Nanosilica enhances morphogenic and chemical parameters of Megathyrsus maximus grass under conditions of phosphorus deficiency and excess stress in different soils.

Phosphorus (P) imbalances are a recurring issue in cultivated soils with pastures across diverse regions. In addition to P deficiency, the prevalence of excess P in soil has escalated, resulting in damage to pasture yield. In response to this reality, there is a need for well-considered strategies, such as the application of silicon (Si), a known element for alleviating plant stress. However, the influence of Si on the morphogenetic and chemical attributes of forage grasses grown in various soils remains uncertain. Consequently, this study aimed to assess the impact of P deficiency and excess on morphogenetic and chemical parameters, as well as digestibility, in Zuri guinea grass cultivated in Oxisol and Entisol soils. It also sought to determine whether fertigation with nanosilica could mitigate the detrimental effects of these nutritional stresses. Results revealed that P deficiency led to a reduction in tiller numbers and grass protein content, along with an increase in lignin content. Conversely, P excess resulted in higher proportions of dead material and lignin, a reduced mass leaf: stem ratio in plants, and a decrease in dry matter (DM) yield. Fertigation with Si improved tillering and protein content in deficient plants. In the case of P excess, Si reduced tiller mortality and lignin content, increased the mass leaf:stem ratio, and enhanced DM yield. This approach also increased yields in plants with sufficient P levels without affecting grass digestibility. Thus, Si utilization holds promise for enhancing the growth and chemical characteristics of forage grasses under P stress and optimizing yield in well-nourished, adapted plants, promoting more sustainable pasture yields.

Nanosilica modulates C:N:P stoichiometry attenuating phosphorus toxicity more than deficiency in Megathyrsus maximus cultivated in an Oxisol and Entisol.

Silicon (Si) nanoparticles can attenuate nutritional disorders caused by phosphorus in forages through nutritional homeostasis. This paper aims to evaluate the effects of P deficiency and toxicity in Megathyrsus maximus cultivated in two types of soils and to verify whether Si application via fertigation can mitigate these imbalances. The following two experiments were carried out: cultivation of forage plants in pots with Entisol and Oxisol, in a 3 × 2 factorial design, with three nutritional levels of phosphorus (deficient, adequate, and excessive) and two Si concentrations in the irrigation water (0 and 1.5 mmol L-1). Height, number of tillers, rate of leaf senescence, dry matter production, C:N, C:Si, C:P, and N:P ratios; and C, P, and N use efficiencies were evaluated in two growth cycles. P imbalances hampered carbon assimilation, C:N:P homeostasis, and dry matter production. Nanosilica fertigation promoted silicon uptake, improving C:N:P homeostasis and nutritional efficiency in plants under P deficiency and toxicity. Leaf senescence was reduced with addition of Si in plants grown in Oxisol in the three nutritional states of P. Silicon attenuated the stress caused by P toxicity in Entisol and Oxisol, improving production in plants without nutritional stress in Oxisol. The supply of Si nanoparticles in the cultivation of M. maximus can contribute to a more efficient and sustainable use of phosphorus in pastures.

Impact of Si on C, N, and P stoichiometric homeostasis favors nutrition and stem dry mass accumulation in sugarcane cultivated in tropical soils with different water regimes.

Studies with silicon (Si) in sugarcane indicate a greater response in productivity in plants under stress, and the underlying mechanisms of Si in the crop are poorly reported. In this context, the benefits of Si in the crop's stem production are expected to occur at the C:N:P stoichiometry level in plant tissues, benefiting plants with and without stress. However, the extension of this response may vary in different soils. Thus, this research aimed to evaluate if fertigation with Si modifies the C:N:P stoichiometry and if it can increase sugarcane's nutritional efficiency and vegetative and productive parameters. Therefore, three experiments were installed using pre-sprouted seedlings to cultivate sugarcane in tropical soils belonging to the Quartzarenic Neosol, Eutrophic Red Latosol, and Dystrophic Red Latosol classes. The treatments comprised a 2 × 2 factorial scheme in each soil. The first factor was composed without water restriction (water retention = 70%; AWD) and with water restriction (water retention = 35%; PWD). The second factor presented Si concentrations (0 mM and 1.8 mM) arranged in randomized blocks with five replications. Fertigation with Si increases the Si and P concentration, the C and N efficiency, the C:N ratio, and the dry mass production. However, it decreases the C and N concentration and the C:P, C:Si, and N:P ratios in sugarcane leaves and stems regardless of the water regime adopted in the three tropical soils. Cluster and principal components analysis indicated that the intensity of the beneficial effects of Si fertigation on sugarcane plants varies depending on the cultivation soil and water conditions. We found that Si can be used in sugarcane with and without water stress. It changes the C:N:P homeostasis enough to improve the nutritional efficiency of C, P, N, and, consequently, the dry mass accumulation on the stems, with variation in the different cultivated soils.

Forms of application of silicon in quinoa and benefits involved in the association between productivity with grain biofortification.

