João Carlos de Moraes Sá

The contribution of biological nitrogen fixation for sustainable agricultural systems in the tropics

Abstract The pressing need to increase food production in the tropics to feed the burgeoning population of the Third World requires that crop yields ha−1 must be increased without prejudicing the resource base for future generations. Biological nitrogen fixation (BNF), especially that associated with legumes, has great potential to contribute to productive and sustainable agricultural systems for the tropics, but more research is required to investigate how biologically fixed N, and the increased BNF contributions resulting from research innovations, can be incorporated into viable agricultural systems to increase crop or pasture yields and to substitute N fertiliser inputs. A majority of the soils of the humid and semi-humid tropics have mineral fractions composed of 1:1 lattice clays or sesquioxides of relatively low capacity to retain nutrients (CEC) and water (WHC). It is the soil organic matter (SOM) which has high CEC (after liming) and WHC, and soils under undisturbed climax vegetation are usually high in organic matter which is responsible for their fertility. The key to the long term fertility of such soils is to maintain their soil organic matter by the preservation of crop residues and the selection of suitable crop rotations or fallows. In this review we examine several types of agricultural systems utilised in the tropics ranging from pastures, ley cropping, zero-till rotations as well as green manuring and discuss the management options that can be adopted to preserve their agricultural productivity through the strategic use of legumes in these systems, and their effects on pasture and crop yields. The introduction of forage legumes into tropical pastures can increase and sustain their productivity, with only modest inputs of lime and P and K fertilisers. Similarly, crop and pasture rotations (ley cropping) maintain SOM and soil fertility and crop yields can benefit greatly from the introduction of pasture legumes into the ley. Continuous cropping under minimum or zero tillage can maintain soil cover, and stimulate the retention of SOM, such that nutrient losses are often minimal, and legume derived N can be efficiently transferred to subsequent crops. The options for the resource-poor small-holder to efficiently utilise biologically fixed N as a N supply for cereal grains are more limited and need more attention from researchers as well as less neglect from government organisations. The addition of lime and P fertiliser in modest quantities in many under-developed regions could make large contributions to increased crop yields. If such modest fertiliser inputs were to be combined with suitable crop rotations including green manure or grain legume crops, larger increases in crops yields could be achieved on a sustainable basis, but in many regions agricultural extension services are non-existent and poor farmers have little access to even these basic chemical inputs.

Low-carbon agriculture in South America to mitigate global climate change and advance food security.

The worldwide historical carbon (C) losses due to Land Use and Land-Use Change between 1870 and 2014 are estimated at 148 Pg C (1 Pg=1billionton). South America is chosen for this study because its soils contain 10.3% (160 Pg C to 1-m depth) of the soil organic carbon stock of the world soils, it is home to 5.7% (0.419 billion people) of the world population, and accounts for 8.6% of the world food (491milliontons) and 21.0% of meat production (355milliontons of cattle and buffalo). The annual C emissions from fossil fuel combustion and cement production in South America represent only 2.5% (0.25 Pg C) of the total global emissions (9.8 Pg C). However, South America contributes 31.3% (0.34 Pg C) of global annual greenhouse gas emissions (1.1 Pg C) through Land Use and Land Use Change. The potential of South America as a terrestrial C sink for mitigating climate change with adoption of Low-Carbon Agriculture (LCA) strategies based on scenario analysis method is 8.24 Pg C between 2016 and 2050. The annual C offset for 2016 to 2020, 2021 to 2035, and 2036 to 2050 is estimated at 0.08, 0.25, and 0.28 Pg C, respectively, equivalent to offsetting 7.5, 22.2 and 25.2% of the global annual greenhouse gas emissions by Land Use and Land Use Change for each period. Emission offset for LCA activities is estimated at 31.0% by restoration of degraded pasturelands, 25.6% by integrated crop-livestock-forestry-systems, 24.3% by no-till cropping systems, 12.8% by planted commercial forest and forestation, 4.2% by biological N fixation and 2.0% by recycling the industrial organic wastes. The ecosystem carbon payback time for historical C losses from South America through LCA strategies may be 56 to 188years, and the adoption of LCA can also increase food and meat production by 615Mton or 17.6Mtonyear-1 and 56Mton or 1.6Mtonyear-1, respectively, between 2016 and 2050.

