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Agronomy Journal 94:305-309 (2002)
© 2002 American Society of Agronomy

TILLAGE

Corn Yield as Affected by Liming and Tillage System on an Acid Brazilian Oxisol

Paulo R. Ernani*, Cimelio Bayer and Leonardo Maestri

Universidade do Estado de Santa Catarina (UDESC), Dep. of Soil Sci., Av. Luis de Camões, 2090, C.P. 281, 88520-000, Lages, Santa Catarina, Brazil

* Corresponding author (prernani{at}cav.udesc.br)

Received for publication January 22, 2001.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 CONCLUSIONS
 REFERENCES
 
Tillage system affects many soil parameters that may influence plant growth. This study evaluated the effect of liming on corn (Zea mays L.) yield and chemical characteristics of a Humic Hapludox (clayey, kaolinitic, goethitic, termic) under both conventional tillage (CT) and no-tillage (NT) systems. Rates of dolomitic lime, from 0 to 18 t ha-1, were plowed into the soil in 1992 in southern Brazil; our study was conducted from 1996 through 1999. Lime rate was allocated to subplots, and tillage systems to main plots, in a split-plot design. Corn yield increased with liming in all years and was higher with CT than with NT in 2 of 3 yr. Averaged across years and systems, liming increased yield by 66%, which ranged from 4.4 to 7.8 t ha-1. The highest average yield (7.8 t ha-1) was obtained at pH 6.5; yields at pH 6.0 or 5.5 were 97 and 89% of the maximum, respectively. Liming reduced soil organic matter (SOM) in both systems, but nutrients (P, K, Ca, Mg, Fe, Cu, Zn, and Mn) remained above sufficiency on all treatments. Aluminum, pH, SOM, and other nutritional parameters did not differ between tillage systems, partly because limestone was initially incorporated in all plots and partly due to dilution effects in the plow layer because sampling was not stratified in small depths. Some soil restriction impaired by absence of plowing, probably increases in bulk density, offset the benefits of NT on plant growth and was responsible for the smaller yield in this tillage system compared with CT.

Abbreviations: CT, conventional tillage • NT, no-till • SOM, soil organic matter


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 CONCLUSIONS
 REFERENCES
 
ALUMINUM TOXICITY normally limits crop production on tropical and subtropical acid soils more than any other chemical factor. Liming is the easiest way to solve this problem, but the pH value to obtain maximum yield varies among plant species and soil conditions (Ernani et al., 2000). Because the adverse effect of Al to plants is eliminated near pH 5.5, plants should maximize yield on soils with pH close to or slightly above this value if nutrient availability is in the sufficient range. Raising soil pH to higher values is a decision that depends on crop yield increase per unit of pH and additional costs of liming, an important factor to consider for highly buffered soils (Ernani et al., 1998).

In addition to liming, Al toxicity can be alleviated by some alternative techniques, such as addition of gypsum (Toma et al., 1999), organic matter (Bloom et al., 1979), or P (Ernani et al., 2000) to the soil. Organic matter bonds Al through organic complexes (Hoyt and Turner, 1975), especially from fresh animal or plant residues; the effect of P is due to Al precipitation as Al phosphate (AlPO4) and increases of P diffusion toward roots that makes P uptake less dependent on a large root system.

No-tillage (NT) affects some chemical characteristics related to soil acidity that may influence plant development. Organic matter (Bayer et al., 2000; Rhoton, 2000) and P (Rhoton, 2000) accumulate in the upper few centimeters under NT compared with CT soil, which may reduce Al toxicity. Other nutrients also accumulate near the surface in NT soils (Rhoton, 2000), causing increases in the concentration of electrolytes, reductions of soil pH, and increases in both Al activity (Ernani and Barber, 1991) and P sorption. These effects may offset the benefits of soil organic matter (SOM) and P accumulation on Al toxicity in NT soils.

