ABSTRACT The accessibility of soil P reserves by plants on highly weathered Brazilian soils remains unclear. In this study, we assessed the contribution of soil P fractions to P uptake by soybean plants in two no-till Oxisols (Latossolos), with low and high initial content of available P. The recommended P rates (viz., 153 and 50 kg ha-1 yr-1 in the low-P and high-P soil, respectively) were applied in the form of triple superphosphate (TSP) or Bayovar rock phosphate (BRP) plus a treatment without fertilizer. Yields of winter cereals and soybean on the studied soils were examined over a period of three years. Soil samples were collected in the 0.00-0.10 m soil layer and subjected to sequential chemical fractionation of P. In the last crop season, the P content of soybean shoot biomass was determined. Soil P fractions and P content of soybean shoots were subjected to path analysis. The addition BRP in the low-P soil resulted in a winter cereal yield of 2.0 Mg ha-1 lower than TSP. In the scenario of high P, it is possible to maintain high crop yields even without phosphate fertilization for three consecutive years. Path analyses demonstrated the addition of P using either TSP or BRP boosted the contribution of the more labile inorganic P fractions. The addition of BRP should be avoided in P-deficient soils. The addition TSP or BRP reduces the pressure of plants to use soil P reserves. Therefore, the soil P legacy should be considered in fertilization recommendations for high-P soils in NT. unclear study notill no till Latossolos, Latossolos , (Latossolos) viz., viz (viz. 15 5 ha1 ha 1 ha- yr1 yr yr- lowP highP respectively (TSP (BRP fertilizer years 0.000.10 000010 0.00 0.10 0 00 10 0.00-0.1 season determined analysis 20 2 2. Pdeficient deficient Therefore NT (Latossolos viz. (viz 000 0.000.1 00001 0.0 010 0.1 0.00-0. 0.000. 0000 0. 01 0.00-0 0.000 0.00-

ABSTRACT High winter cereal yields depend on an adequate supply of nitrogen (N). We developed a system for indicating N rates for wheat and barley in the South-Central region of the state of Paraná, Brazil, using results of 72 field experiments conducted from 2007 to 2012. The N rates recommended for winter cereals were estimated to supply the amounts of N fertilizer needed to obtain increasing yields (<3.5, 3.5-4.5, 4.5-5.5, and >5.5 Mg ha-1) of crops grown after soybean and corn on soils with a variable organic matter content (<40, 40-60, and >60 g dm-3). The apparent mineralization rate of soil N was estimated to be 1 % and the N fertilization efficiency 50 %. The N rates recommended for wheat ranged from 30 to 150 kg ha-1 when cultivated after soybean, and from 30 to 170 kg ha-1 after corn. The N rates for barley ranged from 30 to 120 kg ha-1 when grown after soybean, and from 30 to 130 kg ha-1 after corn. These N rates are consistent with those indicated by the Soil Fertility Commission for the states of Rio Grande do Sul and Santa Catarina (CQFS-RS/SC, 2016), and also with the rates of maximum economic efficiency estimated in our study. The proposed N rate recommendation system can be used by agricultural technicians and producers to manage N fertilization of wheat and barley in the South-Central region of Paraná, Brazil.

ABSTRACT Fertilization programs for annual crops in the state of Paraná, southern Brazil, are based on studies that focused on conventional tillage and were established more than 30 years ago. The primary purpose of this study was to assess potassium (K) fertilization on long-term (>30 years) no-tillage soybean, corn, wheat, and barley crops grown in rotation on Oxisols in the central-southern region of Paraná. A total of 47 experiments were carried out from 2008 to 2013, three of which addressed K calibration and the other 44, crop response to K fertilization. Critical K soil-test value and interpretation classes were established from the ratio between relative crop yield [RY = (yield without K/max yield) × 100] and soil K levels. Winter cereals were found to be more demanding of K than were soybean and corn; also, the former governed critical K soil-test value for crop rotation: 0.23 cmolc dm-3 in the 0.00-0.20 m soil layer. Recommended fertilization rates for soils in the low and medium soil K levels were established by using the build-up approach for soil correction; and those for the high and very high soil K levels were established by removing K at harvest and assessing economic return in crop response experiments. The K rates calculated for the high yield classes exceeded those currently recommended for use in Paraná.

