Soil & Tillage Research, 16 (1990) 337-344 337 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Conventional- and No-Ti l lage Effects on Upper Root Zone Soil Conditions*

PAUL W. UNGER and LARRY J. FULTON

U.S. Department of Agriculture, Agricultural Research Service, Conservation and Production Research Laboratory, Bushland, TX 79012 (U.S.A.)

(Accepted for publication 20 December 1989)

ABSTRACT

Unger, P.W. and Fulton, L.J., 1990. Conventional- and no-tiUage effects on upper root zone soil conditions. Soil Tillage Res., 16: 337-344.

One major objective of tillage is to loosen a soil and, thereby, create an improved soil condition for water infiltration, crop establishment, and plant growth. This implies that where tillage is not performed, as with no-tillage, soil conditions might be inferior to those of a tilled soil. However, no major adverse effects of no-tillage on soil conditions have been noted in the semiarid region of Texas. Also, crop yields on dryland have been favorable. This study was conducted to determine the effects of conventional- and no-tillage crop production methods on water retention, organic matter concentration, mean weight diameter of water-stable aggregates, bulk density, and pene- trometer resistance of Pullman clay loam (Torrertic Paleustoll) at Bushland, Texas. These factors were significantly affected, but there was no consistent advantage or disadvantage for either tillage method. Wheat (Triticum aestivum L. ) and grain sorghum (Sorghum bicolor (L.) Moench)yielcls have been favorable in the dryland rotation fields that were sampled for the soil measurements. Grain sorghum yielded 5.10 Mg ha-1 of grain with conventional tillage and an average of 5.32 Mg ha -~ of grain with no-tillage in 1987, the year in which the soil conditions were evaluated. The favorable yields indicate that no-tillage management does not adversely affect any of the measured Pullman (Torrertic Paleustoll) soil physical conditions to the point that crop yields are adversely affected.

INTRODUCTION

One major objective of tillage is to loosen a soil and, thereby, create an im- proved soil condition for water infiltration, crop establishment, and plant growth. This implies that where tillage is not performed, hs with no-tillage, soil conditions might be inferior to those of a tilled soil. Tillage disrupts crusts, alleviates compaction, and increases porosity, which increase infiltration and

*Contribution from USDA, Agricultural Research Service, Conservation and Production Re- search Laboratory, P.O. Drawer 10, Bushland, TX 79012, U.S.A.

0167-1987/90/$03.50 © 1990 Elsevier Science Publishers B.V.

338 P.W. UNGER AND L.J. FULTON

reduce runoff and soil losses thus contributing toward improved soil and water conservation. Improved water conservation is highly desirable for dryland crop production in rainfall-deficient regions. Crop production in such regions also may be enhanced by tillage that disrupts soil layers that restrict root growth and, consequently, uptake of water and nutrients from beneath the restricting soil layers.

Lower bulk density, penetration resistance, or compaction or higher water infiltration on conventional tillage than on conservation (reduced- or no-til- lage) areas were reported by Dickey et al. (1983), Hamblin et al. (1982), Lind- strom and Onstad (1984), and Whitely and Dexter (1982). Others (Mielke et al., 1984; Packer et al., 1984; Unger, 1984; Lal, 1986) reported that soil condi- tions with conservation tillage were as good as or better than with conventional tillage. The presence of surface residues with conservation tillage was impor- tant for maintaining or achieving such favorable soil conditions as low crust strength, high aggregate stability and low density, and favorable water infil- tration rates.

No-tillage studies involving dryland (non-irrigated) winter wheat (Triti- cum aestivum L.) and grain sorghum (Sorghum bicolor (L.) Moench) grown in rotation were initiated in 1979 at Bushland, Texas. Both crops yielded slightly more grain with no-tillage than with conventional (stubble mulch) tillage (O.R. Jones, personal communication, 1986). Observations at Bushland indicated that soil physical conditions generally were better on no-tillage than on tillage areas, especially near the end of the fallow that followed wheat in the rotation (two crops in 3 years). The objective of this study was to determine if long- term no-tillage cropping of wheat and grain sorghum had an undesirable effect on soil physical conditions of the upper root zone as compared with those where conventional tillage was used.