Variations in soil pH also affect availability of most soil nutrients (Helyar and Anderson, 1974, Ernani et al., 1998), organic matter decay (Azevedo et al., 1996), N mineralization, and some physical and chemical properties (Albuquerque et al., 2000), especially on highly weathered soils. The magnitude of these changes varies with soil, soil pH range, organic matter content, and tillage system (Torbert et al., 1998). Thus, liming has direct and indirect effects on nutrient availability and plant growth that are difficult to isolate.

No-tillage has been widely implemented in the last decades throughout the world. Actually, this conservation system occupies an area of approximately 13.2 million ha in Brazil. Besides reducing soil erosion and lowering operating costs compared with CT, NT saves time with soil preparation. It may also modify some soil physical properties that influence plant growth, such as water-holding capacity (Opoku and Vyn, 1997; Vyn et al., 1998), structure (Rhoton, 2000), surface penetrometer resistance (Vyn et al., 1998), soil temperature (Bordovsky et al., 1998; Vyn et al., 1998), and seedbed conditions (Kladivko et al., 1986; Vyn et al., 1998). The magnitude of these changes varies according to soil type and climatic conditions and may explain why crop yield has varied among systems without a specific trend (Sims et al., 1998; Xu and Pierce, 1998). Because tillage systems may affect Al toxicity and crop yield in different ways, this study was conducted to evaluate the effect of liming on both corn yield and soil chemical characteristics under CT and NT systems on an acid Brazilian soil.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 CONCLUSIONS
 REFERENCES
 
This study was conducted from 1996 through 1999 on an Oxisol in Lages, Santa Catarina, in southern Brazil. The experimental area was used in the previous 4 yr for another trial where the effect of liming on both corn grain yield and dry mass yield of corn for silage was evaluated (Ernani et al., 1998). In that experiment, treatments were set up in a randomized complete block design, under a split-plot arrangement, with four replications. Corn harvest use (grain or silage) was allocated to the main plots (5.0 m wide by 30.0 m long) and lime rate to the subplots (5.0 m wide by 6.0 m long). Liming treatments consisted of increasing rates of dolomitic limestone (27% of CaO and 20% of MgO), equivalent to 0, 4.5, 9.0, 13.5, and 18 t ha-1, based on an acid-neutralizing capacity of 100%. These rates were incorporated into a 17-cm soil depth layer, using moldboard plowing (twice) and disking (twice), in September of 1992. After determination of plant parameters (grain or green matter for silage), corn stover was returned to the respective subplots. Nitrogen, P, and K were broadcast-applied each year at rates of 90, 44, and 100 kg ha-1 as urea [(NH2)2CO], triple superphosphate, and potassium chloride (KCl), respectively.

Treatments in the main plots were changed when the present study began in 1996. The residual effect of liming rate, applied in 1992, was evaluated in the subplots, and corn harvest use was replaced by tillage system (CT or NT) in the main plots. No-tillage was allocated where corn for silage was previously produced; CT remained in the same subplots of the previous experiment. Conventional tillage consisted of moldboard plowing followed by disking.

The main chemical characteristics in the 0- to 17-cm layer, before liming, in 1992 were pH (water), 4.7; P and K (Mehlich-1), 1 and 120 mg kg-1, respectively; SOM, 45 g kg-1; exchangeable Al, 3.3 cmolc kg-1; Al saturation in the effective cation exchange capacity, 56%; and lime requirement to increase pH to 6.0, 13.0 t ha-1. In 1996, when the present study began, there was a small variation in the soil chemical characteristics among liming treatments in the 0- to 17-cm depth: P was between 5.0 and 6.0 mg kg-1, exchangeable K between 140 and 160 mg kg-1, and SOM was 44 g kg-1 in the treatment without liming. On subplots that received the increasing liming rates, values for pH (water) were 4.7, 5.5, 5.7, 6.3, and 6.6, respectively, while values for exchangeable Al were 3.2, 0.6, and 0 cmolc kg-1, respectively.

Corn (cv. Cargill 855) was sown each year in the second half of November, with a hand planter, in 1.0 m wide rows, providing a final population, after hand thinning, of 5 x 104 plants ha-1. Corn was fertilized each year with the same fertilizers and rates used in the previous corn grain plots as described above. Weeds were controlled by a preemergence application of glyphosate to all plots. Grain yield was expressed at 130 g kg-1 moisture content.

