Green Manures and Crop Residues as Source of Nutrients in Tropical Environment

Tropical areas have prevalence of soils with low fertility, which makes the management of soil fertility a necessary practice to maintain a farming system economically and environmentally sustainable. The purpose of this chapter is to demonstrate the importance of green manure and the use of crop residues as management for soil fertility. We highlight the potential of these practices to increase/sustain productivity by providing nutrients. First, we made a short review on the main factors influencing the decomposition and mineralization processes. Subsequently, we discuss green manure techniques, presenting the main green manures, criteria for choosing, managements, potential for nutrient accumulation, and advantages and disadvantages of this practice. Finally, we use some examples to demonstrate the potential nutrient supply of crop residues from the main crops grown in the tropics. The difficulties and limitations involved are also discussed

Biofortificação agronômica de grãos de feijão com zinco

The objective of this work was to evaluate the effects of the split and combinated application of foliar zinc (ZnF) + soil Zn (ZnS) on Zn concentration in the grains (ZnCG) of common bean (Phaseolus vulgaris). Two experiments were carried out in a greenhouse during two seasons. In the first experiment, two common bean cultivars received six ZnF rates (0, 120, 240, 480, 720, or 1,200 g ha-1), with split applications at the R5, R7, and R8, or R7 and R8, or R8 plant stages. In the second experiment, one cultivar received three ZnS rates (0, 5, or 10 kg ha-1) combined with ZnF rates (0, 1, 1.5, 3, 6, or 10 kg ha-1). In the first experiment, with the ZnF increment, ZnCG increased linearly from 15.3 to 20.7 mg kg-1. ZnF splitting did not affect ZnCG. In the second experiment, ZnF without ZnS did not affect ZnCG. ZnS doubled ZnCG in comparison with the treatment without ZnS application. At 5 kg ha-1 ZnS, the highest ZnCG (67.5 mg kg-1) was obtained with 7.8 kg ha-1 ZnF. At 10 kg ha-1, the highest ZnCG (66 mg kg-1) was obtained with 4.9 kg ha-1 ZnF. ZnF splitting is not advantageous over a single application, and the combination of ZnF and ZnS increases ZnCG in common bean, in greenhouse conditions.O objetivo deste trabalho foi avaliar os efeitos da aplicação parcelada e combinada de zinco foliar (ZnF) + Zn no solo (ZnS) sobre o teor de Zn dos grãos (TZnG) do feijão-comum (Phaseolus vulgaris). Dois experimentos foram realizados em casa de vegetação durante dois períodos. No primeiro experimento, duas cultivares de feijão-comum receberam seis doses de ZnF (0, 120, 240, 480, 720, ou 1.200 g ha-1), com aplicações parceladas nos estágios da planta R5, R7 e R8, ou R7 e R8, ou R8. No segundo experimento, uma cultivar recebeu três doses de ZnS (0, 5 ou 10 kg ha-1) combinadas com doses de ZnF (0, 1, 1,5, 3, 6 ou 10 kg ha-1). No primeiro experimento, com o incremento do ZnF, o TZnG aumentou linearmente de 15,3 para 20,7 mg kg-1. O parcelamento do ZnF não afetou o TZnG. No segundo experimento, o ZnF sem o ZnS não afetou o TZnG. O ZnS dobrou o TZnG em comparação ao tratamento sem aplicação de ZnS. Com 5 kg ha-1 de ZnS, o mais alto TZnG (67,5 mg kg-1) foi obtido com 7,8 kg ha-1 de ZnF. Com 10 kg ha-1, o mais alto TZnG (66,0 mg kg-1) foi obtido com 4,9 kg ha-1 de ZnF. O parcelamento do ZnF não é vantajoso em relação à aplicação única, e a combinação ZnF e ZnS aumenta o TZnG do feijão-comum em casa de vegetação

Changes in soil organic matter along a chronosequence of an agrossilvipastoral system of eucalypt cultivation

