Telmo Jorge Carneiro Amado

Organic matter storage in a sandy clay loam Acrisol affected by tillage and cropping systems in southern Brazil.

Soil organic matter decline and associated degradation of soil and environmental conditions under conventional tillage in tropical and subtropical regions underline the need to develop sustainable soil management systems. This study aimed first to evaluate the long-term effect (9 years) of two soil-tillage systems (conventional tillage: CT, and no-tillage: NT) and two cropping systems (oat (Avena strigosa Schreb)/maize (Zea mays L.): O/M; and oatacommon vetch (Vicia sativa L.)/ maizeacowpea (Vigna unguiculata (L.) Walp): OaV/MaC without N fertilization on total organic carbon (TOC) and total nitrogen (TN) concentrations in a sandy clay loam Acrisol in southern Brazil. The second objective was to assess soil potential for acting as an atmospheric CO2 sink. Under NT an increase of soil TOC and TN concentrations occurred, in both cropping systems, when compared with CT. However, this increase was restricted to soil surface layers and it was higher for OaV/MaC than for O/M. The OaV/MaC under NT, which probably results in the lowest soil organic matter losses (due to erosion and oxidation) and highest addition of crop residues, had 12 Mg ha ˇ1 more TOC and 0.9 Mg ha ˇ1 more TN in the 0‐30.0 cm depth soil layer, compared with O/M under CT which exhibits highest soil organic matter losses and lowest crop residue additions to the soil. These increments represent TOC and TN accumulation rates of 1.33 and 0.10 Mg ha ˇ1 per year, respectively. Compared with CT and O/M, this TOC increase under NT and OaV/MaC means a net carbon dioxide removal of about 44 Mg ha ˇ1 from the atmosphere in 9 years. NT can therefore be considered, as it is in temperate climates, an important management strategy for increasing soil organic matter. In the tropicals and subtropicals, where climatic conditions cause intense biological activity, in order to maintain or increase soil organic matter, improve soil quality and contribute to mitigation of CO2 emissions, NT should be associated with cropping systems resulting in high annual crop residue additions to soil surface. # 2000 Elsevier Science B.V. All rights reserved.

Recomendação de adubação nitrogenada para o milho no RS e SC adaptada ao uso de culturas de cobertura do solo, sob sistema plantio direto

O nitrogenio, na maioria das situacoes, e o nutriente que mais influencia o rendimento do milho. O manejo da adubacao nitrogenada deve satisfazer o requerimento da cultura com o minimo de risco ambiental. Para tanto, e necessario que a recomendacao da dose de adubo nitrogenado seja a mais exata possivel. A generalizacao do uso do sistema de plantio direto e culturas de cobertura, no Sul do Brasil, criou a necessidade de ser a recomendacao da adubacao nitrogenada adaptada a este novo cenario agricola. O presente trabalho, alem de considerar o teor de MO e a expectativa do rendimento de graos de milho na recomendacao da adubacao nitrogenada conforme preconiza a CFS-RS/SC (1995), propoe a introducao de um terceiro parâmetro que e a contribuicao em N das culturas de cobertura antecedente. O efeito das culturas de cobertura foi considerado em tres situacoes: leguminosas em cultivo solteiro, gramineas em cultivo solteiro e consorciacoes. No caso de leguminosas e gramineas em cultivo solteiro, a influencia na disponibilidade de N foi considerada com base na producao de materia seca, enquanto, nas consorciacoes, a proporcao da leguminosa foi o principal fator considerado. A recomendacao de adubacao apresentada neste trabalho nao dispensa acompanhamento de campo, visando a ajustes que se fizerem necessarios, especialmente porque sistemas de producao, baseados em culturas de cobertura, dependem de processos biologicos influenciados por condicoes de clima, manejo e solo, que devem ser acompanhados localmente.

Atributos físicos do solo em sistema de integração lavoura-pecuária sob plantio direto

