Sérgio Ely Valadão Gigante de Andrade Costa

Estoques de carbono orgânico e de nitrogênio no solo em sistema de integração lavoura-pecuária em plantio direto, submetido a intensidades de pastejo

Sistemas de integracao lavoura-pecuaria tem um alto potencial de uso no sul do pais, especialmente em areas de soja sob plantio direto, com especies de cobertura no inverno. A conducao de sistemas de integracao com diferentes intensidades de manejo da pastagem resultara, ao longo do tempo, em estoques de C orgânico (CO) e de N diferenciados, decorrentes do aporte diferenciado de residuos. Este trabalho foi realizado para avaliar a evolucao dos estoques de CO e de N total (NT) e em fracoes fisicas da materia orgânica em solo submetido a diferentes intensidades de pastejo, em plantio direto. O experimento foi iniciado em 2001, em um Latossolo Vermelho distrofico, apos a colheita da soja. Os tratamentos constaram de alturas de manejo da pastagem (aveia-preta + azevem): 10, 20 e 40 cm, com bovinos jovens, e sem pastejo, seguido do cultivo de soja, em delineamento de blocos ao acaso. Amostras de solo foram retiradas no inicio do experimento (maio 2001), apos tres anos (maio de 2004) e apos seis anos (maio de 2007), para a avaliacao dos teores e dos estoques de CO e de NT. Intensidades de pastejo moderadas (20 e 40 cm de altura do pasto) promoveram aumento nos estoques de CO total, CO particulado, NT e N na materia orgânica particulada no solo, semelhante ao plantio direto sem pastejo. Na alta intensidade de pastejo (10 cm), houve reducao no estoque desses elementos, com degradacao da qualidade da materia orgânica.

Carbono orgânico e fósforo microbiano em sistema de integração agricultura-pecuária submetido a diferentes intensidades de pastejo em plantio direto

Integrated crop-livestock systems have attracted more interest in the last few years due to their capacity of improving stability and sustainability of agricultural systems as compared to more specialized production systems. Soil organic carbon content has been used as an indicator of soil sustainability and stability. In this sense, this study aimed to measure the stocks of total organic carbon fractions and phosphorus in the microbial biomass in a Rhodic Hapludox (Oxisol) under integrated crop-livestock system with different grazing intensities in the winter. Soil samples were collected in November 2006 in Sao Miguel das Missoes, state of Rio Grande do Sul, Brazil. The experimental area had been cultivated under no-tillage for 10 years before implementing the integrated system in 2001. The experimental design was completely randomized blocks with three replicates. The treatments consisted of grazing intensities represented by sward heights of 10, 20 and 40 cm during the pasture cycle in winter. This pasture was composed of a black oat (Avena strigosa Schreb) and Italian ryegrass (Lolium multiflorum Lam.) mix, and a control area with no grazing. Total and particulate organic matter (POM) carbon stocks, phosphorus and carbon content in the microbial biomass, as well as microbial biomass activity were evaluated. The total organic stocks carbon were not affected by grazing intensities; however, the stocks of POM carbon were smaller in soils under the highest grazing intensity. The microbial biomass was stimulated at the highest grazing intensity, in which greater root growth was observed. The phosphorus content in the microbial biomass increased linearly with the decrease of the grazing intensity, while an inverse pattern was observed for the microbial biomass. Particulate organic matter carbon was more sensitive to changes in soil organic carbon under the experimental pasture management.

Biomassa microbiana do solo em sistema de integração lavoura-pecuária em plantio direto, submetido a intensidades de pastejo

Em sistemas de integracao lavoura-pecuaria, boa parte do suprimento de nutrientes para as pastagens provem das excrecoes dos animais, na forma de esterco e de urina, o que resulta em estimulo a atividade e ao acumulo de nutrientes nas suas celulas. Este estudo foi desenvolvido num experimento de integracao lavoura-pecuaria em plantio direto, iniciado em 2001, e objetivou avaliar o impacto de diferentes intensidades de pastejo da pastagem de inverno (aveia-preta + azevem; 10, 20 e 40 cm, e um tratamento sem pastejo) sobre a atividade microbiana e sobre os teores e estoques de C, N e P na biomassa microbiana na camada de 0-10 cm de um Latossolo Vermelho, no Sul do Brasil, durante o ciclo da pastagem. Os teores e estoques dos nutrientes na biomassa e a atividade microbiana foram alterados pela intensidade de pastejo e pela epoca no ciclo da pastagem. Os teores de C e de P microbiano aumentaram do inicio da pastagem, em maio, ate o periodo de grande producao de fitomassa, em setembro, apos o qual decresceram, acompanhando o inicio de senescencia da pastagem. Por sua vez, o N microbiano decresceu de maio para novembro, possivelmente devido a absorcao desse nutriente pelas plantas. Sistemas de integracao lavoura-pecuaria em plantio direto mantem a qualidade biologica do solo, sendo, sob adequada lotacao animal, similar ao sistema plantio direto sem a entrada de animais. No entanto, sob alta intensidade de pastejo (10 cm) ha perdas nessa qualidade do solo em condicoes de estresse hidrico.

