Marcos A. Pavan

Control of soil acidity in no-tillage system for soybean production☆

Abstract The common practice for liming no-tillage consists of applying dolomite to soil surface without incorporation into the soil by plowing. The effectiveness of surface application of lime to oxisols under no-tillage, particularly with regard to subsoil acidity, is uncertain. A field experiment was conducted from 1986 to 1991 in the State of Parana, Brazil, to evaluate the extent of downward movement of dolomite and phosphogypsum in an acid soil profile under a no-tillage system, and the effect on soybean yields. The experimental treatments were: control (no amendments), surface dolomite, incorporated dolomite (0–20 cm), surface phosphogypsum, surface 1 2 dolomine (half of the lime requirement) plus surface 1 2 phosphogypsum (half of the phosphogypsum requirement), and surface 1 4 dolomine (one-quarter of the lime requirement applied per year over 4 years). The following results were obtained: a significant reduction in Al and increase in Ca and Mg because of increased pH were measured about 40 cm deep when dolomite is surface applied; the effects of surface dolomite on the acid soil chemistry were essentially the same as those produced by incorporated dolomite; surface phosphogypsum had no effect on pH, increased Ca and decreased Mg; combining phosphogypsum with dolomite improved the soil fertility levels; soybean yields increased with surface and incorporated dolomite, phosphogypsum plus dolomite, and surface 1 4 dolomite annually; and soybean yields decreased with single application of phosphogypsum. It was concluded that for a no-tillage system, surface applied dolomite was effective in improving the fertility of an acid soil below the point of placement, and increased soybean grain yields.

Alterações químicas em solos ácidos após a aplicação de resíduos vegetais

Understanding the chemistry behavior in acid soils during the decomposition of plant residues is very important for the management of these soils. The effects of incubation (0, 15, 30, 60 and 90 days) of finely ground residues of oil seed radish (Raphanus sativus), soybean (Glycine max) and wheat (Triticum aestivum) (at 2 and 4%) with samples of Bw horizon of three Oxisols of the state of Parana, Brazil, on the soil pH, dissolved organic carbon (DOC) and soluble and exchangeable Al, Ca, Mg and K were verified during 1995-1996. DOC and total and soluble Ca, Mg and K were determined in the plant residues. Immediately after application of plant residues (zero time), there were increases in pH, in exchangeable and soluble Ca, Mg, and K, in soluble Al and DOC and a decrease in exchangeable Al. The intensity of these changes was associated with the DOC and with the soluble Ca, Mg and K in the residues, in the following order: oil seed radish > soybean > wheat. During incubation, the DOC of the soil solution rapidly decreased. DOC decrease with the incubation time did not affect K, but drastically reduced Al, Ca and Mg in the soil solution, showing the importance of DOC in the maintenance of cations in solution through the formation mechanism of organic complexes. The chemical speciation estimated that more than 90% of the total Al in solution was in the organic form. The organic and inorganic compositions of the water soluble fraction of plant residues were the main factor responsible for the chemical changes observed in the acid soil samples.

Evaluation of Plant Residues on the Mobility of Surface Applied Lime

Greenhouse experiments were conducted with leaching columns (60 cm long by 15 cm diam.) of disturbed acid soil to evaluate the effect of plant residues on the mobility of surface-applied calcite lime in the soil profile. Plant residues were: black oats, rye, mucuna, leucaena, and wheat straw at a rate of 40 Mg ha-1. Lime and plant residues were applied on soil surface and after an irrigation program equivalent to 1500 mm rainfall per year the following observations were made: pH, exchangeable Ca, Mg, K, and Al and the chemical composition of drainage water. Effect of lime without plant residues was limited to the upper 10 cm profile. Lime with plant residues changed pH, Ca, Mg, and Al in the soil profile. The efficiency of plant residues on lime mobility followed the order: black oats > rye > mucuna > leucaena. Wheat residue had no effect on the mobility of lime. The decrease in Al, Ca and Mg in the upper layer of the profile was followed by an increase in K. Metal-organic complexe reactions were assumed to be the main mechanism on lime mobility through plant residues.