Multiple aspects of the physiological and nutritional mechanisms involved with silicon (Si) absorption by quinoa plants remain poorly investigated, as well as the best way of supplying this element to crops. Thus, this study aimed at evaluating whether the application of Si increases its uptake by quinoa plants and consequently the use efficiency of N and P, as well as the levels of phenolic compounds in the leaves, crop productivity and the biofortification of grains. For this purpose, the concentration of 3 mmol L-1 of Si was tested, according to the following procedures: foliar application (F), root application in the nutrient solution (R), combined Si application via nutrient solution and foliar spraying (F + R), and no Si application (0). The provision of Si through the leaves and roots promoted the highest uptake of the element by the plant, which resulted in an increased use efficiency of N and P. Consequently, such a higher uptake favored the productivity of grains. The optimal adoption of the application of Si through leaves and roots promoted the highest Si concentration and ascorbic acid content in quinoa grains.

Silicon as a Sustainable Option to Increase Biomass With Less Water by Inducing Carbon:Nitrogen:Phosphorus Stoichiometric Homeostasis in Sugarcane and Energy Cane.

Climate change has prolonged periods of water deficit in sugarcane and energy cane crops. This condition induces an imbalance of the carbon (C): nitrogen (N): phosphorus (P) stoichiometric homeostasis, impairing accumulated nutrients from being converted into biomass. Silicon (Si) supplementation can mitigate the damage caused by water deficit in plants by improving the C:N:P balance, increasing C, N, and P use efficiencies and the biomass conversion, and reducing climate change effects on crops. This study assesses the beneficial effects of Si applied through fertigation associated with foliar spraying on the alleviation of damage caused by severe water deficit in sugarcane and energy cane for intermediate and long periods. In addition, the effects in maintenance of nutritional homeostasis we assessed and C, N, and P use efficiencies on sugarcane and energy cane under those conditions were increased. Four experiments were conducted during the first growth cycle of each species. The effect of fertigation associated with Si foliar spraying was evaluated by applying Si only during the seedling formation phase in sugarcane and energy cane grown under severe water deficit for 60 days after transplanting (intermediate period). Then, the effect of Si applied during seedling formation and supplemented after transplanting was evaluated in sugarcane and energy cane grown under severe water deficit for 160 days after transplanting (long period). The Si supply decreased C contents, modified the C:N:P ratio, and increased C, N, and P use efficiencies in plants of both species under water deficit at the intermediate and long periods after transplanting. The effects of applying Si through fertigation associated with foliar spraying during seedling formation mitigated the damage caused by severe water deficit in the intermediate period, which was mainly observed in sugarcane. When supplemented with Si after transplanting, the mitigating effects occurred in both species under severe long period water deficit. Therefore, the Si supply through fertigation associated with foliar spraying is a viable alternative to provide Si to the plant. It also comes with beneficial effects that partially reverse the damage to nutritional homeostasis and increase nutritional efficiency in plants under severe water deficit.

New outcomes on how silicon enables the cultivation of Panicum maximum in soil with water restriction.

Climate change increases the occurrence of droughts, decreasing the production of tropical forages through the induction of physiological stress. Si is expected to broaden the limit from physiological stress of forages grown under water restriction, which may come from an improvement in the stoichiometric homeostasis of Si with N and C, favoring physiological aspects. This study assessed whether Si supply via fertigation improves physiological aspects and the water content in the plant by means of an antioxidant defense system and changes in the C:N:Si stoichiometry during the regrowth of two cultivars of Panicum maximum grown under two soil water regimes (70 and 40% of the soil's water retention capacity). The forages studied are sensitive to water deficit without silicon supply. The application of Si via fertigation attenuated the water deficit, favoring plant growth by stabilizing the stoichiometric homeostasis C:N and C:Si, which are responsible for increasing the plant capacity of converting accumulated C in dry mass, favoring the water content of the plant tissue and the photosynthetic efficiency. This study highlights the importance of the physiological function of Si, and effects on the stoichiometry of C and N, which are neglected in most research on forages grown under water restriction.

Water deficit modifies C:N:P stoichiometry affecting sugarcane and energy cane yield and its relationships with silicon supply.

Climate change has increased the occurrence of water deficit in regions where sugarcane and energy cane are cultivated, jeopardizing dry matter production of stems. It was hypothesized that the reasons behind this fact relate to C:N:P stoichiometric modifications in these species that impair the conversion rates of accumulated nutrients in the stems, which could be attenuated by supplying silicon (Si) to the crops. Thus, the aims of this study were to evaluate the effects of water deficit in sugarcane and energy cane ratoons in the presence and absence of Si, in the C:N:P stoichiometry of stems, in the use efficiency of these nutrients and in the accumulation of dry matter in stems. Two experiments were carried out, using sugarcane (Saccharum officinarum) and energy cane (S. spontaneum), cultivated in pots filled with a Typic Quartzipisamment. The treatments for both experiments were arranged in a factorial scheme 2 × 2, without (70% of the soil's water retention capacity) and with (30% of the capacity) water deficit, without and with the application of Si via fertirrigation, associated with foliar pulverization, both at a concentration of 2.5 mmol L-1, arranged in randomized blocks. The reduction in dry matter production of stems in both species caused by water deficit was due to modifications of the C, N and P stoichiometric homeostasis, but the benefit of Si in these plants when increasing dry matter production was not a reflection of the change in homeostasis, thus it may be involved in other mechanisms that remain unknown and should be further studied.