ABSTRACT In no-tillage (NT) systems, there is no plowed layer since the soil is not tilled. Thus, the soil layer for fertility evaluation can be defined as the one in which the fertility indices are affected by the surface application of lime and fertilizers and soil properties have the closest relationship with crop yields. The objective of this study was to determine the most appropriate soil layer under long-term NT for sampling for fertility evaluation in the South-Central region of Paraná, Brazil. A total of 99 field experiments of crop rotations were performed, including soybean, corn, barley, wheat, and white oat, all on Oxisols (Hapludox). Despite the surface application, lime and fertilizers increased base saturation (V) and available K to a depth of 0.20 m. The relationship with crop yields was high for V and low for available K for both soil layers (0.00-0.10 and 0.00-0.20 m); for P, however, the relationships with soybean and corn yields were strongest in the 0.00-0.20 m layer. Thus, considering the soil layer fertilized by the surface application of lime and potassium fertilizers and the highest relationship of soil P contents with the yield of the main crops of the crop rotation, the 0.00-0.20 m layer is the most appropriate for soil fertility evaluation under long-term no-tillage systems.

O Estado do Paraná não dispõe de um sistema de recomendação de adubação para rotação de culturas em plantio direto (PD). Em razão disso, utiliza indicações geradas para culturas individuais há mais de 30 anos e em preparo convencional. Este estudo teve como objetivo consolidar a calibração de P e avaliar a resposta das culturas à adubação fosfatada, visando à proposição de um sistema de indicações técnicas para a adubação fosfatada das culturas da soja, do milho, do trigo e da cevada cultivadas em sistema de rotação em Latossolos com longo histórico de PD (>30 anos) na região centro-sul do Paraná, que se caracteriza por possuir alto potencial produtivo. Três experimentos de calibração foram conduzidos de 2008 a 2013 e consistiram na criação de níveis de P pela aplicação de doses a lanço de até 640 kg ha-1 de P2O5. Quarenta e quatro experimentos de resposta a P foram conduzidos entre as safras de 2011 a 2012/13, tendo como foco avaliar a resposta das culturas a P em solos com distinta disponibilidade do nutriente. Os rendimentos relativos [RR = (rendimento sem P/rendimento máximo) × 100] das culturas e os teores de P no solo (Mehlich-1) foram relacionados, obtendo-se os teores críticos e as classes de disponibilidade de P no solo. Para a estimativa das doses nas classes de disponibilidade Baixa e Média, foram utilizadas as curvas de resposta à adubação de P, seguindo a filosofia de suficiência (adubação de cultura). Nas classes de disponibilidade Alta e Muito Alta, as doses foram com base na exportação pelos grãos. Os cereais de inverno se evidenciaram mais exigentes e determinaram o teor crítico de P de 8 mg dm-3 para a rotação de culturas, considerando a camada de 0-20 cm. As doses de P indicadas para soja, milho, trigo e cevada em solos em PD de longa duração são superiores às de adubação atualmente indicadas no PR, o que, ao menos em parte, justificam-se pelas altas produtividades das culturas e alta capacidade de retenção de P dos solos da região. Embora adotada a filosofia de suficiência/adubação de cultura para a indicação das doses de adubação fosfatada em solos abaixo do teor crítico, estima-se que as doses estipuladas para as culturas elevem o teor de P no solo ao teor crítico após um ciclo da rotação de culturas (três anos).

