ABSTRACT The interaction of Zn with soil compartments influences its bioavailability and uptake by plants. In this study, rice and soybean were cultivated under greenhouse conditions with the aim of evaluating Zn bioavailability and fractionation in a clayey-textured Typic Hapludox as a function of Zn rates (4 or 8 mg kg –1 Zn). The experiment was conducted until grain filling. Two soil subsamples (t 1 and t 2 ) that referred to the seeding and flowering stages, were collected and compared with two single extraction schemes, DTPA (Zn DTPAt1 and Zn DTPAt2 ) and Mehlich-1 (Zn Mt1 and Zn Mt2 ) for Zn available contents. Zn fractionation was carried out with t 2 soil subsamples for the testing of the following fractions: exchangeable Zn (Zn Exc ), Zn bound to carbonates (Zn Carb ), Zn bound to organic matter (Zn OM ), Zn bound to oxides (Zn Oxi ) and residual Zn (Zn res ). Zn applied to soil increased the Zn concentration in labile fractions in decreasing order as follows: Zn Exc > Zn OM > Zn Carb . There was no difference between the lesser or unavailable fractions, Zn Oxi and Zn res, when there was no correlation between the rates either with total accumulated Zn in plants (Zna total ), or the contents extracted by DTPA or Mehlich-1. Total cumulative Zn content in rice and soybean affected by the ZnCl 2 rates applied were positively correlated with Zn content extracted by both solutions. Both extractant solutions presented positive correlation between available contents of Zn with Zn bound to labile fractions.

Summary Andisols are distinguished by a high phosphorus (P) adsorption capacity, which is a restrictive factor for plant growth. This study, it was hypothesized that the availability of P in the different forms extracted sequentially, would vary according to the land use, and its exchange would depend on its chemical characteristics. For this purpose, sequential extraction and isotopic dilution techniques were utilized to measure the effect of land use systems and corresponding P fertilizer inputs on size of inorganic and organic P forms and their lability. An Andisol sample from a field site with a long history of P amendments and another sample from a contiguous forested area under natural vegetation were treated with applied KH2 32PO4. The soil samples were sequentially extracted for P fractions after 49 days (d) of incubation. Recovery of 32P in each P form was evaluated. The recovery of 32P in all soil P fractions exhibited that 32P had undergone exchange with the native P. The exchange reaction occurred mainly in the Pi fractions. Resin-Pi, Bic-Pi and NaOH-Pi were increased by P fertilization, with the greater level occurring for NaOH-Pi. The highest increase of the 32P recovered in the NaOH0.1-Pi fraction of the P-fertilized Andisol shows that the added P changed into this form stays highly exchangeable and contributes P fertility to this soil type. The recalcitrant inorganic fractions contained almost no exchangeable P. In contrast, in native soil with no P input, more than 20% of the 32P was recovered in Bic-Po and NaOH-Po forms 49 d after the labeled P was added. The change in soil P fraction was associated with soil type and P addition. Nonetheless, the applied P persisting in the fraction can be exchangeable with solution P and, hence, can be plant-available.

Resumen Los Andisoles se distinguen por su habilidad para retener fósforo (P), lo cual restringe la productividad agrícola. Se planteó la hipótesis que la disponibilidad de P en las diferentes formas extraídas secuencialmente, variaría de acuerdo al uso del suelo y su intercambio dependería de las características químicas del mismo. En este estudio, se usaron los métodos de extracción secuencial y dilución isotópica para evaluar el efecto del uso del suelo y la adición de fertilizante en las fracciones inorgánicas y orgánicas de P y su disponibilidad. Se incluyeron muestras de suelo de un sitio con una larga historia de fertilización y otro de una área adyacente de bosque nativo, al cual se les aplicó KH2 32PO4. El suelo se fraccionó secuencialmente después de un periodo de 49 días de incubación y se determinó la proporción (%) de 32P recuperado en cada fracción. En todas las fracciones se recuperó 32P, lo que demuestra la existencia de intercambio entre el 32P y P natural del suelo. Las reacciones de intercambio ocurrieron mayormente en las fracciones inorgánicas. Las fracciones de resina-Pi, NaHCO3-Pi e NaOH0.1-Pi aumentaron con la fertilización de P, siendo la fracción de NaOH0.1-Pi, la mayor fuente del nutriente. El mayor incremento de 32P recuperado en la fracción de NaOH0.1-Pi, indica que el P añadido y transformado en esta fracción es altamente intercambiable y contribuye con la fertilidad de este suelo. Las fracciones recalcitrantes presentaron poco P intercambiable. En contraste, en el suelo de bosque sin fertilizar, más del 20% del 32P se recuperó en las fracciones de Bic-Po y NaOH-Po, 49 días después de que se añadió el radiotrazador. La transformación de las fracciones de P fue dependiente del tipo de suelo y la adición de P. El P aplicado permaneció, preferiblemente, en la forma que puede ser intercambiable con la solución del suelo y, por consiguiente, puede estar disponible para la planta.