Resposta do arroz irrigado ao suprimento de amônio e nitrato

In rice cultivated under flooded conditions, the anaerobic condition favors the formation of NH4+ in the soil, and is therefore considered the main available N source for this crop. However, the process of O2 transport through the aerenchyma and its release by roots, create a favorable environment for nitrification in the plant rizosphere. Nitrification intensity determines the proportions between available NH4+ and NO3- . In this case, it is believed that the presence of NO3- can favor rice growth and simultaneously avoid NH4+ toxicity. This experiment was carried out to evaluate the effect of different proportions between NH4+ and NO3- in nutrient solution on rice growth. The experiment was performed in a greenhouse, from September to November 2007, in a nutrient solution with the following NH4+ and NO3- proportions: 100:0, 75:25 and 25:75, in a 10.0 mmol L-1 N concentration. The plots were fulfilled with a inert substrate to create conditions to root growth. The genotypes IRGA 417 and Sasanishiki were compared and the biomass production, root length, root distribution and the N, Ca, Mg and K uptake were evaluated. The presence of NH4+ in the 100:0, 75:25 proportions resulted in plant toxicity, however, as the NO3- proportion increased, toxicity was reduced. The combined supply of NH4+ and NO3- increased biomass production compared to solely NH4+ supply. The rice root system of the two cultivars developed mainly in the 0-10 cm layer and the - greatest root length was observed in the treatment NH4+ 75:25 NO3- for IRGA 417. The presence of NH4+ in soil solution affected negatively calcium absorption, whereas no affect was observed on N, Mg or K absorption. The total absorbed N, K, and Ca indicated a higher absorption efficiency with the combined supply for IRGA 417, but for cultivar Sasanishiki no differences were verified. It was concluded that NH4+ is toxic to rice plants, and is not the main available source of nitrogen. Nitrate is indispensable to increase the N uptake, normal plant growth and total cation absorption.

Phosphorus and root distribution and corn growth as related to long-term tillage systems and fertilizer placement

Soil and fertilizer management during cultivation can affect crop productivity and profitability. Long-term experiments are therefore necessary to determine the dynamics of nutrient and root distribution as related to soil profile, as well as the effects on nutrient uptake and crop growth. An 18-year experiment was conducted at the Federal University of Rio Grande do Sul State (UFRGS), in Eldorado do Sul, Brazil, on Rhodic Paleudult soil. Black oat and vetch were planted in the winter and corn in the summer. The soil management methods were conventional, involving no-tillage and strip tillage techniques and broadcast, row-and strip-applied fertilizer placement (triple superphosphate). Available P (Mehlich-1) and root distribution were determined in soil monoliths during the corn grain filling period. Corn shoot dry matter production and P accumulation during the 2006/2007 growing season were determined and the efficiency of P utilization calculated. Regardless of the degree of soil mobilization, P and roots were accumulated in the fertilized zone with time, mainly in the surface layer (0-10 cm). Root distribution followed P distribution for all tillage systems and fertilizer treatments. Under no-tillage, independent of the fertilizer placement, the corn plants developed more roots than in the other tillage systems. Although soil tillage systems and fertilizer treatments affected P and root distribution throughout the soil profile, as well as P absorption and corn growth, the efficiency of P utilization was not affected.

Crescimento e nutrição da braquiária em função de fontes de fósforo

Avaliaram-se, em casa de vegetacao, as contribuicoes de diferentes fontes de fosforo (P) aplicadas em amostras de Latossolo Vermelho distroferrico (LVdf) (350 mg dm-3 de P2O5) e de Neossolo Quartzarenico (NQ) (200 mg dm-3 de P2O5), coletadas nos municipios de Lavras (MG) e Itutinga (MG), respectivamente, na producao de materia seca, no teor e acumulo de P na parte aerea e raiz da Brachiaria brizantha cv. Marandu. Tambem foi avaliado o indice de eficiencia agronomica (IEA) das fontes. O experimento foi conduzido em um delineamento experimental inteiramente casualizado, em esquema fatorial 2x4 (dois solos e quatro fontes de fosforo (Superfosfato Triplo (ST), Fosfato Reativo de Arad (FR), Fosfato Natural de Araxa (FA), e uma mistura ST+FR - na relacao (1:1), com quatro repeticoes. A dose de fosforo foi baseada no teor de P2O5 total das fontes. Para a producao total de materia seca e o acumulo total de P, as fontes de maior solubilidade, como o ST, FR e a mistura ST/FR foram mais eficientes, principalmente no primeiro, terceiro e quarto cortes no LVdf e em todos os cortes no NQ. O teor total de P na braquiaria ao final do ultimo corte foi maior quando se aplicaram as fonte FR e ST+FR para o LVdf e, ST e ST+FR para o NQ. As fontes de fosforo influenciaram o IEA nos dois solos, que foi maior para as fontes de maior solubilidade.