Are the interaction effects of warming and drought on nutritional status and biomass production in a tropical forage legume greater than their individual effects?

MAIN CONCLUSION: Drought alone and drought plus warming will change the nutrient requirements and biomass distributions of Stylosanthes capitata, while warming will be advantageous only under well-watered condition for the next decades. Climate change effects on natural and managed ecosystems are difficult to predict due to its multi-factor nature. However, most studies that investigate the impacts of climate change factors on plants, such as warming or drought, were conducted under one single stress and controlled environments. In this study, we evaluated the effects of elevated temperature (+ 2 °C) (T) under different conditions of soil water availability (W) to understand the interactive effects of both factors on leaf, stem, and inflorescence macro and micronutrients concentration and biomass allocation of a tropical forage species, Stylosanthes capitata Vogel under field conditions. Temperature control was performed by a temperature free-air controlled enhancement (T-FACE) system. We observed that warming changed nutrient concentrations and plant growth depending on soil moisture levels, but the responses were specific for each plant organ. In general, we found that warming under well-watered conditions greatly improved nutrient concentration and biomass production, whilst the opposite effect was observed under non-irrigated and non-warmed conditions. However, under warmed and non-irrigated conditions, leaf biomass and leaf nutrient concentration were greatly reduced when compared to non-warmed and irrigated plants. Our findings suggest that warming (2 °C above ambient temperature) and drought, as well as both combined stresses, will change the nutrient requirements and biomass distributions between plant aerial organs of S. capitata in tropical ecosystems, which may impact animal feeding in the future.

Silicon modifies C:N:P stoichiometry, and increases nutrient use efficiency and productivity of quinoa.

Recognizably, silicon has a beneficial effect on plant growth and productivity. In this respect, it is also known that the C, N and, P stoichiometric ratios and nutrient conversion efficiency allow identifying the interactions between elements while helping to understand the role Si plays in plant growth. This study aims to investigate whether increasing Si concentrations (0, 1, 2, and 3 mmol L-1) supplied in the nutrient solution is uptaken by quinoa, modifies the C:N:P stoichiometry while increasing nutritional efficiency and crop productivity as well. Our results revealed that the Si supply by promoting a decline in the C levels, associated with greater uptake of N and P, especially decreased the C:N and C:P ratios, favoring the C metabolism efficiency, and modulated the N and P use efficiency for biomass accumulation. This improved nutritional performance and greater use efficiency of C directly favored quinoa productivity. The future perspective is to encourage new field studies with this species to adjust silicon fertilization management to different soils aiming at enhancing quinoa productivity on a sustainable basis.

Effects of potassium and sodium supply on drought-adaptive mechanisms in Eucalyptus grandis plantations.

A basic understanding of nutrition effects on the mechanisms involved in tree response to drought is essential under a future drier climate. A large-scale throughfall exclusion experiment was set up in Brazil to gain an insight into the effects of potassium (K) and sodium (Na) nutrition on tree structural and physiological adjustments to water deficit. Regardless of the water supply, K and Na supply greatly increased growth and leaf area index (LAI) of Eucalyptus grandis trees over the first 3 yr after planting. Excluding 37% of throughfall reduced above-ground biomass accumulation in the third year after planting for K- supplied trees only. E. grandis trees were scarcely sensitive to drought as a result of the utilization of water stored in deep soil layers after clear-cutting the previous plantation. Trees coped with water restriction through stomatal closure (isohydrodynamic behavior), osmotic adjustment and decrease in LAI. Additionally, droughted trees showed higher phloem sap sugar concentrations. K and Na supply increased maximum stomatal conductance, and the high water requirements of fertilized trees increased water stress during dry periods. Fertilization regimes should be revisited in a future drier climate in order to find the right balance between improving tree growth and limiting water shortage.

Photosynthetic and anatomical responses of Eucalyptus grandis leaves to potassium and sodium supply in a field experiment.

Although vast areas in tropical regions have weathered soils with low potassium (K) levels, little is known about the effects of K supply on the photosynthetic physiology of trees. This study assessed the effects of K and sodium (Na) supply on the diffusional and biochemical limitations to photosynthesis in Eucalyptus grandis leaves. A field experiment comparing treatments receiving K (+K) or Na (+Na) with a control treatment (C) was set up in a K-deficient soil. The net CO2 assimilation rates were twice as high in +K and 1.6 times higher in +Na than in the C as a result of lower stomatal and mesophyll resistance to CO2 diffusion and higher photosynthetic capacity. The starch content was higher and soluble sugar was lower in +K than in C and +Na, suggesting that K starvation disturbed carbon storage and transport. The specific leaf area, leaf thickness, parenchyma thickness, stomatal size and intercellular air spaces increased in +K and +Na compared to C. Nitrogen and chlorophyll concentrations were also higher in +K and +Na than in C. These results suggest a strong relationship between the K and Na supply to E. grandis trees and the functional and structural limitations to CO2 assimilation rates.