Soil compaction is one of the most important reasons for decrease in crop yield. The impact of animal trampling on integrated beef cattle raising-crop production systems were studied to evaluate the changes in soil physical properties (bulk density, porosity, soil resistance to penetration and soil water infiltration). The field experiment was carried out in Jari, in the mid- plateau region of Rio Grande do Sul State, Brazil. Three management systems of winter pastures (black oat; Avena strigosa Schreber + ryegrass; Lolium multiflorum Lam.) were studied under different grazing frequencies: (1) No grazing (NG), (2) grazing every 28 days (G28) and (3) grazing every fourteen days (G14). The summer crops soybean (Glycine max (L.) Merr.) or corn (Zea mays L.), as antecedent crop in rotation to the winter pastures, were also studied to measure the increasing or decreasing effects on compaction by animal trampling. The greatest effects of animal trampling were concentrated in the top soil layer (0 to 0.05 m), but under the highest grazing frequency (G14) macroporosity was reduced down to the 0.10-0.15 m layer. The soil resistance to penetration had peaks of 2.61 and 2.49 MPa in the G28 and G14 treatments, respectively, in the 0.05-0.08 layer. In the ungrazed areas the values remained lower, around 1.66 MPa. Soil water infiltration was significantly affected by animal trampling and by the previous summer crop. In the case of corn area, the soil was less sensitive to cattle trampling, unlike in the areas following soybean, where the highest grazing frequency (G14) reduced the water infiltration rates. Soybean induced higher values of macroporosity in the evaluated soil layers; when related with lower beef cattle density or ungrazed pastures, the rates of water infiltration and accumulated infiltration were higher.

Leguminosas e adubação mineral como fontes de nitrogênio para o milho em sistemas de preparo do solo

O nitrogenio e um nutriente requerido em grande quantidade pelo milho. O solo tem limitada capacidade de atender a esta demanda, sendo por isto utilizadas outras fontes de N como leguminosas e adubacao mineral. A combinacao destas duas fontes de N pode contribuir para a sustentabilidade do agroecossistema. Com o objetivo de avaliar a disponibilidade de N em sistemas de preparo do solo e cultura, foi realizada esta pesquisa, utilizando um experimento de longa duracao na UFRGS (RS) em um Argissolo Vermelho-Escuro distrofico. Os tratamentos utilizados foram tres sistemas de preparo: convencional, reduzido e direto; tres sistemas de cultura: aveia/milho, aveia + ervilhaca/milho + caupi e ervilhaca/milho, e tres doses de N: 0, 90 e 180 kg ha-1 aplicadas em cobertura no milho. A associacao do sistema plantio direto com o uso de leguminosas foi eficiente em promover o aumento do estoque de N total no solo. Embora tenha sido constatada maior velocidade de decomposicao de residuos no preparo convencional do que no plantio direto, ambos os sistemas apresentaram potencial de sincronismo da liberacao de N dos residuos com a demanda do milho. Esta cultura no sistema plantio direto apresentou menor producao de materia seca e absorcao de N do que no preparo convencional, porem nao houve diferenca no rendimento entre estes sistemas de preparo. A equivalencia em fertilizante nitrogenado foi estimada em 55 e 38 kg ha-1, respectivamente, para a ervilhaca e aveia + ervilhaca.O nitrogenio e um nutriente requerido em grande quantidade pelo milho. O solo tem limitada capacidade de atender a esta demanda, sendo por isto utilizadas outras fontes de N como leguminosas e adubacao mineral. A combinacao destas duas fontes de N pode contribuir para a sustentabilidade do agroecossistema. Com o objetivo de avaliar a disponibilidade de N em sistemas de preparo do solo e cultura, foi realizada esta pesquisa, utilizando um experimento de longa duracao na UFRGS (RS) em um Argissolo Vermelho-Escuro distrofico. Os tratamentos utilizados foram tres sistemas de preparo: convencional, reduzido e direto; tres sistemas de cultura: aveia/milho, aveia + ervilhaca/milho + caupi e ervilhaca/ milho, e tres doses de N: 0, 90 e 180 kg ha-1 aplicadas em cobertura no milho. A associacao do sistema plantio direto com o uso de leguminosas foi eficiente em promover o aumento do estoque de N total no solo. Embora tenha sido constatada maior velocidade de decomposicao de residuos no preparo convencional do que no plantio direto, ambos os sistemas apresentaram potencial de sincronismo da liberacao de N dos residuos com a demanda do milho. Esta cultura no sistema plantio direto apresentou menor producao de materia seca e absorcao de N do que no preparo convencional, porem nao houve diferenca no rendimento entre estes sistemas de preparo. A equivalencia em fertilizante nitrogenado foi estimada em 55 e 38 kg ha-1, respectivamente, para a ervilhaca e aveia + ervilhaca.

