The disposal of biosolids and water treatment residuals on soils of arid regions: a glasshouse investigation

Land co-application of biosolids and WTR is a new concept. Therefore, information on the effect of co-application of biosolids and WTR on plant growth and elements uptake are very limited especially in alkaline soils. A glasshouse experiments was established to evaluate the effects of co-application of WTR and biosolids on agronomic performance of wheat crop grown in alkaline soils as well as P plant concentration and uptake, and to improve management of industrial and toxic wastes and provides environmentally sound guidelines for their disposal. The results indicated that increases of 47, 359 and 55 % in total dry matter yield were achieved as a result of applying 40 gkg-1 WTR and 10 gkg-1 biosolids to clay, sandy and calcareous soils respectively. In all studied soils treated with a constant biosolid rate 10 gkg-1, application of 20 gkg-1 WTR significantly increased plant P concentration in the plant materials. Combined analyses of all soils ,all treatments of biosolid and WTR rates studied indicated clearly significant relationships between ABDTPA P concentration and P uptake (r = 0.81, p < 0.001)

Resíduos de plantas de cobertura e mobilidade dos produtos da dissolução do calcário aplicado na superfície do solo Cover plant residues and mobility of dissolution products of surface applied lime

As plantas de cobertura têm recebido atenção adicional em função da liberação de ácidos orgânicos de baixo peso molecular capazes de formar complexos orgânicos com alumínio, cálcio e magnésio. Dessa forma, além de neutralizarem o alumínio tóxico, esses ácidos podem aumentar a mobilidade, no perfil do solo, dos produtos originados da dissolução do calcário aplicado na superfície. Os objetivos deste trabalho foram (a) identificar os ácidos orgânicos de baixo peso molecular presentes nos resíduos de plantas de cobertura e na solução do solo; (b) avaliar o efeito desses resíduos, juntamente com a aplicação superficial de calcário, na correção da acidez das camadas subsuperficiais do solo no sistema plantio direto, e (c) verificar a relação dos ácidos orgânicos de baixo peso molecular, liberados na decomposição de resíduos vegetais, com os efeitos, na profundidade do solo, da aplicação superficial de calcário. O experimento foi realizado em casa de vegetação em colunas de PVC com amostras indeformadas de um Cambissolo Húmico Alumínico Léptico argiloso há cinco anos no sistema plantio direto. Os tratamentos constaram da aplicação de resíduos (10 Mg ha-1) de aveia preta (1), ervilhaca (2) e nabo forrageiro (3), calcário (13 Mg ha-1) (4), calcário mais resíduo de aveia preta (5), de ervilhaca (6) e de nabo forrageiro (7) calcário mais ácido cítrico (0,91 Mg ha-1) (8) e uma testemunha (9), dispostos em blocos ao acaso. O uso da cromatografia líquida permitiu identificar os ácidos orgânicos de baixo peso molecular nos resíduos vegetais utilizados. Na aveia preta, houve predomínio do ácido transaconítico, na ervilhaca predominou o ácido málico e no nabo forrageiro os ácidos cítrico e málico. Não foi possível detectar nenhum tipo de ácido orgânico de baixo peso molecular tanto na solução percolada como na solução do solo. Os resíduos vegetais não tiveram efeito na correção da acidez do solo em profundidade. Seus efeitos restringiram-se na camada de 0-2,5 cm, tanto isoladamente como junto com o calcário.<br>Cover plants have received extra attention due to their release of low molecular weight organic acids that form organic complexes with aluminum, calcium and magnesium. Besides neutralizing toxic aluminum, such compounds can increase the mobility in the soil profile of the dissolution products of lime applied on the soil surface. Objectives of this research were (a) to identify the low molecular weight organic acids found in different cover plant species and in soil solution, (b) to evaluate the effects of the residues, alone or together with surface lime application, in relation to acidity neutralization of subsoil layers in no-tillage systems, and (c) to verify the relation between organic acids of low molecular weight, released during the decomposition of plant residues, with the effect on soil acidity properties in the soil profile due to surface lime application. The experiment was carried out in a greenhouse in undisturbed Inceptisol (Haplumbrept) soil samples in columns, collected in a field experiment under no-tillage for five years. Nine treatments were applied: residue (10 Mg ha-1) of black oat (1), common vetch (2), oil seed radish (3), lime (13 Mg ha-1) (4), lime plus residue of black oat (5), of common vetch (6), of oil seed radish (7), and lime plus citric acid (0.91 Mg ha-1), (8) and no treatment (9), arranged in randomized blocks. The liquid chromatography method (HPLC) allowed an identification of the main low molecular weight organic acids in the plant residues. Trans-aconitic acid was the most important in black oat, malic acid in common vetch, and citric and malic acids in oil seed radish. It was not possible to detect organic acids in the percolate or soil solution. Plant residues had no effect on acidity neutralization in the deeper soil since the effects, alone or with lime application on the soil surface, were restricted to the soil surface layer (0-2.5 cm)