Dinâmica de íons em solo ácido lixiviado com extratos de resíduos de adubos verdes e soluções puras de ácidos orgânicos

The influence of green manure residues addition in the dynamic of ions in acid soils is not well known. In this study, ion mobility in a sample of the Bw horizon of an Dark-Red Latosol (Oxisol), leached with citric and succinic acid pure solutions and with aqueous residue extracts of black oats (Avena strigosa) and oil seed radish (Raphanus sativus) were evaluated in soil columns (5, 10, 20, and 40 cm long by 4 cm diameter). After the solutions and extracts passed through the soil columns, the following parameters were determined: solubles contents of Cas, Mgs, Ks, Alst (total), Also (organic), Alsm (monomeric) and dissolved organic carbon. In soil, the parameters evaluated were the exchangeable contents of Caex, Mgex, Kex, and Alex and pH (CaCl2). Citric and succinic acids increased Alst and Cas contents, respectively, resulting in decreasing exchangeable fractions of these elements in soil. Black oats extract was more effective to extract Caex and oil seed radish to extract Alex. The decrease in Caex and Alex was followed by an increase in Kex. Organic complexes formed with low molecular organic ligands and Cas and Alex were suggested to play a role in the mobility of ions in subsoils of acid soils after the addition of both crop residues extracts and pure organic acid solutions.

Alleviating soil acidity through plant organic compounds

A laboratory experiment was conducted to evaluate the effects of water soluble plant extracts on soil acidity. The plant materials were: black oat, oil seed radish, white and blue lupin, gray and dwarf mucuna, Crotalaria spectabilis and C. breviflora, millet, pigeon pea, star grass, mato grosso grass, coffee leaves, sugar cane leaves, rice straw, and wheat straw. Plant extracts were added on soil surface in a PVC soil column at a rate of 1.0 ml min-1. Both soil and drainage water were analyzed for pH, Ca, Al, and K. Plant extracts applied on the soil surface increased soil pH, exchangeable Caex and Kex and decreased Alex. Oil seed radish, black oat, and blue lupin were the best and millet the worst materials to alleviate soil acidity. Oil seed radish markedly increased Al in the drainage water. Chemical changes were associated with the concentrations of basic cations in the plant extract: the higher the concentration the greater the effects in alleviating soil acidity.

Formas orgânicas e inorgânicas de mobilização do cálcio no solo

Lack of Ca and often the presence of Al in subsoil restrict crop-root proliferation. The efficacy of soil surface liming in neutralize subsoil acidity is limited. Laboratory experiments were conducted with leaching columns to evaluate some organic and inorganic techniques to accelerate the mobility of Ca in a variable charge soil. Two different experiments were conducted, one with Ca-salts: CaCO3, CaSO4, Ca(NO3)2, Ca-acetate, and Ca-citrate; and another one with CaCO3 plus plant residues: black oat (Avena strigosa), wheat (Triticum aestivum) and leucaena (Leucaena leucocephala). The observations included MKCl exchangeable Ca in 0 to 5, 5 to 10, 10 to 20, 20 to 30, 30 to 40 and 40 to 50 cm soil depth. The effects of CaCO3 without plant residue was limited to the upper 10 cm of the profile. The efficacy of Ca-salts on the mobility of Caex followed the order: NO3 > Acetate > Citrate > SO4 > CO3. Plant residues were highly efficient as Ca-carrier in the following order black oat > leucaena > wheat. Metal-organic complexes were assumed to be responsible for the movement of Ca in the profile associated with lime and plant residues.

Potencial de extratos de resíduos vegetais na mobilização do calcário no solo por método biológico

Soil surface applied lime shows low efficiency in alleviating subsoil acidity. Lime efficiency is increased through water-soluble organic compounds released from plant residues. A biological test was evaluated to verify the capacity of plant extracts on lime mobility in the soil. The test presents the following steps: plant material preparation; extraction of water soluble organic compounds; soil column preparation; soil surface lime addition; plant extract addition; irrigation with distillated water; biological test with an indicator plant (wheat, cultivar Anahuac); and root growth evaluation. Surface applied lime without plant residue increased pH and Ca, and decreased Al in the top 5 cm of soil. Lime with black oats and oil seed radish extracts increased pH and Ca and decreased Al up to the 20 cm soil depth. Wheat residue had no effect on lime mobility. Indicator root growth followed the effect of treatments on soil chemical composition: lime without plant residue enhanced root growth in the top 10 cm depth and lime with black oats and oil seed radish enhanced root growth up to the 20 cm depth. The biological test was efficient to evaluate the ability of plant residues in relation to lime mobility in the soil.

