Effect of deep-tillage and nitrogen fertilization interactions
on dryland corn (
Zea mays
L.) productivity
M. DõÂaz-Zorita
*EEA INTA Gral.Villegas, CC 153 (6230) Gral.Villegas, Argentina and University of Kentucky, Department of Agronomy, N-122 Agric. Sci. Center North, Lexington, KY 40546-0091, USA
Received 3 June 1999; received in revised form 12 October 1999; accepted 3 November 1999
Abstract
Subsoiling a compacted soil should loosen it, improve the physical conditions, and increase nutrient availability and crop yields. The aim of this work is to compare the effects of different tillage and fertility treatments in a loamy Typic Hapludoll soil, and to determine the interactions of N fertilization with several soil properties and dryland corn (Zea mays L.) productivity. The experiment, conducted in 1995 and in 1997, had a split-plot design consisting of three tillage systems (MBmoldboard plowing, CHchisel plowing or NTno-tillage) in a corn±soybean (Glycine max(L.) Merrill) rotation since 1991 as main treatments. Four subtreatments: (i) subsoil (paratill subsoiler to 40 cm depth in fallow 1995)N fertilization (100 kg haÿ1 N as ammonium nitrate, at the V6 development stage of corn), (ii) subsoilno N fertilization, (iii) no
subsoilingN fertilization, and (iv) no subsoilingno N fertilization. Chemical and physical properties in the top layer of the soils were determined at seeding in 1995. Penetration resistance was measured at seeding, ¯owering and at harvest in 1995 and at seeding in 1997. Corn shoot dry matter during vegetative stages and grain yield components were also determined. The preparation of seedbed using either moldboard or chisel plowing with or without deep-tillage, increased the vegetative biomass by 27% and the grain yield of the corn crops by 9% over the no-tillage system. Subsoiling no-till plots improved the vegetative growth of the crops, but the effect of the deep-tillage did not modify the corn grain yields. Grain yields were strongly related to the N fertilization treatments. Although bulk density values (BD) ranged between 1.05 and 1.33 Mg mÿ3differences in crop yields were attributed to differences in the BD and the N fertilization. In the western Pampas Region of Argentina, the production of high yielding corn crops, under no water stress conditions, is independent of the tillage systems but negatively related with the soil BD values, and positively dependent on N fertilization.#2000 Elsevier Science B.V. All rights reserved.
Keywords:No-tillage; Paratill subsoiler; Loamy soil; Compaction; Bulk density
1. Introduction
The cropped soils of the western Pampas Region of Argentina (34±368S; 61±638W) are loam to
sandy-loam Hapludolls that are affected by physical degra-dation processes (crusting, compaction, etc.) due to intensive agricultural use. Genetic causes have been attributed to the origin of low macroporosity in the ®ne loamy soils of the Pampas Region of Argentina (Taboada et al., 1998). Water de®cits are the main climatic constraints and, in corn crops, they can be
*Tel.:1-606-257-3655; fax:1-606-257-2185.
E-mail address: mdzori2@pop.uky.edu (M. DõÂaz-Zorita).
expected in 3 out of 4 years. Minimum and no-tillage practices have been widely adopted in this region for the purpose of controlling erosion processes, increas-ing water use ef®ciency of summer crops and improv-ing crop productivity (Senigagliesi and Ferrari, 1993; Buschiazzo et al., 1998). Compaction of the topsoils under tillage systems that do not disturb the soil has been described in several studies in the Pampean region (Andriulo and Rosell, 1988; Kruger, 1996a; Buschiazzo et al., 1998). Not only are soil bulk density and soil penetration resistance values higher in the topsoil of no-tilled soils than in tilled soils, but nutri-ents and organic carbon accumulations have been observed in the topsoil of no-tilled soils (Kruger, 1996b; Chagas et al., 1994; Scheiner and Lavado, 1998).