A matéria orgânica do solo (MOS) é a principal propriedade indicadora da sustentabilidade de um sistema de cultivo, principalmente em solos sob condições tropicais. Além disso, ela é o maior compartimento de C orgânico no ciclo global deste elemento, sendo extremamente importante para a manutenção dos seus estoques no ambiente. Sistemas agrossilvopastoris (SASPs) representam práticas de manejo agroflorestal que têm como principal objetivo permitir maior diversidade e sustentabilidade do sistema. Sendo assim, espera-se que eles mantenham ou até mesmo elevem os estoques de carbono (C) do solo, quando comparados a uma área sob vegetação nativa, que neste caso é o Cerrado. Uma medida para se comparar sistemas produtivos é o índice de manejo do C (IMC) proposto por Blair et al. (1995), que compara sistemas produtivos com relação à área de referência. Para isso esse índice se baseia em medida não muito confiável de labilidade do C (C oxidável por permanganato de potássio). Os objetivos deste trabalho foram estudar o impacto dos SASPs de cultivo do eucalipto em diferentes frações de C e de N da MOS, como variável do tempo de implantação dos SASPs, tendo a área de vegetação nativa como referencial (Cerrado). Adicionalmente, propõe-se modificação no IMC proposto por Blair et al. (1995). Para isso, foi amostrada uma cronosseqüência composta por seis tempos de implantação dos SASPs, onde o tempo zero foi representado pela área de referência (Cerrado) e os demais com dois, três, quatro, sete e dez anos de implantação. Foram coletadas amostras de solo das camadas de 0-10, 10- 20, 20-40, 40-60 e 60-100 cm, na linha e na entre-linha de cultivo do eucalipto. Foi feita a caracterização física e química desses solos, assim como as determinações de C orgânico total (COT), N total (NT), C na matéria orgânica leve (MOL), N na MOL e C oxidável por permanganato de potássio, como uma medida de labilidade do C (CL). A partir desses dados foram calculados o IMCCL, proposto por Blair et al. (1995) e o IMCCMOL, que é o índice modificado. Os estoques de COT apresentaram perda inicial de C para as camadas superficiais de 0-10 e 10-20 cm na linha e 0-10 e 20-40 cm na entre-linha, com tendência de recuperação ao final do ciclo (dez anos). As camadas mais profundas (60-100 cm), tanto para a linha quanto para a entrelinha, apresentaram acúmulo inicial de C, sendo maior na linha de plantio do que na entre-linha. Porém, esse acúmulo não foi sustentável e as perdas de C nessa camada foram maiores quanto maior for o ciclo. Para o estoque total de C na camada de 0-100 cm, o manejo da linha de plantio manteve os estoques de COS, enquanto na entre-linha há tendência de perda inicial de C num primeiro momento, sem que esses níveis retornem aos originais (Cerrado) no final do décimo e último ano analisado. As principais mudanças nos estoques de NT ocorreram nas camadas mais profundas (20-40 e 60-100 cm). Nestas camadas, após perda acentuada de N, houve tendência de acúmulo desse elemento ao longo do tempo de implantação dos SASPs. Porém esse acúmulo não foi sustentável e ao final do período estudado esses valores eram menores que os originais (Cerrado). Essa mesma tendência foi observada para o estoque de N na camada de 0-100 cm, sendo que para a entre-linha de plantio essas alterações foram mais acentuadas. A fração da MOL foi a que apresentou as maiores alterações, confirmando sua sensibilidade a alterações de manejo. As perdas de C e N da MOL também foram maiores para a entre-linha de plantio de eucalipto do que para a linha. O C lábil (CL), assim como o índice calculado a partir dele (IMCCL) não possibilitaram ajustes dos seus resultados como variável do tempo de implantação dos SASPs. Entretanto o IMC modificado, calculado a partir do C da MOL (IMCCMOL), apresentou bons ajustes para todas as camadas estudadas. Além disso, apresentou correlação mais elevada com o COT, mostrando-se mais indicado para a comparação dos sistemas de manejo estudados. A partir dos resultados desse estudo pode-se perceber a importância de se estudar camadas mais profundas de solo, já que essas camadas podem apresentar perdas de C significativas e de difícil recuperação. A implantação dos SASPs acarretou diminuição dos estoques de COT das camadas superficiais, sendo que o