Gesso agricola como fonte de enxofre para a cultura do morango / Gypsum as a source of sulfur for strawberry crops

De uma maneira geral, diversos são os estudos sobre a resposta das plantas ao enxofre (S), porém poucos são específicos para a cultura do morangueiro. A exigência por nutrientes e o estado nutricional é um atributo particular de cada espécie e deve ser levada em conta na determinação da demanda nutricional. O objetivo deste trabalho foi avaliar a influência da aplicação de doses S e fósforo (P) no desenvolvimento e produtividade do morangueiro. Foi conduzido um experimento em casa de vegetação, em vasos de 2 Kg de solo (Latossolo Bruno), em Guarapuava-PR. O experimento constituiu-se de um fatorial 6 x 2, delineado em blocos ao acaso, com três repetições, sendo seis doses de S: 0, 10, 20, 30, 40 e 50 mg kg-1, na forma de gesso agrícola e duas doses de P: 300 e 600 mg kg-1 de P2O5. Nos vasos foram transplantadas mudas de morango variedade Albion, cultivadas por 170 dias. Os frutos foram colhidos e pesados ao longo do experimento e a parte aérea ao final do experimento. A parte aérea e os frutos foram secos, pesados, moídos e analisados em relação ao teor de S, Ca e P. A produção de frutos de morango foi influenciada pelas doses de S, sendo que a maior produtividade foi alcançada na dose de 60 mg kg-1 de S com aplicação de 300 mg kg-1 de P e na aplicação de 600 mg kg-1 de P combinada com a dose de 37 mg kg-1 de S.

There are several studies on plant responses to Sulfur (S), but few are specific to the strawberry crop. The requirement for nutrients and the nutritional status of plants is a particular attribute of each species that should be taken into account when determining the plants nutritional demand. The objective of this study was to evaluate the application of S and phosphate (P) rates in the development and productivity of strawberry crops. An experiment was conducted in a greenhouse in pots containing 2 kg soil (Oxisol) in Guarapuava city of Paraná State. The experiment consisted of a 6 × 2 factorial outlined in a randomized block design with three replications, with six doses of S: 0, 10, 20, 30, 40 and 50 mg kg-1 in the form of gypsum, and two doses of P: 300 and 600 mg kg-1 of P2O5. The Albion variety of strawberry plants was transplanted to pots and grown for 170 days. The fruits were harvested and weighed throughout the experiment; a similar procedure was followed for the shoots at the end of the experiment. The shoots and fruits were dried, weighed, ground, and analyzed for the content of S, Ca, and P. The production of strawberry fruits was influenced by S rates, with the highest productivity obtained by using S rates of 60 and 37 mg kg-1 with the application of 300 and 600 mg kg-1 of P, respectively.

Oxidação de metano em solo a longo prazo sob plantio direto no Sul do Brasil / Soil methane oxidation in a long-term no-tillage system in Southern Brazil

Sistemas conservacionistas de manejo de solo são considerados usualmente uma alternativa para restaurar a capacidade de solos agrícolas degradados em oxidar metano (CH4), mas escassa informação é disponível para solos tropicais e subtropicais. O objetivo do presente estudo foi avaliar o efeito de longo prazo (19 anos) do plantio direto (PD) nos fluxos de CH4 em um Argissolo Vermelho (Classificação Brasileira) degradado da região Sul do Brasil, em comparação ao preparo convencional (PC). Fluxos anuais de CH4 do solo foram avaliados nos sistemas PD e PC sob dois sistemas de cultura (aveia/ milho- A/M e ervilhaca/milho-E/M). Amostragem do ar foi conduzida utilizando o método da câmara estática fechada e as análises de CH4 foram realizadas por cromatografia gasosa. Dados históricos do experimento evidenciaram melhoria expressiva da qualidade do solo em PD, especialmente quando associado ao sistema de cultura com leguminosas de cobertura de solo (E/M) que apresentou a mais elevada adição anual de biomassa ao solo. Os fluxos de CH4 variaram de ?42±2 a 38±16 ?g C m-2 h-1 e as emissões anuais de CH4 variaram de ?825±117 (PC E/M) a 453±185 g C ha-1 (PD A/M). Portanto, a capacidade de oxidação de CH4 não teve relação com a qualidade do solo nos distintos sistemas de manejo. Baseado nos resultados do presente estudo e da literatura, nos hipotetizamos que as zonas de oxidação de CH4 e de m

Conservation management systems are usually suggested as alternative to restore the soil methane (CH4) oxidation capacity of degraded soils; however, little information is available on tropical and subtropical soils. Our objective was to evaluate the long-term (19 years) effect of no-tillage (NT) versus conventional tillage (CT) management systems on CH4 fluxes in a formerly degraded Acrisol in Southern Brazil. Annual CH4 fluxes of two cropping systems [O/M-black oat (Avena strigosa)/maize and V/M-vetch (Vigna sativa)/maize] were measured in NT and CT soils. Static chambers were used for air sampling, while chromatography was used for CH4 analysis. Analysis of the historical dataset at this experimental site indicated improvements in soil quality under the NT system, especially in legume-based cropping system (V/M) that exhibited the highest annual biomass input. CH4 fluxes ranged from ?42 ± 2 to 38 ± 16 ?g C m-2 h-1, and annual CH4 emissions ranged from ?825 ± 117 (CT V/M) to 453 ± 185 g C ha-1 (NT O/M). Thus, the annual CH4 oxidation capacity of the soil was not related to the soil quality produced by the soil management systems. On the basis of our results and published literature, we postulate that conservation management systems improve the methane oxidation and soil quality in distinct soil layers, which result in a slow effect of these management systems on the methane o