METHODS AND MATERIALS

The study was conducted at the USDA Conservation and Production Re- search Laboratory at Bushland, Texas, on a Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). Bushland is at 35 ° 11' N latitude and 102 ° 5' W longitude and is ~ 1180 m above mean sea level. Average precipitation and minimum and maximum air temperatures are given in Table 1. Samples for this study were obtained in spring (April) 1987 from fields used for a winter wheat and grain sorghum rotation (two crops in 3 years). The fields were in fallow after wheat (harvested in June 1986) at the time of sampling.

Pullman soils are found on about 1.53 Mha and are highly uniform in a given subregion. At Bushland, the soil has less than 1% slope and contains ~ 170, ~ 530, and ~ 300 g kg- 1 sand, silt, and clay, respectively, in the surface horizon (0-0.15 m depth) (Unger and Pringle, 1981). The clays are mainly illite and montmorillonite (Taylor et al., 1963), which results in a major shrink-swell

CT AND NT EFFECTS ON UPPER ROOT ZONE SOIL CONDITIONS

TABLE 1

Monthly average precipitation and air temperatures, 1939-1987, Bushland, Texas

339

Month Precipitation Temperature ( ° C ) (mm)

Minimum Maximum

January 12 - 6.4 9.7 February 14 - 4.2 12.2 March 20 - 1.1 16.6 April 27 4.3 21.8 May 68 9.6 26.1 June 76 14.6 30.8 July 64 17.3 32.7 August 71 16.3 31.7 September 48 12.3 28.1 October 43 6.1 22.7 November 19 - 0.7 15.5 December 14 - 4.8 11.1

Total or average 476 5.3 21.6

potential with drying and wetting of the soil. The soil may freeze to a depth of ~ 0.15 m. Most precipitation occurs from May to September, but snow in the winter months is possible.

Three fields were sampled for the study. Field 1 (NT-81) was in no-tillage for 6 years (since 1981 ), Field 2 (CT) was an adjacent conventional (stubble mulch) tillage watershed, and Field 3 (NT-79) was in no-tillage for 8 years (since 1979). Field 3 was about 0.4 km from Fields 1 and 2. Fields 1, 2 and 3 were about 4.1, 3.3, and 8.1 ha in size, respectively. For about 25 years before 1981, Fields 1 and 2 were stubble mulch tilled for dryland wheat and grain sorghum grown in rotation. Field 3 was used for irrigated crops (wheat, sorghum, and corn (Zea mays L.) ) for about 8 years before starting the NT study in 1979. Samples were obtained at four sites and near the midpoint of 0-0.10-m (tillage zone of CT) and 0.10-0.20-m depth increments in each field. Actual sampling depths were about 0.04-0.07 m for the upper increment and about 0.14-0.17 m for the lower increment. At the time of sampling, the CT field had not been plowed since the fall of 1986 (about 180 days before sampling).

A 1-1 bulk and 10 core soil samples were obtained at each site and depth position. While still moist, the bulk soil was passed through a sieve with 12.7- mm square openings, then air-dried before determining aggregate size distri- bution by wet sieving (Kemper and Chepil, 1965 ). Subsamples were ground to pass through a 2-mm sieve before determining organic-matter concentration by the modified Walkley-Black procedure (Jackson, 1958). All determina- tions were made on duplicate samples.

340 P.W. UNGER AND L.J. FULTON

The core (54 mm diameter and 30 mm high) samples were trimmed, satu- rated with water, weighed, and subsequently weighed again after equilibrating at 0.98, 2.44, and 4.89 kPa water tension on a tension table. After the equili- bration at 4.89 kPa and weighing, 10 penetration resistance measurements were made on each core with a 4.76-mm diameter flat point hand-held pene- trometer (Model 719-5MRP, John Chatillon & Sons, Kew Garden, NY 11415 ) 1. The cores were then dried at 105 °C and weighed before calculating soil water contents and bulk density.

Data were analyzed by the analysis of variance technique using the proce- dure for a completely randomized experiment with all samples obtained from within a field. Separate analyses were performed for data from each sampling depth. Duncan Multiple Ranges were determined to show which differences were significant at the 5% (P= 0.05) level.