Desenvolvimento de sistemas de produção de milho no sul do Brasil com características de sustentabilidade

De 1991 a 1993, foi desenvolvido um experimento, no Campus da Universidade Federal de Santa Maria (UFSM), em um podzolico vermelho-amarelo, com 0,055 m m-1 de declividade, visando identificar sistemas de producao de milho com caracteristicas de sustentabilidade. As parcelas mediam 22,0 x 3,5 m, conforme metodo para experimentos com chuva natural, e utilizaram-se os seguintes tratamentos: (1) solo descoberto; (2) aveia-preta + ervilhaca comum/milho; (3) tremoco-azul/milho; (4) chicharo/milho; (5) milho + mucuna; (6) milho + feijao-de-porco e (7) campo nativo. Os adubos verdes e o milho foram semeados transversalmente ao declive, no sistema plantio direto. As principais avaliacoes foram a cobertura do solo nos sistemas de producao, as taxas de erosao e, apos 1,5 ano da implantacao dos sistemas, algumas caracteristicas quimicas, fisicas e biologicas do solo. A cobertura do solo manteve-se elevada nos sistemas de producao de milho, especialmente nos sistemas aveia + ervilhaca/milho, milho + mucuna e milho + feijao-de-porco, proporcionando um controle efetivo sobre a erosao hidrica, com reducao superior a 98% nas perdas de solo e 85% nas de agua . Os sistemas de producao com inclusao de adubos verdes apresentaram alta adicao de carbono orgânico ao solo, refletindo no aumento do teor de CO na camada superficial (0-2,5 cm). Em relacao ao solo descoberto, tais sistemas apresentaram maior infiltracao de agua no solo e maior atividade microbiana, na camada de 0-5 cm. Com a utilizacao de leguminosas, foi possivel reduzir a metade a adubacao nitrogenada mineral na cultura do milho, obtendo-se rendimentos de graos superiores ao dobro da media estadual. Considerando as taxas de perdas de solo e agua e as modificacoes induzidas pelos sistemas de producao, nas caracteristicas quimicas, fisicas e biologicas do solo, conclui-se que os sistemas apresentaram caracteristicas de sustentabilidade.

Eficiência da escarificação mecânica e biológica na melhoria dos atributos físicos de um latossolo muito argiloso e no incremento do rendimento de soja

Compaction is one of the main causes of yield decreases in agricultural soils. Mechanical chiseling has been suggested to reduce soil compaction in long-term no-tillage systems. Another option to alleviate soil compaction is the use of cover crops, such as forage radish, with a well-developed tap root system and the capacity of growing into soil compacted layers, forming stable biopores and improving the soil physical properties. This study aimed to evaluate the efficiency of a mechanical (chisel plow) and biological (forage radish) soil decompaction method or the combination of both to improve the physical properties of a very clayey texture Oxisol and to increase soybean grain yield under no-tillage. The treatments were: black oat on no-till (NT-O), consortium of forage radish and black oat on no-till (NT-R+O), black oat on chiseled soil (CH-O) and consortium of forage radish and black oat on chiseled soil (CH-R+O). The following properties were evaluated: soil bulk density, macroporosity, microporosity and total porosity in the layers 0-0.05, 0.05-0.10, 0.10-0.15 and 0.15-0.20 m, soil penetration resistance, soil moisture and soil water infiltration at soybean flowering. The winter cover biomass production and soybean yield were also measured. The treatments did not affect the soil bulk density significantly at any of the soil depths. However, the treatments NT-R+O and CH-R+O doubled the mean soil macroporosity values in the 0-0.20 m layer, with more pronounced effects in the upper soil layers. The treatments NT-R+O and CH-R+O reduced soil penetration resistance compared to NT+O, while treatment CH-O had intermediate results. The treatments NT-R+O and CH-R+O increased the accumulated infiltrated water by 44.6 as compared to treatments NT-O and CH-O .The highest soybean yields were observed in the treatment CH-R+O (3.73 Mg ha-1), which did not differ significantly from treatment NT-R+O (3.49 Mg ha-1). The effect of winter mechanical chiseling was temporary and nine months later no soil physical improvements were observed, apart from the increase of total porosity and macroporosity in the 0-0.05 m layer. Biological chiseling increased soil macroporosity, reduced soil penetration resistance and improved soil water infiltration. Mechanical chiseling was only efficient to improve the soil physical conditions when associated with biological chiseling, which prevented soil reconsolidation.

Culturas de cobertura, acúmulo de nitrogênio total no solo e produtividade de milho

The association of conservation tillage with cover crops is an important tool for improving soil quality. When legumes are used as cover crops there is an increase in nitrogen (N) availability for the first crop in succession (immediate effect). However, the long term use of legumes as cover crop increases soil N availability (residual effect). This long-term experiment was carried out to evaluate the immediate effect and residual effect of cover crops on a Paleadulf from Rio Grande do Sul, Brazil. The experimental design was a split split plot with three replications. The main plots were three tillage systems: conventional, minimum and no-tillage; the subplot consisted of three crop productions: black oat/corn (A/M), oat + common vetch/corn (A + E/M), oat + common vetch/corn + cowpea (A + E/M + C), and the subsubplots consisted of two N fertilizer rates: 0 and 120 kg ha-1. The crop production systems used were: oat/corn, vetch/corn and oat + vetch/corn. In order to evaluate the residual effect of cover crop, the plots were split in bare soil before corn cropping and cover with cover crop. Conservation tillage plus legume cover crop increased total N at soil surface. The use of legumes in A + E/M + C, regardless of the tillage system, increased corn N uptake by 26% and increased corn yield by 19%, when compared to A/M. Despite that, cover crop biomass in the presence of corn was considered the most important N source to corn.