RESUMO O feijão apresenta baixa capacidade de fixação biológica de nitrogênio, o qual pode ser mais eficiente com o fornecimento de molibdênio (Mo). O objetivo deste estudo foi avaliar doses de Mo no crescimento e na fixação biológica de nitrogênio em duas cultivares de feijoeiro usando a técnica de diluição isotópica. O experimento foi realizado em 2014 em delineamento inteiramente casualizado e em esquema fatorial 5 x 3, correspondendo a cinco doses de Mo (controle, 40, 80, 120 e 240 g ha-1), cultivares de feijoeiro Aporé, Ouro Negro e NORH-54, cultivar de feijão não nodulante e três repetições. A aplicação de Mo e a inoculação das sementes com uma estirpe de rizóbio contribuíram para melhorar a fixação de nitrogênio e o peso de grãos. A cultivar Ouro Negro apresentou maior número e peso de nódulos do que a cultivar Aporé e maiores valores de nitrogênio proveniente da atmosfera. A fixação biológica do nitrogênio foi mais dependente da aplicação de Mo na cultivar Aporé. Esses resultados indicaram que a inoculação com rizóbio e o fornecimento de Mo contribuíram com a fixação biológica de nitrogênio e produção de grãos.

ABSTRACT The common bean has been considered to have low biological nitrogen fixation capacity; however, this process can be made more effective with molybdenum (Mo) supplementation. The objective of this study was to evaluate the influence of Mo rates on the growth and biological nitrogen fixation by two Brazilian common bean cultivars using the 15N isotope dilution technique. The experiment was performed in 2014 in a completely randomized design arranged in a 5 x 3 factorial scheme, corresponding to 5 rates of Mo (control, 40, 80, 120 and 240 g ha-1), the common bean cultivars Aporé, Ouro Negro and NORH-54 (a non-nodulating common bean cultivar), and three replicates. The application of Mo and the inoculation with rhizobia strains contributed to improving nitrogen fixation and grain weight. The cultivar Ouro Negro showed a higher number and weight of nodules and a higher amount of nitrogen derived from the atmosphere than the cultivar Aporé. The biological nitrogen fixation of Aporé was more dependent on the application of Mo. These results indicated that inoculation with Rhizobium strains and Mo supply effectively contributed to biological nitrogen fixation and improving grain production.

Resumo: O objetivo deste trabalho foi avaliar os efeitos do uso de plantas de cobertura sobre a produtividade do arroz (Oryza sativa) de terras altas cultivado em sistema plantio direto, na presença e na ausência de adubação nitrogenada, bem como quantificar, em campo, o aproveitamento de N da ureia e de plantas de cobertura pelo arroz, com emprego da técnica de diluição isotópica de 15N. O experimento de campo foi realizado em Selvíria, MS, em um Latossolo Vermelho distroférrico, na região do Cerrado. O delineamento experimental foi o de blocos ao acaso com 15 tratamentos e quatro repetições, em arranjo fatorial 5x3. Os tratamentos foram quatro espécies de plantas de cobertura (Crotalaria juncea, Cajanus cajan, Mucuna pruriens e Pennisetum glaucum) + vegetação espontânea (pousio), combinados com três formas de adubação nitrogenada: controle, sem aplicação de N; 20 kg ha-1 de N em semeadura; e 20 kg ha-1 de N em semeadura mais 60 kg ha-1 de N em cobertura. O arroz não responde à aplicação de N em cobertura, quando leguminosas são usadas como plantas de cobertura. O uso de leguminosas como planta de cobertura resulta em maior produtividade de grãos e aproveitamento do N do fertilizante pelo arroz do que o uso de milheto ou pousio. As leguminosas proporcionam efeito equivalente à aplicação de 60 kg ha-1 de N na forma de ureia sobre a produtividade de grãos de arroz.