Temporary effect of chiseling on the compaction of a Rhodic Hapludox under no-tillage

A escarificacao mecânica tem sido empregada para amenizar os efeitos da compactacao em solos manejados sob sistema plantio direto (SPD). No entanto, nao esta clara a duracao dos seus efeitos sobre as propriedades fisicas do solo. O objetivo deste trabalho foi avaliar o comportamento da densidade do solo (Ds) e do grau de compactacao (GC) em profundidade apos a escarificacao do solo sob SPD durante um ano. O experimento localiza-se no municipio de Ponta Grossa, Parana, em um Latossolo Vermelho distrofico. Medidas de Ds e GC foram feitas em area sob SPD por 16 anos (PD) e imediatamente apos a escarificacao (ESC), em maio/2009; seis meses apos a escarificacao (ESC6M), em outubro/2009; e um ano apos a escarificacao (ESC12M), em maio/2010. Nas camadas de 0,0-0,10, 0,10-0,20 e 0,20-0,30 m, verificou-se reducao significativa da Ds em ESC e aumento expressivo em ESC6M. Em ESC12M, constataram-se valores de Ds similares aos medidos antes da mobilizacao do solo. A escarificacao reduziu o GC nas camadas de 0,0-0,10 e 0,10-0,20 m, com o retorno aos valores originais um ano apos a escarificacao. Nos periodos ESC, ESC6M e ESC12M foram observados aumentos da Ds na camada de 0,30-0,40 m, em comparacao com o PD. Os maiores valores de GC foram observados seis meses apos a escarificacao, porem o solo mostrou grande recuperacao estrutural, possivelmente devido ao elevado grau de resiliencia do solo e a influencia dos ciclos de umedecimento e secagem durante o periodo estudado. Os efeitos da escarificacao, avaliados pela Ds e GC, apresentaram duracao inferior a um ano; portanto, possiveis efeitos beneficos da escarificacao em reduzir a Ds em superficie, em curto prazo, propiciam aumento dos riscos de compactacao do solo em profundidade.

Desempenho de genótipos de milho cultivados com diferentes quantidades de palha de aveia-preta e doses de nitrogênio

The objective of this work was to assess the performance of corn (Zea maysL.) genotypes as affected by inputs of black oat (Avena strigosa Schreb.) residues applied on the soil surface and nitrogen fertilization under no-tillage system in a Typical Haplustox. The experiment was carried out in a complete randomized block design, arranged in split-split plots with three replicates. The main plots consisted of the amount of crop residues on the soil surface (no crop residue, 5.16 and 10.32 mg ha-1). The split plots were three corn genotypes, and the split-split plots were five nitrogen rates: 0, 60, 120, 180, and 240kg ha-1. An increase in the nitrogen rates decreased nitrogen deficiency and provided an adequate nitrogen supply for corn, under all the amounts of black oat residues. The corn genotypes grown with different amounts of black oat residues and nitrogen rates had different grain yield responses, use of mineralized nitrogen from crop residues, and root growth.

Carbon balance and crop residue management in dynamic equilibrium under a no-till system in Campos Gerais

