EFFECT OF DIFFERENT TILLAGE METHODS ON BULK DENSITY, PENETRABILITY AND AGGREGATE SIZE DISTRIBUTION ON A CLAY SOIL.

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1 EFFECT OF DIFFERENT TILLAGE METHODS ON BULK DENSITY, PENETRABILITY AND AGGREGATE SIZE DISTRIBUTION ON A CLAY SOIL. KACEMI M. (1) H. HILALI (1) AND G. MONROE (1) RESUME EFFET DE DIFFERENTS TYPES DE TRA VAUX DU SOL SUR LA DENSITE APPARENTE, LA RESISTANCE A LA PENETRATION, ET LA DISTRIBUTION DE LA TAILLE DES AGREGATS DANS UN SOL ARGILEUX ABSTRACT The present study was conducted to evaluate the effect of different tillage methods on sorne soil physical parameters. Tillage treatments involved the blade implcment "Dutzi" (D), the paraplow "Culti-vie" (CU), the stubble plow (SP), the disk plow (CD), the moldboard plow (CS) and no-till (NL). Secondary tillage consisted of zero (CCO), two (CC2) and three (CC3) offset disk passes. Measurements were taken for bulk density, penetration resistance, aggregate size distribution, and moisture. Bulk density values were signilicantly different among tillage methods at the 15 cm depth. The Dutzi maintained a constant and smaller Bd in the upper 20 cm compared to that of the other tillage implements, for which the Bd was b~sically identical. Beyond the 15-cm depth, SP and NL tended to present higher Bd than the other tillage methods. TIle secondary tillage effect on Bd was confined to the upper 10 cm. Cone index values from the 0 to 10 cm, and 40 to 50 cm depths were not significant among tillage methods. Howevcr, between the 5 and 35 cm soil depths the differences were highly significant. On the average NL, SP and D had consistently higher cone index values than CU, CS and CD. TIle reported cone index differences between these two groups is related to the depth of the primary tillage, and suggests the persistence of the high zone strength with D and S below 15 cm depth. The moldboard plow (CS) maintaincd consistently lower CI, whereas NL had consistently higher CI over the 0 to 50 cm depth. Dry-mean weight diameter was not signilicant among tested tillage systems. La présente étude avait comme objectif d'évaluer l'effet de différents types de labour sur quelques propriétés physiques du sol. Les outils de travail du sol testés étaient comme suit: un outil il lame dit "Dutzi" (D), un outil à dent courbées dit "Cul ti-vie" (CU), le stubble plow (SP), la charrue à disques (CD), la charrue à soc, et le non-labour (NL). Les travaux de reprises consista'ent en: zéro (CCO), deux (CC2) et trois (CC3) passages au "covercrop". Les mesures entreprises consistaient en la densité apparente (Bd), la résistance à la pénétration (CI), la distribution de la taille des agrégats du sol (MWD), et l'humidité du sol. Les densités apparentes différaient singnificativement d'un travail de sol à un autre au niveau de 15 cm de profondeur. Le D a maintenu une Bd constante au niveau des 20 premiers cm du sol par comparaison aux autres types de labour. Au delà de 15 cm de profondeur, le SP, et le NL tendaient à présenter des valeurs élevées de Bd par rapport au reste des types de travaux du sol. L'effet des labours de reprise sur Bd était limité au 10 premiers cm du sol, sans toutefois qu'il y ait une différence entre deux et trois passages au covercrop. La résistance à la pénétration (CI) était significativement différente entre les types de travaux du sol testés, dans l'interval de profondeur 10 et 40 cm. Ces différences n'étaient pas significatives au niveau des profondeurs 0-10 et cm. En moyenne, le NL, SP et D avaient constamment des valeurs de CI élevés par comparaison il ceux observés pour CU, CD et CU. Les différences en terme de CI entre ces deux groupes de types de travaux du sol étaient liées essentiellement à la profondeur à laquelle le sol était travaillé, et suggèrent que le SP et D seraient incapables d'affecter la densité de la couche du sol en deçà de 15 cm. Le travail du sol secondaire avait un effet significatif sur CI au niveau des premiers 10 cm de la surface du sol. Deux et trois passages de covercrop, pour lesquels CI étaient le même, ont significativement réduit la résistance à la pénétration par rapport il la situation où il n'y a pas eu de passage de covercrop. Les résultats relatifs il la distribution de la taille des agrégats du sol inférieurs à 10 mm, mesurées en terme de diamètre pondéré moyen (MWD), n'a pas révélé de différences significatives entre les types de travaux du sol testés. (1) Institut National de Recherche Agronomique - Settat.