Abstract: The objective of this work was to evaluate the effects of cover crops on the yield of upland rice (Oryza sativa) grown under no-tillage system, in the presence and absence of N fertilizer, as well as to quantify, in the field, the use efficiency of N from urea and cover crops by upland rice, through the 15N isotope dilution technique. The field experiment was carried out in the municipality of Selvíria, in the state of Mato Grosso do Sul, Brazil, in an Oxisol (Rhodic Hapludox) in the Cerrado (Brazilian savanna) region. The experimental design was a randomized complete block with 15 treatments and four replicates, in a 5x3 factorial arrangement. The treatments were four cover crops (Crotalaria juncea, Cajanus cajan, Mucuna pruriens, and Pennisetum glaucum) + spontaneous vegetation (fallow in off-season), combined with three forms of N fertilization: control treatment, without N fertilizer application; 20 kg ha-1 N at sowing; and 20 kg ha-1 N at sowing plus 60 kg ha-1 N as topdressing. Rice is not affected by N fertilizer application as topdressing, when legume cover crops are used. The use of legume cover crops provides higher grain yield and use of fertilizer-N by rice than that of millet or fallow. Legume cover crops promote an effect equivalent to that of the application of 60 kg ha-1 N as urea on rice yield.

In the Brazilian Cerrado, P deficiency restricts cotton production, which requires large amounts of phosphate fertilizer. To improve the yield of cotton crops, genotypes with high P use efficiency must be identified and used. The present study evaluated P uptake and use efficiency of different Gossypium barbadense L. genotypes grown in the Cerrado. The experiment was carried out in a greenhouse with a completely randomized design, 15 x 2 factorial treatment structure (15 genotypes x 2 P levels), and four replicates. The genotypes were MT 69, MT 70, MT 87, MT 91, MT 92, MT 94, MT 101, MT 102, MT 103, MT 105, MT 106, MT 110, MT 112, MT 124, and MT 125; P levels were sufficient (1000 mg pot-1, PS treatment) or deficient (PD treatment). Dry matter (DM) and P levels were determined in cotton plant parts and used to calculate plant P content and use efficiency. In general, DM and P content were higher in the PS than in the PD treatment, with the exception of root DM and total DM in some genotypes. Genotypes also differed in terms of P uptake and use capacity. In the PS treatment, genotypes MT 92 and MT 102 had the highest response to phosphate fertilization. Genotype MT 69 exhibited the most efficient P uptake in the PD treatment. Genotype MT 124 showed the best shoot physiological efficiency, apparent recovery efficiency, and utilization efficiency, whereas MT 110 exhibited the highest root physiological efficiency.

Large areas of land are nowadays contaminated by heavy metals and, it is therefore, important to monitor their levels in soils. Vegetables act as transfer mechanisms of such contaminants from soils to higher levels in the food chain. In this study, we aimed to evaluate the effectiveness of chemical extractants by the L-value method for Cd phytoavailability using the 109Cd radionuclide. In a greenhouse experiment, rocket plants (Eruca sativa L.) were cultivated in pots with samples from Typic Hapludox and Typic Quartzipsamment soils. Cadmium concentrations ranging from 0 to 16 mg kg-1 were added to a 200 mL solution containing 148 kBq 109Cd. The available Cd in the soil was extracted by DTPA, Mehlich-1, Mehlich-3, and a mixture of organic acids (acetic, citric, lactic, and oxalic acids). Cd concentrations were determined by atomic absorption spectrophotometry, and 109Cd radionuclide activity was measured by low-level β-counting. The dry matter yield was not influenced by Cd rates, but the Cd content and accumulation in shoots had a positive linear correlation. Generally, Cd was extracted in higher quantities by Mehlich-1 followed by DTPA, Mehlich-3, and organic acids. A linear correlation was found between the chemical extractants and Cd accumulation in shoots for both soils. According to the L Ratio, the extractants based on strong acids and chelating agents presented low efficiency regarding Cd phytoavailability. The organic acids, which presented values close to the L-value, may provide a promising method for evaluating environmental contaminants.

