Liming influence on soil chemical properties, nutritional status and yield of alfalfa grown in acid soil

Influência da calagem nas propriedades químicas do solo, estado nutricional e produção da alfafa em um solo ácido

Abstracts

Alfalfa is an important forage crop with high nutritive value, although highly susceptible to soil acidity. Liming is one of the most efficient and prevailing practices to correct soil acidity and improve alfalfa yield. The objective of this study was to evaluate response to liming of alfalfa grown in a greenhouse on a Typic Quartzipsamment soil. The treatments consisted of four lime rates (0, 3.8, 6.6 and 10.3 Mg ha-1) and two cuts. Alfalfa dry matter increased quadratically with increasing lime rates. In general, dry matter yield was maximized by a lime rate of 8.0 Mg ha-1. Except for the control, the dry matter nutrient contents in the treatments were adequate. The positive linear correlation between root and nodule dry matter with lime rates indicated improvement of these plant traits with decreasing soil acidity. The soil acidity indices pH, base saturation, Ca2+ concentration, Mg2+ concentration, and H + Al were relevant factors in the assessment of alfalfa yield. The magnitude of influence of these soil acidity indices on yield as determined by the coefficient of determination (R²) varied and decreased in the order: base saturation, H + Al, pH, Ca and Mg concentrations. Optimum values of selected soil chemical properties were defined for maximum shoot dry matter; these values can serve as a guideline for alfalfa liming to improve the yield of this forage on acid soils.

Medicago sativa L.; shoot dry matter; nodulation; soil acidity; nutrient uptake

A alfafa é uma importante forrageira com alto valor nutritivo, porém é altamente suscetível à acidez do solo. A calagem é uma das mais eficientes práticas para corrigir esse problema e melhorar a produtividade da alfafa. O objetivo deste trabalho foi avaliar a resposta à calagem da alfafa cultivada em Neossolo Quartzarênico em casa de vegetação. Os tratamentos consistiram de quatro doses de calcário (0; 3,8; 6,6 e 10,3 Mg ha-1) e duas épocas de corte. A produção de matéria seca foi significativamente aumentada com a adição de calcário, com o máximo rendimento estimado obtido com a adição de 8,0 Mg ha-1. Exceto na testemunha, o teor de nutrientes na matéria seca foi adequado. A matéria seca de raízes e de nódulos foi significativamente aumentada com a aplicação de calcário. Os índices de acidez do solo, como pH, saturação por bases, concentração de Ca2+ e de Mg2+ e H + Al, foram importantes na avaliação do rendimento da alfafa. Magnitudes de influência da acidez do solo desses índices no rendimento variaram, conforme determinado pelo coeficiente de determinação (R²) obedeceram a seguinte ordem decrescente: saturação por bases, H + Al, pH, concentração de Ca2+ e de Mg2+ . Os valores considerados ótimos das propriedades químicas do solo selecionados para obtenção da máxima produção estimada podem servir como referência e melhorar o rendimento de culturas forrageiras em solos ácidos.

Medicago sativa L.; produção de matéria seca; nodulação; acidez do solo; absorção de nutrientes

Liming influence on soil chemical properties, nutritional status and yield of alfalfa grown in acid soil(¹)

Influência da calagem nas propriedades químicas do solo, estado nutricional e produção da alfafa em um solo ácido

Adônis Moreira^I; Nand Kumar Fageria^II

^IPesquisador da Embrapa Amazônia Ocidental, Caixa Postal 319, CEP 69010-970 Manaus (AM). Bolsista CNPq. E-mail: [e-mail]

^IIPesquisador da Embrapa Arroz e Feijão. Caixa Postal 179, CEP 75375-000 Santo Antonio de Goiás (GO). Bolsista CNPq. E-mail: [e-mail]

SUMMARY

Alfalfa is an important forage crop with high nutritive value, although highly susceptible to soil acidity. Liming is one of the most efficient and prevailing practices to correct soil acidity and improve alfalfa yield. The objective of this study was to evaluate response to liming of alfalfa grown in a greenhouse on a Typic Quartzipsamment soil. The treatments consisted of four lime rates (0, 3.8, 6.6 and 10.3 Mg ha^-1) and two cuts. Alfalfa dry matter increased quadratically with increasing lime rates. In general, dry matter yield was maximized by a lime rate of 8.0 Mg ha^-1. Except for the control, the dry matter nutrient contents in the treatments were adequate. The positive linear correlation between root and nodule dry matter with lime rates indicated improvement of these plant traits with decreasing soil acidity. The soil acidity indices pH, base saturation, Ca²⁺ concentration, Mg²⁺ concentration, and H + Al were relevant factors in the assessment of alfalfa yield. The magnitude of influence of these soil acidity indices on yield as determined by the coefficient of determination (R²) varied and decreased in the order: base saturation, H + Al, pH, Ca and Mg concentrations. Optimum values of selected soil chemical properties were defined for maximum shoot dry matter; these values can serve as a guideline for alfalfa liming to improve the yield of this forage on acid soils.