Composite soil samples of six cores were collected after corn harvest each year, in each subplot, from the 0- to 17-cm depth. This depth was chosen because the fertilizer recommendation in south Brazil was calibrated by taking into account the nutrient status of this layer. Samples were oven-dried at 65°C; passed through a 2-mm sieve; and analyzed for pH, SOM, P, Al, K, Ca, Mg, Fe, Cu, Zn, and Mn. Soil pH was determined using water as solvent, in a ratio of 1:1 (v/v), and SOM by the Walkley and Black (1947) method. The following solutions were used to extract the elements from the soil solid phase: double acid (Mehlich-1) for P and K; 1.0 mol L-1 KCl for Al, Ca, and Mg; and 0.1 mol L-1 HCl for Fe, Cu, Zn, and Mn. For all extractions, a shaking time of 1 h and a soil/extracting solution ratio of 1:10 was used. Exchangeable Al was determined by titrametry; P by colorimetry; K by flame emission; and Fe, Cu, Zn, Mn, Ca, and Mg by spectroscopy using an inductive coupled plasma (ICP).

Data were analyzed by ANOVA and simple regression methods, using SAS reference. When tillage system vs. liming rate interacted, analysis was done separately for each system. All treatment means were compared using the Tukey test at a 0.05 probability level.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
CONCLUSIONS
 REFERENCES
 
Corn Yield
Liming increased corn yield in all seasons, and the magnitude of the increment varied among the years, probably due to differences in environmental conditions (Fig. 1) . Grain yield ranged from 3.2 t ha-1 in 1997–1998, with no liming, to 8.6 t ha-1 in 1996–1997, in the best liming treatment (Fig. 1). Averaged across years and systems, liming increased corn yield by 66%. The absolute increment caused by liming was 3.6 and 2.7 t ha-1, respectively, under NT and CT, with a relative response of 90 and 52%, respectively. Crop response to liming has often been obtained on acid soils and is mainly due to decreases or elimination of Al phytotoxicity (Ernani et al., 1998). Because yield increased up to pH 6.3 and 6.6 on CT and NT, respectively (Fig. 1), some indirect effects of liming likely positively affected corn growth, such as increases in the rate of root growth (Ernani and Barber, 1991) and availability of nutrients because Al toxicity is eliminated around pH 5.4 in this soil.



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  		Fig. 1. Corn yield from 1996 through 1999 and average across years as affected by liming rates and tillage systems [no-tillage (NT) and conventional tillage (CT)] in a Humic Hapludox in southern Brazil (average of four replications; for all equations P < 0.01).

 
A large amount of limestone was needed for maximum yield, but the slope of the response curve was small near the top (Fig. 1). The highest yield, averaged across systems and years, was obtained with the addition of 17.3 t ha-1 limestone, which increased soil pH to 6.5. Corn yields at pH 5.5 and 6.0 were 89 and 97% of the maximum, and these pH values were the result of 8.4 and 13.0 t ha-1 lime, respectively. Yield with no lime was only 60% of the maximum. This yield response to liming was greater than that obtained in the previous experiment, conducted in the same plots from 1992 through 1996, where the increase in corn yield was only 17% for grain and 20% for green matter for silage (wet weight) (Ernani et al., 1998). These different yield responses between experiments can be partly attributed to the use of different corn varieties and to a decrease in SOM that occurred over time, which probably decreased the beneficial effect of SOM on toxic Al (Hoyt and Turner, 1975). Increases in crop response to liming over time were obtained on a similar soil in another experiment (Ernani et al., 2000).