Oxidação de metano em solo a longo prazo sob plantio direto no Sul do Brasil / Soil methane oxidation in a long-term no-tillage system in Southern Brazil

Sistemas conservacionistas de manejo de solo são considerados usualmente uma alternativa para restaurar a capacidade de solos agrícolas degradados em oxidar metano (CH4), mas escassa informação é disponível para solos tropicais e subtropicais. O objetivo do presente estudo foi avaliar o efeito de longo prazo (19 anos) do plantio direto (PD) nos fluxos de CH4 em um Argissolo Vermelho (Classificação Brasileira) degradado da região Sul do Brasil, em comparação ao preparo convencional (PC). Fluxos anuais de CH4 do solo foram avaliados nos sistemas PD e PC sob dois sistemas de cultura (aveia/ milho- A/M e ervilhaca/milho-E/M). Amostragem do ar foi conduzida utilizando o método da câmara estática fechada e as análises de CH4 foram realizadas por cromatografia gasosa. Dados históricos do experimento evidenciaram melhoria expressiva da qualidade do solo em PD, especialmente quando associado ao sistema de cultura com leguminosas de cobertura de solo (E/M) que apresentou a mais elevada adição anual de biomassa ao solo. Os fluxos de CH4 variaram de ?42±2 a 38±16 ?g C m-2 h-1 e as emissões anuais de CH4 variaram de ?825±117 (PC E/M) a 453±185 g C ha-1 (PD A/M). Portanto, a capacidade de oxidação de CH4 não teve relação com a qualidade do solo nos distintos sistemas de manejo. Baseado nos resultados do presente estudo e da literatura, nos hipotetizamos que as zonas de oxidação de CH4 e de m

Conservation management systems are usually suggested as alternative to restore the soil methane (CH4) oxidation capacity of degraded soils; however, little information is available on tropical and subtropical soils. Our objective was to evaluate the long-term (19 years) effect of no-tillage (NT) versus conventional tillage (CT) management systems on CH4 fluxes in a formerly degraded Acrisol in Southern Brazil. Annual CH4 fluxes of two cropping systems [O/M-black oat (Avena strigosa)/maize and V/M-vetch (Vigna sativa)/maize] were measured in NT and CT soils. Static chambers were used for air sampling, while chromatography was used for CH4 analysis. Analysis of the historical dataset at this experimental site indicated improvements in soil quality under the NT system, especially in legume-based cropping system (V/M) that exhibited the highest annual biomass input. CH4 fluxes ranged from ?42 ± 2 to 38 ± 16 ?g C m-2 h-1, and annual CH4 emissions ranged from ?825 ± 117 (CT V/M) to 453 ± 185 g C ha-1 (NT O/M). Thus, the annual CH4 oxidation capacity of the soil was not related to the soil quality produced by the soil management systems. On the basis of our results and published literature, we postulate that conservation management systems improve the methane oxidation and soil quality in distinct soil layers, which result in a slow effect of these management systems on the methane o

Gesso agricola como fonte de enxofre para a cultura do morango / Gypsum as a source of sulfur for strawberry crops

De uma maneira geral, diversos são os estudos sobre a resposta das plantas ao enxofre (S), porém poucos são específicos para a cultura do morangueiro. A exigência por nutrientes e o estado nutricional é um atributo particular de cada espécie e deve ser levada em conta na determinação da demanda nutricional. O objetivo deste trabalho foi avaliar a influência da aplicação de doses S e fósforo (P) no desenvolvimento e produtividade do morangueiro. Foi conduzido um experimento em casa de vegetação, em vasos de 2 Kg de solo (Latossolo Bruno), em Guarapuava-PR. O experimento constituiu-se de um fatorial 6 x 2, delineado em blocos ao acaso, com três repetições, sendo seis doses de S: 0, 10, 20, 30, 40 e 50 mg kg-1, na forma de gesso agrícola e duas doses de P: 300 e 600 mg kg-1 de P2O5. Nos vasos foram transplantadas mudas de morango variedade Albion, cultivadas por 170 dias. Os frutos foram colhidos e pesados ao longo do experimento e a parte aérea ao final do experimento. A parte aérea e os frutos foram secos, pesados, moídos e analisados em relação ao teor de S, Ca e P. A produção de frutos de morango foi influenciada pelas doses de S, sendo que a maior produtividade foi alcançada na dose de 60 mg kg-1 de S com aplicação de 300 mg kg-1 de P e na aplicação de 600 mg kg-1 de P combinada com a dose de 37 mg kg-1 de S.