Densidade populacional de cafeeiros para melhorar a fertilidade de um latossolo

The objective of this work was to evaluate the effect of coffee (Coffea arabica L.) population densities on the chemical and microbiological properties of an Oxisol. The work was carried out on soil samples of 0-20 cm depth originated from an experimental site which had been used for coffee tree spacing studies during 15 years, in Parana State, Brazil. Eight coffee tree populations were evaluated: 7143, 3571, 2381, 1786, 1429, 1190, 1020, and 893 trees/ha. Increasing plant population increased soil pH, exchangeable Ca, Mg, K, extractable P, organic carbon, moisture content and coffee root colonization by vesicular arbuscular mycorrhizal fungi, and decreased exchangeable Al and microbial biomass. Such results were attributed to better erosion control, improved plant residue management and nutrient cycling, and decreased leaching losses. Increasing coffee tree population per unit of area has shown to be an important reclamation recuperation strategy for improving fertility of the acid soils in Parana, Brazil.

Evaluation of oat extracts on the efficiency of lime in soil

A baixa mobilidade dos componentes soluveis do calcario aplicado na superficie do solo limita a sua eficiencia na reducao da acidez das camadas subsuperficiais de solos com cargas variaveis. Foram conduzidos experimentos de laboratorio com latossolo acido para avaliar a eficiencia de extratos de aveia na mobilidade do calcario aplicado na superficie do solo. Foram avaliadas as seguintes cultivares de aveia: Argentina 5VL3, UPF 90H400-2, IAPAR 61, IA96101-b, SI 83400, EMBRAPA 29, LD 9102, FAPA 1, ER 93247, ER 90148, ER 89144, ER 93152, Alpha 94124, Alpha 94206 and Preta comum. O calcario e a aveia foram aplicados em doses equivalentes a 5 e 10 Mg ha-1, respectivamente. O efeito da calagem sem residuos vegetais limitou-se nos 10 cm superficiais do solo. A calagem na presenca de extratos de aveia aumentou o pH e Ca-trocavel e diminuiu Al-trocavel ate 25 cm de profundidade. As cultivares SI 83400 e UPF 90H400-2 foram as melhores transportadoras de Ca no perfil do solo. Os resultados sugerem que compostos soluveis contidos nos extratos de aveia, melhoram a eficiencia do calcario aplicado na superficie dos solos.

Plantas invasoras para melhorar a eficiência da calagem na correção da acidez subsuperficial do solo

Studies with soil columns (O = 4 cm; h = 25 cm) were carried out under laboratory conditions in the years 1999 and 2000, in Londrina, using the Bw horizon of a Red Latosol. The following weed species were tested: Synedrellopsis grisebachii, Acanthospermum hispidum, Amaranthus hybridus, Leonotis nepetifolia, Parthenium hysterophorus, Ricinus communis, Galinsoga parviflora and Commelina benghalensis. Shoot extracts (3 g in 150 mL of water) were applied onto the soil surface with a lime top dressing and then leached with three pore volumes of deionized water. Alterations of soil pH and exchangeable cation contents were determined, taking samples from soil layers of 5 cm and leached solutions from the columns. Liming without plant extracts increased soil pH and Ca and decreased Al in the top layer, and, less intense, in the 5-10 cm layer. Liming with plant extracts increased soil pH and reduced Al down to 20 cm of depth. Ricinus communis presented the greatest capacity as Ca carrier, increasing its content down to 15 cm of depth. G. parviflora and C. benghalensis reduced soil acidity most effectively and also stimulated highest Al leaching, while least effective weeds were S. grisebachii and A. hispidum. The tested plant extracts present potential to transfer lime alkalinity to acid soil subsurface.