Index terms:Medicago sativa L., shoot dry matter, nodulation, soil acidity, nutrient uptake

RESUMO

A alfafa é uma importante forrageira com alto valor nutritivo, porém é altamente suscetível à acidez do solo. A calagem é uma das mais eficientes práticas para corrigir esse problema e melhorar a produtividade da alfafa. O objetivo deste trabalho foi avaliar a resposta à calagem da alfafa cultivada em Neossolo Quartzarênico em casa de vegetação. Os tratamentos consistiram de quatro doses de calcário (0; 3,8; 6,6 e 10,3 Mg ha^-1) e duas épocas de corte. A produção de matéria seca foi significativamente aumentada com a adição de calcário, com o máximo rendimento estimado obtido com a adição de 8,0 Mg ha^-1. Exceto na testemunha, o teor de nutrientes na matéria seca foi adequado. A matéria seca de raízes e de nódulos foi significativamente aumentada com a aplicação de calcário. Os índices de acidez do solo, como pH, saturação por bases, concentração de Ca²⁺ e de Mg²⁺ e H + Al, foram importantes na avaliação do rendimento da alfafa. Magnitudes de influência da acidez do solo desses índices no rendimento variaram, conforme determinado pelo coeficiente de determinação (R²) obedeceram a seguinte ordem decrescente: saturação por bases, H + Al, pH, concentração de Ca²⁺ e de Mg²⁺ . Os valores considerados ótimos das propriedades químicas do solo selecionados para obtenção da máxima produção estimada podem servir como referência e melhorar o rendimento de culturas forrageiras em solos ácidos.

Termos de indexação: Medicago sativa L., produção de matéria seca, nodulação, acidez do solo, absorção de nutrientes.

INTRODUCTION

Alfalfa is one of the most important forage crops worldwide because of its good forage quality, high forage yield in a wide range of environments, and high adaptability to different climatic conditions (Dordas, 2006; Berg et al., 2007; Zhang et al., 2008; Turan et al., 2009). Alfalfa is grown mainly for forage production while seed yield is secondary (Iannucci et al., 2002). The forage can be used directly for grazing or conserved as silage or hay and is a reliable high-quality nutrient source that could represent a significant contribution to the agricultural sector (Borreani & Tabacco, 2006).

Brazil has large cattle herds and alfalfa is an important component of forages/pastures used for cattle feeding. Most pasture in Brazil are acidic and fertility is low (Fageria & Baligar, 2008). Theoretically, soil acidity is quantified on the basis of pH and Al³⁺ concentrations of soils. For crop production, however, soil acidity is a complex of numerous factors involving nutrient/element deficiencies and toxicities, low activity of beneficial microorganisms and reduced plant root growth that limit nutrient and water uptake (Fageria & Baligar, 2003). The situation is further complicated by various interactions among these factors (Foy, 1992). The practice of correcting soil acidity reduces the available contents of Al, Fe, Mn, Zn, and Cu, but increases the availability of other essential nutrients. For most crops other than alfalfa, nutritional conditions for maximum potential plant growth are most appropriate at pH values in a low acidity range (6.0 to 6.5) (Fageria, 2009). The components of the soil acidity complex have been thoroughly discussed in various publications (Foy, 1984, 1992; Tang & Rengel, 2003).

Liming is an effective and dominant practice to raise soil pH and reduce acidity-related constraints to improve crop yields (Fageria & Baligar, 2008). The quantity of lime required depends on the soil type, quality of liming material, costs and crop species or cultivars (Fageria & Baligar, 2008). Information on appropriate liming rates for alfalfa grown on acid soils in Brazil is limited. The objective of this study was to evaluate liming influence on changes in soil chemical properties and alfalfa growth in an acid soil.