O objetivo deste trabalho foi avaliar a utilização, pela planta de milho, do P proveniente de superfosfato triplo marcado com 32P (32P‑SFT), e do P proveniente do solo influenciado por doses de N e pelos adubos verdes (AV) crotalária (Crotalaria juncea) e milheto (Pennisetum glaucum). O experimento foi realizado em vasos com 5 kg de Latossolo Vermelho distroférrico. Utilizou-se o delineamento inteiramente casualizado, em arranjo fatorial 4x4x2, com quatro repetições. Os tratamentos foram: quatro doses de P, na forma de SFT (0, 0,175, 0,350 e 0,700 g de P por vaso); quatro doses de N, na forma de ureia (0, 0,75, 1,50 e 2,25 g de N por vaso); e crotalária ou milheto, como adubo verde. Foram levadas em consideração as adições de P e N pelos AV. Após a maturação fisiológica dos grãos, foram avaliados: a produção de matéria seca de milho, o teor de P, o P acumulado e o aproveitamento de P nos diferentes tratamentos. O aproveitamento do 32P‑SFT pelo milho aumentou com o incremento da dose de N e diminuiu com o aumento da dose de 32P‑SFT. O fertilizante mineral fornece a maior parte do P acumulado nas plantas de milho. O aproveitamento do 32P‑SFT pelo milho foi de 13,12%, em média. A espécie de adubo verde influencia a assimilação de 32P‑SFT pelas plantas.

The objective of this work was to evaluate the utilization by corn plants of P from triple superphosphate fertilizer labeled with 32P (32P‑TSP), and of P from soil as affected by N rates and by the green manures (GM) sunn hemp (Crotalaria juncea) and millet (Pennisetum glaucum). The experiment was carried out using pots filled with 5 kg Oxisol (Rhodic Hapludox). A completely randomized design was used, in a 4x4x2 factorial arrangement, with four replicates. The treatments were: four P rates as TSP (0, 0.175, 0.350, and 0.700 g P per pot); four N rates as urea (0, 0.75, 1.50, and 2.25 g N per pot); and sunn hemp or millet as green manure. The additions of N and P by the GM were taken into account. After grain physiologic maturation, corn dry matter, P contents, accumulated P, and P recovery in the different treatments were measured. 32P‑TSP recovery by corn increased with N increasing rates, and decreased with increasing rates of 32P‑TSP. The mineral fertilizer provides most of the accumulated P by corn plants. The recovery of 32P‑TSP by corn was 13.12% in average. The green manure species influence the assimilation of 32P‑TSP by the plants.

Ingestion of vegetables containing heavy metals is one of the main ways in which these elements enter the human body. Once entered, heavy metals are deposited in bone and fat tissues, overlapping noble minerals. Slowly released into the body, heavy metals can cause an array of diseases. This study aimed to investigate the concentrations of cadmium, nickel, lead, cobalt and chromium in the most frequently consumed foodstuff in the São Paulo State, Brazil and to compare the heavy metal contents with the permissible limits established by the Brazilian legislation. A value of intake of heavy metals in human diets was also calculated to estimate the risk to human health. Vegetable samples were collected at the São Paulo General Warehousing and Centers Company, and the heavy metal content was determined by atomic absorption spectrophotometry. All sampled vegetables presented average concentrations of Cd and Ni lower than the permissible limits established by the Brazilian legislation. Pb and Cr exceeded the limits in 44 % of the analyzed samples. The Brazilian legislation does not establish a permissible limit for Co contents. Regarding the consumption habit of the population in the São Paulo State, the daily ingestion of heavy metals was below the oral dose of reference, therefore, consumption of these vegetables can be considered safe and without risk to human health.