Although the State of Parana, Brazil, has adopted crop rotation and no-till (NT) systems, fertilizer application is still based on recommendations developed more than 30 years ago for monocropping under conventional tillage because fertilizer recommendations developed specifically for crop rotation under NT are lacking. The objective of our study was to consolidate P calibration and evaluate crop responses to P fertilization so as to propose a system of technical recommendations for P fertilization for soybean, maize, wheat, and barley grown in a crop rotation system in Oxisols under long-term (>30 years) NT systems in the high yield potential South-Central region of Parana. Three calibration trials were conducted from 2008 to 2013, consisting of P broadcast application rates of up to 640 kg ha-1 P2O5. Forty-four P fertilization trials were carried out over the 2011-2012/13 growing seasons to evaluate yield response to P fertilization rates in Oxisols with different levels of P availability. Relative crop yield [RR = (yield without P/maximum yield) × 100] and soil P availability (Mehlich-1) were compared to obtain P critical levels and generate soil P availability classes based on crop response. For soils in the Low and Medium availability classes, recommended P fertilizer application rates were based on the yield response curve following the nutrient sufficiency approach. For soils in the High and Very High availability classes, P fertilizer recommendations were based on P removal through grain harvest. The winter cereal crops were more demanding to achieve maximum yields - the soil critical P level for the crop rotation system was determined at 8 mg dm-3 based on the requirement of these crops, considering the 0-20 cm soil layer. The recommended P fertilization rates for soybean, maize, wheat, and barley in Oxisols under long-term NT developed in our study are higher than the current P fertilization rates used in Parana, which is explained in part by the high crop yields and high P adsorption capacity of soils in the region. Although the nutrient sufficiency approach was used to determine P fertilization rates in the soils below the critical level, it is estimated that the P rates recommended for the crops will raise soil P availability above the critical level after a full crop-rotation cycle (3 years).

Os resíduos culturais na superfície de solos em plantio direto (PD) podem intensificar a volatilização de amônia, quando da aplicação dos fertilizantes nitrogenados em sistemas de produção de cereais. Este estudo visou avaliar a magnitude das perdas de N por volatilização, quando da aplicação superficial de ureia nas culturas do trigo e do milho, em Latossolo Bruno em PD, no centro-sul do Paraná. Adicionalmente, avaliou-se o potencial de fontes alternativas de N (ureia com inibidor de urease, fertilizante líquido, nitrato de amônio e sulfato de amônio) e de variantes no manejo da ureia (fertilizante aplicado pela manhã ou à tarde) em reduzir as perdas de amônia por volatilização. Dois experimentos foram conduzidos, por dois anos, com as culturas do trigo (Triticum aestivum L.) e milho (Zea mays L.), seguindo um delineamento de blocos casualizados, com quatro repetições. As perdas de N por volatilização de amônia foram avaliadas utilizando-se um coletor semiaberto estático, no período de até 21 dias após a aplicação dos fertilizantes. No inverno, as perdas foram baixas para todas as fontes nitrogenadas (<5,5 % N aplicado) em razão das baixas temperaturas e independentes do regime de chuvas. No verão, as taxas de volatilização de amônia, quando da aplicação superficial de ureia, mantiveram-se inferiores a 15 % do N aplicado e foram dependentes da ocorrência de chuvas nos primeiros cinco dias após a aplicação do fertilizante. A utilização de ureia com inibidor de urease, nitrato e sulfato de amônio foi eficiente na redução das perdas de N por volatilização na cultura do milho, enquanto o horário de aplicação (manhã ou tarde) não teve influência.

Crop residues on the soil surface of no-till systems can intensify ammonia volatilization from N fertilizers applied to cereal crops. This study assessed the magnitude of N losses through ammonia volatilization from urea applied to no-till winter (wheat) and summer crops (maize) on a Typic Hapludox in the south-central region of Paraná, southern Brazil. In addition, the potential of alternative N sources (urea with urease inhibitor, liquid fertilizer, ammonium nitrate and ammonium sulfate) and different urea managements (fertilizer applied in the morning or afternoon) were evaluated. Two experiments with maize and wheat were carried out for two years, arranged in a randomized block design with four replications. Nitrogen volatilization losses were assessed with a semi-open static collector until 21 days after fertilization. In winter, the losses were low (<5.5 % of applied N) for all N sources, which were not distinguishable, due to the low temperatures. In the summer, volatilization rates from urea were higher than in the winter, but did not exceed 15 % of applied N. The main factor decreasing N losses in the summer was the occurrence of rainfall in the first five days after fertilization. Urea with urease inhibitor, nitrate and ammonium sulfate were efficient to decrease ammonia volatilization in maize, whereas the application time (morning or afternoon) had no influence.