There are several studies on plant responses to Sulfur (S), but few are specific to the strawberry crop. The requirement for nutrients and the nutritional status of plants is a particular attribute of each species that should be taken into account when determining the plants nutritional demand. The objective of this study was to evaluate the application of S and phosphate (P) rates in the development and productivity of strawberry crops. An experiment was conducted in a greenhouse in pots containing 2 kg soil (Oxisol) in Guarapuava city of Paraná State. The experiment consisted of a 6 × 2 factorial outlined in a randomized block design with three replications, with six doses of S: 0, 10, 20, 30, 40 and 50 mg kg-1 in the form of gypsum, and two doses of P: 300 and 600 mg kg-1 of P2O5. The Albion variety of strawberry plants was transplanted to pots and grown for 170 days. The fruits were harvested and weighed throughout the experiment; a similar procedure was followed for the shoots at the end of the experiment. The shoots and fruits were dried, weighed, ground, and analyzed for the content of S, Ca, and P. The production of strawberry fruits was influenced by S rates, with the highest productivity obtained by using S rates of 60 and 37 mg kg-1 with the application of 300 and 600 mg kg-1 of P, respectively.

Conversion of cerrado into agricultural land in the south-western Amazon: carbon stocks and soil fertility

Land use change and land management practices can modify soil carbon (C) dynamics and soil fertility. This study evaluated the effect of tillage systems (no-tillage - NT and conventional tillage - CT) on soil C and nutrient stocks in an Oxisol from an Amazonian cerrado following land use change. The study also identified relationships between these stocks and other soil attributes. Carbon, P, K, Ca and Mg stocks, adjusted to the equivalent soil mass in the cerrado (CE), were higher under NT. After adoption of all but one of the NT treatments, C stocks were higher than they were in the other areas we considered. Correlations between C and nutrient stocks showed positive correlations with Ca and Mg under NT due to continuous liming, higher crop residue inputs and lack of soil disturbance, associated with positive correlations with cation exchange capacity (CEC), base saturation and pH. The positive correlation (r = 0.91, p 0.05) between C stocks and CEC in the CE indicates the important contribution of soil organic matter (SOM) to CEC in tropical soils, although the exchange sites are - under natural conditions - mainly occupied by H and Al. Phosphorus and K stocks showed positive correlations (0.81 and 0.82, respectively) with C stocks in the CE, indicating the direct relationship of P and K with SOM in natural ecosystems. The high spatial variability of P and K fertilizer application may be obscuring these soil nutrient stocks. In this study, the main source of P and K was fertilizer rather than SOM.

Mudanças de uso da terra e práticas de manejo modificam a dinâmica do C e a fertilidade do solo. Este estudo avaliou as implicações dos sistemas de cultivo (NT e CT) nos estoques de C e de nutrientes e identificou inter-relações entre estes estoques e outros atributos da fertilidade do solo em Latossolo após a mudança do uso da terra no cerrado amazônico. Os estoques de C e de nutrientes (P, K, Ca e Mg) ajustados pela massa equivalente do solo sob cerrado (CE), foram maiores principalmente sob NT. Após a adoção do NT, exceto em 2NT, os estoques de C foram maiores em relação às demais áreas avaliadas. Correlações entre estoques de C e de nutrientes revelaram algumas correlações positivas com Ca e Mg nas áreas sob NT, devido ao uso continuo de calcário, à maior quantidade de resíduos culturais e ao não revolvimento do solo, associado à correlações positivas com CTC, saturação por bases e pH. A correlação positiva (r = 0,91, p 0,05) entre estoques de C e CTC em CE indica a importante contribuição da MOS na CTC de solos tropicais, embora os sítios de troca estejam ocupados principalmente por H + Al. Estoques de P e K mostraram correlações positivas com estoques de C em CE (0,81 e 0,82; respectivamente), indicando a alta relação de P e K com a MOS em ecossistemas naturais. A alta variabilidade espacial associada à aplicação de fertilizantes (P e K) no sulco de plantio pode ter mascarado os resultados dos estoques. A principal fonte destes nutrientes para o solo foi o fertilizante aplicado e não a MOS.

Conversion of cerrado into agricultural land in the south-western Amazon: carbon stocks and soil fertility

Land use change and land management practices can modify soil carbon (C) dynamics and soil fertility. This study evaluated the effect of tillage systems (no-tillage - NT and conventional tillage - CT) on soil C and nutrient stocks in an Oxisol from an Amazonian cerrado following land use change. The study also identified relationships between these stocks and other soil attributes. Carbon, P, K, Ca and Mg stocks, adjusted to the equivalent soil mass in the cerrado (CE), were higher under NT. After adoption of all but one of the NT treatments, C stocks were higher than they were in the other areas we considered. Correlations between C and nutrient stocks showed positive correlations with Ca and Mg under NT due to continuous liming, higher crop residue inputs and lack of soil disturbance, associated with positive correlations with cation exchange capacity (CEC), base saturation and pH. The positive correlation (r = 0.91, p 0.05) between C stocks and CEC in the CE indicates the important contribution of soil organic matter (SOM) to CEC in tropical soils, although the exchange sites are - under natural conditions - mainly occupied by H and Al. Phosphorus and K stocks showed positive correlations (0.81 and 0.82, respectively) with C stocks in the CE, indicating the direct relationship of P and K with SOM in natural ecosystems. The high spatial variability of P and K fertilizer application may be obscuring these soil nutrient stocks. In this study, the main source of P and K was fertilizer rather than SOM.