A adocao do sistema plantio direto e a manutencao dos residuos culturais na superficie do solo resultam, com o passar dos anos, em adicao de carbono (C) ao sistema, o que promove o sequestro de C e a mitigacao de emissoes de C-CO2 para a atmosfera. O objetivo deste trabalho foi avaliar a taxa de sequestro de C e a quantidade minima de residuos culturais necessaria para manter o equilibrio dinâmico (dC/dt = 0) de dois solos (Latossolo) com classes texturais diferentes. O delineamento experimental utilizado foi blocos ao acaso em arranjo fatorial 2 x 2 x 2. Os fatores analisados foram: (a) dois solos: Latossolo Vermelho distrofico tipico, com classe textural franco-argiloarenosa (LVTM), e Latossolo Vermelho distrofico tipico, com classe textural franco-argilosa (LVTA); (b) profundidades de amostragem: 0-0,05 e 0,05-0,20 m; e (c) epocas de amostragem (E1-outubro de 2007; E2-setembro de 2008). As lavouras onde foram coletadas as amostras vinham sendo manejadas em SPD por longo prazo (20 anos), com as seguintes rotacoes de cultura: trigo/soja/aveia-preta + ervilhaca/milho (LVTM) e trigo/milho/aveia-preta + ervilhaca/soja (LVTA). A taxa de sequestro anual de C foi de 0,83 e 0,76 Mg ha-1 para o LVTM e LVTA, respectivamente. A estimativa da quantidade minima de residuos culturais necessaria para manter o equilibrio dinâmico (dC/dt = 0) foi de 7,13 e 6,53 Mg ha-1 ano-1 para o LVTM e LVTA, respectivamente. A taxa de conversao de C em ambos os solos foi inferior a encontrada em outros estudos regionais, resultando numa elevada taxa de remanescente de palha na superficie do solo.

Particulate soil organic carbon and stratification ratio increases in response to crop residue decomposition under no-till

O aporte continuo de residuos na superficie do solo, conduzidos sob sistema plantio direto (SPD), leva ao acumulo de carbono (C). Os objetivos deste estudo foram avaliar a decomposicao dos residuos de aveia-preta (Avena strigosa Schreb.) e relacionar o efeito da decomposicao sobre o carbono orgânico do solo (COS), o carbono orgânico particulado (COP) e a taxa de estratificacao (TE) de C do solo em um Cambissolo Haplico sob SPD na regiao dos Campos Gerais - PR. As avaliacoes foram realizadas durante sete datas de coleta (t0 a t6) em 160 dias, em tres transectos, com seis pontos de coleta para cada um. A produtividade inicial de biomassa de aveia foi de 5,02 Mg ha-1, restando, apos 160 dias, 17,8 % da materia seca inicial. O conteudo de COT foi superior (38 %) na camada de 0-5 cm em comparacao a de 5-20 cm, variando, na primeira, de 27,56 a 30,07 g dm-3 (t0 para t6). A TE aumentou de 1,33 para 1,43 durante os 160 dias. Alem disso, houve aumento do estoque de COP nesse periodo, o qual variou de 8,1 a 10,7 Mg ha-1. O aumento de COS na camada de 0-5 cm, durante os 160 dias, ocorreu principalmente devido ao aumento do COP derivado da decomposicao dos residuos da aveia. A relacao linear entre o COS e o COP mostrou que 21 % do primeiro teve contribuicao da fracao mais labil. Os resultados sao um indicativo de que a entrada continua de residuos pode ser intensificada, como forma de aumentar o estoque e sequestro de C em solos sob SPD.

Relação de estratificação como indicador do sequestro de carbono em macroagregados de Latossolo sob plantio direto

The decrease in soil organic carbon (SOC) content in deeper layers indicates the occurrence of stratification between the surface layer and subsurface layer of soil due to continuous C addition by crop residues. The objective was to evaluate the change (delta) of stratification (RE) of carbon (C) as an indicator of C sequestration and soil total and particulate soil in macroaggregates of two soils (Typic Hapludox) with different textures, managed in no-tillage system. The tests were developed in completely randomized design twelve repetitions.Analyzed factors were: (a) two soils: Oxisol with medium texture and Oxisol with clay texture, (b) sampling depth: 0-5 and 5-20cm, (c) two sampling times (October 2007-T1, September 2008-T2). The results were submitted to variance analysis by program SISVAR 5.3, using the Tukey test at 5% significance. There was a significant linear relationship between the ∆ RE and carbon sequestration rate total macroaggregates Oxisol with medium texture (R²=0.78**) and Oxisol with clay texture (R²=0.81**) indicating that there was C sequestration confirming to be a sensitive indicator of the rate of C sequestration in soil macroaggregates.