Zn availability in Red Latossol (Rhodic Ferralsol) of different pH amended with different rates of sewage sludge was studied by the isotopic 65Zn L value method. Soil chemical properties were found to be altered by SS addition. Zn concentration and Zn derived from SS (ZnpfSS) in plant, and Zn phytoavailability (L value), were increased with increasing SS rates. The linear correlation coefficient of plant Zn with SS rates and with L value was significant at 1% probability. The L value proved an efficient method for predicting Zn phytoavailability in sewage sludge-amended soil with different pH under the soil conditions studied.

Leguminosas, como adubo verde, são fontes alternativas de nitrogênio para as culturas e podem complementar ou mesmo substituir a adubação mineral nitrogenada, devido ao seu potencial de fixação biológica de nitrogênio (FBN). A utilização do nitrogênio pela cana-de-açúcar (Saccharum spp.) fertilizada com crotalária (Crotalaria juncea L.) e sulfato de amônio (SA) foi avaliada utilizando a técnica de traçador 15N. As quantidades equivalentes a 196 e 70 kg de N por hectare foram adicionados como adubo verde crotalária júncea (CJ) e como o sulfato de amônio (SA), respectivamente, nos seguintes tratamentos: (i) controle; (ii) SA15N; (iii) CJ15N + SA; (iv) CJ15N; e (v) SA15N + CJ. A cana-de-açúcar foi cultivada por cinco anos e colhida três vezes. A recuperação do 15N foi avaliada nas duas primeiras colheitas. Na soma das três safras, os maiores rendimentos de colmos foram obtidos com uma combinação de adubos verdes e fertilizantes N inorgânicos, mas, no segundo corte rendimentos superiores foram observados nos tratamentos com CJ em comparação com os observados com SA. A recuperação de N nas primeiras duas safras consecutivas representou 19 a 21% do N aplicado como adubo verde e 46 a 49% do N aplicado como SA. As quantidades de N inorgânico derivado das fontes marcadas, presentes na camada 0-0,4 m do solo na primeira safra após a aplicação do N foram inferiores a 1 kg ha-1.

Legumes as green manure are alternative sources of nitrogen (N) for crops and can supplement or even replace mineral nitrogen fertilization due to their potential for biological nitrogen fixation (BNF). The utilization of nitrogen by sugarcane (Saccharum spp.) fertilized with sunn hemp (Crotalaria juncea L.) and ammonium sulfate (AS) was evaluated using the 15N tracer technique. N was added at the rate of 196 and 70 kg ha-1 as 15Nlabeled sunn hemp green manure (SH) and as ammonium sulfate (AS), respectively. Treatments were: (i) Control; (ii) AS15N; (iii) SH15N + AS; (iv) SH15N; and (v) AS15N + SH. Sugarcane was cultivated for five years and was harvested three times. 15N recovery was evaluated in the two first harvests. In the sum of the three harvests, the highest stalk yields were obtained with a combination of green manure and inorganic N fertilizer; however, in the second cutting the yields were higher where SH was used than in plots with AS. The recovery of N by the first two consecutive harvests accounted for 19 to 21% of the N applied as leguminous green manure and 46 to 49% of the N applied as AS. The amounts of inorganic N, derived from both N sources, present in the 0-0.4 m layer of soil in the first season after N application and were below 1 kg ha-1.