Corn yield differed between soil tillage systems. Yield was higher with CT than with NT in 2 of 3 yr (Fig. 1). Reduced plant growth early in the season, visually verified with NT, could be the main reason for this difference. Similar results were also observed by Kladivko et al. (1986). Plants in NT suffered in the early development stages, probably due to seed placement closer to the surface relative to CT. Because the sowing process was performed with a manual planter, it was difficult to place the seed deeper than 3 cm in the NT system due to a high bulk density at the soil surface. Therefore, seeds remained shallower in NT than in CT, and this may have affected the initial growth. Lower yields have been reported on NT relative to CT due to poor seedbed conditions (Vyn et al., 1998), poor plant stands (Thompson and Whitney, 1998), and nonuniform plant population (Bordovsky et al., 1998). Lower soil temperatures in spring with NT caused by surface plant residues (Vyn et al., 1998) may cause delayed germination and reduced seedling growth rate on NT in most years (Vyn and Raimbault, 1993). Thus, the indirect positive effects of NT on soil physical properties that could enhance crop growth, such as better structure (Rhoton, 2000) and higher moisture (Opoku and Vyn, 1997), were minimized by the low initial corn growth in this system due to shallow planted seed and high bulk density at the soil surface.

The effects of tillage systems on crop yield have not been consistent. In some experiments, yields have not differed among systems (Bordovsky et al., 1998; Kapusta et al., 1996); in some situations, however, yields have been higher under NT (Bordovsky et al., 1998; Sims et al., 1998) and sometimes higher under CT (Vyn and Raimbault, 1993; Bordovsky et al., 1998; Sims et al., 1998; Vyn et al., 1998). Differences in yields among tillage systems have also varied among crops (Bordovsky et al., 1998), growing seasons (Sims et al., 1998), and rainfall distribution (Lopes-Bellido et al., 1996).

Soil Chemical Characteristics
Soil pH increased linearly with liming and was not affected by tillage system. The pH values in the plow layer remained about constant through the entire experimental period, which includes the previous and the present experiment. In this period (7 yr), each tonne of liming per hectare increased soil water pH by a unit of 0.1 (Table 1). Tillage systems had no effect on soil pH because all treatments received the same sources and rates of fertilizers and winter cover crops were not used in any system. Rhoton (2000) obtained variations on soil pH in different tillage systems as a consequence of variations on clay and organic matter content.


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  		Table 1. Regression equations and coefficients of determination between some soil characteristics (y) and liming rate (x, in t ha-1) in a Humic Hapludox in southern Brazil (average of 3 yr, two tillage systems, and four replications).

 
Soil buffer power for H+ is very high in this soil, as a consequence of large amounts of SOM and oxides, and significant drops are obtained only after decades (Azevedo et al., 1996). Thus, the residual effect of liming in this soil is much longer than thought in the past, which was believed to be around 5 yr. The actual liming recommendation to raise the pH of this soil to 6.0 would be 13 t ha-1. Because crop response to liming has only been moderate for southern Brazilian soils that have high clay and organic matter contents, especially at the beginning of the cultivation process (Ernani et al., 1998, Ernani et al., 2000), an alternative recommendation with lower liming rates is being proposed. This new recommendation aims to initially raise the pH of these soils to 5.2 (Almeida et al., 1999). For the present soil, it would be necessary to apply only 5.6 t ha-1 limestone (43% of that required to pH 6.0), which would give 81% of the maximum yield. Because agriculture in Brazil is not subsidized, decreasing initial costs of crop production is important, especially for small growers.

Concentrations of exchangeable Al, Ca, and Mg varied with liming rate but were not affected by tillage system. Soil-exchangeable Al decreased from near 3 cmolc kg-1, in the treatment without liming, to near 1.0 cmolc kg-1 in the treatment that received the smallest rate of liming (4.5 t ha-1), and then to zero thereafter (Table 1). Seven years after liming, exchangeable Al remained about the same and did not differ between tillage systems. Besides the well-recognized effect of organic matter in alleviating Al toxicity (Hoyt and Turner, 1975), changes in exchangeable Al do not appear when it is extracted from the soil with neutral salts because this extraction quantifies the sum of exchangeable and soil solution forms. In addition, because only one soil depth (0 to 17 cm) was sampled, the effect that accumulation of SOM in the soil surface under NT could have on Al was probably diluted. Calcium and Mg increased with liming, respectively, from 1.46 and 0.66 cmolc kg-1, which could be limiting for corn growth, up to 8.3 and 6.4 cmolc kg-1, respectively (Table 1). Addition of the lowest liming rate was sufficient to increase the values of both nutrients to above the sufficiency range of 2.0 and 1.0 cmolc kg-1, respectively (Comissão de Fertilidade do Solo, 1995). In the highest liming rate, Ca/Mg ratio was 1.3, which was not detrimental to corn.