VARIAÇÃO NA RESISTÊNCIA TÊNSIL DE AGREGADOS EM FUNÇÃO DO CONTEÚDO DE CARBONO EM DOIS SOLOS NA REGIÃO DOS CAMPOS GERAIS

Macroscale soil behavior depends on the mechanical properties of individual aggregates. Tensile strength (TS) of soil aggregates has been used as an indicator of management effect on soil quality as related to land use. The objective of this study was to evaluate the change of TS in relation to the variation of soil organic carbon (SOC) content in two soils (Typic Hapludox) with different textures under a long term no-tillage system. The experiment was arranged in a completely randomized 2 x 2 x 2 factorial design with 12 treatments. The analyzed factors were: (a) two soils: Oxisol with medium texture and Oxisol with clay loam texture, (b) two sampling layers: 0-5 and 5-20 cm, (c) two sampling dates (October 2007-T1, September 2008-T2). To determine TS, 1440 soil blocks were sampled. The TS and SOC contents were measured in 1920 aggregates for each sampling time. RT decreased as SOC content increased, with a greater impact on Oxisol with clay loam texture. The clay content affected the TS behavior, to which it was inversely proportional. The impact of SOC content on TS was greater in the soil surface (0-5 cm) than in the 5-20 cm layer.

Why does carbon increase in highly weathered soil under no-till upon lime and gypsum use?

Field experiments have been used to explain how soil organic carbon (SOC) dynamics is affected by lime and gypsum applications, however, how SOC storage occurs is still debatable. We hypothesized that although many studies conclude that Ca-based soil amendments such as lime and gypsum may lead to SOC depletion due to the enhancement of microbial activity, the same does not occur under conservation agriculture conditions. Thus, the objective of this study was to elucidate the effects of lime and gypsum applications on soil microbial activity and SOC stocks in a no-till field and in a laboratory incubation study simulating no-till conditions. The field experiment was established in 1998 in a clayey Oxisol in southern Brazil following a completely randomized blocks design with a split-plot arrangement and three replications. Lime and gypsum were surface applied in 1998 and reapplied in 2013. Undisturbed soil samples were collected before the treatments reapplications, and one year after. The incubation experiment was carried out during 16months using these samples adding crop residues on the soil surface to simulate no-till field conditions. Lime and gypsum applications significantly increased the labile SOC stocks, microbial activity and soil fertility attributes in both field and laboratory experiments. Although the microbial activity was increased, no depletion of SOC stocks was observed in both experiments. Positive correlations were observed between microbial activity increase and SOC gains. Labile SOC and Ca2+ content increase leads to forming complex with mineral soil fractions. Gypsum applications performed a higher influence on labile SOC pools in the field than in the laboratory experiment, which may be related to the presence of active root system in the soil profile. We conclude that incubation experiments using lime and gypsum in undisturbed samples confirm that soil microbial activity increase does not deplete SOC stocks under conservation agriculture.

No-till corn performance in response to P and fertilization modes

No-tillage systems provide soil changes that affect nutrient dynamics, hence, changing rates and forms of fertilizer application. This study aimed to evaluate the effect of phosphorus (P) and modes of nitrogen (N) and P application in corn under long-term no-tillage in a clayey Oxisol. Two experiments were carried out in the same experimental area and in the same year, in a randomized blocks design with four replications. In experiment I, the treatments consisted of five doses of phosphorus (0, 40, 80, 120 and 160 kg ha -1 of P 2 O 5 ) applied in the sowing furrow. In experiment II, the treatments consisted of the N and P application modes (topdressing, in the sowing furrow and control - without N and P). Experiment I evaluated the root length, P uptake and grain yield and, the Experiment II, the firing height and yield. The P rates provided linear increases in root length in the 0-10 cm layer , P uptake and grain production. The different modes of application provided differences in the firing height and corn yield. The control treatment (0 kg ha -1 of N and P) provided the highest firing height, superior than those of topdressing and application in the furrow , which were not significantly different. The topdress application of N and P provided an increase in corn yield that exceeded 16 and 42% of the application in the furrow and the control, respectively . Thus, the results confirmed that increasing rates of P 2 O 5 , in soil with high initial P content, influence positively corn production factors, but with little significant responses, and the topdress application of N and P on soil with high P content, without water restriction, provided increased grain yield in relation to the application in the furrow .