A fixação biológica do nitrogênio (FBN) constitui-se em uma valiosa fonte deste nutriente para o feijão comum e, sobretudo, para o feijão-caupi, tendo sua magnitude influenciada pela disponibilidade de N mineral na solução do solo. Os objetivos deste trabalho foram: avaliar os efeitos de doses de nitrogênio, na forma de uréia, sobre a fixação simbiótica de N2 em feijão comum e caupi, pela técnica isotópica, e quantificar as contribuições relativas das fontes N2-fixação simbiótica, N-solo e N-uréia no desenvolvimento do feijão comum e caupi, usando como controle a soja não nodulante. O estudo foi desenvolvido em casa de vegetação, utilizando-se vasos com 5 kg de terra, coletada de Latossolo Vermelho-Amarelo distrófico. O delineamento experimental foi em blocos casualizados em esquema fatorial 5x3x2 e três repetições. Os tratamentos compreenderam cinco doses de N, na forma de uréia: 2, 15, 30, 45 e 60 mg kg-1 de N; três épocas de amostragens de plantas: 23, 40 e 76 dias após a semeadura (DAS) e duas culturas: feijão comum e feijão caupi. A FBN decresceu com o incremento da dose de N, variando de 81,5% a 55,6% para o caupi e de 71,9% a 55,1% para o feijão comum. A FBN em caupi submetido à inoculação pode substituir totalmente a adubação nitrogenada, inclusive a dose de arranque. A absorção do N do solo não é influenciada pela dose de fertilizante nitrogenado. O aproveitamento do N do fertilizante, aos 76 DAS, foi, em média, de 60,7% pelo feijão comum e 57,1% pelo caupi. O feijão comum necessita de dose de arranque (40 kg ha-1 de N) para a obtenção de produtividade economicamente aceitável.

Biological nitrogen fixation (BNF) constitutes a valuable source of this nutrient for the common bean Phaseolus vulgaris L. and cowpea Vigna unguiculata (L.) Walp., being its avaibility affected by mineral N in the soil solution. The objectives of this work were to evaluate the effects of nitrogen rate, as urea, on symbiotic fixation of N2 in common bean and cowpea plants, using the isotopic technique, and quantifying the relative contributions of N sources symbiotic N2 fixation, soil native nitrogen and urea N on the growth of the common bean and cowpea. Non nodulating soybean plants were used as standard. The research was carried out in greenhouse, using pots with 5 kg of soil from a Typic Haplustox (Dystrophic Red Yellow Latosol). The experimental design was completely randomized blocks, with 30 treatments and three replications, arranged in 5x3x2 factorial outline. The treatments consisted of five N rates: 2, 15, 30, 45 and 60 mg N kg-1 soil; three sampling times: 23, 40 and 76 days after sowing (DAS) and two crops: common bean and cowpea. The BNF decreased with increase N rates, varying from 81.5% to 55.6% for cowpea, and from 71.9% to 55.1% for common bean. The symbiotic N2 fixation in cowpea can substitute totally the nitrogen fertilization. The nitrogen absorption from soil is not affected by nitrogen fertilizer rate. The N recovery from fertilizer at 76 DAS was of 60.7% by common bean, and 57.1% by cowpea. The symbiotic association in common bean needs the application of a starting dose (40 kg N ha-1) for economically acceptable yields.

Estudou-se o efeito do cultivo prévio de leguminosas sobre a produtividade e lucratividade da cana-de-açúcar. Foram determinados a produtividade de biomassa, o acúmulo de nutrientes das leguminosas, a ocorrência natural de fungos micorrízicos arbusculares, bem como o efeito das leguminosas sobre a população de nematoides do gênero Pratylenchus à cana-de-açúcar. O experimento foi desenvolvido em Piracicaba (SP), Brasil, em solo classificado como Argissolo Vermelho-Amarelo distrófico, utilizando-se a cultivar de cana-de-açúcar (Saccharum spp.) IAC87-3396. As avaliações dos efeitos do cultivo prévio das leguminosas foram realizadas durante cinco cortes consecutivos. Os tratamentos consistiram do cultivo prévio das leguminosas: Amendoim (Arachis hypogaea L) - cultivares IAC-Tatu e IAC-Caiapó, crotalária júncea IAC 1 (Crotalaria juncea L) e mucuna preta [Mucuna aterrima (Piper & Tracy) Holland], e um tratamento-testemunha. Adotou-se o delineamento em blocos casualizados com cinco repetições. A leguminosa mais produtiva de biomassa seca (parte aérea+raízes) foi a crotalária júncea IAC 1 (10.264 kg ha-1), seguida da mucuna preta (4.391 kg ha-1) e dos amendoins, IAC-Caiapó (3.177 kg ha-1) e IAC-Tatu (1.965 kg ha-1). O amendoim IAC-Caiapó e a mucuna preta foram as espécies mais infectadas por fungos micorrízicos. O amendoim, independente da cultivar, foi a leguminosa que mais reduziu a infestação de Pratylenchus spp. na cana-de-açúcar. Após cinco cortes da cana-de-açúcar o melhor desempenho foi notado no tratamento com cultivo prévio de crotalária júncea IAC 1, o qual promoveu incrementos de 30% e 35% na produtividade de colmos e de açúcar respectivamente e o melhor desempenho econômico.