Cover Crop Effects Increasing Carbon Storage in a Subtropical No‐Till Sandy Acrisol

The long‐term (8‐year) effects of summer (Mucuna spp.) and winter cover crops (Avena strigosa + Vicia sativa and Lolium multiflorum + Vicia sativa) in maize‐based cropping systems on the total, particulate, and mineral‐associated soil carbon (C) stocks in the 0‐ to 0.2‐m layer of a no‐till South Brazilian Acrisol (87 g kg−1 clay) were evaluated. Annual C sequestration rates and the carbon management index (CMI) were calculated taking a fallow/maize (F/M) system as reference. A greater average C sequestration rate (0.68 Mg ha−1 yr−1) and greater C lability (particulate C/mineral‐associated C) were observed in the soil under the Mucuna system, and this was related to the higher biomass input in comparison to the winter cover crop systems. These cropping system effects on amount and lability of soil C were summarized through the CMI. The results highlight the potential of C retention in soils under warm and humid subtropical climate through the adoption of high C input summer cover crops in no‐till production systems aimed at further improvement in soil and environmental quality.

Variabilidade espacial e temporal da produtividade de culturas sob sistema plantio direto

O objetivo deste trabalho foi avaliar a variabilidade espacial e temporal da produtividade de soja, milho e trigo, em uma lavoura comercial de 57 ha, nao irrigada, manejada ha mais de dez anos sob sistema plantio direto, em um Latossolo Vermelho distrofico tipico, em Palmeira das Missoes, RS. A coleta de dados de produtividade de seis cultivos, entre 2000 e 2005, foi realizada por colhedora equipada com monitor de produtividade. Analises estatisticas e geoestatisticas foram realizadas a fim de avaliar a variabilidade espacial e a presenca de dependencia espacial ao longo dos anos. A produtividade da soja, do milho e do trigo alcancada apresenta variabilidade com continuidade espacial, correlacionando-se entre si, ao longo dos anos. Em anos de deficit hidrico, verifica-se aumento da variabilidade espacial da produtividade. A cultura do milho e mais eficiente do que a da soja em detectar a variabilidade espacial da produtividade existente na lavoura.

Carbon stock and its compartments in a subtropical oxisol under long-term tillage and crop rotation systems

Soil organic matter (SOM) plays a crucial role in soil quality and can act as an atmospheric C-CO2 sink under conservationist management systems. This study aimed to evaluate the long-term effects (19 years) of tillage (CT-conventional tillage and NT-no tillage) and crop rotations (R0-monoculture system, R1-winter crop rotation, and R2- intensive crop rotation) on total, particulate and mineral-associated organic carbon (C) stocks of an originally degraded Red Oxisol in Cruz Alta, RS, Southern Brazil. The climate is humid subtropical Cfa 2a (Koppen classification), the mean annual precipitation 1,774 mm and mean annual temperature 19.2 oC. The plots were divided into four segments, of which each was sampled in the layers 0-0.05, 0.05-0.10, 0.10-0.20, and 0.20-0.30 m. Sampling was performed manually by opening small trenches. The SOM pools were determined by physical fractionation. Soil C stocks had a linear relationship with annual crop C inputs, regardless of the tillage systems. Thus, soil disturbance had a minor effect on SOM turnover. In the 0-0.30 m layer, soil C sequestration ranged from 0 to 0.51 Mg ha-1 yr-1, using the CT R0 treatment as base-line; crop rotation systems had more influence on soil stock C than tillage systems. The mean C sequestration rate of the cropping systems was 0.13 Mg ha-1 yr-1 higher in NT than CT. This result was associated to the higher C input by crops due to the improvement in soil quality under long-term no-tillage. The particulate C fraction was a sensitive indicator of soil management quality, while mineral-associated organic C was the main pool of atmospheric C fixed in this clayey Oxisol. The C retention in this stable SOM fraction accounts for 81 and 89 % of total C sequestration in the treatments NT R1 and NT R2, respectively, in relation to the same cropping systems under CT. The highest C management index was observed in NT R2, confirming the capacity of this soil management practice to improve the soil C stock qualitatively in relation to CT R0. The results highlighted the diversification of crop rotation with cover crops as a crucial strategy for atmospheric C-CO2 sequestration and SOM quality improvement in highly weathered subtropical Oxisols.