Mechanical impedance to root growth has been shown to limit root elongation and is related with the reduction of plant shoot and grain yields. The effect of compaction on crop yields depends on weather conditions interacting with soil properties (Lowery and Schuler, 1994; Vepraskas, 1994). A compacted soil layer, because of its high strength and low porosity, con®nes the crop roots in the top layer and reduces the volume of soil that can be explored by the plant for nutrients and water (Ham-mel, 1994). Where no-till systems are practiced poor early vegetative growth, resulting from the hardness of the soil, can be a major factor limiting the ability of crops to fully utilize soil moisture at depth during the critical grain ®lling stage (Mead and Chan, 1988). Reductions in leaf nutrient concentrations that appar-ently affected crop yields in compacted soils have been described (Lowery and Schuler, 1994; Bennie and Krynauw, 1985). Compaction also reduces plant growth and yields by affecting water in®ltration, aeration and disease pressure (Unger and Kaspar, 1994). Bulk density and penetrometer resistance are two of the most common parameters used to determine the presence of compacted soil layers in agricultural soils. The interpretation of penetrometer resistance values in terms of root growth depends on soil particle size distribution and soil structure. Penetration resis-tance lacks a clearly de®ned theoretical basis with which to extrapolate results to different soils but it is usually considered that soil strength is a problem for crop growth in the ®eld if penetrometer values (cone index) are greater than 2±3 MPa (Ehlers et al., 1983;
Gupta and Allmaras, 1987; Boone et al., 1986). Other authors suggested that instead of focusing on soil strength, it may be easier to use bulk density values to determine the presence of root impedance pro-blems. Cone index and bulk density values that impede root growth vary with texture increasing as the sand content increases (Gerard et al., 1982; Jones, 1983; Vepraskas, 1994).
Tillage pans occur in many sandy-loam agricultural soils due to repeated tillage practices and hardening in no-tilled soils, and must be ripped by using a form of deep-tillage to maximize yields. Deep-tillage break up high density soil layers, improves water in®ltration and movement in the soil, enhances root growth and development, and increases crop production (Bennie and Botha, 1986). Sene et al. (1985) concluded that increments in corn yield due to subsoiling are highly related to the soil texture and the soil structure. Many farmers and researchers from the Pampean Region of Argentina have speculated that the use of deep-tillage practices may improve crop yields in some compacted soils. Nevertheless, the effects of deep soil loosening on crop yields are not well documented. Studies that show bene®ts of deep-tillage practices on wheat ( Tri-ticum aestivum L.) or soybean (Glycine max (L.) Merrill) crops conclude that the increments in grain yields in the deep-tilled soils are related to soil types and weather conditions (Scotta and Herrera, 1991; Ripoll and Kruger, 1996).
In soils under no-till practices, the subsequent tillage of the soil redistributes soil nutrients within the plow layer and stimulates the mineralization and availability of nitrogen (Pierce et al., 1994). Subsoil-ing a compacted soil should loosen it and improve its physical condition and nutrient availability. Conse-quently, the nitrogen fertilization requirements could be reduced and the grain yields increased. For these reasons, the aim of this work was to compare the effects of deep-tillage practices using a subsoiler in a sandy-loam soil under different tillage systems and to determine their interactions with nitrogen availability on dryland corn (Zea maysL.) productivity.
2. Materials and methods
``General Villegas'', Instituto Nacional de TecnologõÂa Agropecuaria (INTA) in Drabble (34854'S and 63844'W, Buenos Aires, Argentina) on a sandy-loam Typic Hapludoll (clay145 g kgÿ1 and silt385 g kgÿ1). 63 000 viable seeds haÿ1 of Corn (``Pionner 3456'') were planted on 18 October 1995 and on 15 October 1997. 60 kg of triple superpho-sphate per hectare were broadcast before planting in 1995.
The experiment was a three-factor study in a split-plot design with three replications. Main split-plots (2040 m2) consisted of three tillage management treatments (MBmoldboard plowing, CHchisel plowing or NTno-tillage) in a corn±soybean rotation since 1991. Subplots (1020 m2) were (a) deep-til-lage (DT) treatments with or without paratill subsoiler to 40 cm depth, in August 1995, and (b) with or without N fertilization (100 kg haÿ1of N as ammo-nium nitrate) applied 30 days after corn seeding (V6 development stage).