A adoção do plantio direto (PD) em substituição ao preparo convencional promove alterações na dinâmica de nutrientes e na acidez no solo, podendo influenciar as relações solo-planta e, portanto, os critérios de manejo da fertilidade do solo. Este estudo teve como objetivo determinar os critérios de recomendação de calagem e os teores críticos de fósforo (P) e potássio (K) para o sistema de rotação de culturas envolvendo soja, milho, trigo, cevada e aveia branca, amplamente adotado na região Centro-Sul do Paraná. O estudo foi com base em 13 experimentos de campo conduzidos em Latossolos Brunos em longo prazo em PD (>15 anos), nos municípios de Guarapuava, Pinhão e Candói. Desses, cinco envolveram calagem e oito adubação de P e K. Em amostras de solo das camadas de 0-0,10 e 0,10-0,20 m, foi determinado o pH (CaCl2) e calculada a saturação por bases (V%) nos experimentos de calagem e os teores de P e K disponível (Mehlich-1) nos experimentos de adubação. O método dos quadrantes foi utilizado para determinar os critérios de recomendação de calagem; e o nível crítico de pH e V% consistiu no valor em que, acima do qual, as culturas apresentaram rendimento relativo (RR) superior a 90 % e nunca inferior a 80 %. A relação entre os teores de P e K e os valores de RR foi verificada pela equação de Mitscherlich, sendo o teor crítico aquele correspondente ao RR de 90 %. Os resultados indicaram que os níveis críticos relacionados à acidez e disponibilidade de P e K foram maiores para a camada de 0-0,10 m do que para a de 0-0,20 m. A cultura da soja foi mais sensível à acidez do solo, enquanto os cereais de inverno foram mais exigentes em P e K. Tomando-se como referência as culturas mais restritivas do sistema de rotação e a camada de 0-0,20 m, os níveis críticos para calagem foram pH (CaCl2) de 4,9 e saturação por bases de 60 %, enquanto os teores críticos para adubação foram 8 mg dm-3 de P e 0,30 cmol c dm-3 de K para Latossolos cultivados no longo prazo em sistema PD na região Centro-Sul do Paraná.

When conventional tillage is replaced by no-tillage (NT) changes occur in the dynamics of soil nutrients and acidity, which may influence the soil-plant relationships and consequently, the criteria for soil fertility management. This study determined the criteria for liming as well as the soil critical levels for P and K in a crop rotation of soybean, maize, wheat, barley, and white oat, widely used in the South-Central region of the State of Parana, in Southern Brazil. The study involved 13 field experiments on Hapludox soils under long-term no-tillage (>15 years) in Guarapuava, Pinhão and Candói; five of the experiments were related to liming and eight to P and K fertilization. In soil samples from the layers 0-0.10 and 0.10-0.20 m, of the liming studies, CaCl2-pH and base saturation (V%) were quantified and available P and K (Mehlich-1) in the samples from the fertilization. The quadrant method was used to determine the liming criteria; the critical levels for pH and base saturation were based on values that ensured relative crop yields above 90 % and never below 80 %. The ratio between the soil P and K levels and the relative crop yields could be represented by the Mitscherlich equation, where the levels required for relative crop yields of 90 % represent the critical values. The results indicated that the critical levels of soil acidity and available P and K were higher in the 0-0.10 m than the 0-0.20 m layer. Soybean was most sensitive to soil acidity, while the winter cereals were most demanding in P and K. Based on the most restrictive crop in the rotation and 0-0.20 m soil layer as reference, the critical levels for liming were CaCl2-pH of 4.9 and base saturation of 60 %, while the critical levels of fertilization were 8.0 mg dm-3 for P and 0.30 cmol c dm-3 for K for Oxisoils under long-term no-tillage, in the South-Central Region of Paraná.