Liming decreased SOM, which was not affected by tillage system. In the 3 yr of the current experiment, addition of 18 t ha-1 lime reduced SOM from 44 to 26 g kg-1 (Table 1). Decreases in SOM caused by liming have been reported (Albuquerque et al., 2000) and is caused mainly by better soil chemical conditions for microorganism activity. In addition, because liming increases clay dispersion (Albuquerque et al., 2000), it facilitates disruption of soil aggregates, and thus allows microorganisms to decompose some SOM stocks that were physically protected inside small pores in microaggregates (Shang and Tiessen, 1998). A decrease in SOM is normally detrimental to soil sustainability and crop growth, especially in acid soils, because SOM binds Al and decreases its activity in the soil solution (Bloom et al., 1979). In the present study, tillage had no influence on SOM content, probably because of the relative short experimental period (3 yr) and the dilution effect of SOM in the entire plow layer due to only the 0- to 17-cm depth being sampled. Alvarez et al. (1998) also did not find differences in total C and microbial biomass and activity between NT and CT in Argentina. Some studies, however, have shown increases in SOM after years of cultivation without tillage (Salinas-Garcia et al., 1997; Bayer et al., 2000) or lower decreases over time with NT compared with CT, especially in the upper 2.5 cm (Rhoton, 2000).

Liming did not have a consistent effect on the concentration of cationic micronutrients in the soil. As liming rate increased, Fe and Cu decreased, but Zn and Mn were not affected. Soil values for all of these micronutrients, however, remained above sufficiency levels, even in the treatment that received the highest rate of lime (Table 1). The decrease in Fe was likely caused by precipitation reactions that occur when soil pH increases. Manganese should also decrease with liming, but the values are modified during soil drying. Chemical adsorption of cationic micronutrients, as inner sphere complexes, also increases with liming, but this phenomenon was not observed in the current study because the extraction method used, in addition to decreasing pH of the soil suspension, gives the sum of adsorbed and solution forms. The amount extracted of any of these nutrients was not affected by tillage system. Rhoton (2000) also did not find a consistent relationship between tillage system and extractable micronutrients, and differences that occurred between systems in some years were related to changes in clay and SOM contents.

Extractable P and K in the 0- to 17-cm depth were not affected by either residual liming rate or tillage system. Availability of P in soil normally goes up with increases in soil pH (Ernani et al., 2000), but the effect is due to changes in soil solution concentration, which is not detected by normal routine extraction methods. The concentration of both nutrients, however, was above the sufficiency level in all treatments (Comissão de Fertilidade do Solo, 1995). Because soil sampling was not stratified in small depths, the amount applied on the surface was diluted in the plow layer and differences did not appear.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 CONCLUSIONS
REFERENCES
 
1. In addition to Al toxicity, some other factors are contributing to corn yield because it increased with liming up to soil pH values higher than those required for eliminating exchangeable Al.

2. Corn yield was greater with CT than with NT in most years, and this was probably caused by initial slow plant development with NT, likely as a result of soil compaction.

3. Tillage systems did not affect SOM and any parameter related to acidity or nutrient availability in the plow layer. If some of these parameters were positively affected in the upper centimeters of the NT soil, it was of such a small magnitude that it had no effect on corn yield.


   ACKNOWLEDGMENTS
 
We are grateful to CAPES (Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for providing funds to the Soil Science Post-Graduation Program, which partly supported this research. Special appreciation is expressed to CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), a Brazilian agency related to scientific development, for providing scholarships to all authors.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 CONCLUSIONS
 REFERENCES
 




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This Article
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