2 INTRODUCTION Tillage generally improves soil conditions for plant growth, especially under the circumstances where the soil presents zones of high strength and compaction. However, tillage may also exert adverse effect on soil conditions when it is performed in less than adequate soil moisture, or when inadequate tillage implements are used. Campbell et al (1974) found that the chisel was the most effective at disrupting soils with localized high strength, such as plow pans. Bauder et al. (1981) indicated that inversion plowing provided the most effective way to remove compaction of soils with initially uniform strength. They reported that under such circumstances moldboard plowing yielded lower mechanical resistance than the chisel plowing. Disk tillage while effective in removing soil crust, tends to compact the soil (Taylor and Burnett, 1964), which results in zones with high soil strength. Bulk density and penetration resistance are the widely used soil physical parameters to assess soil loosening or compaction in tillage studies. The difficulty in using bulk density to investigate soil strength or detect tillage depth is related to the fact that it is a tedious and time consuming method. Second, several reports have indicated contrasting results as to the effect of tillage on bulk density. Blevins et al. (1983a) reported that tillage had~no effect on bulk density after a 10-year period of tillage treatments on a medium textured soil. However, other studies have reported a drastic increase in bulk density with no-till compared to moldboard plowing of a clay loam soil (Griffith et al. 1977; Gantzer and Black, 1978). Blevins et al. (1983b) found similar bulk density values with conventional and no-till systems and smaller bulk density with chisel tillage on a poody drained soil. Resistance ta penetration was, however, much more effective in detecting zones of soil strength, depth of tillage and the extent of tillage induced soil loosening or compaction and the degree of their persistence over time. Carter (1988) measured mechanical resistance in a tillage study and found that moldboard plowing produced more soil loosening than chisel plowing in a loam ta sandy loam sail. He reported that the depth of tillage declined over a period of five months by 30 and 60 %, respectively for the moldboard and the paraplow. Pelgrin et al. (1990) reported that bulk densities, measured three weeks after tillage application, were similar in the upper 20 cm of a sandy clay loam where tillage was done with disk plow, moldboard plow, cultivator, disk harrow, and no-till. He indicated that bulk density values increased with time and were significantly higher in no-till, dise plow, and cultivator than moldboard plow and disc harrow. He also, reported that sail penetration resistance, measured immediately after tillage application, was identical among tillage treatments in the upper 15 cm, and significantly different between 15 and 40 cm depth. Dorenko (1924) and Kvasnikov (1928), cited by Braunack and Dexter (1990), reported maximum wheat yields with seedbeds of 2-3 mm aggregates. Jaggi (1972) concluded that a seedbed of 1-2 mm aggregates with a dry bulk density of glcm3 would give the best wheat grain yield on a clay soil. Braunack and Dexter (1988) found that intermediate size aggregates (2-3 mm) resulted in earher emergence and higher wheat yields than with larger aggregates (> 4mm) on a loam soil. Piner aggregates «Imm) tend to restrict aeration and reduce emergence under more wet soil conditions, but result in earlier emergence in drier years (Braunack and Dexter 1988). The objective of the present study was ta evaluate the effect of contrasting tillage treatments on soil bulk density, mechanical resistance and aggregate size distribution measured as mean weight diameter, and also to identify the tillage treatments that are more likely ta affect favorably the soil loosening condition of this clay soil. MATERIALS AND METHODS The study was initiated in at the experiment station of Allal Tazi (340 TN, 50 8'W), Morocco. The soil, of clay type, is poorly drained and experiences a lot of compaction that would hinder the growth of root crops like sugarbeet. The particle size analysis shows that it has 12 % sand, 30 % silt, and 58 % clay. The experiment was laid 97