RESULTS AND DISCUSSION

Organic matter concentration

Organic matter (OM) concentrations at the 0.04-0.07-m depth were highest on the CT field and lowest on the NT-81 field (Table 2). At the 0.14-0.17-m depth, the OM concentrations were higher on the CT and NT-79 fields than on the T-81 field. The low OM concentration of the NT-81 soil and the sur- prisingly lower OM concentration on the NT-79 field than on the CT fields may have resulted from removing (nonsampling) the surface 40 mm of soil. Sampling nearer the surface possibly would have resulted in higher OM con-

T A B L E 2

Bulk soil sample data for convent ional tillage (CT) and no-tillage (NT-81 and NT-79) 1 fields, Bushland, Texas, 1987

Measurement Depth Field (m)

CT NT-81 NT-79

Organic mat te r concentra t ion (g kg- 1 )

Mean weight diameter (MWD) (mm)

0.04-0.07 18.1 a 14.2 ¢ 17.75 0.14-0.17 14.3 a 12.95 14.4 ~ 0.04-0.07 1.045 1.41 b 2.81 ~ 0.14-0.17 1.97 b 1.52 b 2.65 ~

1NT-81 and NT-79 (no-tillage) fields were last tilled 6 (in 1981) and 8 (in 1979) years before sampling, respectively. Row values followed by the same superscript are not significantly different (Duncan Multiple Range Test, 5% level).

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CT AND NT EFFECTS ON UPPER ROOT ZONE SOIL CONDITIONS 341

centrations in the no-tillage fields because of the residues maintained on the surface. On the CT field, tillage distributed the OM throughout the tillage zone (0-0.10-m depth). Subsequent sampling by small depth increments has shown that organic matter concentrations are higher at the surface of no-tillage than of conventional tillage fields on the Pullman soil (Unger, 1989).

Water-stable aggregates

The mean weight diameter (MWD) of water-stable aggregates was higher at both depths on the NT-79 field than on the CT and NT-81 fields (Table 2 ). On the CT field, MWD increased with depth, which suggests low stability of soil within the plow layer when wetted (for example, by rainfall). This could lead to soil surface sealing and greater,runoff than from more stable or pro- tected surfaces. Benyamini and Unger (1984) obtained greater surface sealing and lower infiltration of simulated rainfall on bare-surfaced than on residue- protected Pullman soil. The MWD of soil from the NT-81 field probably was lower than from the NT-79 field because the NT-81 field had a shorter history of no-tillage management. The lower OM concentration on the NT-81 field also may have been a factor.

Soil water content

Soil water content (WC) at saturation at the 0.04-0.07-m depth was highest on the NT-81 field and lowest on the CT field (Table 3). For all fields, the water content at saturation exceeded the soil porosity as calculated from the measured bulk density and an assumed particle density of 2.65 Mg m -3. This discrepancy is attributed to swelling of the soil at saturation. At 0.98 and 2.44 kPa tension, WC differences among fields were not statistically significant. The WC was highest at 4.89 kPa tension on the NT-79 field. Water content differences among fields were not significant at any tension at the 0.14-0.17- m depth.

High WC at saturation indicates high total porosity. As the soil drains as a result of increasing tension, large pores drain more readily than small pores. The data indicate that the NT-81 soil at the 0.04-0.07-m depth had more large and fewer small pores than the CT and NT-79 soils because these latter soils had lower WC at saturation and higher WC at 4.89 kPa tension. The change in WC from saturation to 4.89 kPa tension was 0.062, 0.134, and 0.059 per- centage units for the CT, NT-81, and NT-79 soils, respectively. At the 0.14- 0.17-m depth, the WC changes were 0.053, 0.061, and 0.045 percentage units for the respective soils.

The higher WC at all tensions (0.98, 2.44, and 4.89 kPa) and the smaller change in WC from saturation to 4.89 kPa tension for the NT-79 soil at the 0.04-0.07-m depth suggests that this soil has relatively fine pores, which could

342 P.W. UNGER AND L.J. FULTON

TABLE 3

Core soil sample data for conventional tillage (CT) and no-tillage (NT-81 and NT-79) 1 fields, Bushland, Texas, 1987

Measurement Depth Field (m)

CT NT-81 NT-79

Water content (m 3 m -3) At saturation 0.04-0.07 0.462 c 0.525 a 0.4935 At 0.98 kPa tension 0.04-0.07 0.438 a 0.470 a 0.471 a At 2.44 kPa tension 0.04-0.07 0.416 a 0.422 a 0.448 a At 4.89 kPa tension 0.04-0.07 0.4005 0.3915 0.434 ~ At saturation 0.14-0.17 0.477 a 0.484 a 0.470 ~ At 0.98 kPa tension 0.14-0.17 0.459 a 0.459" 0.456 ~ At 2.44 kPa tension 0.14-0.17 0.437 ~ 0.436 ~ 0.436 ~ At 4.89 kPa tension 0.14-0.17 0.424 a 0.423 ~ 0.425 ~