Mudanças de uso da terra e práticas de manejo modificam a dinâmica do C e a fertilidade do solo. Este estudo avaliou as implicações dos sistemas de cultivo (NT e CT) nos estoques de C e de nutrientes e identificou inter-relações entre estes estoques e outros atributos da fertilidade do solo em Latossolo após a mudança do uso da terra no cerrado amazônico. Os estoques de C e de nutrientes (P, K, Ca e Mg) ajustados pela massa equivalente do solo sob cerrado (CE), foram maiores principalmente sob NT. Após a adoção do NT, exceto em 2NT, os estoques de C foram maiores em relação às demais áreas avaliadas. Correlações entre estoques de C e de nutrientes revelaram algumas correlações positivas com Ca e Mg nas áreas sob NT, devido ao uso continuo de calcário, à maior quantidade de resíduos culturais e ao não revolvimento do solo, associado à correlações positivas com CTC, saturação por bases e pH. A correlação positiva (r = 0,91, p 0,05) entre estoques de C e CTC em CE indica a importante contribuição da MOS na CTC de solos tropicais, embora os sítios de troca estejam ocupados principalmente por H + Al. Estoques de P e K mostraram correlações positivas com estoques de C em CE (0,81 e 0,82; respectivamente), indicando a alta relação de P e K com a MOS em ecossistemas naturais. A alta variabilidade espacial associada à aplicação de fertilizantes (P e K) no sulco de plantio pode ter mascarado os resultados dos estoques. A principal fonte destes nutrientes para o solo foi o fertilizante aplicado e não a MOS.

Root systems and soil microbial biomass under no-tillage system

Some root parameters such as distribution, length, diameter and dry matter are inherent to plant species. Roots can influence microbial population during vegetative cycle through the rhizodeposits and, after senescence, integrating the soil organic matter pool. Since they represent labile substrates, especially regarding nitrogen, they can determine the rate of nutrient availability to the next crop cultivated under no-tillage (NT). The root systems of two crop species: maize (Zea mays L.) cultivar Cargill 909 and soybean [Glycine max (L.) Merr.] cultivar Embrapa 59, were compared in the field, and their influence on spatial distribution of the microbial C and N in a clayey-textured Typic Hapludox cultivated for 22 years under NT, at Tibagi, State of Paraná (PR), Brazil, was determined. Digital image processing and nail-plate techniques were used to evaluate 40 plots of a 80 ´ 50 ´ 3 cm soil profile. It was observed that 36% and 30% of the maize and soybeans roots, respectively, are concentrated in the 0 to 10 cm soil layer. The percent distribution of root dry matter was similar for both crops. The maize roots presented a total of 1,324 kg C ha-1 and 58 kg N ha-1, with higher root dry matter density and more roots in decomposition in the upper soil layer, decreasing with depth. The soybean roots (392 kg C ha-1 and 21 kg N ha-1) showed higher number of thinner roots and higher density per length unity compared to the maize. The maize roots enhanced microbial-C down to deeper soil layers than did the soybean roots. The microbial N presented a better correlation with the concentration of thin active roots and with roots in decomposition or in indefinite shape, possibly because of higher concentration of C and N easily assimilated by soil microorganisms.

Parâmetros radiculares como distribuição, comprimento, diâmetro e matéria seca são inerentes a cada espécie de planta. As raízes podem influenciar a população microbiana durante o ciclo vegetativo através das rizodeposições e, após a senescência, integrando a matéria orgânica do solo. Pelo fato de representarem um substrato lábil, especialmente de nitrogênio, podem ditar o ritmo da disponibilidade de nutrientes na seqüência de culturas sob o sistema de plantio direto (SPD). A comparação dos sistemas radiculares do milho (Zea mays L.), cultivar Cargill 909 e da soja [Glycine max (L.) Merr.], cultivar Embrapa 59, e sua influência sobre a distribuição espacial do C e N microbianos foi feita em um Latossolo Vermelho-Escuro, textura argilosa, cultivado durante 22 anos sob SPD, no município de Tibagi (PR). Técnicas de processamento de imagens e de placa de pregos foram empregadas na avaliação de 40 quadrículas de um perfil de 80 ´ 50 ´ 3 cm, revelando que 36% das raízes de milho e 30% das raízes de soja estão concentradas na camada 0-10 cm do solo. A distribuição percentual no perfil do solo de matéria seca radicular foi semelhante nas duas culturas. O sistema radicular do milho apresentou 1.324 kg C ha-1 e 58 kg N ha-1, com maior densidade por matéria seca e de raízes em vias de decomposição na camada superficial do solo, decrescendo com a profundidade. O sistema radicular da soja (392 kg C ha-1 e 21 kg N ha-1) teve contribuição maior de raízes finas e de densidade por comprimento do que do milho. O efeito das raízes do milho sobre o C microbiano alcançou camadas mais profundas do que o das raízes da soja. O N microbiano apresentou melhor correlação com a concentração de raízes finas ativas e com as raízes em decomposição ou de forma indefinida, provavelmente em função da maior quantidade de C e N de fácil assimilação pelos microrganismos.