tempo necessário para a recuperação dos estoques originais está além do período de tempo máximo estudado. A fração mais sensível ao manejo adotado foi a MOL livre.Soil organic matter (SOM) is the main property that indicates the sustainability of a cropping system, especially in tropical soils. Additionally, SOM is the major global organic C pool, making this pool a very important sink or source of C to the atmosphere, depends on the soil management. Agrossilvipastoral (AGSP) systems known to impove diversity and sustainability of cropping systems. Furthermore, it is expected that this system maintain or increase C stocks in soil when compared with soils under native Cerrado (Brazilian savannah) vegetation. One simple way to compare cropping systems is through the C management index (CMI), proposed by Blair et al. (1995). It compares cropping systems to a reference area. This index is based in a measure of C lability (C oxidizable by potassium permanganate), which isn t very reliable. The objectives of the present work are to study the impact of eucalypt cultivation under agrossilvipastoral systems on C and N stocks of different SOM fractions in an AGSP chronosequence, and to compare these results with those from soils under native vegetation (Cerrado). Additionally, is proposed a modification in the CMI proposed by Blair et al. (1995). A chronosequence compound of six implantation times of an AGSP system was sampled. The zero time is represented by the soil under Cerrado, followed by 2, 3, 4, 7 and 10 year-old AGSP systems. The soil layers sampled in each area were from 0-10, 10-20, 20-40, 40-60 e 60-100 cm deep, taken in the eucalypt planting line and between lines. The soil samples were chemically and physically characterized. It was also determined the total organic carbon (TOC), total nitrogen (TN), C and N in the light organic matter fraction (LOM) and C oxidizable by potassium permanganate, hereafter called labile carbon (LC). Based on these data, the CMI proposed by Blair et al. (1995) was calculated (CMILC), as well as a modified CMI, which is based on the use of C in the LOM (CMILOM). The TOC stocks showed an initial decrease in the 0-10 and 10-20 cm soil layers in the planting line and in the 0-10 and 20-40 cm soil layer between the eucalypt planting line, with a trend to recover in the older stands (10 years). Deeper soil layers (60- 100 cm) showed an initial increase in C stocks, more in the line than in between line, but this increase was not sustainable. Thus, the C losses would be greater for longer rotation cycles. The total C stock up to 100 cm deep, was similar to the initial TOC stock in the planting line, while in the between line the trend was to loose C without returning to the levels observed in the reference (Cerrado) at the end of the cycle. The main change in the N stocks occurred in deeper soil layers (20-40 and 60-100 cm). In these layers, N stocks showed a rapid initial decrease, followed by a great increase. But this last increase was not sustained and by the end of the cycle the N stocks were less than the original ones in the soil under native vegetation. The same trend was observed for the N stocks at 0-100 cm soil layer. The free LOM fraction presented the major changes, what confirms its great sensibility to management changes. The free LOM C and N losses were greater in soils to between planting lines than in the planting line. Labile C, as well as the CMILC, was not a good indicator of the changes that occurred after the implantation of the AGSP system. But the modified CMI, calculated based on the LOM C (CMICLOM) fitted well for all soil layers analyzed. In addition, the CMICLOM showed the best correlation with TOC, thus been more indicated to compare the cropping system studied. These results show the importance to study deeper soil layers; moreover, they can show relatively large losses of C, which are difficult to recover. The AGSP systems caused a decrease of the soil organic C in upper soil layers and the time that takes to it recover to the original stocks are beyond the time frame of the present study. The free light organic matter was the fraction more sensitive to the changes in soil use and management.Conselho Nacional de Desenvolvimento Científico e Tecnológic