Bulk density ( Mg m- 3) 0.04-0.07 1.50 a 1.30 c 1.435 0.14-0.17 1.46 ~ 1.46 ~ 1.46 ~

Porosity (m 3 m -a) (calculated) 2 0.04-0.07 0.43 c 0.51 a 0.465 0.14-0.17 0.45" 0.45 ~ 0.45"

Penetration resistance (MPa) 0.04-0.07 0.50" 0.265 0.57" 0.14-0.17 0.70 a 0.75 ~ 0.66 ~

1NT-81 and NT-79 (no-tillage) fields were last tilled 6 (in 1981) and 8 (in 1979) years before sampling, respectively. 2Calculated from measured soil bulk densities and an assumed particle density of 2.65 Mg m -3. Row values followed by the same superscript are not significantly different {Duncan Multiple Range Test, 5% level).

l ead t o a e r a t i o n p r o b l e m s . P o o r c rop y ie lds o n p o o r l y d r a i n e d soils were ob- t a i n e d w i t h no - t i l l age in h u m i d r eg ions ( T r i p l e t t e t al., 1970) . H o w e v e r , no a e r a t i o n a n d d r a i n a g e p r o b l e m s a s s o c i a t e d w i t h no - t i l l age h a v e b e e n e n c o u n - t e r e d o n th i s soil, even w h e n i r r iga ted . T h e n e e d for w a t e r c o n s e r v a t i o n g r e a t l y exceeds t h e n e e d for d r a i n a g e in m o s t y e a r s a t t h e s e m i a r i d l o c a t i o n in T e x a s w h e r e th i s s t u d y wa s c o n d u c t e d .

Soil bulk density

Soil b u l k d e n s i t y ( B D ) a t t h e 0 . 0 4 - 0 . 0 7 - m d e p t h was h i g h e s t on t h e C T area , fo l lowed b y t h a t o n t h e N T - 7 9 a n d N T - 8 1 fields ( T a b l e 3) . T h e B D s were iden t i ca l a t t h e 0 . 1 4 - 0 . 1 7 - m dep th . T h e h i g h B D o n t h e C T field was n o t ex- p e c t e d b e c a u s e soil a t t h e 0 . 0 4 - 0 . 0 7 - m d e p t h was l o o s e n e d b y t i l lage. H o w e v e r , t he t i l lage was p e r f o r m e d a b o u t 180 d a y s be fo re s a m p l i n g , a n d ra in fa l l h a d c o n s o l i d a t e d t h e l o o s e n e d soil. D u r i n g t h e p e r i o d f r o m fall p l o w i n g to s a m p l i n g in Apri l , p r e c i p i t a t i o n t o t a l e d a b o u t 157 ram, w h i c h was a b o u t 80 m m g r e a t e r t h a n t he l o n g - t e r m a v e r a g e for t h a t p e r i o d a t B u s h l a n d . U n d o u b t e d l y , t h e u n -

CT AND NT EFFECTS ON UPPER ROOT ZONE SOIL CONDITIONS 343

stable (low MWD ) soil on the CT field resulted in relatively rapid reconsoli- dation of the tillage-loosened soil. Contributing to the relatively low BD on the NT-81 and NT-79 fields was soil disturbance during wheat seeding, which was performed with a hoe-opener drill with drill rows spaced at 0.25 m. The hoe drill was operated at a depth of about 0.05-0.08 m.

Penetration resistance

Soil penetration resistance (PR) was greatest on the NT-79 field and least on the NT-81 field at the 0.04-0.07-m depth (Table 3). At the 0.14-0.17-m depth, PR differences were not significant. The PR was high on cores from the NT-79 field, even though those cores had an intermediate BD and the highest WC when the PR measurements were made. These results (high PR, low BD, and high WC) are contrary to PR trends frequently encountered and suggest that no-tillage soils cannot be satisfactorily characterized by measuring a given soil factor or condition. The high PR in spite of the high WC and relatively low BD may be due to the high MWD, which resulted from the relatively high percentage of water-stable aggregates and is indicative of a stable pore system. The latter was suggested also by the relatively small change in soil WC with tension increases from saturation to 4.89 kPa of water.