3 out as a split plot design with three replications. Tillage methods were assigned to the subplots, and include the blade tillage implement "DUTZI" (0), paraplow cailed "Culti-vie" (CU), moldboard plow (CS), three-disk plow (CD), stubble plow (SP), along with the no-till system (NL). Secondary tillage, applied to the whole plots, consisted in zero (CCO), two (CC2) and three (CC3) offset disk passes. The size of the whole plot and subplot was 20 X 74 m and 20 x 9 m, respectively. Tillage depth was 15 to 20 cm with the stubble plow, 30 to 35 cm with the moldboard plow and Culti-vie, 20 to 25 cm with the Dutzi and the disk plow. Secondary tillage depth was 10 to 15 cm and was accomplished with measured to evaluate the aggregate size distribution. Soil samples, taken from 0 to 5, 5 to 10, and 10 to 15 cm depths using a shovel, were air dried, passed through a 1O-mm sieve, and then subjected to a 5-minute sieving period through a 5, 4, 2, 1, and 0.25 mm series of sieves, mounted on, a portable sieve shaker. AlI measurements were undertaken in two repli cations and data were analyzed using the analysis of variance procedure and the least significant difference method available in the SAS program. RESULTS AND DISCUSSION the offset disk. The measurements of bulk density, Bulk density data as affected by tillage resistance to penetration and mean weight diameter methods are reported in table 1. The same data are were done two months after tiilage application, depicted in figure 1. There were significant period during which the weather was unusuaily dry. differences in bulk density values among tillage Bulk density was measured at 10, 20, 30 and 40 cm treatments at the 15 cm depth. The Dutzi depths along a transect perpendicular to the tillage maintained a constant and smailer Bd in the upper direction with a double-eylinder, hammer-driven 20 cm compared to the bulk density values of the sampler. Soil moisture to 40-cm depth was other tillage implements or notill treatment. At the determined at the same time. Soil resistance to 35 cm depth CS and CD had the lowest Bd penetration was measured from 0 to 50 cm depths compared to ail other tillage treatments. SP had in a 5-cm Increment along a transect perpendicular higher Bd than NL from 10 to 35 cm depth, but the to the tillage direction by means of a hand-held difference between these two tillage methods was penetrometer manufactured by HCH Inc. in not significant. Such a result was not expected, Russelville, Kentucky, USA The cone had a because of the high compaction this clay soil standard 1.3 cm2 base area, and the penetrometer undergoes when left untilled. There may be more rod ailowed a maximum depth of measurement into hardpan formation with SP than any of the tillage the soil of about 50 cm. The penetrometer gauge methods that were tested. Secondary tillage had a had a scale in bars, and cone index values were significant effect on Bd at the 5 to 10 cm depth obtained using the multiplication factor of 77 found layer, which is in agreement with the depth of after the calibration of the penetrometer, secondary tillage using the harrow disk. There was calibration which was performed using an accurate no effect on Bd between 2 or 3 passes of the harrow platform scale. Mean weight diameter (MWD) was disk for the preparation of seedbed. Table 1 : Bulk density as affected by tillage on a clay soil at Allal Tazi, Morocco NS CUSP CDNL 1.52 CS Depth (cm) 1.42 Tillage methods D=Dutzi, CU=Culti-vie, SP=Stubble plow, CS=Moldboard plow CD=Disk plow, NL=No-till NS means not significant; means significant at the probability level of 0.05.

4 l'~ Bt:ilk denslty ( g/cm3). ~ c t(l ,,~. '0,," - - -,,\..., ~ '-; ~,~:.\:---., 1\ ~Q. 1 \... :'. \... 1 \ 1 \....,,~ " l "1 \. " \' " '\ \ ", \ "\' \ '\~ ",.\ }. "8.., ~ '0 Figure 1. Effeet of different tiiiage methods on bulk density of a clay soil al Allal Tazi, Morocco, (0 Outzi, CU Culti-vie SP Stubble plow, CS Moldboard plow, CD Disk plow and NL No-till). c lj i (l l: Cone Index (!<Pa) Figure 2. Effeet of different tillage methods on penetration resislance of a clay soil al Allal Tazl, Morocco. (D Ou1zl, SP Slubble plow, CS Moldboard plow, CD Disk plow CU Cultivle, and NL No-lill ).