Pouco se conhece sobre a eficiência relativa de fosfatos solúveis e naturais em sistemas de alta produtividade de culturas em plantio direto no centro-sul do Paraná. Este trabalho objetivou avaliar a eficiência agronômica de fosfatos naturais reativos em comparação a um fosfato solúvel na produtividade de várias espécies vegetais anuais em dois ciclos de um sistema de rotação de culturas trienal. O experimento foi conduzido sobre um Latossolo Bruno, em Guarapuava, PR, de 2000 a 2006. Dois fosfatos naturais reativos (FNR: Gafsa e Arad) e um fosfato solúvel (superfosfato triplo, SFT) foram aplicados, a lanço, nas doses de 0, 40, 80 e 160 kg ha-1 de P2O5, no início do primeiro e do segundo ciclo de rotação de culturas trienal (aveia branca/milho/trigo/soja/cevada/soja). À exceção da cevada, a produtividade das culturas não foi alterada pela adição de qualquer dos fosfatos no primeiro ciclo de rotação, provavelmente, devido ao alto teor de P previamente existente no solo (8,7 mg dm-3 na camada de 0-10 cm). No segundo ciclo de rotação, quando o solo tinha 4,1 mg dm-3 de P, a aplicação de P na semeadura da aveia branca incrementou em 11 % a produtividade das culturas de verão e em 20 % a das culturas de inverno, tendo o menor incremento ocorrido no milho (8 %) e o maior na cevada (44 %). Neste ciclo, o SFT proporcionou maior produtividade do que os FNR nas culturas de inverno (aveia branca, trigo e cevada), numa média de 11 %, não tendo havido diferença de produtividade entre os FNR. O fosfato solúvel em água é mais eficiente do que os fosfatos naturais reativos em solos sob plantio direto, tanto no efeito imediato quanto na fase residual. Apesar disso, não é necessário aplicar fertilizantes fosfatados para obter alta produtividade em solos com altos teores de P em plantio direto, a não ser para culturas muito exigentes, a exemplo da cevada.

Little is known about the agronomic effectiveness of phosphate rocks in high-yielding crop rotation systems under no-till in the Center-South of the state of Paraná, Brazil. This field study was undertaken to compare the effectiveness of rock phosphates and soluble P fertilizers to increase the yield of several annual crops grown in two consecutive triennial crop-rotation cycles under no-tillage. The experiment was carried out in an Oxisol, in Guarapuava, PR, from 2000 until 2006. Two phosphate rocks (PR - Gafsa and Arad) and a soluble P fertilizer (TSP - triple superphosphate) were broadcast over the soil surface at rates of 0, 40, 80 and 160 kg ha-1 P2O5, at the beginning of the first and the second rotation cycle of the triennial crops (oat, maize, wheat, soybean, barley and soybean). With exception of barley, crop yields were not affected in the first rotation cycle by any phosphate fertilizer regardless of type and rate, probably due to the high P contents available in the soil (8.7 mg dm-3 in the 0-10 cm layer). In the second rotation cycle, when soil available P was 4.1 mg dm-3; P application at oat sowing increased the yield of summer crops by 11 % and of winter crops by 20 %. The yield increment was lowest for maize (8 %) and highest for barley (44 %). In this cycle, TSP resulted in higher yield than PR, though only for winter crops (oat, wheat and barley), in a mean of 11 %, with no difference between Gafsa and Arad. Water soluble fertilizer (TSP) was more efficient than phosphate rocks in soils under no-till system both in the short and long term. Nevertheless, it is not necessary to apply phosphates for high yields in soils with high available P contents under no-till, except for species with high P requirement, e.g., barley.