MATERIAL AND METHODS

The experiment was conducted under greenhouse conditions. The soil used in the experiment (0-20 cm depth) was a Typic Quartzipsamment (Neossolo Quartzarênico, Brazilian classification - Embrapa, 1999) from the Experimental farm of Embrapa Cattle, South-East Research Center, in São Carlos, state of São Paulo, Brazil (latitude 27 ^o 04 ' 39 ", longitude 53 ^o 00 ' 4 ", 264 m asl). The following chemical (Raij et al., 2001) and texture properties were determined (Embrapa, 1997).: pH (CaCl₂ 0,1 mol L^-1) = 3.8, pH (water) = 4.7, soil organic matter (SOM) = 28 g kg^-1; P (resin) = 4.0 mg kg^-1; K (resin) = 0.07 cmol_c kg^-1; Ca (resin) = 0.4 cmol_c kg^-1; Mg (resin) = 0.2 cmol_c kg^-1; Al (KCl 1.0 mol L^-1) = 1.9 cmol_c kg^-1; H + Al = 8.0 cmol_c kg^-1; V (base saturation) = 7.7 %, B (hot water) = 0.42 mg kg^-1; Cu (DTPA-TEA extractant, DTPA 0.005 mol L^-1 + TEA 0.1 mol L^-1 + CaCl₂ 0.01 mol L^-1 at pH 7.3) = 1.8 mg kg^-1; Fe (DTPA-TEA) = 38.0 mg kg^-1; Mn (DTPA-TEA) = 1.3 mg kg^-1; Zn (DTPA-TEA) = 0.1 mg kg^-1; 860 g kg^-1 sand, 60 g kg^-1 silt and 80 g kg^-1 clay.

The experiment was conducted in clay pots filled with 3.0 dm³ of air-dried soil, sieved through a 2.0 mm mesh. The experimental design was a completely randomized block with four replications in a factorial combination (2x4) of four lime rates with aboveground plant harvests repeated over time (two cuts). Dolomitic limestone (27.1 % CaO, 17.5 % MgO and effective calcium carbonate - ECC of 95 %) were incorporated 30 days before planting, at rates of 0, 3.8, 6.6 and 10.3 Mg ha^-1; respectively.

The basal application of P, K, B, Cu, Fe, Mn and Zn was supplied according to recommended solutions adapted from Allen et al. (1976) and Malavolta (1980), for greenhouse experiments (200 mg dm^-3 P as MAP, 50 mg dm^-3 K as KCl, 0.5 mg dm^-3 B as H₃BO₃, 1.5 mg dm^-3 Cu as CuSO₄, 5.0 mg dm^-3 Mn as MnSO₄, 5.0 mg dm^-3 Mn as FeSO₄ and 5.0 mg dm^-3 Zn as ZnSO₄). Forty-five days after planting, an additional 100 mg dm^-3 K was applied as K₂SO_4. The pots were irrigated daily with distilled water to replace the moisture lost by evapotranspiration and to maintain the soil near 70 % of field capacity (FC), according to the method described by Cassel & Nielsen (1986).

After scarification, the alfalfa seeds (cultivar LEN 4) were inoculated with Sinorhizobium meliloti and then treated with 0.01 mg L^-1 Co using, CoSO₄, 0.1 mg L^-1 Ni using NiSO₄, and 0.1 mg L^-1 Mo using NaMoO₄. Ten seeds were planted in each pot and after germination thinned to three plants per pot. Three months after planting (Ninety days), the plants were cut, while thirty days after the second cut was made. The harvested material was oven-dried to constant weight at 65 ºC, weighed and digested (Walinga et al., 1995). The total concentration of N (H₂SO₄ digestion - Kjeldahl), P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn (digested with a mixture of HNO₃ and HClO₄) in the shoot dry matter - stems and leaves (Walinga et al., 1995).

Soil samples were collected from each treatment before planting (composites of the four replications) and at each harvest to determine the pH in CaCl₂, soil organic matter (SOM), P, K, Ca, Mg, S-SO₄, H + Al, base saturation (V %), B, Cu, Fe, Mn, and Zn, according to the method described by Raij et al. (2001). At the end of the experiment, roots and nodules were extracted to quantify their dry matter yield (RDM and NDM, respectively). The total concentrations of N, P, K, Ca, and Mg in the nodules were determined according to the method proposed by Walinga et al. (1995). From data of soil analysis and base saturation, the saturation of K, Ca and Mg was calculated using the following formula (Fageria, 2008):

The values of K, Ca, Mg, and cation exchange capacity (CEC = ΣK, Ca, Mg, H + Al) are given in cmol_c kg^-1.