5 Observed cone index values under tested tillage methods are reported in table 2. The data are depicted in figure 2. The resistance to penetration trom 0 to lü cm, and trom 40 to 50 cm depths were not significant among tillage methods. However, between the 5 and 35 cm soil depths, the differences were highly significant. On the average, NL, SP and o had consistently higher cone index values than CU, CS, and CO. The difference between these two groups in term of cone index values, is related to the depth of the primary tillage, and not to the differences in soil moisture because soil water content under ail the tillage methods was identical in the upper 50 cm depth. Similar results from a study conducted on a clay loam soil were reported by Bauder et al. (1981). They found small CI in the moldboard tilled plots, intermediate CI in chisel plowed plots, and finally high resistance in the no-till plots or disk tilled plots. Aggregate size distribution data, measured in term of MWD (mm) for aggregates less than 10 mm, are reported in table 3. There were no differences among tillage methods for MWD. Such a result was not expected. It may be due to bad sampling method and/or to the way aggregates were hand broken prior to the lü-mm samples sieving, or simply due to the short history of tillage treatments. Bulk density data do not seem to agree totauy with the resistance to penetration data. However, mechanical resistance appears to reflect a genuine picture in term of soil loosening and strength conditions th an the observed bulk densities. The high cone index values observed in plots tilled with the stubble plow, values that are not significantly different from those of no-till, suggest the presence of a plow pan at 15 cm depth with this tillage method. These data are in agreement with the tillage history at Allal Tazi station, where the stubble plow was the common primary tillage implement in use for several years. Soil compaction is commonly induced by disk tillage implements (Taylor and Burnett, 1964), especially when tillage is do ne under moist soil conditions. Soil structure of the upper 20 cm depth of the plots tilledwith the Outzi was better compared to that of au other plots tilled with any of the tested tillage implements. Field observations of wheat stand NS NS cusp CDNL CS Depth Tillage (cm) methods Table 2 : Resistance to penetration as affected by tiiiage on a clay soil at Allal Tazi, Morocco~. D=Dutzi, CU=Culti-vie, SP=Stubble plow, CS = Moldboard plow, CD=Disk plow, NL=No-till. NS = not significant, = significantat 0.05, and = highly significantat 0.01 and probabilities,respectively. 100

6 CCO E 10 ' " <.13>.,',,.. " ( kpa) Cone index 5000 ~Ç>"...~ < J (,) ~ ,{;,--_ Cl 30 CC2 CC3. El Q) ~ Figure 3. Effect of offset disk passes on penetration resistance of a clay soil at Allal Tazi. Morocco. (CCO = Zero passe. CC2 = Two offset disk passes. CC3 = Three offset disk passes). Table 3. Dry-mean weight diameter (MWD)of aggregates < 10 mm as affected by tillage on a clay soil at Allal Tazi, Morocco. Depth (cm) D cu SP Ti}lage methods cs CD NL 0-5 means significant. CS=Moldboard CD=Disk not plow NS CU=Culti-vie, plow, plow, NSP=Stubble mm 101

7 indicated better crop establishment with the Dutzi than with any other implement. However, the data indicated that such an implement was unable to reduce soil strength below the 20 cm depth (figure 2). Root growth could be hindered below this depth when using either the Stubble plow or the Dutzi. When considering the cloddy rough surface generally created when this soil is tilled with the moldboard plow or the disk plow, rough surface which requires more passes with the disk harrow to break the clods and level the soil, thus increasing the chances of more compaction due to traffic, the paraplow appears to be the appropriate implement to use in any similar high strength clay soil. The main disadvantage of using the paraplow is that it requires a lot of traction power. CONCLUSION penetration The data show that the resistance