Distribuição de potássio e de raízes no solo e crescimento de milho em sistemas de manejo do solo e da adubação em longo prazo

Soil tillage systems can greatly influence potassium and root distribution in the soil and, as a result, affect corn growth and development. To improve the understanding of these interrelationships, a soil was analyzed after 18 years of cultivation under different management systems. A detailed soil sampling was carried out in a clayey Red Argisol (Udult) profile in the beginning of the grain filling stage of corn in the 2006/07 growing season. The experimental design consisted of a completely randomized scheme with two replicates, with the following treatments: conventional tillage (Con) and no-tillage (Dir) with potassium fertilization: along the rows (Fx), broadcast (Lan) and in stripes (Lin). Independently of the soil and fertilizer management, potassium formed gradients from the soil surface downwards and around the corn plant stem. The gradients, however, differed according to the soil management; concentrations were higher at the surface under no-tillage, regardless of the fertilization method. Maize roots were concentrated predominantly in the soil surface layer, with greater growth in no-tillage. Potassium uptake and maize growth were not associated with K distribution in soil and roots. The efficiency of K use by plants was increased by the broadcast application of potassium fertilizer, regardless of the tillage system.

Concentração do potássio do solo em sistema de integração lavoura-pecuária em plantio direto submetido a intensidades de pastejo

A dinâmica de K em sistemas de integracao lavoura-pecuaria (ILP) diverge daquelas de outros sistemas de manejo, porque os sistemas ILP sao mais complexos e envolvem, alem das praticas relacionadas a cultura de interesse economico, a introducao do animal. Objetivou-se, neste trabalho, avaliar as concentracoes do K do solo em um sistema ILP, em plantio direto, com diferentes intensidades de pastejo (aveia-preta + azevem) de bovinos no inverno e a cultura da soja cultivada no verao. O experimento foi iniciado em maio de 2001 em area pertencente a Fazenda do Espinilho, localizada no municipio de Sao Miguel das Missoes - RS, em Latossolo Vermelho distroferrico que vinha sendo cultivado em plantio direto desde 1991. Os tratamentos constaram de intensidades de pastejo: 10, 20, 30 e 40 cm de altura do pasto e um tratamento sem pastejo, distribuidos num delineamento experimental de blocos ao acaso, com tres repeticoes. Os teores de K disponivel eram originalmente altos e assim se mantiveram ao longo do tempo, independentemente do tratamento de pastejo. Em todas as situacoes houve a formacao de um gradiente decrescente de concentracao de K a partir da superficie, sendo maior apos pastagem que apos soja. A ausencia do pastejo, apesar de propiciar menor ciclagem de K, resultou em maiores teores do nutriente no solo, em relacao as areas com animais, especialmente aquelas intensamente pastejadas, devido as perdas causadas, provavelmente, pelas excretas.

Umidade do solo e fisiologia da soja afetados por estiagem em sistema de integração lavoura‑pecuária

The objective of this work was to evaluate the impact of grazing intensities after 11 years of an integrated crop‑livestock system, under no‑tillage, on soil moisture and soybean physiological parameters during a summer season affected by drought. The experiment was established in 2001 on a Rhodic Hapludox. Treatments consisted in the succession of soybean (summer) and a mixed pasture of black oat + Italian ryegrass (winter), under different beef‑cattle grazing intensities: intensive grazing, with 0.10‑m pasture height; moderate grazing, with 0.20‑m pasture height; and no grazing. During the soybean cycle, in the 2011/2012 crop season, rainfall was 40% of the climatological normal. The soil moisture was within the limits of available water both under moderate grazing and no grazing, at 0.00–0.50‑m soil depth, but, under intensive grazing, it was below the permanent wilting point, especially up to the grazing height of 0.20 m. Intensive grazing affected negatively the plant physiology parameters, reaching peaks of ‑2.5 MPa and +6°C for leaf water potential and leaf‑air temperature difference, respectively. Moderate grazing or the absence of grazing, during the winter season, results in similar physiological responses, contributing to soybean plant homeostasis.