The research aimed to evaluate and characterize the biomass of leguminous residues, the natural arbuscular mycorrhizal (AM) fungus occurrence and the effect of leguminous on the nematodes (Pratylenchus spp.) in sugarcane crop. The experiment was carried out in Piracicaba, São Paulo State, Brazil. The soil was classified as Paleudalf and the sugarcane (Saccharum spp.) cultivar was IAC87-3396. The effects of previous cultivation of legumes were evaluated for five consecutive harvests. The treatments consisted of previous cultivation of legumes: peanut (Arachis hypogaea L.) cultivars IAC-Tatu and IAC-Caiapó, sunn hemp IAC 1 (Crotalaria juncea L.) and velvet-bean [Mucuna aterrima (Piper & Tracy) Holland], and a control treatment. We adopted the randomized block design with five replications. The legume most productive was sunn hemp IAC 1 with 10.264 kg ha-1, followed by velvet-bean with 4.391 kg ha-1 and peanuts IAC-Caiapó and IAC-Tatu with 3.177 kg ha-1 and 1.965 kg ha-1, respectively. The peanut IAC-Caiapó and velvet bean were the leguminous crops that resulted in the greater percentage of AM fungus. The lowest population of Pratylenchus spp. was found in the treatments with peanut IAC-Tatu and IAC-Caiapó. After five harvests, sunn hemp was the leguminous crop that induced the greatest sugarcane yield, with 30% increase in cane yield and 35% in sugar yield.

Sugarcane (Saccharum spp.) is an important crop for sugar production and agro-energy purposes in Brazil. In the sugarcane production system after a 4- to 8-year cycle crop rotation may be used before replanting sugarcane to improve soil conditions and give an extra income. This study had the objective of characterizing the biomass and the natural colonization of arbuscular mycorrhizal fungi (AMF) of leguminous green manure and sunflower (Helianthus annuus L.) in rotation with sugarcane. Their effect on stalk and sugar yield of sugarcane cv. IAC 87-3396 grown subsequently was also studied. Cane yield was harvested in three subsequent cuttings. Peanut cv. IAC-Caiapó, sunflower cv. IAC-Uruguai and velvet bean (Mucuna aterrimum Piper and Tracy) were the rotational crops that resulted in the greater percentage of AMF. Sunflower was the specie that most extracted nutrients from the soil, followed by peanut cv. IAC-Tatu and mung bean (Vigna radiata L. Wilczek). The colonization with AMF had a positive correlation with sugarcane plant height, at the first cut (p = 0.01 and R = 0.52) but not with the stalk or cane yields. Sunflower was the rotational crop that brought about the greatest yield increase of the subsequent sugarcane crop: 46% increase in stalk yield and 50% in sugar yield compared with the control. Except for both peanut varieties, all rotational crops caused an increase in net income of the cropping system in the average of three sugarcane harvests.

A cana-de-açúcar (Saccharum spp.) vem sendo cultivada no Brasil para produção de açúcar e agroenergia. Em seu sistema de produção, após um ciclo de 4 a 8 anos, é possível a rotação com plantas de cobertura, antes do seu replantio, para melhoria do solo e geração de renda. Estudou-se a caracterização e produtividade de biomassa de leguminosas (como adubos-verdes) e girassol (Helianthus annuus L.), a ocorrência natural de micorrizas, o teor de açúcar e a produtividade em colmos da cana-de-açúcar IAC 87-3396 e a viabilidade econômica desse sistema com cultivo após as opções de rotação, com quantificação da produtividade durante três cortes consecutivos. O amendoim (Arachis hypogaea L.) cv. IAC-Caiapó, girassol cv. IAC-Uruguai e mucuna-preta (Mucuna aterrimum Piper and Tracy) foram as culturas que apresentaram maior percentagem de colonização por fungos micorrízicos. O girassol foi a planta de cobertura que mais extraiu nutrientes do solo, seguido por amendoim (Arachis hipogaea L.) cv. IAC-Tatu e feijão-mungo (Vigna radiata L. Wilczek). A colonização por fungos micorrízicos mostrou correlação positiva com a altura de plantas de cana no primeiro corte (p = 0,01 e R = 0,52), mas não se correlacionou com a produtividade de colmos ou açúcar. No primeiro corte, o girassol foi a cultura de rotação que ocasionou o maior aumento de produtividade, da ordem de 46% em colmos e de 50% na quantidade de açúcar, em comparação com a testemunha. Com exceção dos amendoins, todas as culturas em rotação aumentaram a renda líquida do sistema na média de três cortes de cana-de-açúcar.