to is a much more accurate method than the bulk density measurement in the assesqment of soil loosening induced by different tillage methods. ln such a high clay content soil, the moldboard plow, the three disk plow, and the paraplow provided better soil loosening conditions up to 35 cm depth than the Dutzi and the stubble plow. However, when other considerations are taken into account, espeeially the high risk of soil compaction as a result of more traffic to break the clods generated with the moldboard and disk plow, the paraplow seems to be the appropriate tillage implement because it does not invert the soil. REFERENCES BAUDER, J.W., G.W. RANDALL, AND J.B. SWANN Effect of four continuous tillage systems on mechanical impedance of a clay loam soil. Soil Sci. soc. Am. J. 45: BLEVINS, RL., SMITH, M.S., THOMAS, GW. AND FRYE, W.W. 1983a. Influence of conservation tillage on soil properties. J. Soil Water Conserv. 38: BLEVINS, RL., SMITH, M.S., THOMAS, GYV., FRYE, W.W, AND CORNELIUS. 1983b. BRAUNACK, M.V. AND DEXTER, AR BRAUNACK, M. V. AND DEXTER, AR Changes in soil properties after 10 years continuous non-tilled and conventionally tilled corn. Soil tillage Res. 3: The effect of aggregate size in the seedbed on surface crusting and growth of yield of wheat (Triticum eastivum, L. ev. Halberd) under dryland conditions. Soil Tillage Res. 11: Soil aggregation in the seedbed: A review. Sail Tillage Res. 14: CAMPBELL, RB., B.e. REICOSKY, AND e.w. DOTY Physical properties and tillage of Paleudilts in the eastern Costal Plains. J. Soil Conserv. 29: CASSEL, D.K, RD. BOWEN, AND L.A NELSON An evaluation of mechanical impedance for three tillage treatments on Norf0lk sandy loam. Sail Sei. Soc. Am. J. 42 :

8 GANTZER, c.j. AND BLACKE, G.R Physical characteristics of le Sueur clay loam soil following no-till and conventional tillage. Agron. J. 70: GRIFFITH, D.R., J.V. MANNERING, AND W.c. MOLDEHAUER Conservation tillage in the eastern Corn Bell. J. Soil Conserv. 32: JAGGI, I.K. GORANTIW AR, S.M. AND RHANNA, S.S TAYLOR, H. M., AND E. BURNETT Effect of bulk density and aggregate size on wheat growth. J. Indian Soc. Soil Sei., 20: Influence of soil strength on the root-growth habits of plants. Soil Sei. 98: PELGRIN, F. F. MORENO, J. MARTIN-ARANDA AND M. CAMPS The influence of tillage methods on soil physical properties and water balance for a typical crop rotation in SW Spain. Soil Tillage Res. 16: sert-maroc ~ ~,.-i.-.j1 ~ ~ J ; ~ ~ ~ _~.r---j l ~ ~----:.JJ SOCIETE CENTRALE POUR L'EQUIPEMENT DU TERRITOIRE _ MAROC SCET.MAROC Soc,.I< anonym< au cap,tal d< 3 &l(,0000f-: RABAT -<1(07) 3)0 21 / / 30" 1.9 / :J. 2C )0 (hùrlq AI A\aouYlnf _ RABAT _ T~ltx n~ 3' 9CJ' M F,,~,< CAISSE DE OEPOT fol DE GE::,TION '- L G' NIVEAU DES ETUDES RoAvant. E 'uj( G~ne-rQlf'::. _ P!er.s [lfil h'urs FO(i1bd\tc Avent projet C;OrT,rr,Clr~ nn Ahmentatlon en eo'j potal>lf (Ad~\.Jctlon. distribution) A~.;al::1S5tmlr.t Traite:rren! d'c'.j'j potctle: (1 'Jsct.Statlons de':pompo,]e':s Equlf:~menl proj~te:~tal~:r:~~'~~cdt~~<ec~"~~baines d< lotisstrr <nt s YRO DEPT DEVELOPPEMENT :.GRICOLE ET RESSOURCES EN EAU Inventaire des ressources ln lcu Pt001ogli" Ci (~CSSt"rTe.n! cje.s sols I;,ventc.:re,:> culturaux [tllrl!s agrce.conomlques_ Arr~r'lp_ gemfnts hydroag"co:!s Barrcges colllnqlrcs OuvrGge:s hyd raul1quf's OEPT. BATIHEt-<T - BE TON ARM E Tout.s <Iude, ba\im.nls lous corp~ d'<lcl Ens<mbl<s 'mmobli ius _Complex.s_ Hol"ll,trS.1 touristiqu.s..ens.mbl.s Hospitali<rs _ Ensembles Industric~s Programmes ~ EducallOr. Lyct<S iechniqu<s_ Facult< sen 5 E! - ::- DossiHS d. consultation d.s.ntr<pris<s Control. g<ntrai d.s travaux œ"o"~:f;~~[,~ii:~~;~;;;;;;,~ CELLULE TRAVAUX PUBLICS ET OUVRAGES 0 'ART E~ujfS routlfrcs route.s nouv '!\e.s Con1ort~molnt d rc'j!:-,e.nagcllq-nt ;-outes ~xi5~antr'.:. C'Jrr""O'Jrs ouvrc]","',_ ;.>ûrt'jgîres et 1errovialr'ls. OlJvrag(',:, dnr~ CELLULE INFORMATIQUE R~alÎsalion (t e.xl='!oi~ation de logicliis en g<sllon <1 calcul sci<ntifiqu<-mis< e.n I='lace de syste;nes organisatlone.:ls ilt informatiquf's ]03