The ratios Ca/K, Ca/Mg, and Mg/K were also calculated from the soil analysis data. The data were submitted to analyses of variance (ANOVA) and regression analysis (Hicks, 1973) was performed to determine adequate lime rates. All statistical inferences were based on a significance level of 0.05.

RESULTS AND DISCUSSION

Soil chemical properties

All soil chemical properties evaluated were significantly influenced by increasing lime rates in the range of 0 to 10.3 Mg ha^-1; except P, B and Zn (Table 1). The cut versus lime interactions were only significant for K, Mg, H + Al, Mn and sulfur (S-SO₄), indicating variation in these properties according to the date of alfalfa cut. Significant increase in the soil pH, Ca, Mg and base saturation with liming was expected. Dolomitic limestone is a source of Ca and Mg and in the presence of water the carbonates dissolve and the OH^- and HCO₃^- ions are released, reducing soil acidity (Havlin et al., 1999). Fageria (2001) also reported significant increase in these soil chemical properties with liming in the Brazilian Oxisols. The reduction of exchangeable K from 0.8 to 0.5 cmol_c kg^-1 in the first cut and 0.4 cmol_c kg^-1 in the second cut was due to a higher uptake by alfalfa plants (Moreira et al., 2008). In highly fertile soils, Lloveras et al. (2001) found extraction rates of 1.5 to 1.7 Mg ha^-1 of K₂O, with shoot dry matter yield of 21.5 Mg ha^-1. In the second cut there was a decrease in the soil organic matter (SOM), P, K, Ca, Mg, base saturation, S-SO₄ and B content, compared with the first cut. This may be associated with the uptake by the crop because alfalfa dry matter yield was higher in the second than in the first cut.

Ca/K, Mg/K, Ca and Mg saturation increased significantly with increasing lime rates in the range of 0 to 10.3 Mg ha^-1 (Table 2). The increase in these soil indices may be related to increased Ca and Mg soil contents due to liming. Moreira et al. (2005) and Fageria (2006) reported similar results in Brazilian Oxisols with legumes (alfalfa and bean, respectively).

Lime rates versus shoot dry matter

Shoot dry matter increased quadratically with increasing lime rates in the range of 0 to 10.3 Mg ha^-1 in the first and second cuts and in the average of both (Figure 1), with a significant interaction between cut and lime rate (F value = 6.2958, p < 0.05). In the first cut, maximum shoot dry matter was achieved with the addition of 7.3 Mg ha^-1 lime. Similarly, in the second cut, maximum shoot dry matter was achieved with 8.6 Mg ha^-1 lime. In general, maximum shoot dry matter was obtained with a lime rate of 8.0 Mg ha^-1. The higher lime rate required to achieve maximum shoot dry matter in the second cut compared to first cut can be associated with higher shoot weight and lower pH and base saturation (Table 1). The improvement in alfalfa shoot dry matter with liming in acid soils is widely reported (Adams & Pearson, 1984; Lathwell & Reid, 1984; Moreira et al., 1999). The yield increase of field crops with liming is due to improvement of the Ca and Mg soil contents and reduction of soil acidity (Fageria & Baligar, 2003; Fageria, 2009). In addition, liming also improves biological N₂ fixation in acid soils and enhances net mineralization of organic N (Edmeades & Ridley, 2003). Fageria (2008) reported that N deficiency was observed two weeks after sowing of common bean (Phaseolus vulgaris) in unlimed Oxisol plots, while no N deficiency was observed in the limed plots.