Root systems and soil microbial biomass under no-tillage system

Some root parameters such as distribution, length, diameter and dry matter are inherent to plant species. Roots can influence microbial population during vegetative cycle through the rhizodeposits and, after senescence, integrating the soil organic matter pool. Since they represent labile substrates, especially regarding nitrogen, they can determine the rate of nutrient availability to the next crop cultivated under no-tillage (NT). The root systems of two crop species: maize (Zea mays L.) cultivar Cargill 909 and soybean [Glycine max (L.) Merr.] cultivar Embrapa 59, were compared in the field, and their influence on spatial distribution of the microbial C and N in a clayey-textured Typic Hapludox cultivated for 22 years under NT, at Tibagi, State of Paraná (PR), Brazil, was determined. Digital image processing and nail-plate techniques were used to evaluate 40 plots of a 80 ´ 50 ´ 3 cm soil profile. It was observed that 36% and 30% of the maize and soybeans roots, respectively, are concentrated in the 0 to 10 cm soil layer. The percent distribution of root dry matter was similar for both crops. The maize roots presented a total of 1,324 kg C ha-1 and 58 kg N ha-1, with higher root dry matter density and more roots in decomposition in the upper soil layer, decreasing with depth. The soybean roots (392 kg C ha-1 and 21 kg N ha-1) showed higher number of thinner roots and higher density per length unity compared to the maize. The maize roots enhanced microbial-C down to deeper soil layers than did the soybean roots. The microbial N presented a better correlation with the concentration of thin active roots and with roots in decomposition or in indefinite shape, possibly because of higher concentration of C and N easily assimilated by soil microorganisms.

Parâmetros radiculares como distribuição, comprimento, diâmetro e matéria seca são inerentes a cada espécie de planta. As raízes podem influenciar a população microbiana durante o ciclo vegetativo através das rizodeposições e, após a senescência, integrando a matéria orgânica do solo. Pelo fato de representarem um substrato lábil, especialmente de nitrogênio, podem ditar o ritmo da disponibilidade de nutrientes na seqüência de culturas sob o sistema de plantio direto (SPD). A comparação dos sistemas radiculares do milho (Zea mays L.), cultivar Cargill 909 e da soja [Glycine max (L.) Merr.], cultivar Embrapa 59, e sua influência sobre a distribuição espacial do C e N microbianos foi feita em um Latossolo Vermelho-Escuro, textura argilosa, cultivado durante 22 anos sob SPD, no município de Tibagi (PR). Técnicas de processamento de imagens e de placa de pregos foram empregadas na avaliação de 40 quadrículas de um perfil de 80 ´ 50 ´ 3 cm, revelando que 36% das raízes de milho e 30% das raízes de soja estão concentradas na camada 0-10 cm do solo. A distribuição percentual no perfil do solo de matéria seca radicular foi semelhante nas duas culturas. O sistema radicular do milho apresentou 1.324 kg C ha-1 e 58 kg N ha-1, com maior densidade por matéria seca e de raízes em vias de decomposição na camada superficial do solo, decrescendo com a profundidade. O sistema radicular da soja (392 kg C ha-1 e 21 kg N ha-1) teve contribuição maior de raízes finas e de densidade por comprimento do que do milho. O efeito das raízes do milho sobre o C microbiano alcançou camadas mais profundas do que o das raízes da soja. O N microbiano apresentou melhor correlação com a concentração de raízes finas ativas e com as raízes em decomposição ou de forma indefinida, provavelmente em função da maior quantidade de C e N de fácil assimilação pelos microrganismos.

Nitrogen dynamics in a soil-sugar cane system

Results of an organic matter management experiment of a sugar cane crop are reported for the first cropping year. Sugar cane was planted in October 1997, and labeled with a 15N fertilizer pulse to study the fate of organic matter in the soil-plant system. A nitrogen balance is presented, partitioning the system in plant components (stalk, tip and straw), soil components (five soil organic matter fractions) and evaluating leaching losses. The 15N label permitted to determine, at the end of the growing season, amounts of nitrogen derived from the fertilizer, present in the above mentioned compartments.

São apresentados resultados de um experimento sobre matéria orgânica em cultura de cana-de-açúcar, relativos ao primeiro ano (cana planta). A cultura foi instalada em outubro de 1997 e marcada com um pulso de fertilizante 15N, para estudar o destino da matéria orgânica no sistema solo-planta. É apresentado um balanço de nitrogênio, subdividindo o sistema em componentes de planta (colmo, ponteiro e palha), componentes de solo (cinco frações de matéria orgânica do solo) e estimando perdas por lixiviação. O 15N permitiu a determinação das quantidades de nitrogênio provenientes do fertilizante nos compartimentos acima mencionados, no final do ciclo da cultura.