Estudo do compartimento do solo do ciclo global do carbono

Mudanças climáticas globais causadas pelo aumento da concentração de CO2 atmosférico tem estimulado uma melhor compreensão do ciclo global do C. Os solos representam um dos maiores compartimentos de C na Terra, contendo mais C que na biomassa vegetal e na atmosfera. Além disso, o C orgânico do solo (COS) também é um compartimento bastante dinâmico. Portanto, compreender o papel do COS para o ciclo global do C e como ele é afetado por diferentes condições edafoclimáticas se faz extremamente importante, especialmente para países como o Brasil, onde a maioria das emissões de gases causadores do efeito estufa são provenientes de mudanças de uso do solo e atividades agropecuárias. O objetivo geral deste trabalho foi estudar quantitativa e qualitativamente o COS, visando a melhor compreensão dos fatores que levam à sua estabilização. Para isso foram investigados três estágios que afetam a ciclagem do C nos solos, sendo eles: as concentrações e eficiências de reabsorção global do C e de nutrientes em plantas terrestres (Chapter 1), o estudo da estrutura e do comportamento dos ácidos húmicos pela técnica de titulação calorimétrica isotérmica (microcalorimetria) (Chapter 2) e a influência das argilas e de condições climáticas nos estoques de COS no Brasil (Chapter 3). Do primeiro estudo (Chapter 1) resultaram novas estimativas globais de concentrações e de eficiências de reabsorção de nutrientes. Neste trabalho foi incorporada a perda de massa que ocorre nas folhas durante a senescência, fato esse até então desconsiderado em estimativas globais e responsável pela subestimação da real reabsorção de C e nutrientes. Em geral, as folhas verdes perdem 24% de sua massa seca durante o processo de senescência. Levando essa perda em consideração as reabsorções de C, N, P, K, Ca e Mg foram de 23,2; 62,1; 64,9; 70,1; 10,9 e 28,6%, respectivamente. Esses resultados devem levar à melhoria de modelos que explicitamente representam a ciclagem de C e nutrientes, além de permitir que os pesquisadores que trabalham com modelagem associem os ciclos de outros nutrientes ao nível de grupos de plantas e ecossistemas. No segundo trabalho (Chapter 2) empregou-se uma técnica relativamente nova para o estudo da estrutura e comportamento dos ácidos húmicos. A partir desta análise foi possível demonstrar que existe uma estrutura básica (monômeros) dos ácidos húmicos e que, ao contrário do que o usual modelo supramolecular prega, essa estrutura básica não é formada por unidades simples fracamente unidas passíveis de sofrer divisões ou mudanças conformacionais durante interação. Adicionalmente, esses monômeros se mostraram similares no ambiente, não importando sua fonte, composição ou processo de estabilização. Finalmente, no último trabalho (Chapter 3) foram analizados os estoques de COS em áreas de vegetação nativa, eucalipto e pastagem de três principais biomas brasileiros. Em geral, os estoques de COS na camada de 0-100 cm para as áreas de vegetação nativa, eucalipto e pastagem de todos os biomas em conjunto foram 137,3; 127,9 e 127,1 t ha-1, respectivamente. Este tipo de trabalho em escala regional é necessário para melhorar as estimativas globais de COS. Neste trabalho foi mostrado que partículas de argila de solos argilosos, especialmente nas camadas mais profundas, ainda não se encontram saturadas com COS, indicando que existe a possibilidade de aumento do sequestro de C em solos brasileiros. Adicionalmente, o aumento da mineralização do COS após mudança de uso do solo se correlacionou positivamente com o aumento da temperatura, indicando que a oxidação do COS será ainda maior em um cenário de mudanças climáticas globais. Em geral, este trabalho contribui de diferentes maneiras para a melhor compreensão do compartimento solo no ciclo global do C.Conselho Nacional de Desenvolvimento Científico e TecnológicoClimate changes caused by increased atmospheric concentration of CO2 have stimulated a better understanding of the global C cycle. Soils represent one of the largest compartments of C on Earth, with higher C content than plant biomass and atmosphere. Besides its size, soil organic C (SOC) is also a very dynamic compartment. Thus, comprehend the role of SOC and how it is affected by edaphoclimatic conditions is of great importance, especially to Brazil, once the majority of its greenhouse gases emissions come from land use change and agriculture. The general objective of this work was to study SOC quantitative and qualitatively, in order to improve the knowledge about the factors that lead to its stabilization. To this end we attempted to investigate three different stages of it, namely: global resorption efficiencies and concentrations of C and nutrients in terrestrial plants (Chapter 1), the evaluation of humic acid s structure and behavior through isothermal titration calorimetry (microcalorimetry) (Chapter 2), and the role of clay and climatic conditions onto soil organic carbon in Brazilian soils (Chapter 3). On the first study (Chapter 1) we provided new global estimates for nutrient concentrations and resorption efficiencies. In this work we took into account the leaf mass loss occurring during senescence, which to our knowledge has been neglected so far in global estimates and leads to an underestimation of the real resorption. In general, leaves lose up to 24% of its dry mass during senescence. Taken it into account, C, N, P, K, Ca, and Mg resorptions were, on average, 23.2, 62.1, 64.9, 70.1, 10.9, and 28.6%, respectively. It should improve models that explicitly represent the cycling of C and nutrients, and also allow the modeling community to represent more explicitly the coupling of other nutrient cycles within plants and ecosystems. On Chapter 2 we employed a fairly recent technique and showed new insights on humic acid s structure and behavior. The results demonstrated that indeed humic acids show a basic structure (monomers) and that, contrary to what the well accepted supramolecular model preaches, humic acid basic structure is not loosely held nor does it show any division or conformational change when undergoing an interaction. We also demonstrated here that these monomers are kept virtually the same regarding differences on its sources, composition, and humification processes. Lastly, on Chapter 3 we showed data on SOC stocks under native vegetation, eucalyptus, and pasture within three major Brazilian biomes. In general, SOC stocks at the first soil meter for native vegetation, eucalyptus, and pasture areas were 137.3, 127.9, and 127.1 t ha-1, respectively. This kind of regional scale work is necessary to improve overall estimates of SOC stocks globally. Besides that, our results showed that clay particles in clayey soils, especially in deeper layers, are still not saturated with SOC, showing that there is still room to sequester C deep in Brazilian soils, helping offset CO2 emissions. Still on the light of global climate changes, our results showed that increasingly temperature is associated with an increase on SOC mineralization after land use change, making it more difficult to remediate. Overall, our work contributes in different ways to a better understanding of the soil compartment of the global C cycle