At seeding in 1995, composite soil samples were taken from the 3 to 20 cm soil layer in each subplot. Soil samples were air dried and passed through a 2 mm sieve. The following determinations were car-ried out on each soil sample: total organic carbon (TOC) by wet combustion (Nelson and Sommers, 1982), total nitrogen (Nt) by the Kjeldahl semimicro method (Bremner and Mulvaney, 1982), NO3-N
extracted with 2.0 N KCl (Keeney and Nelson, 1982) and available phosphorus (Pa) extracted with
an acid±¯uoride solution (Bray and Kurtz, 1945). The BD, in the 3±20 cm layer, was determined with core samples (244 cm3). The residue cover was measured at seeding in 1995 using a 10 m rope with 30 knots (0.30 m apart) and counting the number of knots that have residues greater than 0.005 m long under them. The rope was stretched diagonally across the rows and the procedure was repeated three times in different areas of each plot.
Soil mechanical impedance to root growth from the soil surface to 0.40 m depth was measured at intervals of 0.05 m down using a hammer-driven cone penet-rometer with a 308 right circular cone point of 4.22 cm2lateral area. Five penetration resistance mea-surements at every 0.30 m were obtained per subplot (O'Sullivan et al., 1987) at seeding, ¯owering and harvest in the 1995±1996 crop and only at seeding in the 1997±1998 crop. These measurements were done
48 h after rainfall events, when the soil water content (gravimetric method) was approximately 80% of the ®eld capacity.
For shoot dry matter (DM) production in 1995, two middle corn rows (1.53 m2) were hand harvested at 41, 48 and 68 days after seeding (V10, V11 and r1 growth stages). The daily crop DM production was calculated from the dry matter levels according to Eq. (1).
CGR DM2ÿDM1 t2ÿt1ÿ1 (1)
where CGR is the crop growth rate in kg haÿ1per day, DM2the dry matter production at the date 2 (t2) and
DM1the dry matter production in the previous
sam-pling date (t1).
For grain yield, in both periods, four corn rows (33 m2) were hand harvested and grain weights adjusted to 140 g kgÿ1moisture content. Plant density and individual grain weight were also determined in each plot.
Crop and soil results were subjected to analysis of variance as a three factor (main tillage system, deep-tillage and N fertilization) experiment and signi®cant means separated by the LSD (T) test. Multiple regres-sion analysis (stepwise method) between grain yield and soil properties was also considered including the deep-tillage and nitrogen subtreatments as class vari-ables (Analytical Software, 1998).
3. Results and discussion
3.1. Soil properties
and leave biopores which may increase water move-ment and gaseous diffusion (Unger and Kaspar, 1994). Penetration of plant roots into compact soils has been described to be a possible natural process which may ameliorate compacted soils (Dexter, 1991). In the 1995±1996 season subsoiling signi®cantly decreased the penetration resistance of the 10±20 cm layer of the
tilled soils at seeding stage. After the measurement at seeding in 1995, no differences due to this treatment were observed in the soil resistance pro®les. In the no-tilled soil deep-tillage decreased signi®cantly the penetration resistance in the 3±35 cm layer at seeding in 1995. This effect was also observed in the 10±25 cm layer during the remainder of the 1995±1996 season
but not 2 years after the deep-tillage treatment appli-cation (Fig. 1).
The bulk density in the 3±20 cm layer of the soils was signi®cantly increased when the intensity of the tillage system decreased (Table 1). The deep-tillage treatment signi®cantly decreased the bulk density in the no-tilled soils, but not in the tilled soils (Table 1). Another consequence of the subsoiling was the promotion of mineralization observed from the increment in the NO3-N levels in the soils under no
tillage practices and the reduction in the soil residue cover at seeding in 1995 for all the main tillage systems (Table 1). These soils, mainly under no-till practices, present greater amounts of available P in the topsoil layers than in the subsoil layers (DõÂaz-Zorita, 1999). The absence of differences in the available P values observed between tilled soils or due to the subsoiling practice (Table 1) suggests that little vertical mixing between subsoil and topsoil layers took place due to the deep-tillage treatment.