The objective of the study was to evaluate the effect of phosphorus on the Cd availability to plants of a contaminated soil using 109Cd isotope and chemical extractants. The experiment was set in a randomized block design and the soil was labeled with 222 KBq of 109Cd per pot and received 5 rates of P as triple superphosphate, growing lettuce plants as test crop. The use of phosphorus reduced pH of soil which altered the Cd availability in DTPA and Mehlich extractants. The lettuce Cd content decreased but its accumulation and L value increased in all treatments compared to the control, demonstrating the inefficiency of phosphorus in reducing the Cd availability.

O objetivo deste trabalho foi avaliar o efeito do modo de aplicação do superfosfato triplo (SFT), do fosfato natural reativo de Gafsa e da mistura entre essas fontes no aproveitamento do fósforo (P) por plantas de milho e de soja. Os experimentos foram realizados em casa de vegetação, e as plantas foram cultivadas em vasos com Latossolo Vermelho-Amarelo distrófico. As fontes fosfatadas foram aplicadas isoladamente ou em misturas (proporção 1:1), à dose de 90 mg kg-1 de P, de modo não localizado ou localizado no solo. Para a quantificação do P absorvido pelas plantas das diferentes fontes, empregaram-se tratamentos com o solo e com o SFT marcados com 32P. O aproveitamento do fósforo do superfosfato triplo aplicado de forma localizada (9,8%) foi superior ao da não localizada (7%). A aplicação não localizada do fosfato natural reativo proporcionou maior aproveitamento do fósforo (3,8%), em comparação à localizada (0,5%). Em comparação à aplicação isolada do fosfato de Gafsa, o aproveitamento do fósforo pelas plantas de milho e soja aumentou quando essa fonte foi aplicada como mistura compactada; em presença do superfosfato triplo, a aplicação do fosfato natural reativo de Gafsa de modo não localizado proporcionou maior aproveitamento do P pelas plantas de soja. O aproveitamento do fósforo do fosfato natural de Gafsa aumenta quando aplicado ao solo com o superfosfato triplo, e esse efeito depende do método de aplicação das fontes fosfatadas.

The objective of this work was to evaluate the effects of methods of applying triple superphosphate (TSP), Gafsa reactive phosphate rock and mixtures between these sources on phosphorus (P) utilization by maize and soybean plants. The experiments were carried out in a greenhouse, and the plants were grown in pots containing Typic Haplustox soil. The phosphorus sources were applied isolatedly or mixed (1:1 ratio) in a P rate of 90 mg kg-1, in a non-localized or in a localized manner in the soil. To quantify plant-absorbed phosphorus from the different sources, treatments with soil and TSP labeled with 32P were used. Phosphorus utilization from triple superphosphate applied locally was superior (9.8%) to the P utilization of this source applied non locally to the soil (7%). Inversely, better results with Gafsa phosphate rock occurred with P applied non locally to soil (3.8%), compared to the values obtained when the fertilizer was applied locally (0.5%). The phosphorus utilization from the Gafsa phosphate rock by maize and soybean plants increased when it was applied as compacted triple superphosphate and Gafsa phosphate rock mixture. In the presence of triple superphosphate, the soil-incorporated application of Gafsa phosphate rock led to greater utilization of phosphorus by soybean plants. The utilization of Gafsa phosphate rock phosphorus increases when it is applied together with triple superphosphate; and this effect depends on the methods of application of these phosphate sources.