Machine learning in nutrient management: A review

In agriculture, precise fertilization and effective nutrient management are critical. Machine learning (ML) has recently been increasingly used to develop decision support tools for modern agricultural systems, including nutrient management, to improve yields while reducing expenses and environmental impact. ML based systems require huge amounts of data from different platforms to handle non-linear tasks and build predictive models that can improve agricultural productivity. This study reviews machine learning based techniques for estimating fertilizer and nutrient status that have been developed in the last decade. A thorough investigation of detection and classification approaches was conducted, which served as the basis for a detailed assessment of the key challenges that remain to be addressed. The research findings suggest that rapid improvements in machine learning and sensor technology can provide cost-effective and thorough nutrient assessment and decision-making solutions. Future research directions are also recommended to improve the practical application of this technology

Nitrogen release from urea with different coatings

Coatings or urease inhibitors are designed to reduce losses of ammonia [NH 3(g) ] from urea fertilizers. However, nitrogen (N) release and its effects on soil solution have not previously been evaluated under standardized conditions in soils. In this study, the urea fertilizers were incubated in chambers filled with sandy loam soil, adapted for the collection of NH 3(g) and soil solution by centrifugation. In the fast-release N fertilizers, around 93% and 100% of urea-N applied was recovered within the first hours of incubation. In contrast, in the slow-release N fertilizers, less than 40% of urea-N applied, was recovered at 19 days of incubation. The maximum N release from the fertilizers followed the order: UP1 (106%) ≈ UNBPT (102%) ≈ urea (93%) > USP2 (57%) ≈ USP3 (57%) > USP4 (31%) ≈ USP5 (18%). NH 3(g) volatilization accounted for only 3% of the applied N in the slow-release fertilizers, which corresponded to about 88% less than the NH 3(g) loss from prilled urea. This study demonstrated distinct N release patterns, which changed the N dynamics in the soil. Some coatings effectively delayed urea release from granules and reduced NH 3(g) gas losses, while other were not efficient