3.2. Corn shoot dry matter and grain production
The effects of the deep-tillage and the N fertiliza-tion treatments on the dry weight of the corn shoot were analyzed separately between tilled and non-tilled soils because of signi®cant interactions due to tillage practices (Table 2). In general, the shoot dry matter was signi®cantly higher in the tilled treatments than in those under no-tillage. Between tilled systems, the
largest dry matter production was observed in the treatment with moldboard plow only 41 days after seeding. The deep-tillage treatment increased shoot dry weight only in the no-till treatments. Differences in the shoot dry matter accumulation due to the nitrogen fertilization were observed only in the no-till treatments at ¯owering.
The crop growth rate (CGR) between planting and the V10 growth stage showed a signi®cant interaction between the main tillage systems and the subsoiling treatment. The deep-tillage practices enhanced the CGR of the crop only in the system under continuous no tillage (Table 3). By decreasing the intensity of the tillage the initial crop growth was signi®cantly reduced. This behavior can be partially explained by the lower soil NO3-N levels in the NT than in
CH or MB systems (Table 1). When the CGR between V10 and V11 or V11 and R1 growing stages were considered, there were no signi®cant interactions or differences between N fertilization, deep-tillage and the main tillage systems (Table 3).
The corn grain yield components in both periods did not present signi®cant interactions between the three factors (main tillage system, deep-tillage and nitrogen fertilization). No signi®cant differences between any of the treatments were observed in the plant density and in the weight of the grains (Table 4). The main tillage system and the nitrogen fertilization treatment signi®cantly increased the grain yields in both periods. The highest corn grain yields were observed in the tilled soils and when the nitrogen fertilizer was
Table 1
Effect of three tillage systems and the deep-tillage on the crop residue cover and several soil properties in the 3±20 cm layer of a Typic Hapludoll from the western Pampas Region of Argentinaa
Deep-aTOCtotal organic carbon, Nttotal nitrogen, NO
3-Nnitrate nitrogen, Pavailable phosphorus, BDbulk density, NTno-tillage, CHchisel plowing and MBmoldboard plowing.
applied. No differences were detected due to the deep-tillage treatment (Table 4).
The enhancement of the corn shoot dry matter production because of subsoiling indurate soil layers, and the lack differences on the corn grain weights and yields can be explained by considering the rainfall during the growing season (Table 5). Varsa et al. (1997) indicated that adequate rainfall events mini-mize the bene®ts derived from deep-tillage practices. In this study the rainfall during grain ®lling stages (end
of January and February) was above the normal values (DõÂaz-Zorita et al., 1998) and potential rainfall de®cits were only detected during vegetative stages (October± December) in the 1995±1996 period.
Although the observed bulk density values can be considered non-limiting for the normal crop growth (Daddow and Warrington, 1983; Vepraskas, 1994), differences in crop yields were related to differences in the soil BD of the 0±20 cm layer at seeding and the nitrogen fertilization (Fig. 2). In both periods,
Table 3
Effect of nitrogen fertilization or deep-tillage on CGR of corn crops cultivated in a Typic Hapludoll from the western Pampas Region of Argentina under NT and tillage (chisel (CH) or moldboard (MB) plowing) systems
Tillage Deep-tillage CGR (kg haÿ1per day)a
Without N fertilization With N fertilization
0±41 days after seeding
41±48 days after seeding
48±62 days after seeding
0±41 days after seeding
41±48 days after seeding
48±62 days after seeding
NT No 31.9b 93.3 38.3 28.5 28.5 33.3
Yes 40.4c 86.7 93.3 44.4 44.4 73.3
Mean (NT) 36.1 90.0 65.8 36.4 36.4 53.3
CH No 48.9 66.7 113.3 45.0 45.0 70.0
Yes 50.1 83.3 78.3 50.1 50.1 46.7
Mean (CH) 49.5 75.0 95.8 47.5 47.5 58.3
MB No 54.6 70.0 105.0 48.9 48.9 73.3
Yes 52.4 93.3 100.0 51.8 51.8 50.0
Mean (MB) 53.5 81.7 102.5 50.4 50.4 61.7
aMeans in the same column within each tillage or means by tillage within each N fertilization treatment followed by the same superscript or the absence of superscripts are not signi®cantly different at the 5% level by the LSD (T) test.