Macro and micronutrient uptake

Significant interaction (p < 0.05) was observed between cut and lime rate for most nutrients analyzed in alfalfa dry matter. The results of two cuts for nutrient uptake showed that the concentration of all nutrients studied in the second cut was lower than in the first cut (Table 3). Similarly to results of Moreira et al (2008), this may be due to a dilution effect, since dry matter was higher in the second than in the first cut and soil nutrient levels exported by shoot dry matter were lower. Fageria (2009) reported that nutrient concentration (nutrient content per unit dry matter) decreased with increasing shoot dry matter in crop plants. This phenomenon is known as dilution effect in plant mineral nutrition (Marschner, 1995; Fageria, 2009). In general, the N, Ca, and Mg concentrations increased with increasing lime rates. This may be associated with higher N₂-fixation rate by N₂-fixing bacteria and higher Ca and Mg uptake with increasing lime rates. The application of limestone significantly increased the N, Ca and Mg concentrations in the dry matter yield, with visual symptoms of Ca deficiency in the control. The adequate nutrient levels for alfalfa are in the range of N: 30 to 50 g kg^-1; P: 2.5 to 7.0 mg kg^-1; K: 20 to 38 mg kg^-1; Ca: 5 to 30 mg kg^-1; Mg: 2.5 to 10 mg kg^-1; S: 2.5 to 5 mg kg^-1; B: 20 to 80 mg kg^-1; Cu: 5 to 30 mg kg^-1; Fe 30 to 250 mg kg^-1; Mn: 25 to 200 g kg^-1; and Zn: 20 to 70 mg kg^-1 (Plank, 1988; Moreira et al., 2008). Using these values as reference, we observed that in the absence of liming, the N, Ca and Mg concentrations were average below the range considered suitable, the inverse was observed for K, P, Fe, Mn and Zn, but these levels declined significantly with increasing the lime rates (Table 3).

Root and nodule dry matter and macronutrient contents in nodule dry matter

There was a significant increase in root and nodule dry matter with increasing lime rates in the range of 0 to 10.3 Mg ha^-1. The variation in root dry matter was 93 % and the variation in nodule dry matter (NDM) was 82 % with liming. Hence, RDM was relatively more sensitive to liming than NDM (Table 4). In agreement with Moreira et al. (2008), a significant effect of liming on these two variables (root and nodule dry matter) was observed. The NDM was significantly correlated with the shoot dry matter (SDM) (SDM = -0.031 + 0.029NDM, R² = 0.77; p < 0.05). As reported by Rhykerd & Overdahl (1972) regarding the sensitivity of biological N₂ fixation because of soil acidity, an increase of 46 % in the N content of nodules at rates of 3.8 to 10.3 Mg ha^-1 was also found. In the case of the P, Ca and Mg levels in the NDM, no influence of the limed treatments was observed (Table 4).

Optimal soil acidity indices

The regression models (Table 5) can indicate the extent to which the dependent variable can be predicted by independent variables. On average, based on R²; the soil acidity indices influencing alfalfa yield followed the order: Mg saturation, base saturation > acidity > pH and Ca saturation. Under tropical conditions, the optimum acidity indices for maximum dry matter yield were pH 5.4, base saturation 57 %, Ca saturation 40 %, and Mg saturation 24 %. Rechcigl et al. (1988) observed that alfalfa can be grown on acid soil at a pH of 5.7 (soil/water slurries) in the 0-15 cm layer.

The relative yield (%) was correlated with the exchangeable Ca, Mg and Ca + Mg (highest values estimated at 2.9, 2.0 and 4.4 cmol_c kg^-1; respectively) (Figure 2). These values are independent of the Ca/Mg ratio, since studies carried out by Moreira et al. (2005) showed an absence of response in function of the Ca and Mg molar ratios at proportions of 1:0, 1:1, 2:1, 3:1, and 4:1, but that excess of Mg in soil (0:1 ratio) can cause phytotoxicity, significantly reducing alfalfa dry matter yield (Gomes et al., 2002).

CONCLUSIONS

1. Liming improved alfalfa root growth and nodulation of the alfalfa root system with N₂-fixing bacteria.

2. Soil chemical properties such as pH, base saturation and Ca and Mg contents were increased, which may be responsible for higher alfalfa yields.

3. The optimum lime rate for a maximum alfalfa dry matter yield is estimated to be about 8.0 Mg ha^-1.

4. Optimum soil acidity indices for maximum yield alfalfa were pH 5.4, base saturation 57 %, Ca saturation 40 % and Mg saturation 24 %.

5. Alfalfa can tolerate acidity of H + Al up to 1.0 cmol_c kg^-1 without reducing dry matter yield.

LITERATURE CITED

Recebido para publicação em agosto de 2009 e aprovado em abril de 2010.

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1

) Trabalho parcialmente financiado pelo CNPq.

Publication Dates

• Publication in this collection
  13 Oct 2010
• Date of issue
  Aug 2010

History

• Received
  Aug 2009
• Accepted
  Apr 2010