Nitrogen release from urea with different coatings

Coatings or urease inhibitors are designed to reduce losses of ammonia [NH 3(g) ] from urea fertilizers. However, nitrogen (N) release and its effects on soil solution have not previously been evaluated under standardized conditions in soils. In this study, the urea fertilizers were incubated in chambers filled with sandy loam soil, adapted for the collection of NH 3(g) and soil solution by centrifugation. In the fast-release N fertilizers, around 93% and 100% of urea-N applied was recovered within the first hours of incubation. In contrast, in the slow-release N fertilizers, less than 40% of urea-N applied, was recovered at 19 days of incubation. The maximum N release from the fertilizers followed the order: UP1 (106%) ≈ UNBPT (102%) ≈ urea (93%) > USP2 (57%) ≈ USP3 (57%) > USP4 (31%) ≈ USP5 (18%). NH 3(g) volatilization accounted for only 3% of the applied N in the slow-release fertilizers, which corresponded to about 88% less than the NH 3(g) loss from prilled urea. This study demonstrated distinct N release patterns, which changed the N dynamics in the soil. Some coatings effectively delayed urea release from granules and reduced NH 3(g) gas losses, while other were not efficient

Value of copper, zinc, and oxidized charcoal for increasing forage efficiency of urea N uptake

Volatilization losses reduce the efficiency of surface-applied urea for crop N uptake, and can be controlled using urease inhibitors to retard hydrolysis or by the presence of other amendments that enhance retention of NH4+ formed by urea hydrolysis. A greenhouse study was conducted to evaluate the effectiveness of oxidized charcoal (OCh; 150 g kg−1 fertilizer) applied with or without Cu and/or Zn (∼0.5–2 g kg−1 fertilizer), and of Cu and/or Zn applied without OCh, for increasing uptake of urea 15N by a common tropical pasture grass, capim-Mombaça (Panicum maximum Jacq. Cv. Mombaça), grown on a coarse-textured Oxisol. Cuttings were collected 5, 14, 28, 42, and 56 days after surface placement of amended or unamended urea pellets to estimate dry matter production, total N uptake, and 15N recovery. Soil sampling was carried out in conjunction with the first and fourth cuts to evaluate exchangeable NH4+ and NO3− concentrations. At the concentrations studied, OCh was more effective than Cu and/or Zn for prolonging NH4+-N availability in urea-treated soil; however, OCh alone or in combination with Zn and Cu had no effect on biomass production or N recovery and can safely be eliminated as a useful option for pasture improvement. The most promising amendment was Zn, which significantly increased total N uptake and the efficiency of urea N fertilization. The use of Zn in conjunction with urea has practical potential to improve forage production on tropical soils

Iron Availability in Tropical Soils and Iron Uptake by Plants

ABSTRACT Given the increase in crop yields and the expansion of agriculture in low fertility soils, deficiency of micronutrients, such as iron, in plants grown in tropical soils has been observed. The aim of this study was to evaluate Fe availability and Fe uptake by corn (Zea mays L.) plants in 13 different soils, at two depths. Iron was extracted by Mehlich-1, Mehlich-3, and CaCl2 (Fe-CC) and was fractionated in forms related to low (Feo) and high (Fed) crystallinity pedogenic oxyhydroxides, and organic matter (Fep) using ammonium oxalate, dithionite-citrate, and sodium pyrophosphate, respectively. In order to relate Fe availability to soil properties and plant growth, an experiment was carried out in a semi-hydroponic system in which part of the roots developed in a nutrient solution (without Fe) and part in the soil (the only source of Fe). Forty-five days after seeding, we quantified shoot dry matter and leaf Fe concentration and content. Fed levels were high, from 5 to 132 g kg-1, and Feo and Fe-CC levels were low, indicating the predominance of Fe as crystalline oxyhydroxides and a low content of Fe readily available to plants. The extraction solutions showed significant correlations with various soil properties, many common to both, indicating that they act similarly. The correlation between the Mehlich-1 and Mehlich-3 extraction solutions was highly significant. However, these two extraction methods were inefficient in predicting Fe availability to plants. There was a positive correlation between dry matter and Fe levels in plant shoots, even within the ranges considered adequate in the soil and in the plant. Dry matter production and leaf Fe concentration and content were positively correlated with Fep concentration, indicating that the Fe fraction related to soil organic matter most contributes to Fe availability to plants