Table 2
Effect of nitrogen fertilization (N fert.) or deep-tillage (DT) on corn dry matter (kg haÿ1) in a Typic Hapludoll from the western Pampas Region of Argentina under no-tillage (NT) and tillage (chisel (CH) or moldboard (MB) plowing) systems
Dry matter yield (kg haÿ1)a
41 days after seeding 48 days after seeding 62 days after seeding
NT No N fert. 1481.7 2011.7 3033.3b
With N fert. 1493.3 1966.7 3225.0c
Without DT 1236.7b 1680.0b 2770.0b
With DT 1738.3c 2298.3c 3488.3c
Tilled CH 1989.2b 2455.8 4071.7
MB 2129.2c 2630.8 3867.5
No N fert. 2111.7 2426.7 3890.8
With N fert. 2006.7 2660.0 4048.3
Without DT 2024.2 2514.2 3972.5
With DT 2094.2 2572.5 3966.7
Table 4
Effect of tillage systems, nitrogen fertilization (N fert.) or deep-tillage (DT) treatments on the yield components of corn crops cultivated in a Typic Hapludoll from the western Pampas Region of Argentinaa
1995±1996 1997±1998
Stand (plants per m2)
Grain weight (mg per grain)
Grain yieldb (kg haÿ1)
Stand (plants per m2)
Grain weight (mg per grain)
Grain yield (kg haÿ1)
MB 6.05 245.9 5236.9c 5.98 247.5 10089.3c
CH 5.83 243.7 5048.3c 6.02 248.1 10015.3c
NT 5.92 241.5 4709.6d 5.93 245.9 8294.3d
No N fert. 5.93 242.5 3916.2c 5.99 243.3 8929.3c
With N fert. 5.93 244.9 6080.3d 5.97 250.9 10003.2d
Without DT 5.96 240.5 4941.5 5.98 248.1 9184.3
With DT 5.90 247.0 5055.0 5.91 246.3 9748.2
aCHchisel plowing; MBmoldboard plowing; NTno-tillage.
bMeans in the same column within each subtreatment followed by the same superscript or the absence of superscripts are not signi®cantly different at the 5% level by the LSD (T) test.
Table 5
Normal, 1995±1996, and 1997±1998 monthly rainfall at Drabble (Buenos Aires, Argentina) during the corn growing season
Rainfall (mm)
October November December January February
1995±1996 64 78 69 93 108
1997±1998 155 92 401 118 159
Normala 92 101 114 130 90
aSource: DõÂaz-Zorita et al. (1998).
increasing the soil BD reduced the grain yields independent of the N fertilization treatment. The negative effect of increasing levels of BD on corn yields could be because of limitations in the available soil for root development in soils with low water holding capacity and moderate to low nitrogen avail-ability. In these soils, DõÂaz-Zorita (1996) found that corn grain yields decreased from 8190 to 2490 kg haÿ1 when the thickness of the soil above an endured layer diminished from 65 to 45 cm. No other soil properties (e.g. penetration resistance per layer or cumulated in the 0±20 cm layer) or management practices (e.g. tillage system) were related to the yields.
In the absence of cultivation, this soil tends to set hard resulting in high bulk density and high soil penetration resistance in surface layers. A deep-tillage operation is an effective method for over-coming soil physical limitations under no-tillage systems in soils with similar characteristics to the studied soil. This may be a suitable strategy for improving the early shoot growth of corn crops in the initial stages of the adoption of the no-tillage system. Nitrogen fertilization requirements must also be considered in order to achieve high crop productivity.
4. Conclusions
The preparation of seedbed using either moldboard or chisel plowing with or without deep-tillage increased the vegetative and grain yield of the crops when compared with the no-tillage system. The poor vegetative growth of the no-tilled plots was improved by deep-tillage. Subsoiling did not modify the corn grain yields of the crops which were independent of the tillage practice. Soil bulk density and nitrogen fertilization control the grain yields of corn crops in agricultural production systems in the western Pampas Region of Argentina.
Acknowledgements
I express my thanks to Dr. Edmund Perfect who critically reviewed the manuscript. The ®nancial sup-port by INTA Gral. Villegas is greatly appreciated.
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