GENERAL DISCUSSION

Significant differences in soil conditions existed among the conventional tillage (CT) and no-tillage (NT-79 and NT-81) fields, but most differences were relatively small and there were no definite advantages for any tillage method. The data suggested that the NT-79 field (no-tillage since 1979) soil had a fine pore system, which, along with the higher percentage of water-stable aggregates (higher mean weight diameter), possibly resulted in higher pene- tration resistance than for the CT field. The bulk density at the 0.04-0.07-m depth was highest on the CT field and lowest on the NT-81 field. At the 0.04- 0.07-m depth, organic matter concentrations were highest on the CT field and lowest on the NT-81 field. At the 0.14-0.17-m depth, OM concentrations were similar on CT and NT-79 fields, and both were higher than on the NT-81 field.

In conclusion, NT does not adversely affect Pullman soil physical conditions in a winter wheat-grain sorghum crop rotation system on dryland under pres- ent management practices. In addition, crop yields are favorable on the no- tillage areas. Wheat grain yields have been similar on the CT and NT fields, and sorghum grain yields usually have been slightly higher on the NT than on the CT fields. As an example, dryland sorghum grain yields averaged 5.10, 5.28, and 5.36 Mg ha -1 on the CT, NT-81, and NT-79 fields, respectively, in 1987, which was a very favorable year. An advantage of the NT system has been improved water conservation, undoubtedly because of the crop residues re-

344 P.W. UNGER AND L.J. FULTON

ta ined on the soil surface, especially dur ing the fallow per iod f rom wheat har- vest to so rghum plant ing.

ACKNOWLEDGMENT

The au thors grateful ly acknowledge the ass is tance provided by T .W. Po- pham, Stat is t ic ian, Stil lwater, Oklahoma, regarding stat is t ical analyses of the data.

REFERENCES

Benyamini, Y. and Unger, P.W., 1984. Crust development under simulated rainfall on four soils. Agron. Abstr., Am. Soc. Agron., Madison, WI, pp. 243-244.

Dickey, E.C., Peterson, T.R., Gilley, J.R. and Mielke, L.N., 1983. Yield comparisons between continuous no-till and tillage rotations. Trans. ASAE, 26: 1682-1686.

Hamblin, A.P., Tennant, D. and Cochrane, H., 1982. Tillage and growth of wheat in a loamy sand. Aust. J. Agric. Res., 33: 887-897.

Jackson, M.L., 1958. Organic matter determination for soils. In: Soil Chemical Analysis. Prentice- Hall, Englewood Cliffs, NJ, pp. 205-226.

Kemper, W.D. and Chepil, W.S., 1965. Size and distribution of aggregates. In: C.A. Black (Edi- tor), Methods of Soil Analysis, Part I. Agronomy, 9: 499-510.

Lal, R., 1986. Effects of eight tillage treatments on a tropical Alfisol: Maize growth and yield. J. Sci. Food Agric., 37: 1073-1082.

Lindstrom, M.J. and Onstad, C.A., 1984. Influence of tillage systems on soil physical parameters and infiltration after planting. J. Soil Water Conserv., 39: 149-152.

Mielke, L.N., Wilhelm, W.W., Richards, K.A. and Fenster, C.R., 1984. Soil physical characteris- tics of reduced tillage in a wheat-fallow system. Trans. ASAE, 27: 1724-1728.

Packer, I.J., Hamilton, G.J. and White, I., 1984. Tillage practices to conserve soil and improve soil conditions. J. Soil Conserv. {NSW), 40: 78-87.

Taylor, H.M., Van Doren, C.E., Godfrey, C.L. and Coover, J.R., 1963. Soils of the Southwestern Great Plains Field Station. Texas Agric. Exp. Stn., Misc. Publ., MP-669, 14 pp.

Triplett, Jr., G.B., Van Doren, D.M. and Johnson, W.H., 1970. Response of tillage systems as influenced by soil type. Trans. ASAE, 13: 765-767.

Unger, P.W., 1984. Tillage effects on surface soil physical conditions and sorghum emergence. Soil Sci. Soc. Am. J., 48: 1423-1432.

Unger, P.W., 1989. Organic matter, pH, and nutrient distribution in no- and conventional-tillage soil. Agron. Abstr., Am. Soc. Agron., Madison, WI, p. 296.

Unger, P.W. and Pringle, F.B., 1981. Pullman soils: Distribution, importance, variability, and management. Texas Agric. Exp. Stn., Bull., B-1372, 23 pp.

Whitely, G.M. and Dexter, A.R., 1982. Root development and growth of oilseed, wheat, and pea crops on tilled and nontilled soil. Soil Tillage Res., 2: 379-393.