Differences between soil solutions obtained from rhizosphere and non-rhizosphere soils by water displacement and soil centrifugation

Soil solution was obtained from potted rhizosphere or non-rhizosphere soils by water displacement or soil centrifugation. The pH of the displaced solutions was lower than that of bulk soils when solutions were obtained from non-rhizosphere soil, although it increased as plants grew. This increase probably reflected true changes in rhizosphere pH, generated by the uptake by plants of NO3-N. In contrast, the pH of soil centrifugates was usually close to that of the bulk soils, implying that buffering by colloids had occurred during sampling. Concentrations of elements in solutions from non-rhizosphere soil were similar for both methods when soils were incubated at ambient pCO(2). However, when non-rhizosphere soils were incubated at elevated pCO(2), displacement solutions had lower pH values, and much larger concentrations of elements, compared to soil centrifugates. Comparison of mass flow of elements versus actual plant uptake showed that Ca and Mg accumulated, while K, Zn and Cd were depleted from the rhizosphere. Displacement solutions showed this accumulation or depletion of the elements more clearly than soil centrifugates. These differences were attributed to the fact that, at constant soil moisture, the rhizosphere developed mainly in larger pores, which were sampled by displacement. With centrifugation, a mixture of pore sizes was sampled, so that rhizosphere solution was only obtained when all of the soil had become rhizosphere. Soil centrifugates obtained after 22 days of growth also contained higher concentrations of organic carbon than displacement solutions, indicating contamination due to the disruption of roots and/or micro-organisms. We conclude that water displacement is suitable for sampling solution from light to medium textured rhizosphere or non-rhizosphere soils and that soil centrifugation is only of limited suitability

Composição química da solução de solo sob diferentes coberturas vegetais e análise de carbono orgânico solúvel no deflúvio de pequenos cursos de água Chemical composition of soil solution under different land cover and soluble organic carbon in water from small creeks

O cultivo intensivo pode alterar a composição química da solução do solo, favorecendo a perda de solutos. Dessa forma, poderia mudar a composição química dos cursos de água. Foi realizado um estudo na fazenda da EPAMIG em Oratórios, Minas Gerais, de junho de 1996 a maio de 1997, para avaliar o efeito do manejo do solo na composição química da solução do solo, considerando as condições climáticas. O carbono orgânico solúvel também foi determinado na solução do solo e no deflúvio de pequenos cursos de água. Foram realizadas extrações mensais da solução do solo sob diferentes coberturas vegetais, nas camadas de 0-20, 20-40 e 40-100 cm de profundidade. A extração da solução do solo foi feita por centrifugação, a uma força centrífuga relativa correspondente a 900 g. Em acréscimo, foram feitas coletas semanais de deflúvio de quatro pequenos cursos de água com uso variado de suas respectivas áreas de drenagem. Foi observada uma ligeira elevação na concentração de íons em solução com o início do período chuvoso, sendo esse fato mais acentuado para o carbono orgânico solúvel na solução do solo e no deflúvio. A adubação mineral promoveu o deslocamento de íons trocáveis, em profundidade. A lixiviação foi favorecida, principalmente, no solo sem cobertura vegetal. A movimentação de carbono orgânico solúvel foi maior no solo sob pastagem, apesar do menor teor na solução do solo, em comparação aos outros solos. No curso de água drenado em área de pastagem, também foi encontrada a maior concentração de carbono orgânico solúvel.<br>Intensive land use can change the chemical composition of the soil solution and cause solute losses. Thus, it can alter the chemical composition of water courses. A study was carried out in a farm of EPAMIG in Oratorios, state of Minas Gerais, Brazil, from June 1996 to May 1997, to evaluate the effect of soil management on the chemical composition of soil solution, taking climatic conditions into consideration. Soluble organic carbon was also determined in the soil solution and in water streams of small watersheds. Soil solution was extracted monthly from soils under different land uses from three layers: 0 to 20, 20 to 40 and 40 to 100 cm. The soil solution was extracted by centrifugation, at a relative centrifuge force of 900 g. Additionally, water samples were collected from four creeks draining out of watersheds under different land uses. A slight increase in the ion concentration was observed in the soil solution in the beginning of the wet season. The changes were pronounced for the soluble organic carbon in the soil solution and water streams. Soil fertilization promoted the displacement of exchangeable ions to the soil solution down through the soil profile. The highest soil leaching was found for the bare soil. The soluble organic carbon movement across the soil profile was higher under pasture, even though its concentration was the lowest compared to the other land uses. The highest soil organic carbon was observed in water of a creek draining out of a pasture watershed