, M. – 52Żukowski, K. – 131

Zulfahmi, J. – 431 Zwolak, J. – 182Zwolak, J. – 893 Zydlik, P. – 408Zydlik, Z. – 408

From the beginning of 1995 the Agricultural Academy in Bulgaria is publishing Bulgarian Journal of Agricultural Science (BJAS) - the first agricultural scientific journal in Bulgaria for fundamental and applied researches, pub-

lished entirely in English language, and one of the few such journals in Central Europe.Bulgaria is an agricultural country with traditions and long standing experience in the development of agrarian

science and production. BJAS, printing in English, in accordance with international standards, provides possibili-ties for Bulgarian agricultural science to enter adequately into the worlds scientific field, to find its place in reviews, abstracts and electronic means for processing and transfer of scientific information. Besides scientific articles pro-

vided in Bulgarian universities and research institutes, BJAS publishes also articles from Eastern Europe and other countries all over the world. The Editorial board of the journal includes prominent scholars from United Kingdom,

Belgium, Slovenia, Italy, Poland, Hungary, Germany, Greece, Czech Republic and Bulgaria.

THE JOURNAL IS INDEXED BY:Abstr. Hyg., AgBiotech, Agri. Eng. Abstr., Anim. Breed. Abstr., Bio-Contr. News & Info.,

Crop Physiol. Abstr., Dairy Sci. Abstr., Field Crop Abstr., Food Sci. & Tech. Abstr., Forest Abstr., HelminthoL Abstr., Herb. Abstr., Hort. Abstr., IMS Atomind., Ind. Vet., Irr. & Drain. Abstr., Maize Abstr., Nutr. Abstr.,’Ornam. Hort., Pig News & Info., Plant Breed. Abstr., Plant Gen. Res. Abstr., Plant Grow. Reg. Abstr., Postharvest, Potato

Abstr., Poult. Abstr., Rev. Appl. EntomoL, Rev. Med. & Vet. Mycol., Rev. Plant Path., Rice Abstr., Seed Abstr., Soils & Fert, Soybean Abstr., Triticale Abstr., Vet. Bull., Weed Abstr., World Ag. Econ. & Rur. Soc. Abstr.

Editorial Board of BJASContact address: Bulgarian Journal of Agricultural Science

125, Tsarigradsko shosse Blvd.; Bl. 1, Room 214, 1113 Sofia, Bulgariae-mail: bjas_sb@abv.bg

NOTE TO CONTRIBUTORSTypes of papers, published in the journal:- papers reporting results of original research- short communications- reviews- A detailed Guide for authors is printed in the first issue to appear each year (see the web page of BJAS).Acceptance of manuscriptsAfter the receiving the opinions of the Editorial board expert, the editor-in-chief decides on acceptance of the articles,

necessary corrections or revisions. The day the manuscript reaches the Editorial Secretariat for the first time is given upon publication as the date of receipt; the day of the editor-in chief decision is given as the date of acceptance for printing.

Text(a) The manuscript should begin with an abstract of not more 250 words or 10% of the paper(b) The first page should include the title, author’s names and their affiliations (c) The text should include Introduction, Materials and Methods, Results, Discussion, Conclusion, Acknowledgements

(if any) and ReferencesReferences(a) The references in the text should be cited as the name of the first author plus “et al.”, followed by the year of pub-

lication(b) The reference list should be in alphabetical orderTables(a) The tables should be as simple and as few as feasible for the presentation of the essential data. They should be in

Word or Excel program and in separate files, not in the text(b) Explanations essential to the understanding of the table should be given at the bottom marked in an appropriate

wayElectronic manuscriptsYour disk should be submitted to the editorial secretariat or the article should be send by e-mailThe preferred word-processing packages are Word, WINDOWS